Microstructural characteristics and mechanical properties of friction stir lap welding joint of Alclad 7B04-T74 aluminum alloy

摘要

Alclad 7B04-T74 aluminum alloy was friction stir lap welded at different welding parameters. The microstructural characteristics and mechanical properties of the joints were investigated. After welding, the initial Alclad at the faying interface upward migrated and penetrated into the stir zone from the retreating side. This reduced the postweld thickness of the upper sheet and formed a potential crack propagation path in the stir zone during tensile shear testing. During welding, the stirred Alclad was lifted by the probe-driven material flow and pressed down by the shoulder-driven material flow. The higher tool rotation speed or the lower welding speed made the redistributed Alclad in the stir zone more disperse. Higher fracture strength of the joint was obtained when the retreating side of upper sheet was loaded. A mathematical relationship between the fracture strength and the welding parameters was developed by applying the Box-Behnken experimental design, and the optimized fracture strength of 749 N/mm was obtained.