Jet Composition in Magnetic Pulse Welding: Al-Al and Al-Mg Couples

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MPW jet phenomena were investigated and jet material composition for similar Al alloys and two samples of dissimilar Al-Mg alloy couples were observed

BY A. STERN, O. BECHER, M. NAHMANY, D. ASHKENAZI, AND V. SHRIBMAN

the maximum magnetic pressure. The ABSTRACT acceleration of the outer tube through the standoff gap is higher near the open Magnetic pulse welding (MPW) produces a mechanically induced essentially solid end of the tube due to higher magnetic state but partially fusion-type weld, with an extremely small fusion zone and pressure and decreases down to zero at extremely high cooling rates. Composition of material jet emission in MPW was inves- the weld end where there is no move- tigated for similar and dissimilar metal lap joints. The jet residues emitted from Al/Al ment of the outer tube (Refs. 6–8). As a and Al/Mg lap joints were collected and characterized, and their composition was mi- croanalyzed by scanning electron microscopy with energy-dispersive spectometry result, the collision is oblique and the (SEM-EDS). The composition of the jet remains was governed by the degree of rela- initial part of the joint collides at a high tive density difference between the two metal components. The metal jet emitted collision angle and at very high collision during Al/Mg welding was mainly composed of Mg, the metal component with lower velocity; frequently, no bond is formed density. The approximate thickness of the layers, peeled during the MPW process, in this area. In MPW, just as in explo- was calculated; an average thickness of 15 μm was found for the Al-Al couple and for sion welding (EXW), there is a welding Al-Mg couples the values were about 10 μm. window defining the angular impact range in which welding can take place (Refs. 10, 11). As the weld progresses, KEYWORDS the outer component is accelerated and collapses under the magnetic pressure; • Magnetic Pulse Welding • Al-Al Couple • Al-Mg Couple meanwhile, the collision angle decreases • Jet Material Composition and the collision velocity declines gradually to zero. Simultaneously, the local Introduction lision of the metal couple creates a jet temperature of the materials’ interfaces consisting of a mixture of surface con- is increased significantly under the ac- The principle of magnetic pulse taminants, gases, and hot metal, eject- tion of the shock waves and the severe welding (MPW) is briefly summarized ed from the adjacent surfaces of both plastic deformation (Refs. 2–4). below. metals. The two parts of the joint are Many researchers have studied geo- During the MPW process, the metal then forced together to form a solid- metrical and metallurgical features parts collide with each other at a high state weld, while the whole process along the interfacial zone of EXW and velocity as a result of repulsion be- takes less than 100  sec — Fig. 1. MPW joints and discussed the possible tween magnetic fields. The magnetic As well established, the collision impact on the joint properties. Perti- pressure is produced through a rigid pressure is proportional to the flyer mo- nent elements include wavy interface coil, while the impulse current is sup- mentum, which is dependent on the col- geometry, pockets and films of molten plied via a capacitor bank. The repul- lision velocity. With increasing pulse en- and resolidified material, and inter- sion between the coil magnetic field ergy, the traveling velocity of the flyer metallic phase formation. Also, the and the induced magnetic field on the workpiece increases the collision pres- spallation effects, formation of cracks outer workpiece results in a J × B force sure at the interface and likewise in- and pores, incomplete welding zones, (Lorenz force) that causes an oblique creases. Since the open end of the weld- and local plastic deformation are de- collision of the outer workpiece onto ed sample is located near the middle of bated (Refs. 1–25). From literature the inner part to be welded, at speeds the coil (where the magnetic flux densi- and our own experiments, it is not en- reaching 700 m/s (Refs. 1–9). The col- ty is maximum), this area is subjected to tirely clear if the formation of inter-

A. STERN and O. BECHER are with the Department of Mechanical Engineering, Afeka Academic College of Engineering, Tel Aviv, Israel, and A. STERN is also with Department of Materials, Ben-Gurion University of the Negev, Beer Sheva, Israel. M. NAHMANY is with the Department of Materials, NRCN, Beer Sheva, Israel. D. ASHKENAZI ([email protected]) is with the School of Mechanical Engineering, Tel Aviv University, Ramat Aviv, Israel. V. SHRIBMAN is with Bmax Srl., Toulouse, France.

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metallic phase during MPW of dissimilar metal couples can be completely avoided. Nevertheless, it was clearly demonstrated that the geometry, structural, and chemical composition of the interfacial zone is difficult to control by the process parameters. This is of much importance, since as soon as the intermetallic phase film exceeds a critical thickness of about a few microns, voids, pores, and exten- sive cracking may considerably deteri- orate the weld quality. Few comprehensive reviews were published in referred journals during Fig. 1 — General view of a tubular configuration MPW set-up scheme. The outer compo- the last three years discussing the cur- nent is electrically conductive and plastically deformable because MPW uses an electro- rent state-of-the-art of MPW technol- magnetic field to perform the welding (Ref. 15). ogy (Refs. 1, 11, 24, 26).

