Microstructure and mechanical properties of TIG welded-brazed AZ61 Mg alloy and mild steel joints with and without interlayer

In this paper, the effects of Zn foil on the wetting ability, microstructure and mechanical properties of Mg-steel joints were investigated. TIG welding-brazing technology was performed to achieve the joining of Mg alloy and steel. The main results are shown as follows. With the applying of Zn foil, the wetting property of molten metal on solid steel plate was improved and the contact angle of Mg-steel joint decreased at the same time. The width of weld seam increased under the influence of Zn interlayer. A 2 mu m thick Fe-Al reaction layer formed at the interfacial area of joint gained by directly welding of Mg-steel. However, an Mg-Zn reaction layer with the thickness of 10 mu m occurred with the applying of Zn interlayer, which is the key to achieve reliable joining of Mg-steel. And the thickness of Mg-Zn layer increased with the increase of current. For the traditional TIG welded Mg-steel joint, the maximum tensile shear load is only 158 N mm(-1). With the applying of Zn foil, the maximum tensile shear load of Mg-steel joint increased to 211 N mm(-1) and fracture location was at the fusion area.