International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 10 | Oct 2019 www.irjet.net p-ISSN: 2395-0072 DEVELOPMENT OF HIGH STRENGTH TO WEIGHT RATIO ALUMINIUM – MAGNESIUM ALLOY WITH ENHANCED CORROSION RESISTANCE Cinto C.J1, Sreejith P.S2 1Workshop Superintend, Thiagarajar Polytechnic College, Alagappanagar, Thrissur, Kerala, 680302 2Professor, Dean, Faculty of Engineering CUSAT, Kerala, India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract – Aluminium and aluminium alloys are widely alloying process. Normally aluminium alloys are used at a used in industrial and automobile applications in the recent temperature of 400 – 5000C and for long term usage it is past. Nowadays Al6061 (Al – Mg alloy) is widely used in limited to 250 – 3000C. many applications like marine, towers, pipe line and automobile field etc. It is having good mechanical In pure state, aluminium has low strength. So it properties. But there arises pitting corrosion as the main cannot be used in the application where resistance to problem when this alloy is used in marine application. deformation and fracture is required. Strength can be improved by adding alloying elements to aluminium [1]. The This project aims to develop an aluminium alloy which has low density combined with high strength has made better corrosion resistance and better mechanical properties aluminium alloys attractive in applications where strength- compared with Al6061. It is done by adding minor elements to-weight ratio is a major design consideration. The strength like manganese, zirconium etc. and durability of aluminium alloys vary widely according to the specific alloying, heat treatments and manufacturing Al – Mg alloys are the better choice. We found that when Mg is processes [1]. Aluminium is mainly used in alloyed form, added to Al in small quantity, it results in forming alloys which which results in increasing its mechanical properties. It is leads to higher strength and ductility than the pure used in pure metal form only when corrosion resistance or Aluminium. workability is more important than strength or hardness. A lack of knowledge of these aspects results in improper As a part of study the wt. % of Mg in the Al – Mg base alloy is designed structures and bad reputation to aluminium. The fixed as 4% and the effect of minor alloying elements in the typical alloying elements are copper, magnesium, base alloy are also examined. These alloys derive their manganese, silicon and zinc [1]. strength from the solid-solution strengthening due to presence of magnesium. Other minor alloying elements such as The aluminium alloy Al6061 is widely used in large manganese 0.2 wt. % and zirconium 0.1 wt. % are added for number of engineering applications such as transport, the control of grain and sub grain structures, which also construction, aircrafts and other structural applications contribute to strengthening. The weight percentage of where strength and weldability are needed. But when this magnesium addition is limited below 0.2 wt. % in order to alloy is used in marine application, pitting corrosion arises avoid the formation of coarse intermetallics. Zirconium has a as the main problem [21]. The objective of this project is to low solubility in aluminium and only small additions of Zr are develop an aluminium alloy which has better corrosion therefore necessary to form dispersions. Comparative study of resistance and better mechanical properties by adding some the new developed alloys with Al6061 is done by alloying elements and to compare the alloy with Al6061. Microstructure observations, Edax analysis, Density, Hardness and Corrosion test. 2. LITERATURE REVIEW Key Words: Al6061, Selecting and Fixing Compositions 2.1 ALUMINIUM of Alloys, Stir Casting, Testing Aluminium and aluminium alloy are achieving huge 1. INTRODUCTION industrial applications due to their outstanding fusion of mechanical, physical and tribological properties over the The properties of aluminium are very attractive. base alloys. They have high specific strength, high wear and Light weight, ease of fabrication, corrosion resistance, seizure resistance, high stiffness, high temperature strength, electrical & thermal conductivity, recycling, surface controlled thermal expansion coefficient and improved treatment suitability is some of its properties. But it has damping capacity. These properties are obtained by the some disadvantages such as low elastic modulus and low addition of alloying elements, cold working and heat elevated temperature. Important properties of aluminium treatment [1]. are its versatility and high strength to weight ratio. The mechanical properties of aluminium can be increased by © 2019, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 1010 International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 06 Issue: 10 | Oct 2019 www.irjet.net p-ISSN: 2395-0072 strength as well as improves the low – cycle fatigue resistance and corrosion resistance [1]. 