Dissimilar Laser Welding/Brazing of 5754 Aluminum Alloy to DP 980 Steel: Mechanical Properties and Interfacial Microstructure

摘要

A diode laser welding/brazing technique was used for lap joining of 5754 aluminum alloy to DP 980 steel with Al-Si filler metal. The correlation between joint interfacial microstructure, wettability of filler metal, and mechanical properties was systematically investigated. At low laser power (1.4 kW), a layer of intermetallic compounds, composed of theta-Fe(Al,Si)(3) and tau (5) -Al7.2Fe1.8Si, was observed at the interface between fusion zone and steel. Because of the poor wettability of filler metal on the steel substrate, the joint strength was very low and the joint failed at the FZ/steel interface. When medium laser power (2.0 kW) was applied, the wettability of filler metal was enhanced, which improved the joint strength and led to FZ failure. With further increase of laser power to 2.6 kW, apart from theta and tau (5), a new hard and brittle eta-Fe-2(Al,Si)(5) IMC with microcracks was generated at the FZ/steel interface. The formation of eta significantly degraded the joint strength. The failure mode changed back to interfacial failure. (C) The Minerals, Metals & Materials Society and ASM International 2015