Applicability of Bobbin Tool Friction Stir Welding for Dissimilar Al-Mg Joint

Abstract

Stringent material property demand for fuel economy in automobile and aerospace industry can be addressed only by either reducing weight or improving efficiency of the engine. Structural weight reduction requires dissimilar materials with varying thickness and geometry to be joined. Friction stir welding (FSW) is one of the latest additions to the joining processes. Bobbin tool friction stir welding (BTFSW) is a novel derivative of FSW process utilizing two shoulders for even heat distribution with advantage of eliminating backup support. This paper reports conventional FSW and feasibility trials of BTFSW for similar aluminum alloy (AA6061-T6), similar magnesium alloy (AZ31B) and dissimilar aluminum alloy (AA6061-T6) to magnesium alloy (AZ31B). Conventional FSW trials report successful welds without any observable surface defects. However, BTFSW weld surface presents defects like flash and groove, and material sticking to the tool pin is observed. Pin length, bigger diameter of the lower shoulder and flat surface of tool shoulder without chamfered edge are considered to be responsible for flash and groove defects. Process parameters which could have restricted joint formation are discussed. Though these feasibility trials of dissimilar aluminum and magnesium alloy BTFSW achieved limited success, it paves a path for successful joining using BTFSW.