Friction Performance of Aluminum-Silicon Alloy Cylinder Liner After Chemical Etching and Laser Finishing

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Article Friction Performance of Aluminum-Silicon Alloy Cylinder Liner after Chemical Etching and Laser Finishing

Fengming Du 1,*, Chengdi Li 2, Zetian Mi 3, Ruoxuan Huang 4, Xiaoguang Han 4, Yan Shen 1,* and Jiujun Xu 4

1 College of Marine Engineering, Dalian Maritime University, Dalian 116026, China 2 Xinyu Key Laboratory of Materials Technology and Application for Intelligent Manufacturing, Xinyu University, Xinyu 338004, China; [email protected] 3 College of Information Science and Technology, Dalian Maritime University, Dalian 116026, China; [email protected] 4 Key Lab of Ship-Maintenance & Manufacture, Dalian Maritime University, Dalian 116026, China; [email protected] (R.H.); [email protected] (X.H.); [email protected] (J.X.) * Correspondence: [email protected] (F.D.); [email protected] (Y.S.); Tel.: +86-0411-8472-3376 (F.D.); +86-0411-8472-6002 (Y.S.) Received: 22 March 2019; Accepted: 9 April 2019; Published: 11 April 2019

Abstract: In order to enhance the surface friction performance of the aluminum-silicon (Al-Si) alloy cylinder liner, chemical etching and laser finishing techniques are applied to improve the friction performance. The cylinder liner samples are worn against a Cr-Al2O3 coated piston ring by a reciprocating sliding tribotester. The friction coefficient and weight loss are measured to determine the friction performance; a stress contact model is developed to ascertain the wear mechanism. The results show that the optimal etching time is 2 min for the chemical etching treatment and the optimal laser power is 1000 W for the laser finishing treatment. The chemical etching removes the surface aluminum layer and exposes the silicon on the surface, thereby avoiding metal-to-metal contact. The laser finishing results in the protrusion and rounded edges of the silicon particles, which decreases the stress concentration. The laser finishing results in better friction performance of aluminum-silicon alloy cylinder liner than the chemical etching.

Keywords: friction performance; aluminum-silicon alloy cylinder liner; chemical etching; laser ﬁnishing

1. Introduction Aluminum-silicon (Al-Si) alloy materials was widely used for the energy-saving design of small and medium power engines, given its characteristics of being light weight, and having good thermal conductivity and a high recovery rate [1–6]. Ye reported the development of aluminum-silicon (Al-Si) alloy for engine application and focused on improving the material’s fatigue limit and wear resistance. Some techniques such as alloying, composite production and casting are also discussed [7]. Elmadagli et al. researched the relationship between the microstructure and wear resistance of Al-Si alloys under dry conditions, they believed that the eﬀect of the individual contribution of each microstructural feature on the wear resistance could be isolated [8]. Chen et al. conducted experiments using a pin-on-disk tester and researched the wear resistance of Al-Si alloys for a boundary-lubricated contact, and founded that the silicon particles standing exposed of the aluminum matrix would present good wear resistance [9]. Slattery et al. studied the microstructure evolution of a eutectic Al-Si engine under severe conditions and researched the subsurface deformation in a liner-less Al-Si engine [10,11].

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Since aluminum alloys are soft and have a certain viscosity, the plastic flow of aluminum easily occurs on the surface during friction, resulting in a weaker wear resistance of Al-Si liners than cast iron cylinder liners [12,13]. Therefore, surface treatments are needed to improve the wear resistance [14–17]. Li et al. founded that the chemical etching method could expose the silicon, they researched the etching time on the wear behaviors of etched surface using a self-designed reciprocating wear machine and explored the wear mechanisms [18]. Riahi et al. pointed out that chemical etching could improve the scuffing resistance of Al-Si alloy, and the best scuffing resistance was achieved after an etching time of 7 min [19]. Das et al. slid a steel ball on Al-Si flats, they found that the etched surface hardened the alloy and gave rise to silicon particles, and the plastic deformation was initiated at a load much higher than that of the unetched Al-Si alloy [20]. However, chemical etching pollutes the environment and the edges of the exposed silicon particles are sharp. During the friction process, the sharp edges of Si particles are more likely to cause stress concentration than that of the rounded edge, so it may relatively result in a higher wear loss of the Al-Si alloy than the ones with rounded Si particles. Laser processing has also been widely used in the machinery industry. Laser finishing has the characteristics of instant heating and cooling, which causes the silicon particles to protrude from the surface and also results in rounded edges. Laser quenching technology can improve the hardness and wear resistance of the cylinder liner, but a large number of holes tend to appear around the quenching area, and the hardened layer is easily broken under high load to induce the change of wear mechanism [21]. Laser cladding technology is used to treat the alloy, and laser honing technology also has certain applications on the surface of the alloy cylinder liner [22,23]. Compared to other laser processing techniques such as laser cladding and laser surface alloying, laser finishing would improve the friction performance without any alloy powders. Laser finishing is also different from laser remelting because the size of silicon particle is not reduced [24]. As engines develop toward high-speed and heavy-duty, the thermal load and mechanical load on the cylinder liner-piston ring are also increasing. Conventional chrome-plated, molybdenum-impregnated piston rings exhibit scuffing and severe wear under high power density conditions. The chromium-based ceramic composite plating named Chrom-Keramik-Schicht (CKS) adopts a layer-by-layer deposition method, and the current is periodically commutated, and the ceramic particles, such as Al2O3, SiC, and TiO2, are embedded in the microcracking texture in the chrome plating layer [25–27]. The piston ring prepared by the process has outstanding wear resistance and excellent high temperature bearing performance [28,29]. In this study, chemical etching and laser finishing treatments are compared in terms of the friction performance of an Al-Si alloy cylinder liner. The Al-Si alloy cylinder liner was worn against a CKS piston ring. The friction reduction mechanism of the two surface treatments is analyzed in-depth using contact stress calculations. The results of this study provide new insights into the friction reduction mechanism of an Al-Si cylinder liner.

