On the Size, Shape and Spatial Distribution of Si Particles in A356 Castings After Single and Multiple Passes of Friction Stir Processing: The Effect of As-Cast Microstructures

The relationship between as-cast and post-friction-stir-processed microstructures was assessed by a combination of quantitative metallography and statistical analysis. Two distinct as-cast microstructures, resulting from commercial and continuous casting processes, were subjected to multiple friction stir passes and subsequent metallography by SEM with EDS. X-ray maps were used to elucidate Si particles for quantitative image processing. Progressive homogenization with each successive pass was observed in both alloys. Continuously cast samples exhibited Si particle coarsening, while commercially cast alloys undergo Si particle refinement. Aspect ratio of particles remains constant throughout multiple FSP passes despite changes in spatial and particle size distribution. Trends in distributions of Si particle size and nearest neighbor distances with each pass are presented.