Microstructures and Mechanical Properties of Plasma Arc Welded Joints of Ultra-high Strength Steel and Aluminum Alloy Using Al-Si and Al-Cu Fillers

The weld appearance, microstructures and mechanical properties of plasma arc welded joints of ultra-high strength steel and aluminum alloy were studied. The weld appearance was improved when the single bevel groove was used. The steel-aluminum joint is divided into weld zone, bond zone and interface zone. The welds with Al-Cu and Al-Si fillers consist mainly of alpha-Al + Al2Cu and alpha-Al + Si, respectively. The interface zone has a double-layer structure, the Fe2Al5 layer at steel side and the Fe4Al13 layer at aluminum weld side. The interface IMC layer is the weakest region in the joint and its evolution process has been summarized. The welding current and filler wire composition have great effects on the interface layer and joint properties. With the increase of welding current, the interface layer thickness increased and the crack appeared in the interface layer when the welding current exceeded 100 A. The joint strength with Al-Si and Al-Cu fillers can reach 62 MPa and 118 MPa respectively at the welding current of 90 A. It is favorable to use Al-Cu filler and welding current of 90 A for improving mechanical properties of the steel-aluminum joint.