2. Experimental Details

2.1. Materials and Samples The selected Al-Si alloy is a high-silicon aluminum alloy and its chemical composition is listed in Table1. An Al-Si alloy cylinder liner with a diameter of 110 mm and a wall thickness of 8 mm was equally divided into 40 samples in the circumferential direction; the length of each sample was 9 mm, as shown in Figure1, its surface morphology is shown in Figure2. The piston ring is a chromium-based ceramic composite plated (CKS) ring with an outer diameter of 110 mm and a ring height of 3 mm; an equal division of 32 cuts was performed in the circumferential direction. The CKS piston ring is coated by chromium and small Al2O3 ceramic particles on the cast iron substrate, it is obtained by means of layer by layer deposition to embed the Al2O3 particles into the micro crack of chrome layer, the hardness of the selected CKS piston ring is 761 HV0.1, the surface morphology and section morphology are showed in Figure3. Metals 2019, 9, x FOR PEER REVIEW 3 of 13 Metals 2019, 9, x FOR PEER REVIEW 3 of 13 chrome layer, the hardness of the selected CKS piston ring is 761 HV0.1, the surface morphology and chrome layer, the hardness of the selected CKS piston ring is 761 HV0.1, the surface morphology and section morphology are showed in Figure 3. section morphology are showed in Figure 3. The surface roughness measurements of piston ring and cylinder liner are both carried out The surface roughness measurements of piston ring and cylinder liner are both carried out using a Hommel tester-T6000 surface profiler (Hommel, Jena, Germany). The samples are fixed on using a Hommel tester-T6000 surface profiler (Hommel, Jena, Germany). The samples are fixed on the profiler stage by a special clamp. The stylus is moved smoothly on the sample surface to be the profiler stage by a special clamp. The stylus is moved smoothly on the sample surface to be tested. It is not possible to touch the samples during the measurement process. The results are tested. It is not possible to touch the samples during the measurement process. The results are analyzed according to the drawings after the measurement is completed, then the results are marked analyzed according to the drawings after the measurement is completed, then the results are marked andMetals printed.2019, 9, 431 The roughness of the ring and original cylinder are 0.24 μm (Ra) and 0.89 μm 3(R ofa), 13 and printed. The roughness of the ring and original cylinder are 0.24 μm (Ra) and 0.89 μm (Ra), respectively. Ra is called the contour arithmetic mean deviation or the center line average. respectively. Ra is called the contour arithmetic mean deviation or the center line average. Table 1. The chemical compositions of aluminum-silicon (Al-Si) alloy. Table 1. The chemical compositions of aluminum-silicon (Al-Si) alloy. Table 1. The chemical compositions of aluminum-silicon (Al-Si) alloy. Element Al Si Fe Cu Mg Zn Element Al Si Fe Cu Mg Zn Elementwt.% Al 71 Si20.1 Fe0.9 Cu 5 0.6 Mg 1.0 Zn wt.% 71 20.1 0.9 5 0.6 1.0 wt.% 71 20.1 0.9 5 0.6 1.0

Figure 1. Schematic diagram of the cylinder liner (a) and samples (b). FigureFigure 1.1. SchematicSchematic diagramdiagram ofof thethe cylindercylinder linerliner ((aa)) andand samplessamples ((bb).).

Figure 2. Surface morphology (a) and energy spectrum analysis (b) of Al-Si cylinder liner. Metals 2019, Figure9Figure, x FOR 2.2. PEER SurfaceSurface REVIEW morphologymorphology ((aa)) andand energyenergy spectrumspectrum analysisanalysis ((bb)) ofof Al-SiAl-Si cylindercylinder liner.liner. 4 of 13

Figure 3. Surface morphology morphology ( a)) and and section section morphology morphology ( (b)) of of chromium-based chromium-based ceramic composite plated (CKS) piston ring.

2.2. Chemical Etching The surface of the Al-Si alloy cylinder liner was chemically etched using a 5% NaOH solution. The cylinder liner sample was completely immersed in the alkali etching solution, was removed after the predetermined chemical etching time, and was washed under running water. The chemically etched cylinder liner samples were sequentially soaked in gasoline and alcohol for ultrasonic cleaning to ensure sufficient cleanliness. Figure 4 shows the surface topographies of the etched Al-Si cylinder liner after different etching time by a Philips-30TMP scanning electron microscope (Philips, Amsterdam, Netherlands). The aluminum is etched by the solution, resulting in the silicon particles being protruded on the surface; the protrusion height of silicon increases with the increase of etching time.

Figure 4. Surface morphologies of primary and etched Al-Si cylinder liner after different etching time.

Figure 5 shows the surface morphologies and outlines by an OLYMPUS LEXT OLS4000 laser scanning confocal microscopy (Olympus, Tokyo, Japan). Seen from Figure 5a, the surface of untreated cylinder liner is flat; while chemical etching may scour the aluminum substrate on the surface, which exposes the silicon particles, as shown in Figure 5b.

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The surface roughness measurements of piston ring and cylinder liner are both carried out using a Hommel tester-T6000 surface profiler (Hommel, Jena, Germany). The samples are fixed on the profiler stage by a special clamp. The stylus is moved smoothly on the sample surface to be tested. It is not possible to touch the samples during the measurement process. The results are analyzed according to the drawings after the measurement is completed, then the results are marked and printed. µ µ The roughnessFigure 3. Surface of the morphology ring and original (a) and cylindersection morphology are 0.24 m (b) ( Rofa) chromium-based and 0.89 m (R ceramica), respectively. compositeR a is calledplated the contour (CKS) piston arithmetic ring. mean deviation or the center line average. 2.2. Chemical Etching 2.2. Chemical Etching The surface of the Al-Si alloy cylinder liner was chemically etched using a 5% NaOH solution. The surface of the Al-Si alloy cylinder liner was chemically etched using a 5% NaOH solution. The cylinder liner sample was completely immersed in the alkali etching solution, was removed after The cylinder liner sample was completely immersed in the alkali etching solution, was removed the predetermined chemical etching time, and was washed under running water. The chemically after the predetermined chemical etching time, and was washed under running water. The etched cylinder liner samples were sequentially soaked in gasoline and alcohol for ultrasonic cleaning chemically etched cylinder liner samples were sequentially soaked in gasoline and alcohol for to ensure sufficient cleanliness. ultrasonic cleaning to ensure sufficient cleanliness. Figure4 shows the surface topographies of the etched Al-Si cylinder liner after di fferent etching Figure 4 shows the surface topographies of the etched Al-Si cylinder liner after different etching time by a Philips-30TMP scanning electron microscope (Philips, Amsterdam, The Netherlands). time by a Philips-30TMP scanning electron microscope (Philips, Amsterdam, Netherlands). The The aluminum is etched by the solution, resulting in the silicon particles being protruded on the aluminum is etched by the solution, resulting in the silicon particles being protruded on the surface; surface; the protrusion height of silicon increases with the increase of etching time. the protrusion height of silicon increases with the increase of etching time.

Figure 4.4. SurfaceSurface morphologiesmorphologies of of primary primary and and etched etched Al-Si Al-Si cylinder cylinder liner liner after after diﬀerent different etching etching time. time. Figure5 shows the surface morphologies and outlines by an OLYMPUS LEXT OLS4000 laser scanningFigure confocal 5 shows microscopy the surface (Olympus, morphologies Tokyo, and Japan). outlines Seen by from an Figure OLYMPUS5a, the LEXT surface OLS4000 of untreated laser cylinderscanning linerconfocal is ﬂat; microscopy while chemical (Olympus, etching Tokyo, may scourJapan). the Seen aluminum from Figure substrate 5a, onthe thesurface surface, of whichuntreated exposes cylinder the silicon liner is particles, flat; while as shownchemical in Figureetching5b. may scour the aluminum substrate on the surface, which exposes the silicon particles, as shown in Figure 5b.

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Figure 5. Polished surface morphologies and outlines of the cylinder liner. (a) Untreated; (b)

chemical etching; (c) laser finishing. Figure 5.5. PolishedPolished surface surface morphologies morphologies and and outlines outlines of the of cylinder the cylinder liner. (aliner.) Untreated; (a) Untreated; (b) chemical (b) 2.3. Laseretching;chemical Finishing ( cetching;) laser ﬁnishing. (c) laser finishing.