Jet Formation C The interfacial bonding layer, created during MPW, generally has a semi- regular wavy morphology and the wavelength is not uniform along the D interface. The transition from a planar to a wavy interface appears to be asso- A B ciated with the increase in shear stresses and in local plastic strain. The magnitude of the interfacial wave is considered to reflect the collision pressure at the interface (Ref. 13). Howev- er, the reasons for the formation of the wavy interface between the sur- E F faces are still in discussion. The collision pressure in MPW is estimated to be in the range of one GPa. During EXW, much higher pressure is generat- ed, probably several 10s of GPa, and the magnitude of the interfacial waves are likewise larger than those observed in MPW joints. The local pressure Fig. 2 — Mapping of MPW Sample 1 (Al 6082-T6, Al/Al system) jets’ locations. A — Gen- must be of sufficient magnitude to ex- eral view, upper jet; B — general view, lower jet; C — panoramic LM observation of the ceed the dynamic elastic limit of the upper captured jet (the direction of the welding is shown by the dashed arrow); D — material to ensure deformation of the panoramic LM image of the lower captured jet; E — SEM image of the upper jet; F — metal surfaces into a jet. Due to the jet SEM image of the lower jet. formation, a scavenging action occurs between the two mating surfaces. Jet- both EXW and MPW. nent with lower density, Al. ting makes metallurgical bonding pos- In Kakizaki et al. research (Ref. 12), On the other hand, when the density sible by causing the breakup of the several types of lap joints were fabri- difference was small or zero, such as for contaminant surface films and by ex- cated by MPW, and the emitted metal Cu/Ni and Al/Al lap joints, the metal jet posing virgin metal surfaces, which are jet was collected. The emission behav- was composed of both metal compo- brought into intimate contact under ior of the metal jet and the resultant nents, more or less equally. Metal jets high pressure. According to Crossland interface morphology were investigat- emitted from Al/Cu and Cu/Al lap joints et al. (Ref. 13), during the impact, ed, and the chemical composition of were collected, and they were mainly welding kinetic energy in the jet would the metal jet and the interface mor- composed of the metal component with be dissipated as heat, causing melt at phology were compared with simula- lower density, Al. In the case of Al/Mg the interface. On the basis of experi- tion results. When the density differ- and Mg/Al lap joints, metal jet composi- mental evidence, it is commonly ac- ence was large, such as Al/Cu and tion changed, depending on the colli- cepted that jet formation is an impor- Al/Ni lap joints, the metal jet was sion conditions. Through observation of tant prerequisite for a sound weld in mainly composed of the metal compo- the whole simulation process, they

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and Al-Mg couples, components with A B close physical properties. The melting point of pure Al (density 2.69 g/cm3) is 660°C and the melting point of pure Mg (density 1.74 g/cm3) is 650°C. In all MPW experiments, the flyer component was in a tubular form, while the stationary component was a round bar placed inside the outer tube. The welding was carried out using a single turn CuCr induction coil with a width of 10 mm, mounted around the outer workpiece. The maximum energy load capacity of 20 kJ at 9 kV ma- C D chine was employed. The welding root opening range applied was between 1 and 1.5 mm for the three weld combinations, while the energy level range was 9 to 15 kJ. Optimum parameters for the samples were initially checked by peel testing and metallographic surveillance of the interface. The magnetic field in the gap between the coil and the welded components peaked at 16 Tesla. Three specimens were cross- sectioned after welding and then examined. The couples included one sample Fig. 3 — Metallographic SEM observation of the upper jet captured in Sample 1. A — The of a similar Al couple, from Al 6082-T6 central area of the jet; B — the left side of the jet shown in Fig. 2C; C — the right side of (Samples 1); one sample of an Al-Mg the jet; D — the local points of the EDS analysis at the central-right area of the jet. couple of Al 1050 and Mg AZ31 (Sample 2); and one sample of an Al-Mg couple found that most of the jet material orig- jet emission during EXW and MPW of Al 4014 and Mg AZ91 (Sample 3). inates from the low density material have been reported in the literature, as The Al was the outer (flyer) tube in all and as the jet symmetry decreases, the described above. A further investiga- the Al/Mg couples. The chemical com- higher density material increases its tion of the jet nature and composition positions of the outer and inner work- contribution to jetting (Ref. 12). The ex- during the bond formation is impor- pieces (bulk material) are shown in perimental results were quite well re- tant due to its high practical signifi- Table 1. produced in these simulations, as cance (Refs. 11, 24, 26–28). This paper In order to obtain a sound weld in shown for jet formation in Al-Mg cou- attempts to integrate and analyze the MPW, the outer part should be highly ples (Ref. 12, Fig. 10, p. 1006). data we produced during the last few ductile under dynamic stresses; Al and Aizawa and his colleagues (Refs. 9, years on the jetting remains accumu- Cu are usually used as flyers. By using 22, 23) directly observed the metal lated during MPW of similar metals, an alloy (i.e., Mg) with different me- jets emitted from Al/Al thin sheet lap Al-Al couples, and dissimilar metal chanical properties, the joint forma- joints, during MP welding. The jets couples of Al-Mg. tion and properties can drastically emitted brilliant lights in the air and change; the composition of the jet re- the length of the perceived lights was mains may also be different. 1 to 2 mm. They also showed that the Materials and Experiments The dissimilar couples (Al-Mg) were jet created in Al-Fe couples contains selected for this research due to the mostly Al. In this research, the jet phenomenon poor weldability of such pairs when Only a few experimental studies on was investigated for similar Al alloys using conventional fusion welding

