Effect of Welding Speed on Microstructure and Properties of Aluminum Alloy/Copper Laser Welding-Brazing Joints

The 5052 aluminum alloy and T2 copper were butt welded by laser welding-brazing at different welding speeds (4, 5, 6, 7, 8 mm · s⁻¹). The effect of welding speed on the macromorphology, microstructure, microhardness, tensile strength and tensile fracture mechanism of the joint was studied. The results show that with the increase of welding speed, the weld forming quality of laser welding-brazing joint first became better and then worse, and the weld forming quality was the best when the welding speed was 6 mm · s⁻¹. With the increase of welding speed, the dendritic Al-Cu eutectic structure decreased and the Zn-Al eutectic structure increased. When the welding speed was 6 mm · s⁻¹, Al₄Cu₉ and Al₂Cu intermetallic compounds were formed in the copper side interface reaction zone of the joint, and the fusion welding zone consisted of α-Al solid solution, η-Zn solid solution, Al-Cu eutectic structure and Zn-Al eutectic structure. With the increase of welding speed, the hardness of fusion welding zone of the aluminum alloy/copper laser welding-brazing joint had little change, the hardness of copper side interface reaction zone gradually decreased, the tensile strength of the joint increased first and then decreased, and the tensile fracture mode changed from the cleavage fracture, quasi-cleavage fracture, ductile fracture to quasi-cleavage fracture in sequence. When the welding speed was 6 mm · s⁻¹, the tensile strength of the joint was the largest (212 MPa) and the fracture mode was ductile fracture.