Effect of Tool Pin Profile on Material Flow in Double Shoulder Friction Stir Welding of AZ91 Magnesium Alloy

The double shoulder friction stir welding of AZ91 magnesium alloy is numerically modeled based on the Eulerian method using the ABAQUS software. The material flow in the integrated form is demonstrated properly and the shoulder driven and pin driven zones are predicted very well. The effects of pin profile on the temperature and strain distributions, material flow, material coalescence, grain size and tensile properties are investigated. Results show that, the material flow patterns in the shoulder driven and pin driven zones are different. While the material moves from the advancing side toward the retreating side in the pin driven zone, it is reverse in the shoulder driven zone. Although the trigonal pin comprises the longest sweeping lever and can move larger boxes of material, the most uniform material movement with the best material coalescence is produced by hexagonal pin tool. The inward conical pin tool produces the weakest material flow pattern leading to generation of tunnel cavity in the welding zone. However, the outward conical pin tool generates a subsidiary material flow and improves the material coalescence and consequently results in a higher strain, smaller grain size and superior mechanical properties compared to those of the inward conical pin tool.