Table 1 — Chemical Compositions

Sample Alloy Compositions eight percentage (wt-%) 1 Al 6082-T6 Al Si Fe Cu Mn Mg Cr Zn Ti Other 95.2–98.3 0.7–1.3 ≤0.5 ≤0.1 0.4–1 0.6–1.2 ≤0.3 ≤0.2 ≤0.1 ≤0.2 2 Al 1050 99.5≤ ≤0.3 ≤0.4 ≤0.1 ≤0.1 ≤0.1 – ≤0.1 ≤0.1 ≤0.1 Mg AZ31 2.5–3.5 ≤0.1 – ≤0.1 0.2≤ 97.0 – 0.6–1.4 – ≤0.3 3 Al 4014 95.4–98.3 1.4–2.2 ≤0.7 ≤0.2 ≤0.4 0.3–0.8 – ≤0.2 – ≤0.2 Mg AZ91 8.3–9.7 ≤0.5 – ≤0.1 ≤0.1 90.0 – 0.4–1.0 – –

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tively high quality welding zone with a A B typically wavy interface and no heat- affected zone — Fig. 2. The up and down locations showed a similarly shaped defect. The couples are cylindrical in shape and the jet material has a ring shape that extends the entire circumference of the tube joint. Up and down locations are randomly located depending on the sample orien- tation when it was sectioned. All samples exhibited permanent plastic deformation of both the outer and inner workpieces (Figs. 2, 5, 7). In C D the interfacial welded zones, a few discontinuities such as inclusions, pores, and cracks were occasionally observed. Features observed in this work are con- sistent with those observed in Ref. 29. Similar Al Alloy

Sample 1 (Al 6082-T6 Couple)

The general location of the upper and lower jets in the metallographic (LM) samples is shown in Fig. 2A, B, Fig. 4 — Metallographic SEM observation of the lower jet captured in Sample 1. A — respectively. The panoramic metallo- General view of the jet (the darkest region here are cavities); B — image of the right side graphic picture of the similar Al alloy of the jet; C — Central-right side of the jet showing the points examined by the EDS couple (sample 1, Al 6082-T6 alloy), analysis; D — Higher magnification of the dashed square marked in C, showing the shows the L cross-sectional area of the points that were examined by EDS. jet’s residue ejected and captured, during welding; one area located at the techniques; the formation of large The VT and stereoscopic microscopy upper welding zone (Fig. 2C, upper amounts of low ductility intermetallic were performed on all samples in order jet), and the other located at the lower compounds in the weld metal is detri- to detect any visible discontinuities and welding zone (Fig. 2D, lower jet). In or- mental to the joint mechanical proper- defects in the welding zone. The metal- der to estimate the thickness of the ties (Ref. 1). Al alloys were successfully lographic samples were examined under layer that the jet peeled off during the MP welded to Mg alloys and the jet- a Zeiss Axio Scope A.1 optical micro- MPW process, jet residual cross-sec- ting nature research is important for scope (LM). The samples were charac- tional area was measured and divided understanding the bonding process terized by SEM and the composition by the length of the welded interface. (Refs. 1, 2, 5, 6, 8, 19). was analyzed by EDS (Philips Micro FA Since the upper jet’s area was about Metallurgical methods were used in SEM, FEI Quanta 200). Microanalysis 375,000 m2 and the length of the order to determine the welding quality, by EDS was used to evaluate the local welded interface was 11,000 m, the including visual examination (VT), distribution of alloying elements at the estimated thickness of the upper layer stereoscopic microscopy, light optical joint and its vicinity, as well as the jet is about 17 m. Since the material microscopy (LM), and scanning electron composition. Special MPW joint config- mostly consists of Mg, one can safely microscopy (SEM) with energy-disper- urations ensured trapping of jet re- assume that the majority of the 17 mi- sive spectrometry (EDS) microanalysis. mains created during the process. The crons layer came from the Mg side. The metallographic samples (1–3) jet’s structure and composition were mi- Since the lower jet’s area was about were sectioned in the longitudinal cross croanalyzed by the SEM/EDS technique. 255,000 m2, the estimated thickness section (L-CS), according to the ASTM- of the lower layer is 13 m. Using the E3 Standard, one from each of the Results above approximations, we can safely workpieces. Each sample contains two assume that the average layer of metal regions (up and down notation), of the Initial VT observation performed removed by the jet along both inter- welding zone. The samples were mount- on all three samples revealed the pres- faces is less than 20 m. ed; then the surface was ground with ence of jet remnants accumulated in SEM observation of jet residue silicon-carbide 240–2400-grit papers, nooks, located at the end of the weld- emitted during the process is shown in followed by polishing with 5 to 0.3-mi- ing zone. For each sample, two regions Fig. 2E and F for the upper jet and the cron alumina pastes and 0.05-micron were observed (up and down loca- lower case, respectively. The upper jet colloidal silica suspensions. tions). All three samples had a rela- had a main crack running along the jet