2.3. Laser The Finishinglaser finishing of the Al-Si alloy cylinder liner samples was conducted using a CO2 continuous transverse-flow laser. The advantage of this type of laser is that the output laser beam is The laser finishing of the Al-Si alloy cylinder liner samples was conducted using a CO continuous continuousThe laser and finishingthe energy of is the stable, Al-Si which alloy is cylinder beneficial liner to stably samples control was the conducted surface melting using2 aof COthe2 transverse-flow laser. The advantage of this type of laser is that the output laser beam is continuous and aluminum-siliconcontinuous transverse-flow alloy. The laser. defocus The advantage amount is of setthis to type 2 mm,of laser and is thatthe thelaser output spot laserdiameter beam is the energy is stable, which is beneficial to stably control the surface melting of the aluminum-silicon approximatelycontinuous and 2 themm. energy is stable, which is beneficial to stably control the surface melting of the alloy. The defocus amount is set to 2 mm, and the laser spot diameter is approximately 2 mm. aluminum-siliconFigure 6 shows alloy. the schematic The defocus diagram amount of laser is finishingset to 2 process.mm, and The the high laser temperature spot diameter of laser is Figure6 shows the schematic diagram of laser finishing process. The high temperature of laser causesapproximately the aluminum 2 mm. layer on the surface of the cylinder liner to melt and evaporate, which exposes causes the aluminum layer on the surface of the cylinder liner to melt and evaporate, which exposes the siliconFigure particles. 6 shows Thethe schematicmelting point diagram is higher of laser for finishingthe silicon process. particles The than high the temperature aluminum matrix.of laser the silicon particles. The melting point is higher for the silicon particles than the aluminum matrix. Therefore,causes the thealuminum silicon particleslayer on themelt surface after theof the aluminum cylinder matrix liner to and melt when and evaporate,the aluminum which melts exposes and Therefore, the silicon particles melt after the aluminum matrix and when the aluminum melts and evaporates,the silicon particles. the exposed The siliconmelting particles point is beginhigher to for me thelt in silicon the convex particles corners. than the The aluminum laser has matrix.instant heatingevaporates,Therefore, and the instantaneous the silicon exposed particles silicon cooling, melt particles so after the beginsiliconthe aluminum to pa meltrticles in matrix are the rapidly convex and when cooled corners. the after aluminum The being laser melted, has melts instant andand dueheatingevaporates, to the and lowest the instantaneous exposed surface silicon energy cooling, particles principle, so the begin silicon the sito particleslicon melt particles in arethe rapidlyconvex are rounded cooledcorners. afterby The the being lasersurfacemelted, has tension, instant and whichdueheating to reduce the and lowest instantaneous the surface surface energy energy cooling, during principle, so the the silicon melting the silicon pa rticlesand particles re-cooling are rapidly are molding rounded cooled process. after by the being surfaceOn themelted, premise tension, and ofwhichdue a certainto reducethe lowestmaterial the surfacesurface removal energyenergy rate, during principle,a certain the surfac meltingthe sielicon quality and particles re-cooling is ensured are molding rounded and free process. byof burrs.the surface On The the rounded premisetension, profileofwhich a certain reduceof silicon material the surfaceparticles removal energy can rate, be during a seen certain thein surface meltingFigure quality 5c.and The re-cooling is change ensured molding in and the free laserprocess. of burrs.power On The theaffects roundedpremise the protrusionprofileof a certain of silicon height material particles of removalthe silicon can berate, particles, seen a certain in Figure which surfac5c. also Thee quality affects change is the inensured friction the laser and performance. power free of a ffburrs.ects Figure the The protrusion rounded7 shows theheightprofile surface ofof the silicon morphologies silicon particles particles, and can which outlines be seen also of ain ffthe ectsFigure Al-Si the friction5c.alloy The cylinder performance.change liner in thewith Figure laser different7 showspower laser theaffects surfacepower. the Themorphologiesprotrusion protrusion height and height of outlines the of silicon the of sili the particles,con Al-Si particles alloy which cylinder increases also affects liner from with the 0.7 friction di μffmerent to performance. 1.7 laser μm power. with Figurethe The increase protrusion 7 shows of µ µ laserheightthe surface power. of the morphologies silicon particles and increases outlines from of the 0.7 Al-Sim to alloy 1.7 cylinderm with theliner increase with different of laser power.laser power. The protrusion height of the silicon particles increases from 0.7 μm to 1.7 μm with the increase of laser power.

Figure 6. Laser finishing process of Al-Si alloy cylinder liner. Figure 6. Laser ﬁnishing process of Al-Si alloy cylinder liner. Figure 6. Laser finishing process of Al-Si alloy cylinder liner.

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Figure 7. Surface morphologies and outlines of the cylinder liner with different laser power.

