STUDY OF MECHANICAL PROPERTIES OF FRICTION STIR PROCESSED CAST Al-Si ALLOY

Abstract

In the present study, changes in microstructural and mechanical properties of cast A356 aluminum alloy resulting from the friction stir processing (FSP) were analyzed. It has been observed that friction stir processing breaks up the coarse Si particles in to finer Si particles and distributes them uniformly along the matrix. FSP causes breaking of Al dendrites and eliminate the porosity defects. FSP can also refine the coarse grains of as- cast A356 alloy. The microstructure of overlapping zone of multipass FSP has much smaller grains as compared to the stir zone of single pass FSP. Due to greater amount of plastic deformation at the double pass processed zone, the grain size in overlapped zone is 28% smaller than the SZ of single pass FSP. After doing FSP by using any of the three conditions (processing at one side of the sample, both side of the sample or processing the whole sample) or after hot rolling, the mechanical properties i.e. proof stress, UTS and ductility of the parent material has been improved significantly. But among the above mentioned conditions, the best mechanical properties were obtained by processing at both side of the sample and processing the whole sample. The sample, which was processed on both side have a crack initiation site inside it. As both of the sides of the sample were processed, so the probability of crack initiation on the surface is very less. As a result, the sample has shown very good ductility. In case of the samples obtained after hot rolling, it has been observed that the coarse Si particles are broken but they are not homogeneously distributed in the matrix. As a result, the samples have shown less ductility. All processing conditions have shown almost similar improvement in proof stress and UTS.