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A B A B

C C D

Fig. 5 — Mapping of MPW Sample 2 (Al/Mg couple) captured Fig. 6 — Metallographic SEM-EDS image and elemental mapping jets’ locations. A — General view of the metallographic sample of Sample 2 (Fig. 5). A — The metallographic image of the lower showing the lower jets’ locations; B — SEM image of the jet re- jet captured at the end of the MPW interface; B — elemental mains that were sprayed on the opposite Mg wall showing the mapping showing the presence of Al mostly outside the jet; C — local area of the EDS analysis; C — SEM image of the jet re- high concentration of Mg inside the jet area; D — higher concen- mains at the end of the MPW interface. tration of O inside the jet area is displayed.

remains from one side to the other ty is that the jet material was captured Point 1–2) was about 97.0 wt-% Al with (SEM images, Figs. 2E, 3) created by a and filled the cavity, but a portion of the no presence of oxygen. In addition, the local stress concentration in the low material escaped through a narrow pas- Mg, Si, and Mn present in the alloy was ductility residues. The general mor- sage present at the end of the weld. A measured along with some iron (about phology of the upper jet was of a few perpendicular cracks were also ob- 3.0 wt-% of alloying elements). porous material containing several 50- served in the jet material layer attached m large pores and a huge amount of to the walls. Longitudinal tensile stress- Al-Mg Dissimilar Couples, medium and small pores — between 1 es created in the Al workpieces and as- Components with Similar Physi- to 20 m (Fig. 3). The EDS analysis of sociated with the components radial re- cal Properties the upper jet revealed that the jet re- duction during the process, along with mains were composed of a mixture of material contraction during the solidifi- Sample 2 (Al 1050/Mg AZ31 couple) spongy aluminum and aluminum ox- cation phase, probably played a major ide, with an average composition of role in the layer perpendicular cracking Metallographic (LM, SEM) observa- 91.9–93.5 wt-% Al and 1.6–3.7 wt-% (Ref. 19). The morphology of the lower tion of the Al/Mg couple (Sample 2, Al O, as well as the Al 6082 alloying ele- jet was similar to the upper jet material, 1050 and Mg AZ91), revealed only one ments Mg, Si, Mn, and some Fe (Fig. i.e. a porous material containing several captured jet residual area with two 3D, points 1–4). In comparison, the 50-m holes and hundreds of medium separate jet material leftovers (Fig. 5). composition of the Al workpiece adja- and small pores between 1 m to 20 m The morphology of Sample 2’s materi- cent to the jet (Fig. 3D, point 5) re- (Fig. 4). The EDS analysis revealed that al is quite similar to the jet material vealed a composition of 96.7 wt-% Al the lower jet remains were rich in alu- observed in the Al/Al sample (Figs. 3, along with 0.2 wt-% O, and Mg, Si, minum oxide particles, containing 4), e.g., a spongy material containing Mn, and some Fe. 37.8–82.1 wt-% Al and 4.8–20.9 wt-% O several 50-m holes and many small The lower jet also had a main crack and up to 1.4 wt-% Mg, up to 0.9 wt-% pores between 1 to 20 m. Conversely, running through the jet material (SEM Mn, and between 10.5–40.3 wt-% Si the structure of the jet material shown images, Fig. 2F and Fig. 4A–C), but in (Fig. 4D, points 1–4). According to the in Fig. 5B was very different from the this case a large oval-shaped hole (about original alloy (Al 6082-T6) bulk compo- material observed in Fig. 5C; the un- 400 × 800 m in size) was observed in sition, the amount of Si should be up to cracked material in Fig. 5C appears the central area of the jet residuals. The 1.3 wt-%. The local SEM-EDS high sili- denser and contains substantially less hole was probably created because a rel- con composition may have resulted porosity. The small triangular-shaped atively small amount of jet material was from remains of SiC grinding and col- jet material located at the end of the captured in this location, and the jet loidal silica polishing particles inside the weld appears to be detached from both material solidified along the cavity pores. the Al and Mg cavity walls. This may walls, according to the local geometry of The measured composition of the Al be the reason that no cracks were the parts. Another (but slight) possibili- workpiece adjacent jet material (Fig. 4C, found in the material.

