Friction stir welding of similar and dissimilar Al and Cu lap joints: Effect of work piece material on conducive welding speed window, weld strength and hardness

This study used friction stir welding to make comparable (AA2219-AA2219 and Cu-Cu) and dissimilar (AA2219-Cu) lap joints. The tool retained its rotating speed at 1500 rpm and tilt angle at 2 degrees, while welding speed varied from 23.5 mm/min to forward. Changing work-piece material affects welding speed, joint strength and hardness, and intermetallic compound formation. Similar lap joints have a welding speed window of 23.5-475 mm/min for Cu-Cu lap joints and 23.5-275 for AA2219-AA2219. However, dissimilar welding had a significantly smaller window of favorable speed: 23.5-30 mm/min for AA2219-Cu joints and 23.5-37.5 for Cu-AA2219 joints. The tensile strength analysis showed a maximum lap shear strength of similar to 33 MPa for similar joints at extreme speeds, whereas dissimilar joints achieved similar to 23 and similar to 12 MPa for AA2219-Cu and Cu-AA2219 configurations, respectively, at 23.5 mm/min, mainly due to the formation of IMCs. Hardness testing indicated a significant increase to similar to 79 Hv in dissimilar joints at 30 mm/min when copper was layered over AA2219, a result of extrusion and stirring effects. The high hardness in the dissimilar Al-Cu joints can be attributed to the formation brittle IMCs AlCu (Al2Cu) and Al4Cu9.