Interfacial microstructures and mechanical property of Ni/Al dissimilar butt joint made by laser welding

Abstract

Although welding structures with Ni/Al dissimilar metals have great application potential, the interfacial metallurgy is not fully understood. The interfacial microstructures and its formation mechanisms of the Ni/Al joint were investigated by controlling the laser beam offset toward to Al side. Two modes of Ni dissolution and melting were discovered during the laser welding. When the offset was relatively big, the Ni dissolved to the weld first and then the intermetallic compounds (IMCs) formed during the welding. The IMCs consisted of Al3Ni2 in the precipitation and Al3Ni in the peritectic reaction and precipitation. The weld was divided into hypereutectic reaction zone (Hyper-ERZ) near to the interface and hypoeutectic reaction zone (Hypo-ERZ) far from the interface. When the offset was relatively small, the Ni surface layer adjacent to the weld melted first and then complex interfacial reaction occurred. The IMCs were composed of AlNi in the precipitation, Al3Ni2 and Al3Ni in peritectic reactions and precipitations. The melted layer transformed to double peritectic reaction zone(DPRZ). The weld consisted of Hyper-ERZ. With increasing the offset, the tensile strength of the joints increased first and then decreased. The highest value was up to 136.2 MPa, which is 80 % of 5052 Al tensile strength.