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B A B A

Fig. 8 — Metallographic SEM observation of the upper jet captured in Sample 3 showing two different jet areas. A — Jet remains that were observed attached to the Al side wall; B — jet remains that Fig. 7 — Mapping of MPW Sample 3 (Al/Mg system) captured were observed on the Mg side wall. jets’ locations. A — General view of the metallographic sample showing the upper jet’s location; B — SEM image of the jet leftover locations (the darkest region here are cavities). A B

The EDS local area analysis (Fig. 5C, wall (Fig. 8A) area 1) revealed that the jet residue was was heavily composed of 69.0 wt-% Mg, 16.7 wt-% cracked and con- Al, and 10.1 wt-% O, as well as 4.2 wt-% tained some fine Si. EDS local analysis of the jet material porosity. The (point 1, Fig. 6A) is composed of 77.6 EDS local area wt-% Mg, 14.0 wt-% Al, and 7.3 wt-% O, analysis re- as well as 1.1 wt-% Si. The white inclu- vealed that the sion embedded in the Mg AZ31 alloy composition was (point 2, Fig. 6A) contains 42.5 wt-% Al, 48.2–54.0 wt-% 33.0 wt-% Mn, and 22.5 wt-% Mg, as Mg, 40.5–42.7 Fig. 9 — Metallographic SEM observation of the upper jet captured in Sample 3. A — Jet remains that were observed far from the end well as 1.9 wt-% Si, as expected for a wt-% Al, and of the MPW interface, as shown in Fig. 7B; B — graph of the Mg, Al, Mn-Al alloying elements and inclusions 4.8–5.0 wt-% O, O composition at points 1–6 from Fig. 9A. normally found in Mg AZ31 alloys. No as well as up to attempt was made to determine the Al- 3.4 wt-% Si and Mg compounds in Fig. 6. Based on pre- 0.7–0.8 wt-% Zn (Fig. 8A, points 1 and (point 1) to 53.8 wt-% Mg (point 6), vious experience with MPW of Al-Mg 2). The Al 4014 original bulk composi- the aluminum composition was in- couples, one may expect metastable in- tion contains less than 0.2 wt-% Zn, creased from 20.3 wt-% Al (point 1) to termetallics. The metallographic image and the MgAZ91 original bulk compo- 43.3 wt-% Al (point 6), while the oxy- and elemental EDS area mapping of sition contains about 0.8 wt-% Zn. Ac- gen concentration remained quite con- Sample 2 (Fig. 6A) indicates that the jet cording to the local jet’s composition, stant (Fig. 9B). Elemental mapping of material contains primarily Mg (Fig. 6C) it can be seen that the jet next to the Sample 3 showed that the jet material and some oxygen (Fig. 6D). However, Al area contains much more Zinc than captured in this sample contains most- the local SEM-EDS relatively high sili- the Al bulk material, with Zn composi- ly magnesium and low quantities of con local composition may result from tion close to the Mg bulk material. On aluminum (Fig. 10, SEM-EDS). remains of SiC grinding and colloidal sil- the other hand, EDS analysis showed ica polishing particles, found inside that the jet’s local composition, at- Discussion pores and cracks. tached to the Mg wall, was 70.0–78.9 wt-% Mg, 17.2–26.3 wt-% Al, and 3.3– In this study, MPW jet phenomena Sample 3 (Al 4014/Mg AZ91 couple) 3.9 wt-% O (Fig. 8B, points 1–3). For were investigated and focused on the comparison, the composition of the observation of jet material composi- Metallographic observation of the aluminum alloy was 96.8 wt-% Al, 1.0 tion for similar Al alloys, Al 6082-T6, Al/Mg couple revealed the upper jet’s wt-% Mg, and 2.2 wt-% Si; and the and two samples of dissimilar Al-Mg location (Fig. 7). Since at the right side composition of the magnesium alloy alloy couples. of the couple a passage was open be- near the jet (in 20-m distance) was In all the experiments, the accelera- tween the parts, the jet material has 93.2 wt-% Mg, 4.1 wt-% Al, 2.0 wt-% tion of the outer aluminum component probably escaped. SEM observation of O, and 0.7 wt-% Zn. through the opening was higher at the the upper jet region revealed scattered The average composition of the ac- open end of the tube, due to higher jet leftovers (Figs. 7, 8) located and at- cumulated jet material near the nar- magnetic pressure at this area and detached along the cavity between the row opening varied between 53.8–78.5 creasing down to zero at the weld end walls, with most of the material accu- wt-% Mg, 17.9–43.3 wt-% Al, and 2.9– where there is no movement of the out- mulated at the opening cavity between 4.3 wt-% O (Fig. 9A, Point 1–6). er tube (Refs. 2–4). As a result, the colli- the Al and Mg parts’ walls. Whereas the magnesium composition sion is oblique and the impact angle was The jet material attached to the Al was reduced from 75.4 wt-% Mg formed. As the weld progresses, the col-