2.2 ALLOYING ELEMENTS IN ALUMINIUM 4) Zinc (Zn) Alloying elements are selected according to the required property, effects and suitability. The alloying Zinc is only present in 7xx series aluminium cast elements are classified into major and minor elements, alloys. Aluminium – zinc alloys containing other elements microstructure modifiers or impurities; but the impurity offer the highest combination of tensile properties. Stress elements in some alloys act as major elements in others [1]. corrosion cracking is occurring in aluminum alloys The different alloying elements, such as silicon, magnesium containing Mg greater than 3.5%. Addition of 1 – 2 and copper are used as the major alloying elements. Nickel, wt.% Zn to theses Al – Mg alloy leads to reduce stress Tin etc are used as the minor alloying elements. Titanium, corrosion cracking due to the formation of Al – Mg – Zn zirconium, scandium, boron etc are used as the Phase [1]. microstructural modifying elements [1]. 5) Copper (Cu) Alloying of aluminium plays a major role in enhancing the properties such as increased strength, Copper improves the strength and hardness in cast hardness and resistance to wear, creep, fatigue etc. The alloy [3]. Both cast and wrought Al – Cu (aluminum – intensity and range of each alloying elements adding to copper) alloys respond to solution heat treatment and aluminium is specific and it effects properties of aluminium subsequent ageing. The strength is maximum between 4 and according to different alloying elements and combinations of 6 wt. % of Cu [2]. It improves machinability and reduces them. Although most elements readily alloying with corrosion resistance [1]. aluminium, comparatively very few have sufficient solid solubility to serve as major alloying additions. Among the 6) Nickel (Ni) commonly used elements only copper, magnesium, silicon Nickel is commonly used with copper for increasing and zinc have significant solubility [2]. However, other elevated temperature properties. It also reduces coefficient elements like Zirconium and chromium with solubility below of thermal expansion [3]. When nickel is added to Al alloys it 1% confer important improvements to alloy properties. forms intermetallic compound Al Ni which leads to increase Some of the important elements alloyed with aluminum are 3 hardness, compression and flexion resistance [1]. discussed below. 7) Magnesium (Mg) 1) Silicon (Si) Magnesium provides substantial strengthening and It provides better castability (high fluidity, low improvement of the work hardening characteristics of Al. It shrinkage) and improved hot tear resistance in castings. can impart good corrosion resistance, weldability and Silicon’s high heat of fusion contributes a lot to alloy fluidity. extremely high strength [1]. Si combines with Mg to form the It has very low solubility in Al therefore precipitates as hardening phase Mg Si that provides the strengthening. virtually pure Si which is hard and thereby improves the 2 Optimum strength is obtained by employing Mg in the range wear resistance. Si reduces thermal expansion coefficient of of 0.40 to 0.70 wt. %, beyond which it leads to reduce the Al – Si alloys. Machinability is poor with addition of silicon in thermo-mechanical properties [3]. aluminum [1]. 8) Strontium (Sr) 2) Titanium (Ti) and Boron (B) Strontium is used to modify the morphology of Titanium and boron are used in aluminium and its eutectic silicon in Al – Si alloy. Effective modification can be alloys as grain refiners. Boron is more effective as grain achieved at very low addition levels, but a range of refiner when it is used in combination with titanium in the recovered Sr of 0.008 to 0.04 wt. % is commonly used. ratio 1:5. It was found that with normal Ti contents, (ie in the Higher addition levels are associated with casting porosity, range of 0.015%) the grain refinement is effective. However, especially in processes or in thick-section parts in which upon larger Ti additions to the levels around 0.15%, the solidification occurs more slowly. Degassing efficiency may grain structure becomes coarser. It leads to increase also be adversely affected at higher Sr levels in the melt [3]. corrosion resistance but these alloys showed higher wear rates when comparing with binary alloy [1]. 9) Iron (Fe) 3) Manganese (Mn) When iron content is increased, it leads to promote When the manganese content