Abstract
In the present work, the hot rolled AZ31B magnesium alloy plate of 6 mm thickness is subjected to a friction stir process (FSP) under submerged condition. The process parameters of FSP considered are tool pin profile (simple cylindrical, stepped cylindrical, stepped square), rotational tool speed, and traverse speed. The output responses considered in this study are microhardness, elongation, and ultimate tensile strength. TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution), a new method is used for optimizing the multiple responses. ANOVA showed the tool pin profile as a most influencing parameter. The results indicated the stepped square pin profiled tool with a rotational speed of 1000 rpm and a traverse rate of 30 mm min^–1 exhibited a superior surface property by grain refinement, which increased the microhardness and mechanical properties in the nugget zone of the processed material.

Key words
submerged friction stir processing, welding, processing, TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution), microstructure, tool pin profiles, magnesium alloy, mechanical properties

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