Effect of Brazing Flux Pb on Microstructure and Mechanical Property of CMT Weld-Brazed Lap Joint of 5052 Aluminum Alloy to Galvanized Q235 Steel

Abstract

5052 aluminum alloy and galvanized Q235 steel sheets with thickness of 1mm were lap welded/brazed by cold metal transfer technology (CMT) with ER4043 as the filler wire and Pb foil as the brazing flux. Scanning electron microscope (SEM), microscope with super-depth, X-ray diffraction (XRD), electronic universal tensile testing machine and hardness tester were employed to study the microstructure and mechanical properties of the joint. The results indicate that Pb foil effectively improved the mechanical properties of the joint with tensile strength up to 160Mpa which is higher than that of the joint without the brazing flux of Pb foil. Intermetallic compound (IMC) layer in the brazing joint unequally distributed in the interface of aluminum alloy and galvanized steel. The thickness of IMC layer was about 1~3.5um. The main phases of the IMC layer were FeAl and AlFe6Si. Fine equiaxial crystals existed in the weld metal while columnar crystals existed in the fusion zone of aluminum alloy. The hardness of fusion zone was higher than base metal while the hardness of heat affected zone was lower than base metal. In most case, the lap joint was broken in the junction of base metal and fusion zone.