2.4. Wear Tests

Tribotests are conducted on a reciprocating sliding tribotester as shown in Figure 8. The piston Figure 7. SurfaceSurface morphologies morphologies and outlines of the cylinder liner with different different laser power. ring sample is fixed in the jag of the upper holder, while the cylinder liner sample is fixed in the heat block,2.4. Wear which Tests is dragged by a motor through wheel and nod. The reciprocating stroke length is 30 mm. The tribotester can accommodate a wide range of speeds (5–500 r/min), loads (5–380 MPa), and Tribotests are conducted on a reciprocating sliding tribotester as shown in Figure8. The piston temperaturesTribotests (30–300 are conducted °C) between on athe reciprocating piston ring slidingand cylinder tribotester liner. as The shown model in parametersFigure 8. The used piston in ring sample is fixed in the jag of the upper holder, while the cylinder liner sample is fixed in the thisring study sample are is fixeddetermined in the jag by of a the large upper number holder, of while previous the cylinder experiments liner sample to simulate is fixed thein the wear heat heat block, which is dragged by a motor through wheel and nod. The reciprocating stroke length is performanceblock, which of is the dragged piston ringsby a motorand cylinder through liners wheel under and boundary nod. The lubricationreciprocating conditions. stroke length The load is 30 30 mm. The tribotester can accommodate a wide range of speeds (5–500 r/min), loads (5–380 MPa), consistedmm. The of tribotester two stages, can which accommodate are running-in a wide stage range and of steadyspeeds stage. (5–500 The r/min), first stageloads is(5–380 a low MPa), load of and 5 and temperatures (30–300 ◦C) between the piston ring and cylinder liner. The model parameters used in MPatemperatures for 1 h to reduce(30–300 the °C) effect between of burrs the pistonon the testring repeatability; and cylinder theliner. second The model stage is parameters a high load used of 20 in this study are determined by a large number of previous experiments to simulate the wear performance MPathis forstudy 4 h arebecause determined the maximum by a large explosion number pressure of previous of the dieselexperiments engine tois aboutsimulate 20 MPa.the wear To of the piston rings and cylinder liners under boundary lubrication conditions. The load consisted of simulateperformance the surface of the temperaturepiston rings andof the cylinder cylinder liners liner under when boundary the first piston lubrication ring is conditions. near the top The dead load two stages, which are running-in stage and steady stage. The first stage is a low load of 5 MPa for 1 h centerconsisted (TDC), of twothe teststages, temperature which are isrunning-in set to 150 stage°C. In and order steady to ensure stage. theThe boundary first stage lubrication is a low load state of 5 to reduce the effect of burrs on the test repeatability; the second stage is a high load of 20 MPa for 4 h andMPa consider for 1 h tothe reduce wear efficiency,the effect of the burrs speed on isthe select test edrepeatability; as 200 r/min. the The second lubricating stage is oila high is RP-4652D load of 20 because the maximum explosion pressure of the diesel engine is about 20 MPa. To simulate the surface (15W-40/CF-4),MPa for 4 h because which isthe supplied maximum at aex speedplosion of pressure0.1 mL/min. of the By dieselthe pre-experiments engine is about and 20 MPa.contact To temperature of the cylinder liner when the first piston ring is near the top dead center (TDC), the test resistancesimulate themethod, surface the temperature oil film thickness of the cylinderratio near liner the whentop dead the firstcenter piston is calculated ring is near to be the about top dead 0.8 temperature is set to 150 C. In order to ensure the boundary lubrication state and consider the wear undercenter the (TDC), condition the test of thistemperature◦ parameters, is set and to 150the friction°C. In order coefficient to ensure is between the boundary 0.1 and lubrication 0.15, which state is efficiency, the speed is selected as 200 r/min. The lubricating oil is RP-4652D (15W-40/CF-4), which generallyand consider considered the wear to efficiency,be in the theboundary speed islubricat selectedion as state. 200 r/min. Each testThe islubricating repeated oilfour is RP-4652Dtimes to is supplied at a speed of 0.1 mL/min. By the pre-experiments and contact resistance method, the oil obtain(15W-40/CF-4), a stable result. which is supplied at a speed of 0.1 mL/min. By the pre-experiments and contact film thickness ratio near the top dead center is calculated to be about 0.8 under the condition of this resistanceThe friction method, coefficient the oil film and thickness weight loss ratio are near used the to top determine dead center the isfriction calculated performance. to be about The 0.8 parameters, and the friction coefficient is between 0.1 and 0.15, which is generally considered to be in frictionunder thecoefficient condition is the of thisratio parame of the ters,friction and to the th efriction normal coefficient load. The is weight between loss 0.1 is andthe difference0.15, which in is the boundary lubrication state. Each test is repeated four times to obtain a stable result. weightgenerally before considered and after tothe be experiment. in the boundary lubrication state. Each test is repeated four times to obtain a stable result. The friction coefficient and weight loss are used to determine the friction performance. The friction coefficient is the ratio of the friction to the normal load. The weight loss is the difference in weight before and after the experiment.

FigureFigure 8. 8.DiagramDiagram of of the the tribotester tribotester (a ()a and) and the the contact contact between between the the pist pistonon ring ring and and cylinder cylinder liner liner (b (b).).

The friction coeﬃcient and weight loss are used to determine the friction performance. The friction

coeﬃcient is the ratio of the friction to the normal load. The weight loss is the diﬀerence in weight

beforeFigure and 8. after Diagram the experiment. of the tribotester (a) and the contact between the piston ring and cylinder liner (b).

Metals 2019, 9, 431 7 of 13 MetalsMetals 20192019,, 99,, xx FORFOR PEERPEER REVIEWREVIEW 77 ofof 1313 3. Experimental Results 3.3. ExperimentalExperimental ResultsResults 3.1. Friction Performance after Chemical Etching 3.1.3.1. FrictionFriction PerformancPerformancee afterafter ChemicalChemical EtchingEtching Figure9 shows the worn surface morphologies of the etched cylinder liner after di fferent etching FigureFigure 99 showsshows thethe wornworn surfacesurface morphologiesmorphologies ofof thethe etchedetched cylindercylinder linerliner afterafter differentdifferent time. The friction coefficient and weight loss tend to first decrease and then increase with the increase etchingetching time.time. TheThe frictionfriction coefficientcoefficient andand weightweight lossloss tendtend toto firstfirst decreasedecrease anandd thenthen increaseincrease withwith thethe in the chemical etching time, as shown in Figure 10. If the cylinder liner is unetched or the etching time increaseincrease inin thethe chemicalchemical etchingetching time,time, asas shownshown inin FigureFigure 10.10. IfIf thethe cylindercylinder linerliner isis unetchedunetched oror thethe is very short, an insufficient amount of aluminum is removed from the surface to expose the silicon; etchingetching timetime isis veryvery short,short, anan insufficientinsufficient amouamountnt ofof aluminumaluminum isis removedremoved fromfrom thethe surfacesurface toto in contrast, if the etching time is very long, the silicon may easily peel off and abrasive grains form, exposeexpose thethe silicon;silicon; inin contrast,contrast, ifif thethe etchingetching timetime isis veryvery long,long, thethe siliconsilicon maymay easilyeasily peelpeel offoff andand which would increase the friction coefficient and wear loss. As the etched time increases, the friction abrasiveabrasive grainsgrains form,form, whichwhich wouldwould increaseincrease thethe frictifrictionon coefficientcoefficient andand wearwear loss.loss. AsAs thethe etchedetched timetime coefficient decreases from 0.133 to 0.13, and then increases to 0.146. While the wear loss decreases from increases,increases, thethe frictionfriction coefficientcoefficient decreasesdecreases fromfrom 0.0.133133 toto 0.13,0.13, andand thenthen increasesincreases toto 0.146.0.146. WhileWhile thethe 0.45 mg to 0.35 mg, then increases to 1 mg. The friction coefficient and wear amount both reach the wearwear lossloss decreasesdecreases fromfrom 0.450.45 mgmg toto 0.350.35 mg,mg, thenthen increasesincreases toto 11 mg.mg. TheThe frictionfriction coefficientcoefficient andand minimum value at a chemical etching time of 2 min; the protruding height of the silicon particles is wearwear amountamount bothboth reachreach thethe minimumminimum valuevalue atat aa chemicalchemical etchingetching timetime ofof 22 min;min; thethe protrudingprotruding about 1.1–1.2 µm. heightheight ofof thethe siliconsilicon particlesparticles isis aboutabout 1.1–1.21.1–1.2 μμm.m.

FigureFigure 9. 9. TheThe wornworn ss surfaceurfaceurface morphologiesmorphologies ofof thethe etchedetched cylinder cylinder liner liner after after different didifferentﬀerent etchingetching time.time.

Figure 10. Effect of chemical etching time on the weight loss and friction coefficient. Figure 10. EffectEﬀect of chemical etching time on the weight loss and friction coecoefficient.ﬃcient.

