Effects Of Alloying Elements On The Microstructure And Mechanical Properties Of Dissimilar Metal Joints Between Aluminum Alloy And Steel With Gas Tungsten Arc Welding

The connection of aluminum alloy and steel was paid more attention in industry for the low cost and energy reducing. And, only the joining of these two metals can satisfied the requirement of the manufacture application. But it is hard to realize due to the low solution ability at normal temperature and the great difference of thermal-physical properties between aluminum and iron. This paper lap joined aluminum alloy to carbon steel successfully through two methods, coating carbon steel with zinc and using solid filler wires, arc joining aluminum alloy to carbon steel directly with flux cored filler wire. More important, the effect of alloying elements on the microstructure and mechanical properties was researched.Aluminum alloy sheets were lap joined to galvanized steel sheets by gas tungsten arc welding (GTAW) with Al-5%Si, Al-12%Si, A1-6%Cu, Al-10%Si-4%Cu and Zn-15%A1filler wires. Different amounts of Si, Cu and Zn were introduced into the weld through different filler wires. The effects of alloying elements on the microstructure in the weld and tensile strength of the resultant joint were investigated. It was found that the thickness of the intermetallic compound (IMC) layer decreased and the tensile strength of the joint increased with the increase of Si content in the weld. The thickness of the IMC layer could be controlled as thin as about2μm and the tensile strength of the dissimilar metal joint reached136MPa with Al-12%Si filler wire. Al-Si-Cu filler wire could result in thinner interfacial layer than Al-Cu filler wire, and fracture during tensile testing occurred in the weld for the former but through the intermetallic compound layer for the latter filler wire. A Zn-rich phase formed in the weld made with Zn-15%A1filler wire. Moreover, the Zn-Al filler wire also generated thick interfacial layer containing a great amount of intermetallic compounds and coarse dendrites in the weld, which led to a weak joint.The intermetallic layer of aluminum alloy/carbon steel joint with Zn-15%A1flux cored filler wire was above15μm and detached into weld during welding. An iron rich zone formed due to the diffusion between detached layer and the molten weld metal. Meanwhile, the intermetallic layer of joint with Al-12%Si flux cored filler wire was less than5μm and with no detachment. However, the tensile strength of former joint was much higher than the later. The Zn element was weaker in inhibiting the growth of intermetallic compound than Si element. But the Zn element joined the reaction of aluminum and iron, decreased the brittleness of the intermetallic layer and improved the tensile strength. Post welded heat treated was taken for both joints. Because of the releasing of stress, the tensile strength of both joints increased.