Research Of Process And Properties On CMT Welding-brazing Of Dissimilar Metal Aluminum/Steel

In this paper,5052aluminum alloy and Q235galvanized steel with their thickness of lmm, as well as5052aluminum alloy and304stainless steel with their thickness of3mm, were used as the base materials, and ER4043were employed as the filler metal. CMT welding process was employed to achieve the weld-braze lap joint of aluminum alloy/steel. It analysed macrostructures and microstructures of joints’ various parts in different welding parameters and tests mechanical properties of joints.The weld-braze lap joint of aluminum alloy/steel can be achieved in different suitable welding parameters. The weld-braze lap joints mainly consist of weld width, interfacial zone and heat affected zone (HAZ). The amount of welding aluminum alloy/steel, as well as the grain size of HAZ and weld width increase with the increase of heat input. The steel side of the interfacial reaction layer is smooth while the other side near the welding zone is uneven. The change of gradient of the amount of Al、Fe demonstrates that different kinds of intermetallic compound are produced on the interfacial reaction layer. The welded zone mainly consistes of dendritic a-Al matrix and inter granular Al-Si eutectic, both of which grow to the weld center perpendicular to interfacial reaction layer and fusion line.When welding current is66A, aluminum alloy and galvanized steel with their thickness of lmm reach their maximum tensile strength of115.7MPa. The lap joints break initially at the HAZ of aluminum in tensile-shear test due to grain coarsening. And the thickness of interfacial reaction layer is between2.55and6.86μm, when the heat input is low, intermetallic compound Fe2Al5、FeAl3are easily produced on the reaction layer while FeAl2、FeAl are produced when the heat is high.The weld-braze lap joints can be formed on the aluminum alloy with the thickness of3mm and galvanized steel without special surface treatment, but the welding wire’s spreading towards steel side is not good and the joint strength can only achieve36.7MPa, and the lap joints break on the interfacial reaction layer, so it can not be used. Intermetallic compound of6.5μm produced on the interfacial reaction layer are Fe2Al5,FeAl3and a small amount of FeAl2.The CMT weld-braze lap joints of aluminum alloy and stainless steel can be produced in different welding parameters after coating the surface of steel with special flux. Due to the special flux, the welding wire’s spreading towards steel side is good and the welding line will have bad appearance and have much weakness when the heat input is not stable. Besides, intermetallic compound Fe2Al5、FeAl3will be produced apparently on the interfacial reaction layer. Due to the effect of flux, Si is also involved in the reaction and Fe2SiAl8、Fei.8SiAl7.2are produced. Since the arc on the upper part is harder, the intermetallic compound layer is thicker while the intermetallic compound layer is thinner when the weaker arc is on the lower part. When the heat input was between100-120J/mm, as the result of the effect of flux the occurring of intermetallic compound on the interfacial reaction layer is restrained and the joints have better appearance and mechanical properties but the flux is not involved in the interfacial reaction. When the welding current is66A and welding speed is6.5mm/s the joints gain the maximum tensile strength of111.6MPa. And the lap joints also break on the interfacial reaction layer. when the welding heat input is between110and120J/mm, we can get welding joints of better properties.