3.2.3.2. FrictionFriction PerformancePerformance afterafter LaserLaser FinishingFinishing TheThe frictionfriction coefficientcoefficient andand weightweight lossloss exhibitexhibit thethe samesame trendtrend asas thethe laserlaser powerpower isis increased.increased. WhenWhen thethe laserlaser powerpower isis veryvery lowlow oror veryvery high,high, thethe performanceperformance isis low.low. IfIf thethe laserlaser powerpower isis low,low, itit

Metals 2019, 9, x FOR PEER REVIEW 8 of 13 Metals 2019, 9, 431 8 of 13 cannot effectively make the silicon exposed; if the laser power is high, the silicon may be prone to fall 3.2.off and Friction became Performance abrasive after grains. Laser As Finishing the laser power increases, the friction coefficient decreases from 0.138 to 0.11, and then increases to 0.126. While the wear loss decreases from 0.35 mg to 0.2 mg, then The friction coefficient and weight loss exhibit the same trend as the laser power is increased.2 increasesMetals 2019 , to9, x0.5 FOR mg. PEER When REVIEW the laser power is 1000 W and the according intensity is 31 kW/cm8 ,of the 13 Whenweight the loss laser and powerthe friction is very coefficient low or very reach high, the lowest the performance value, as shown is low. in If Figure the laser 11. powerThe protrusion is low, it cannot effectively make the silicon exposed; if the laser power is high, the silicon may be prone to heightcannot ofeffectively the silicon make particles the silicon is about exposed; 1.2 μm if at the this la serlaser power power. is high, the silicon may be prone to fall fall off and became abrasive grains. As the laser power increases, the friction coefficient decreases off and became abrasive grains. As the laser power increases, the friction coefficient decreases from from 0.138 to 0.11, and then increases to 0.126. While the wear loss decreases from 0.35 mg to 0.2 mg, 0.138 to 0.11, and then increases to 0.126. While the wear loss decreases from 0.35 mg to 0.2 mg, then then increases to 0.5 mg. When the laser power is 1000 W and the according intensity is 31 kW/cm2, increases to 0.5 mg. When the laser power is 1000 W and the according intensity is 31 kW/cm2, the the weight loss and the friction coefficient reach the lowest value, as shown in Figure 11. The protrusion weight loss and the friction coefficient reach the lowest value, as shown in Figure 11. The protrusion height of the silicon particles is about 1.2 µm at this laser power. height of the silicon particles is about 1.2 μm at this laser power.

Figure 11. Effect of laser power on the weight loss and friction coefficient.

3.3. Friction Performance of the Two Surface Treatments The optimal cylinder liner samples resulting from the two surface treatments are used to compare the friction performance. Figure 12 shows the weight loss and friction coefficients between the piston ring Figureand the 11. EffectEcylinderffect of laser liners power with on thedifferent weight losssurface and frictiontreatments. coecoefficient.fficient. The largest friction coefficient of 0.14 is observed for the untreated cylinder, because the aluminum is in direct with the 3.3. Friction Performance of the Two SurfaceSurface TreatmentsTreatments piston ring during friction process, so it is prone to transfer to the surface of piston ring, resulting in the adhesionThe optimaloptimal wear cylinder cylinder and a linerhigh liner samplesfriction samples coefficient. resulting resulting from The from the friction two the surface twocoefficients surface treatments of treatments the are cylinders used are to comparewithused the to thetwocompare friction surface the performance. treatments friction performance. methods Figure 12are Figureshows lower the12than shows weight that theof loss the weight and untreated friction loss and cylinder coe frictionfficients because coefficients between the protrusion the between piston ringofthe the piston and silicon the ring cylinder particles and linersthe reduces cylinder with ditheff erentliners adhesive surface with wear. di treatments.fferent The surfacelaser The finishing largest treatments. friction treatment The coe ffilargest cientresults of frictionin 0.14 the is observedsmallestcoefficient friction for of the0.14 untreated iscoefficient observed cylinder, offor 0.11the becauseuntreatedbecause the cyth aluminumelinder, silicon because particles is in directthe aluminumare with rounded the is piston in and direct ring the with duringstress the frictionconcentrationpiston ring process, during is reduced. so friction it is prone process, to transfer so it is to prone the surface to transfer of piston to the ring, surface resulting of piston in the ring, adhesion resulting wear in andthe adhesion aThe high weight friction wear losscoe and ffiresults cient.a high Theexhibit friction friction the coefficient. coesameffi cientstrend The ofas friction the the cylinders friction coefficients withcoefficient; the of twothe thecylinders surface weight treatments with loss the is methodslowesttwo surface for are the treatments lower laser than finishing methods that of treatment the are untreated lower at than 0.2 cylinder mg.that Theof becausethe surface untreated the of protrusionthe cylinder cylinder because of liner the silicon afterthe protrusion chemical particles reducesetchingof the siliconis the sharp adhesive particles and easily wear. reduces breaks The laser the when finishingadhesive applying treatmentwear. friction. The results Abrasivelaser infinishing the grains smallest aretreatment formed friction resultsand coe ffiscourcient in the of 0.11surface,smallest because resultingfriction the silicon incoefficient higher particles weight of are0.11 loss rounded because than for and theth thee lasersilicon stress finishing concentrationparticles treatment. are isrounded reduced. and the stress concentration is reduced. The weight loss results exhibit the same trend as the friction coefficient; the weight loss is lowest for the laser finishing treatment at 0.2 mg. The surface of the cylinder liner after chemical etching is sharp and easily breaks when applying friction. Abrasive grains are formed and scour the surface, resulting in higher weight loss than for the laser finishing treatment.

Figure 12. Weight loss and friction coefficient coefficient for different different surface treatments. ( (aa)) Friction Friction coefficient; coefficient; (b) weight loss.loss.

Figure 12. Weight loss and friction coefficient for different surface treatments. (a) Friction coefficient; (b) weight loss.

Metals 2019, 9, 431 9 of 13

The weight loss results exhibit the same trend as the friction coefficient; the weight loss is lowest for the laser finishing treatment at 0.2 mg. The surface of the cylinder liner after chemical etching is sharp and easily breaks when applying friction. Abrasive grains are formed and scour the surface, resultingMetals 2019, in 9, x higher FOR PEER weight REVIEW loss than for the laser finishing treatment. 9 of 13

3.4. Surface Morphology of the Piston Ring Figure 13 shows the the surface surface morphology morphology before before and and after after the the CKS CKS piston piston ring ring is isworn. worn. It can It can be beseen seen that that the the dark dark ceramic ceramic particles particles are are inlaid inlaid in in the the chrome chrome layer, layer, and and the the vertical vertical stripes are the original machining marks of the piston ring in thethe circumferentialcircumferential directiondirection (Figure(Figure 1313a).a). When the piston ring is worn against the untreated Al-Si cylinder liner, a layer of aluminum adheres to the surface ofof thethe piston piston ring ring and and the the ceramic ceramic particles partic areles covered are covered by the by plastic the ﬂowplastic layer; flow this layer; indicates this thatindicates adhesive that wearadhesive occurred wear on occurred the piston on ringthe piston surface ring (Figure surface 13b). (Figure When 13b). worn When against worn the cylinder against linerthe cylinder after chemical liner after etching, chemical the piston etching, ring the exhibits piston damagering exhibits marks damage on the surface.marks on The the surface surface. of The the pistonsurface ring of the is easilypiston scratched ring is easily during scratched the friction during due the to thefriction sharp due edge to ofthe the sharp raised edge silicon of the particles. raised Thesilicon original particles. machining The original marks aremachining not observed marks on ar thee not worn observed surface on (Figure the worn 13c). Whensurface the (Figure piston 13c). ring isWhen worn the against piston the ring cylinder is worn liner against after the laser cylinder ﬁnishing, liner the after original laser machiningfinishing, the marks original are stillmachining clearly visible,marks are which still indicatesclearly visible, that only which slight indicates wear occurs that only (Figure slight 13 weard). occurs (Figure 13d).

