Zinc-aluminium alloys for automobile applications

Commercial zinc-aluminium alloys are basically used as a versatile foundry casting materials and are finding increasing engineering applications including automobile industry. It is well know that zinc-aluminium (ZA alloys) posses a unique combination of excellent fluidity, wide range of mechanical properties lying between aluminium alloys (LM6) and ductile iron. They have very good bearing and wear resistance properties comparable to conventionally used bearing bronzes. At present ZA alloys are replacing many non-ferrous alloys, gray cast iron and malleable cast iron in a number of applications in automobile industries. Normally special high grade zinc is used for the preparation of zinc-aluminium alloys for specific applications such as bearings, bushes and other gravity die castings. Impurities such as Pb, Sn, Cd and Fe present in zinc adversely affect the physical, mechanical and corrosion properties as well as the workability of the alloys. The paper deals with the work carried out at NML in order to reduce/remove the adverse effect of these impurities by suitable flux treatment and minor additions like Boron and Misch metal, which bring about the favourable morphological changes preferentially interact with these impurities. Although commercial ZA alloys are susceptible to intergranular corrosion, work carried out at NML using special flux and minor additions, ZA alloys showed superior corrosion resistance as compared to conventionally cast alloys. Results of industrial scale trial carried out as a sequel to laboratory scale work for the production of automobile component are also presented in this paper. The paper also deals with the typical applications of ZA alloys in the production of various automobile components.