FRACTURE AND FATIGUE STUDIES OF STIR CAST AI-Si-Mg ALLOYS

Abstract

Semi-solid forming process, such as thixo-casting, forging, and molding processes is an emerging new technology for net-shape production of engineering components and is being used for producing lightweight parts of Al and Mg alloys. Alloys with a vigorous stirring during soldification produced a microstructure having rounded primary phase particles, each surrounded by lower melting phases. The main requirement for alloys to be shaped in the semi-solid state is that they should exhibit a fine spherical or non-dendritic grain structure. This led to a realization of the significance of the rheological behavior of alloys in the semi-solid state. Existing semi-solid casting processes rely upon controlling the morphology of the solid phase so that the solid phase possesses a globular, spheroidal or ellipsoidal shape. It has been discovered that various processing and physical property advantages can be achieved by casting or otherwise forming metal components from a non-dendritic, semi-solid metal slurry. This allows for easier movement of the solid phase as it freezes because of the prevention of the formation of a dendritic network. In this dissertation work, study of microstructure and hardness is carried out for two different aluminium alloys with different stirring condition. A comparison is also made with as-cast aluminium alloy. Further fatigue crack growth rate behavior is also investigated.