Figure 13. Surface morphologies of the CKS piston ring before and after wear. (a) Unworn; (b) worn against an untreated Al-Si cylinder liner; (c) worn against an untreateduntreated Al-Si cylindercylinder liner after chemical etching; (d)) wornworn againstagainst anan untreateduntreated Al-SiAl-Si cylindercylinder linerliner afterafter laserlaser ﬁnishing.finishing.

4. Simulation The contactcontact wear wear models models of theof the piston piston ring ring and theand chemically the chemically etched andetched laser-ﬁnished and laser-finished cylinder linerscylinder are liners created are to created compare to thecompare contact the stress contact of thestress silicon of the particles silicon inparticles a static in state, a static as shown state, inas Figureshown in14 .Figure Most 14. scholars Most scholars have studied have studied the asperities the asperities and assumed and assumed that thethat asperities the asperities shapes shapes are hemisphericalare hemispherical (3D) (3D) or semicircular or semicircular (2D) [ 30(2D),31 ].[30,31]. This work This also work assumes also assumes that the pistonthat the ring piston asperities ring areasperities semicircular. are semicircular. The material The property material parameters property parameters are shown are in Tableshown2. in Table 2.

Figure 14. Geometric representation of the contact model. (a) Chemical etching model; (b) laser finishing model.

Metals 2019, 9, x FOR PEER REVIEW 9 of 13

3.4. Surface Morphology of the Piston Ring Figure 13 shows the surface morphology before and after the CKS piston ring is worn. It can be seen that the dark ceramic particles are inlaid in the chrome layer, and the vertical stripes are the original machining marks of the piston ring in the circumferential direction (Figure 13a). When the piston ring is worn against the untreated Al-Si cylinder liner, a layer of aluminum adheres to the surface of the piston ring and the ceramic particles are covered by the plastic flow layer; this indicates that adhesive wear occurred on the piston ring surface (Figure 13b). When worn against the cylinder liner after chemical etching, the piston ring exhibits damage marks on the surface. The surface of the piston ring is easily scratched during the friction due to the sharp edge of the raised silicon particles. The original machining marks are not observed on the worn surface (Figure 13c). When the piston ring is worn against the cylinder liner after laser finishing, the original machining marks are still clearly visible, which indicates that only slight wear occurs (Figure 13d).

Figure 13. Surface morphologies of the CKS piston ring before and after wear. (a) Unworn; (b) worn against an untreated Al-Si cylinder liner; (c) worn against an untreated Al-Si cylinder liner after chemical etching; (d) worn against an untreated Al-Si cylinder liner after laser finishing.

4. Simulation The contact wear models of the piston ring and the chemically etched and laser-finished cylinder liners are created to compare the contact stress of the silicon particles in a static state, as shown in Figure 14. Most scholars have studied the asperities and assumed that the asperities shapes Metalsare hemispherical2019, 9, 431 (3D) or semicircular (2D) [30,31]. This work also assumes that the piston10 ring of 13 asperities are semicircular. The material property parameters are shown in Table 2.

Figure 14.14. Geometric representation of the contactcontact model.model. ( a)) Chemical etching model; (b) laserlaser ﬁnishingfinishing model.model.

Table 2. Material property parameters.

Material Elasticity Modulus (GPa) Poisson’s Ratio Density (g/cm3) Si 190 0.28 2.33 Al 71.7 0.33 2.7

The following assumptions are made for the stress model:

1. The asperity of the piston ring only contacts the silicon particles. 2. The piston ring/silicon particle contact is rigid to ﬂexible so that the piston ring elements cannot penetrate the silicon. 3. The wear depth is the same for the two cases and a given downward displacement of 0.05 µm is applied to the piston ring.

The boundary conditions for the stress model are as follows:

1. The bottom nodes of the silicon particle are ﬁxed:

Ux = Uy = 0 (1)

where Ux and Uy are the degrees of freedom along the x- and y-direction. 2. The downward displacement of the piston ring is:

Uy = 0.05 µm (2) −

Figure 15 shows the contact stress of the silicon particles at the contact positions for chemical etching and laser finishing. The maximum stress occurs at the corners of the silicon particles and is 737 MPa after chemical etching, whereas the edges of the silicon particles are relatively smooth after laser finishing and the maximum stress is 561 MPa, exhibiting less stress. During the contact process, the silicon particles on the surface of the cylinder liner are subjected to greater stress after chemical etching; therefore, wear is more likely to occur and the weight loss of the cylinder liner is larger than for the laser finishing. Metals 2019, 9, x FOR PEER REVIEW 10 of 13

Table 2. Material property parameters.

Material Elasticity Modulus (GPa) Poisson's Ratio Density (g/cm3) Si 190 0.28 2.33 Al 71.7 0.33 2.7

The following assumptions are made for the stress model: 1. The asperity of the piston ring only contacts the silicon particles. 2. The piston ring/silicon particle contact is rigid to flexible so that the piston ring elements cannot penetrate the silicon. 3. The wear depth is the same for the two cases and a given downward displacement of 0.05 μm is applied to the piston ring. The boundary conditions for the stress model are as follows: 1. The bottom nodes of the silicon particle are fixed:

Ux = Uy = 0 (1)

where Ux and Uy are the degrees of freedom along the x- and y-direction. 2. The downward displacement of the piston ring is:

Uy = −0.05 μm (2) Figure 15 shows the contact stress of the silicon particles at the contact positions for chemical etching and laser finishing. The maximum stress occurs at the corners of the silicon particles and is 737 MPa after chemical etching, whereas the edges of the silicon particles are relatively smooth after laser finishing and the maximum stress is 561 MPa, exhibiting less stress. During the contact process, the silicon particles on the surface of the cylinder liner are subjected to greater stress after chemical etching;Metals 2019 therefore,, 9, 431 wear is more likely to occur and the weight loss of the cylinder liner is larger 11than of 13 for the laser finishing.

