Welding of Al-Mg aluminum alloy to aluminum clad steel sheet using pulsed gas tungsten arc process

Abstract

Al-Mg aluminum alloy was lap joined to aluminum clad steel sheet using pulsed gas tungsten arc welding process and Al-Si filler metal. The effects of the welding heat-input were investigated on the joint microstructure and mechanical properties. Weld metal microstructure, formation of intermetallic compounds (IMCs) at the joint interface and the fracture locations were studied using stereo, optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The joint strength of the welds was evaluated by shear-tensile test. The results showed that presence of a thin aluminum clad layer with 350 μm thickness drastically decreased the Al-Fe intermetallic thickness at the weld seam/steel interface to less than 2.5 μm. The joint strength increased with enhancement of the heat-input up to an optimum value and then decreased beyond it. This behaviour was justified in the light of the contradictory effects of the weld metal microstructure and adhesion of the weld metal to the aluminum clad layer near the weld root. In the optimum heat-input of 250 J mm−1, the joint strength reached to ∼90% of Al-Mg aluminum base metal strength. In all the welds, fracture path had an angle of 75 ± 3° with respect to the horizontal base plane. Stress analysis in the weld showed that fracture in the joint was controlled predominantly by the maximum normal stress rather than the maximum shear or von Mises effective stress.