Interface microstructure and fracture behavior of single/dual-beam laser welded steel-Al dissimilar joint produced with copper interlayer

Dissimilar metal welding of Q235 low carbon steel and 5052 aluminum alloy was carried out by a single/dual-beam laser in a steel-on-aluminum overlap configuration with a copper interlayer. The weld appearance, microstructure, and fracture behavior of the joints made by the single/dual-beam laser welding were investigated comparatively. The results showed that dual-beam laser welding, compared with single-beam laser welding, had better process stability which made better weld appearance and bigger effective joining width which enhanced tensile capacity. With a copper interlayer, a contact reaction zone appeared between the copper interlayer and aluminum matrix, which enlarged effective joining zone. The microstructures of the welding joint welded by a single/dual-beam laser were composed of the ligulate fusion zone with Fe-Al interface and the contact reaction brazing zone with Al-Cu interface. The Fe-Al interface mainly consisted of alpha-Al and Al2Cu eutectic structure, FeAl, FeAl2, and a certain amount of Al-Cu intermetallics, Fe2Al5 and FeAl3. The Al-Cu interface mainly consisted of eutectic phase Al2Cu and metastable phase of Al-Cu intermetallics. The tensile property was enhanced by a dual-beam laser, and the addition of the copper-foil interlayer might improve the metallurgical reaction of interfacial reaction region and promote the load-carrying ability of weld joint. An ideal joint with fewer defects could be obtained when the welding speed is 0.9-1.25 m/min of dual-beam laser welding and 1.5-1.75 m/min of single-beam laser welding.