FigureFigure 15. 15. ContactContact stress stress distribution distribution of of silicon silicon particles particles at at the the contact contact areas. areas. (a ()a Chemical) Chemical etching etching model;model; (b ()b laser) laser finishing finishing model. model. 5. Wear Mechanism 5. Wear Mechanism Figure 16 shows the piston ring-cylinder liner wear mechanism after different surface treatments. Figure 16 shows the piston ring-cylinder liner wear mechanism after different surface In the untreated cylinder liner, the silicon particles are integrated into the aluminum matrix, so a layer treatments. In the untreated cylinder liner, the silicon particles are integrated into the aluminum of aluminum is in direct contact with the piston ring and is prone to adhesive wear, thus resulting in matrix, so a layer of aluminum is in direct contact with the piston ring and is prone to adhesive wear, a higher friction coefficient and weight loss. When the cylinder liner is treated by chemical etching, thus resulting in a higher friction coefficient and weight loss. When the cylinder liner is treated by the silicon particles protrude from the surface. The hard silicon particles prevent the direct contact chemical etching, the silicon particles protrude from the surface. The hard silicon particles prevent between the piston ring and the aluminum, which reduces the adhesive wear. Meanwhile, the relatively the direct contact between the piston ring and the aluminum, which reduces the adhesive wear. concaveMetals 2019 aluminum, 9, x FOR PEER base REVIEW can retain the lubricating oil. When the piston ring reaches the top dead11 center of 13 Meanwhile, the relatively concave aluminum base can retain the lubricating oil. When the piston (TDC), it is not conducive to the formation of oil film due to the low sliding speed, high gas pressure ring reaches the top dead center (TDC), it is not conducive to the formation of oil film due to the low andcondition. high temperature, Therefore, the which wear is underof the thecylinder boundary liner lubricationis large at condition.the top dead Therefore, center. theAfter wear the ofAl-Si the sliding speed, high gas pressure and high temperature, which is under the boundary lubrication cylinderalloy is treated liner is by large chemical at the top etching dead or center. laser Afterfinishing, the Al-Si the protruded alloy is treated hard bysilicon chemical particles etching could or laserbear finishing,the heavy theload, protruded while the hard relative silicon concave particles surface could of bearaluminum the heavy could load, retain while the theoil. relativeWhen the concave piston surfacering is in of the aluminum middle couldof the retaincylinder the liner, oil. When the oil the could piston be ringstored is inin the the middle concave of surface; the cylinder when liner, the thepiston oil couldring reaches be stored the inTDC, the concavethe lubrication surface; condition when the is piston severe, ring and reaches the oil theobtained TDC, thein the lubrication concave conditionsurface could is severe, help to and form the oil oil film obtained to enhance in the concavethe lubrication surface [32]. could Laser help finishing to form oilnot film only to results enhance in thethe lubricationprotrusion [32of]. the Laser silicon finishing particles not only but results also inin therounded protrusion edges, of thewhich silicon reduces particles the but stress also inconcentration. rounded edges, Therefore, which reducesthe friction the stresscoefficient concentration. and the weight Therefore, loss exhibit the friction better coe performancesfficient and thefor weightthe laser loss finishing exhibit than better the performances chemical etching. for the laser finishing than the chemical etching.

Figure 16. SchematicSchematic diagram diagram of the of thewear wear mechanism. mechanism. (a) Untreated; (a) Untreated; (b) chemical (b) chemical etching; etching;(c) laser (finishing.c) laser finishing. 6. Conclusions 6. Conclusions The effects of chemical etching and laser finishing techniques on the friction performance of The effects of chemical etching and laser finishing techniques on the friction performance of an an Al-Si cylinder liner were investigated by a reciprocating wear test. The following conclusions Al-Si cylinder liner were investigated by a reciprocating wear test. The following conclusions were were drawn: drawn: 1. The friction coefficient and weight loss of the Al-Si cylinder liner tend to decrease first and then increase with the increase in the chemical etching time; the optimum etching time is 2 min. 2. As the laser power increases, the friction coefficient and weight loss also decrease first and then increase; the optimum laser power is 1000 W. 3. Chemical etching and laser finishing both remove the surface aluminum layer and result in the protrusion of the silicon particles, which bear the load. Under the boundary lubrication state, the lubricating oil retained in the concave surface could help to form oil film to enhance the lubrication. 4. Unlike chemical etching, laser finishing results in rounded edges of the silicon particles, which decreases the stress concentration. As a result, the surface friction performance of the Al-Si cylinder liner is better when laser finishing is used.

Author Contributions: Data curation, C.L.; Investigation, Z.M.; Project administration, X.H.; Resources, R.H.; Supervision, J.X.; Validation, Y.S.; Writing—original draft, F.D.

Funding: This research was supported by the China Postdoctoral Science Foundation (2017M611209) and Natural Science Foundation of Liaoning Province (20170540083).

Conflicts of Interest: The authors declare no conflict of interest.

References

1. Dwivedi, D.K. Adhesive wear behaviour of cast aluminium-silicon alloys: Overview. Mater. Des. 2010, 31, 2517–2531. 2. Shahrbabaki, Z.K.M.; Pahlevani, F.; Gorjizadeh, N.; Hossain, R.; Ghasemian, M.B.; Gaikwad, V.; Sahajwalla, V. Direct transformation of metallized paper into Al-Si nano-rod and Al nano-particles using thermal micronizing technique. Materials 2018, 11, 1964.

Metals 2019, 9, 431 12 of 13

1. The friction coefficient and weight loss of the Al-Si cylinder liner tend to decrease first and then increase with the increase in the chemical etching time; the optimum etching time is 2 min. 2. As the laser power increases, the friction coefficient and weight loss also decrease first and then increase; the optimum laser power is 1000 W. 3. Chemical etching and laser finishing both remove the surface aluminum layer and result in the protrusion of the silicon particles, which bear the load. Under the boundary lubrication state, the lubricating oil retained in the concave surface could help to form oil film to enhance the lubrication. 4. Unlike chemical etching, laser finishing results in rounded edges of the silicon particles, which decreases the stress concentration. As a result, the surface friction performance of the Al-Si cylinder liner is better when laser finishing is used.

