EFFECT OF FSP ON SPRAY FORMED Al-Si ALLOY

Abstract

Spray Forming (SF) is an advanced materials processing technology that transforms molten metal into a near-net-shape solid by depositing atomized droplets onto a substrate. As Aluminum (Al) – Silicon (Si) alloy with addition of graphite provides for low weight, low cost and high performance in structural materials [3]. Processing of these composites by the conventional casting routes is difficult due to liquid immiscibility and floating of low-density graphite(Gr) powder during melt solidification. In the present investigation, Al-Si-Gr composite is produced by spray forming and then friction stir processing (FSP) was introduced to refine the microstructure of spray formed Al-Si-Gr composite. The aim of the current research work is to study the Al-Si alloy with addition of graphite and examine the changes produced in microstructure and mechanical properties of the material after FSP. In this study, Al-Si-Gr composites for cylinder liner application were synthesized using spray forming technique, aiming on improving its wear resistance. Silicon (Si) and graphite (Gr) particles, which do not get distributed uniformly in Al-matrix by conventional processes, are distributed uniformly throughout the casting using spray forming. Disc shape spray deposit castings were made of Al–6Si-5Gr, Al-12Si-5Gr and Al–18Si-5Gr composite, and then their microstructures were studied. In spray form castings, it was found that the Si particles were distributed homogeneously in the Al-matrix. In addition to that, spray formed Al-Si-Gr composites were subjected to the friction stir processing (FSP). FSP was introduced to eliminate the porosity present in the spray formed composite and also for further refinement of microstructure of spray formed Al-Si-Gr composite. Microstructure of stir zone (SZ) was observed to be highly refined compared to the spray formed material. FSP resulted in complete homogenization and elimination of casting defects especially porosity. Mechanical properties like hardness and tensile strength were sharply improved after FSP.