The effect of pin thread on material flow and mechanical properties in friction stir welding of AA6068 and pure copper.

This study investigated the effects of friction stir welding thread on the quality of dissimilar joints between AA6068 aluminum alloy and copper. The developed computational fluid dynamic (CFD) method was employed to simulate the tool's heat generation and thermo-mechanical action. The materials flow, microstructure, mechanical properties, and hardness of joints were assessed. The results indicated that the threaded pin increased heat generation during welding. The maximum temperature recorded on the aluminum side was 780 K for the cylindrical joint and 820 K for the threaded pin joint. The size of the stir zone in the threaded pin joint was bigger than the cylindrical pin. On the other hand, mechanical interlocking between AA6068 aluminum alloy and copper increased in the threaded pin joint. The material's velocity and strain rate increased by the higher stirring action of the threaded tool. Higher strain rate and materials velocity decreased microstructure size in the stir zone. The experimental result shows that the ultimate tensile strength of the cylindrical pin joint was 272 MPa, and the threaded pin joint was 345 MPa. The average microhardness of the cylindrical pin joint was near 104 H V, and for the threaded pin was 109 H V. The results show that the ultimate tensile strength and hardness of threaded pin joint increases by 25% and 5% in comparing cylindrical pin joint.