Gas tungsten arc lap welding of aluminum/steel hybrid structures

Al-1050 clad St-12 sheets were first produced by cold roll bonding process with clad layer thickness of 350 and 1000 mu m. Then, Al-5052 aluminum alloy and Al-1050/St-12 sheets were lap joined using gas tungsten arc welding with Al-Si filler metal. The effects of the clad layer thickness and welding current were studied on the joint properties. Macro/microstructural observations were done using optical and scanning electron microscopes (SEM) equipped with energy dispersive spectroscopy (EDS). Shear-tensile and microhardness tests were used for evaluation of the mechanical behavior of the joint. The results indicated that presence of the aluminum clad layer reduced the Al-Fe intermetallic thickness at the steel/weld seam or steel/Al-1050 clad layer interface to less than 4 mu m. During the shear-tensile test, fracture in all the joints was started from the root of the weld and then propagated inside the weld metal mostly through the Al-Si eutectics. The shear-tensile strength of the joint decreased almost linearly by enhancement of the welding current at both clad layer thickness of 350 and 1000 mu m. However, aluminium clad layer thickness had a significant effect on the shear-tensile strength of the joints. At a constant welding current, the strength of the joint was higher for the thinner Al-1050 clad layer due to the higher width of the melted zone in the Al-1050 clad layer. Maximum shear-tensile strength of the joint reached to similar to 197 MPa (similar to 80% of the tensile strength of Al-5052-H34 base metal).