Author Contributions: Data curation, C.L.; Investigation, Z.M.; Project administration, X.H.; Resources, R.H.; Supervision, J.X.; Validation, Y.S.; Writing—original draft, F.D. Funding: This research was supported by the China Postdoctoral Science Foundation (2017M611209) and Natural Science Foundation of Liaoning Province (20170540083). Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. Dwivedi, D.K. Adhesive wear behaviour of cast aluminium-silicon alloys: Overview. Mater. Des. 2010, 31, 2517–2531. [CrossRef] 2. Shahrbabaki, Z.K.M.; Pahlevani, F.; Gorjizadeh, N.; Hossain, R.; Ghasemian, M.B.; Gaikwad, V.; Sahajwalla, V. Direct transformation of metallized paper into Al-Si nano-rod and Al nano-particles using thermal micronizing technique. Materials 2018, 11, 1964. [CrossRef] 3. Ni, J.Q.; Yu, M.H.; Han, K.Q. Debinding and sintering of an injection-moulded hypereutectic Al-Si alloy. Materials 2018, 11, 807. [CrossRef][PubMed] 4. Chiang, K.T.; Tsai, D.C. Effect of silicon particles on the rapidly resolidified layer of Al-Si alloys in the electro discharge machining process. Int. J. Adv. Manuf. Technol. 2008, 36, 707–714. [CrossRef] 5. Chen, C.; Lu, C.Y.; Feng, X.M.; Shen, Y.F. Effects of annealing on Al-Si coating synthesised by mechanical alloying. Surf. Eng. 2017, 33, 548–558. [CrossRef] 6. Burkinshaw, M.; Neville, A.; Morina, A.; Sutton, M. ZDDP and its interactions with an organic antiwear additive on both aluminium-silicon and model silicon surfaces. Tribol. Int. 2014, 69, 102–109. [CrossRef] 7. Ye, H.Z. An overview of the development of Al-Si-Alloy based material for engine applications. J. Mater. Eng. Perform. 2003, 12, 288–297. [CrossRef] 8. Elmadagli, M.; Perry, T.; Alpas, A.T. A parametric study of the relationship between microstructure and wear resistance of Al-Si alloys. Wear 2007, 262, 79–92. [CrossRef] 9. Chen, M.; Meng-Burany, X.; Perry, T.A.; Alpas, A.T. Micromechanisms and mechanics of ultra-mild wear in Al-Si alloys. Acta. Mater. 2008, 56, 5605–5616. [CrossRef] 10. Slattery, B.E.; Perry, T.; Edrisy, A. Microstructural evolution of a eutectic Al-Si engine subjected to severe running conditions. Mat. Sci. Eng. A. 2009, 512, 76–81. [CrossRef] 11. Slattery, B.E.; Edrisy, A.; Perry, T. Investigation of wear induced surface and subsurface deformation in a linerless Al-Si engine. Wear 2010, 269, 298–309. [CrossRef] 12. Zandrahimi, M.; Rezvanifar, A. Investigation of dislocation characterisation in worn Al-Si alloys with different sliding speeds using X-Ray diffraction. Tribol. Lett. 2012, 46, 255–261. [CrossRef] 13. Dwivedi, D.K. Wear behaviour of cast hypereutectic aluminium silicon alloys. Mater. Des. 2006, 27, 610–616. [CrossRef] 14. Shen, Y.; Lv, Y.T.; Li, B.; Huang, R.X.; Yu, B.H.; Wang, W.W.; Li, C.D.; Xu, J.J. Reciprocating electrolyte jet with prefabricated-mask machining micro-dimple arrays on cast iron cylinder liner. J. Mater. Process. Tech. 2019, 266, 329–338. [CrossRef] 15. Mansuri, M.; Hadavi, S.M.M.; Zare, E.; Nabi, M.M. Thermal fatigue behaviour of Al-Si coated Inconel 713LC. Surf. Eng. 2016, 32, 201–206. [CrossRef] Metals 2019, 9, 431 13 of 13

16. Viswanathan, A.; Sastikumar, D.; Kamachimudali, U.; Kumar, H.; Nath, A.K. TiC reinforced composite layer formation on Al-Si alloy by laser processing. Surf. Eng. 2007, 23, 123–128. [CrossRef] 17. Meng, X.C.; Liu, B.; Luo, L.; Ding, Y.; Rao, X.X.; Hu, B.; Liu, Y.; Lu, J. The Portevin-Le Chatelier effect of gradient nanostructured 5182 aluminum alloy by surface mechanical attrition treatment. J. Mater. Sci. Technol. 2018, 34, 2307–2315. [CrossRef] 18. Li, C.D.; Li, B.; Shen, Y.; Jin, M.; Xu, J.J. Effect of surface chemical etching on the lubricated reciprocating wear of honed Al–Si alloy. Proc. IMechE. Part J J. Eng. Tribol. 2018, 232, 722–731. [CrossRef] 19. Riahi, A.R.; Perry, T.; Alpas, A.T. Scuffing resistances of Al-Si alloys: effects of etching condition, surface roughness and particle morphology. Mater. Sci. Eng. A. 2003, 343, 76–81. [CrossRef] 20. Das, S.; Perry, T.; Biswas, S.K. Effect of surface etching on the lubricated sliding wear of an eutectic aluminium-silicon alloy. Tribol. Lett. 2006, 21, 193–204. [CrossRef] 21. Cai, Z.H.; He, J.W.; Di, Y.L.; Zhang, P. Microstructure and high temperature wear resistance of laser quenching and ion sulphidizing composite layer on cylinder inwall. Heat. Treat. Metal. 2011, 36, 55–59. 22. Ghosh, K.; Mccay, M.H.; Dahotre, N.B. Formation of a wear resistant surface on Al by laser aided in-situ

synthesis of MoSi2. J. Mater. Process. Tech. 1999, 88, 169–179. [CrossRef] 23. Tomida, S.; Nakata, K.; Shibata, S. Improvement in wear resistance of hyper-eutetic Al-Si cast alloy by laser surface remelting. Surf. Coat. Technol. 2003, 169, 468–471. [CrossRef] 24. Sušnik, J.; Šturm, R.; Grum, J. Inﬂuence of laser surface remelting on Al-Si alloy properties. Strojniški vestnik-J. Mech. Eng. 2012, 58, 614–620. [CrossRef]

25. Gao, J.F.; Suo, J.P. Preparation and characterization of the electrodeposited Cr–Al2O3/SiC composite coating. Appl. Surf. Sci. 2011, 257, 9643–9648. [CrossRef] 26. Jang, J.H.; Joo, B.D.; Lee, J.H.; Moon, Y.H. Effect of hardness of the piston ring coating on the wear characteristics of rubbing surfaces. Met. Mat. Int. 2009, 15, 903–908. [CrossRef] 27. Zhu, F.; Xu, J.J.; Han, X.G.; Shen, Y.; Jin, M. Tribological performance of three surface-modified piston rings matched with chromium-plated cylinder liner. Ind. Lubr. Tribol. 2017, 69, 276–281. [CrossRef] 28. Shen, Y.; Yu, B.H.; Lv, Y.T.; Li, B. Comparison of heavy-duty scuffing behavior between chromium-based ceramic composite and nickel-chromium-molybdenum-coated ring sliding against cast iron liner under starvation. Materials 2017, 10, 1176. [CrossRef] 29. Shen, Y.; Xu., J.J.; Jin, M.; Yuan, X.S.; Wang, J.P.; Liu, Y.; Zhu, F.; Wang, Z.Q. Scuffing behavior of CKS piston ring with alloy cast iron cylinder liner. Lubr. Eng. 2014, 39, 40–43. 30. Liu, W.Q.; Zhang, J.H.; Hong, J.; Zhu, L.B. Elastic contact model of elliptical parabolic asperity. J. Xi’an Jiaotong. Univ. 2015, 49, 34–40. 31. Zhao, Y.W.; Maietta, D.M.; Chang, L. An asperity microcontact model incorporating the transition from elastic deformation to fully plastic flow. J. Tribol. 2000, 122, 86. [CrossRef] 32. Sun, T.F.; Guo, M.X.; Zhu, H.Y.; Chen, D.H.; Sun, Y.H.; Wang, F.D. The friction wearing properties research of high-silicon aluminium alloy cylinder sleeve. Vehicle. Power. Tech. 2007, 2, 14–18.

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