Multi-Overlap-Passed Friction Stir Additive Alloying for Enhanced Wear Characteristics, Mechanical and Metallurgical Attributes

An alloy of AZ31 Mg with pure Al particulates added by friction stir additive alloying (FSAA) process was developed to enhance the quality attributes of the formed alloy by overlapping multi-passes. Mechanical, metallurgical and tribological aspects of the alloyed samples were studied in detail. In a multi-pass operation, the solid solution formed in the first pass can be decomposed in the subsequent pass leading to the formation of finer Mg-Al solid solution precipitates. The number of subsequent passes can help in grain fineness and uniform distribution of the intermetallics and lead to improvement in mechanical and metallurgical properties. The formed alloy grains were extremely refined because of the dynamic recrystallization, and the added Al particles act as enucleating agent for easy formation of new grains. The tensile strength at 6% Al alloying in the triple-pass case is 95% compared to the base material. Formation of favourable intermetallics at the stir zone depending on the temperature contributed from the number of passes enhances the hardness up to 185% of the base metal. The triple-pass FSAA at 6% Al alloying sample has the best mechanical and metallurgical attributes. The multi-pass effect helps in microstructural modification because of severe plastic deformation, finer grains and minimal clustering as well as minimal agglomeration, enhancing the tribological properties.