Transformation of cast A356 ingots to wrought sheets with enhanced mechanical and tribological properties by different thermo-mechanical processing routes

Abstract

The dendritic microstructure with non-uniform distribution of hard second phase particles degrades the mechanical and tribological properties of AlSi alloys. Severe plastic deformation methods are found effective in refining microstructure and enhancing the material properties. In our present study, two different thermo-mechanical processing routes were employed on a cast hypo-eutectic AlSi alloy to produce wrought sheets with refined microstructure. In one processing route, the material is subjected to cryorolling after solution treatment and in the other route, the material is subjected to a thermal-treatment between solution treatment and cryorolling. Cryorolling imposes severe plastic deformation onto the material resulting in refinement and redistribution of second phase particles leading to enhanced strength and ductility. Cryorolling with pre-roll thermal-treatment resulted in finer grain structures than the material without thermal-treatment. The tribological behaviour of processed materials are studied and compared with the base materials by pin-on-disk method. Maximum wear resistance is observed in thermal-treated material followed by cryorolled material with pre-roll thermal-treatment. Transformation from adhesion wear to oxidative-delamination wear is found to be the primary reason for the enhanced wear resistance in thermal-treated material. The various wear mechanisms involved are explained in detail based on the microstructural evolution and mechanical properties.