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A B C A

Fig. 10 — Metallographic SEM-EDS image and elemental mapping of Sample 3 showing the upper jet. A — General metallographic view of the captured jet; B — elemental mapping showing presence of Mg inside the jet; C — presence of Al mostly outside the jet. B

lision angle gradually decreases and sta- sition of the upper and lower remains bilizes in the welding window leading to were similar, with a composition of an interfacial condition that is consid- ~90 wt-% Al and ~5 wt-% O for most ered to shift from a nonweldable condi- points, as well as small amounts (~5 tion to weldable condition. In all three wt-%) of Mg, Si, Mn, and Fe (elements samples, a relatively high-quality weld- that exist in the Al bulk material). Mg, ing zone with a typically wavy interface Si, and Mn are alloying elements in the was observed (e.g., Fig. 2) leading to the Al 6082-T6 and the Fe is an impurity. conclusion that all the welds were pro- According to this composition, it was Fig. 11 — MP welded Al to Mg couples duced under the ‘welding window’ con- concluded that the jet’s material was SEM-BSE micrographs. A — Al 1050 to dition for each couple. composed of the Al thin layers peeled Mg AZ91 weld, zoom on the captured The local pressure created by the off from both workpiece surfaces and and accumulated jet material; B — Al impact is of sufficient magnitude to its oxide formed during the jetting. 1050 to Mg AM50 weld, zoom on the exceed the dynamic elastic limit of the The jet material emitted during heavily cracked captured jet material material and ensure severe shear de- MPW of the dissimilar Al-Mg couples (Ref. 25). formation of thin layers of metal at (Samples 2 and 3, SEM-EDS analysis), the adjacent interfaces, forming a jet. was composed of magnesium, alu- of our experiments, conducted under a Jetting makes metallurgical bonding minum, and oxides created during the cylindrical configuration, show that the possible by exposing virgin metal sur- process. All these components were jet’s composition for Al/Mg couples faces, which are brought into close mixed at the elevated local tempera- varies as a function of the local geome- contact under high pressure. By meas- tures creating the jet material. Remains try, as described by Kakizaki et al. (Ref. uring the jet residue volumes, the ap- of the same particular jet were observed 12) for the planar configuration experi- proximate thickness of the layers as having different compositions in var- ments and simulations. While density ejected during the welding process was ious locations (Fig. 8). Sample 3 jet com- likely plays a key role in the fraction of estimated; an average thickness of 15 position at point 1 was 75.4 wt-% Mg, jet material from each material pair, m was found for the Al-Al couple, and the Mg composition at point 6 was other properties, such as the melting and using the same scheme for Al-Mg only 53.8 wt-% Mg (Fig. 8C, D). The re- temperature, may also contribute signif- couples (Fig. 11), the calculated values sults show that the jet’s composition icantly. In our case, the Mg alloys have a were ~10 m. varies as a function of the local geome- slightly lower melting temperature and The jet material, according to the try and distance from the welding zone. a lower density; it is safe to assume that SEM-EDS analysis, was composed of a Kakizaki et al. (Ref. 12) showed that in both properties can lead to high levels mixture of spongy metals and oxides the case of Al/Mg and Mg/Al joints, of Mg concentration in the jet material. originating from the thin layers of metal jet composition changes depend- Two types of jet residue material metal ejected from both surfaces during on the local collision conditions. were found: cracked (Al/Al, Figs. 2, 3 ing the MPW process. In the similar Al They found that, typically, most of the and Al/Mg, Fig. 10), and uncracked ma- alloys couple, the captured remains jet material originates from the low terial (Al/Mg, Fig. 5 and Al/Mg, Fig. 8). were composed of aluminum and alu- density material and as the jet symme- The structure of the second type was minum oxide, where the Al composi- try decreases, the higher density mate- usually different from that of the first tion was identical to the composition rial increases its contribution to jetting. one. The uncracked material looks of the bulk metal. The Al-Al jet’s mate- This behavior may explain the changes denser and contains significantly less rial was very porous, most likely as the in concentrations of the Mg and Al, as a porosity. The triangular-shaped materi- result of gases trapped during the so- function of the local geometry as meas- al located at the end of the weld (Fig. lidification period at the end of the ured in Sample 3. It is well documented 5B) appears to be detached from both welding process. The presence of the in all Al-Mg micrographs (Figs. 5–10) the Al and Mg cavity walls. This may be longitudinal cracks (seen in Figs. 2, 3) that the jet material is very porous, oc- the reason that no cracks were found in originates from the existence of high casionally containing a few large holes this material. In the first stage of jet springback stresses in the low ductility and large amounts of medium and small material solidification, a coherent net- jet residue material. Chemical compo- pores in the 1–50 m range. The results work does not form and cracks would

