Abstract
The 6061 aluminum alloy and 304 stainless steel were welded by hybrid cold metal transfer (CMT) welding with external axial magnetic field. The effects of magnetic intensity and frequency on joint microstructure and mechanical properties were studied. It was found that the magnetic field can promote the spreading of aluminum weld metal on the steel surface and thus increase the bonding area of Al/steel butt joint. The welding process stability improved, while the wetting behavior worsened with the introduction of alternating frequencies. The thickness of the intermetallic compound (IMC) layer at Al/steel interface was reduced to 3 μm with the coil current of 2 A. The application of the magnetic field promoted the aggregation of Si atoms at the interface and inhibited the formation of brittle (Al, Si)13Fe4 phase. The fracture paths were transformed from (Al, Si)13Fe4 layer to Al8Fe2Si layer with the application of the magnetic field. The maximum tensile strength reached 130.2 MPa, an increase of 61.6% in comparison to the normal CMT process.
Highlights
In order to save fossil energy and reduce greenhouse gas emissions, the lightweight automobile has become one of the development directions of automobile industry
The results indicated that the intermetallic compound (IMC) layer thickness increased and the joint strength decreased with the increase of the duration and temperature of heat treatment
Welding current of 73 A and welding speed of 6 mm/s with lower heat input were selected to reduce the formation of brittle Al/Fe IMCs
Summary
In order to save fossil energy and reduce greenhouse gas emissions, the lightweight automobile has become one of the development directions of automobile industry. Due to its high specific strength, good corrosion resistance, and low cost, aluminum and its alloys have great potential to replace the conventional steel component. The sound aluminum and steel welded joint has gained extensive attention [1]. Distinct differences in thermal physical properties and the formations of brittle intermetallic compounds (IMCs) at the bonding interface are obstacles to achieve effective connection [2]. The key of Al/steel welding is to control the IMC layer thickness at the interface. Chen et al [4] considered that only when the thickness of IMC layer is less than 10 μm will the joints achieve good properties. Cao et al [5] analyzed the relationship between joint strength and IMCs and found that the tensile strength of the joint decreased when the IMC layer was thicker than 5 μm
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