Effect of Y contents on surface wetting and interfacial behavior of Al-Si-Cu-Zn-Ni-xY brazing filler alloys on 7072 aluminum alloy

In this paper, the wetting and interfacial behavior of Al-Si-Cu-Zn-Ni-xY (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) brazing filler alloys on 7072 aluminum alloy substrate are investigated. Results show that the trace element Y can effectively improve the stability of the characteristic transition temperature of brazing filler alloys and reduce the melting interval at the same time. Accroding to the results of molecular dynamics simulations and arc wetting tests, the surface wetting process of the filler alloy is of five stages, i.e., preheating film-breaking stage, initial stage, rapid diffusion stage, limited diffusion stage and stabilization stage. When the content of Y in the Al-Si-CuZn-Ni-Y brazing alloy increased from 0 wt% to 0.8 wt%, the wetting diffusion area of the brazing alloy increased from 261.298 mm2 to 305.658 mm2, and the wetting angle decreased from 18.28 degrees to 12.857 degrees.The microstructure shows that element Y can purify the wetted interface because Y reacts easily with Al2(Cu,Ni) in the brazing alloy to form Al4.4(Cu,Ni)6.6Y phase. The latter phase distributes discretely along the wetting interface and thus, the fluidity of the brazing alloy is improved.