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not occur. As the dendrites grow and thesis, Ben-Gurion University. als Science 45: 4645–4651. come into contact, a coherent network 5. Zhang, Y., Babu, S. S., Prothe, C., 18. Raoelison, R. N., Racine, D., Zhang, forms. Further solidification would pro- Blakely, M., Kwasegroch, J., LaHa, M., and Z., Buiron, N., Marceau, D., and Rachik, M. duce stress, when the material contrac- Daehn, G. S. 2011. Application of high ve- 2014. Magnetic pulse welding: Interface of tion is restrained by the cavity walls. locity impact welding at varied different Al/Cu joint and investigation of inter- length scales. Journal of Materials Process- metallic formation effect on the weld fea- Figure 10 demonstrates that the low ing Technology 211: 944–952. tures. Journal of Manufacturing Processes ductility remains were prone to tearing 6. Stern, A., and Aizenshtein, M. 2002. 16: 427–434. when attached to the cavity walls, and On the bonding zone formation in mag- 19. Stern, A., and Aizenshtein, M. no cracking was observed when the ma- netic pulse welds. Science and Technology of 2011. Magnetic pulse welding of Al to Mg terial was detached. Welding and Joining 7: 339–342. alloys: Structural mechanical properties of The experimental results of this re- 7. Shribman, V., Stern, A., Livshitz, Y., the interfacial layer. Materials Science and search may shed some light on MPW and Gafri, O. 2002. Magnetic pulse welding Technology 27: 1809–1813. solid-state welding principles and in produces high-strength aluminum welds. 20. Göbel, G., Beyer, E., Kaspar, J., and particular will contribute to the under- Welding Journal 81: 33–37. Brenner, B. 2012. Dissimilar metal joining: standing of the jetting phenomenon. 8. Stern, A., Aizenshtein, M., Moshe, Macro- and microscopic effects of MPW. G., Cohen, S. R., and Frage, N. 2013. The 5th International Conference on High Speed Such knowledge may help to improve nature of interfaces in Al-1050/Al-1050 Forming, Dortmund, Germany, April product design in the MPW manufac- and Al-1050/Mg-AZ31 couples joined by 24–26, pp. 179–188. turing process of similar and dissimilar magnetic pulse welding (MPW). Journal of 21. Haiping, Y., Zhidan, X., Zhisong, F., metal alloy couples. Materials Engineering and Performance 22: Zhixue, Z., and Chunfeng, L. 2013. Proper- 2098–2103. ty and microstructure of aluminum alloy 9. Watanabe, M., Kumai, S., Okagawa, — Steel tubes joint by magnetic pulse Acknowledgments K., and Aizawa, T. 2008. In-situ observa- welding. Materials Science and Engineering A tion of magnetic pulse welding process for 561: 259–265. similar and dissimilar lap joints using a 22. Aizawa, T., Kashani, M., and Oka- The authors would like to thank A. high-speed video camera. Aluminum Alloys gawa, K. 2007. Application of magnetic 2: 1992–1997. pulse welding for aluminum alloys and Gienko and I. Rosenthal of the Depart- 10. Deribas, A. A., Simonov, V. A., and SPCC steel sheet joints. Welding Journal 86: ment of Materials Engineering, Ben- Zakcharenko, I. D. 1975. Investigation of 119-s to 124-s. Gurion University of the Negev; Ena explosive welding parameters for arbitrary 23. Lee, K.