Effect of rotational speed in friction stir processing on the microstructural and mechanical characteristics of cast AS21A magnesium alloy

Magnesium-Aluminum-Silicon (Mg-Al-Si) alloys are well recognised for elevated temperature applications as they contain the thermally stable Mg₂Si intermetallic compound. However, the coarse and brittle nature of Mg₂Si deteriorates the mechanical properties; therefore researchers are working on its modification and refinement to enhance the widespread use of heat resistant Mg-Al-Si alloys. In the present work, Mg-Al-Si based AS21A alloy was subjected to Friction Stir Processing (FSP) at three different rotational speeds of 400, 800 and 1200 rpm with a constant travel speed of 50 mm min⁻¹. Microstructural features exhibit the fragmentation of coarse Mg₂Si to fine particles thus creating their homogeneous dispersion and eliminate the casting defects present in the parent material. The morphological structure modification achieved through friction stir processing resulted in the significant enhancement of mechanical properties like strength, ductility etc Further, fracture surface analysis depicted though fractography images proved the brittle nature of cast AS21A alloy and ductile nature of friction stir processed material. (paper)