Effects of tool geometry on friction stir welding of AA6061 to TRIP steel

With the appropriate process parameters, both large and small tools can produce sound joints with tensile strengths (TS) 80% higher than those fabricated with Al base metal. As a large tool moves into the steel, it can peel off and embed steel fragments into the Al matrix, causing critical defects around the embedded fragments. Using small tools and lower rotational speed (RS) will significantly reduce the welding heat, resulting in an unwelded Al/steel interface at the bottom of the weld. Since the tool size and process parameters determine the amount of generated heat, they also determine the thickness of the intermetallic compound (IMC) layer that forms at the Al/steel interface. The welding forces in the weld plane are primarily affected by the tool offset.