-J., Shinji, K., Takashi, A., Millionshckik of the Ilse Katz Institute combinations of metals and alloys. Proc. and Aizawa, T. 2007. Interfacial mi- for Nanoscale Science & Technology, 5th Int. Conf. on High Energy Rate Fabrica- crostructure and strength of steel/alu- Ben-Gurion University of the Negev; tion, Denver, Colo., p. 4.3. minum alloy lap joint fabricated by mag- and O. Golan of the Department of 11. Cuq-Lelandais, J. P., Ferreira, S., netic pressure seam welding. Materials Sci- Mechanical Engineering, Afeka Aca- Avrillaud, G., Mazars, G., and Rauffet, B. ence and Engineering A 471: 95–101. demic College of Engineering, for their 2014. Magnetic pulse welding: Windows 24. Kang, B. Y. 2015. Review of magnet- valuable assistance. and high velocity impact simulations. ic pulse welding. Journal of Welding and ICHSF 2014, Daojon, Korea, May 26–29. Joining 33(1): 7–33. 12. Kakizaki, S., Watanabe, M., and Ku- 25. Stern, A., Admon, U., Ben-Artzy, A., mai, S. 2011. Simulation and experimental Aizenshtein, M., and Shribman, V. References analysis of metal jet emission and weld in- 2001–2005. Magnetic pulse welding char- terface morphology in impact welding. Ma- acterization of Al 1050 to Mg alloys joints. terials Transactions 52: 1003–1008. Unpublished results. 13. Crossland, B., and Williams, J. D. 26. Kapil, A., and Sharma, A. 2015. Mag- 1. Stern, A., Shribman, V., Ben-Artzy, 1970. Explosive welding. Metals Review 15: netic pulse welding: An efficient and envi- A., and Aizenshtein, M. 2014. Interface 79–100. ronmentally friendly multi-material joining phenomena and bonding mechanism in 14. Kore, S. D., Date, P. P., and Kulkarni, technique. Journal of Cleaner Production, magnetic pulse welding. Journal of Materi- S. V. 2007. Effect of process parameters on 100:35–58. als Engineering and Performance 13(10): electromagnetic impact welding of alu- 27. Golovaschenko, S. 2006. Electro- 3449–3458. minum sheets. International Journal of Im- magnetic forming and joining for automo- 2. Ben-Artzy, A., Stern, A., Frage, N., pact Engineering 34: 1327–1341. tive applications. 2nd International Confer- Shribman, V., and Sadot, O. 2010. Wave 15. Shribman, V., and Blakely, M. 2008. ence on High Speed Forming, Dortmund, formation mechanism in magnetic pulse Benefits of the magnetic pulse process for Germany, pp. 215–220. welding. International Journal of Impact En- welding dissimilar metals. Welding Journal 28. Cui, J., Sun, G., Li, G., Xu, Z., and gineering 37: 397–404. 87: 56–59. Chu, P. K. 2014. Specific wave interface 3. Shribman, V., and Kramer, H. 2008. 16. Faes, K., Baaten, T., De Waele, W., and its formation during magnetic pulse Proceedings: The first technical confer- and Debroux, N. 2010. Joining of copper welding. Appl. Phys. Lett. 105(22): 221901. ence on industrialized magnetic pulse to brass using magnetic pulse. Welding 4th 29. Becher, O., Nahmany, M., Ashke- welding and forming. SLV Munich, Ger- International Conference on High Speed nazi, D., Shribman, V., and Stern, A. 2014. many, July 3. Forming, Columbus, Ohio, March 9–10. On bond formation in magnetic pulse 4. Ben-Artzy, A., Stern, A., Frage, N., and 17. Zhang, Y., Babu, S. S., and Daehn, welded joints. The Annals of “Dunarea De Shribman, V. 2008. Interface phenomena in G. S. 2010. Interfacial ultrafine-grained Jos” University of Galati Fascicle XII, Weld- aluminum magnesium magnetic pulse weld- structures on aluminum Alloy 6061 joint ing Equipment and Technology 25: 23–28. ing. Science and Technology of Welding and and copper Alloy 110 joint fabricated by Joining 13: 402–408 and A. Ben-Artzy, PhD magnetic pulse welding. Journal of Materi-

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