Interfacial characteristics and mechanical properties of aluminum/steel butt joints fabricated by a newly developed high-frequency electric cooperated arc welding-brazing process

3 mm thick Al-steel dissimilar metals were butt welded by a newly developed high frequency electric cooperated arc welding-brazing (HFAW-B) without grooves or shaping board. Microstructure characteristics and mechanical property of the joint were investigated and compared with that of the traditional single MIG joint. Results showed that sound joint with satisfactory weld appearance was achieved by the HFAW-B process under a low welding heat input (826 J/cm), while much higher heat input (1036 J/cm) was required for the traditional MIG process. The interfacial IMCs layer of the HFAW-B joint was homogeneous and thin (limited to 4.0 mu m). In the traditional MIG joint, even with the same heat input, the maximum thickness of the IMCs layer exceeded 5.0 mu m and massive Al-Fe brittle IMCs were found in the weld seam. When acceptable back weld appearance was obtained, a 20 mu m IMCs layer was observed in the traditional MIG joint, which was extremely uneven and cracked after welding. Detailed analysis revealed that the uniform heating in thickness direction, preheating ahead of weld pool and differentiate heating of the HFAW-B process were beneficial to realize compatible regulation of interface characteristics and (back) weld appearance of Al/steel joint, i.e., to achieve not only a good weld appearance but also a thin compound layer under a low heat input. Benefitted from the sound weld appearance, thin interfacial IMCs layer and uniform stress distribution, the HFAW-B joint necked at Al side, and presented a tensile strength exceeded 90 % the strength of Al base metal.

Automated summary

The newly developed HFAW-B welding process achieved a sound joint with a thin interfacial IMCs layer under a low heat input, while the traditional MIG process required higher heat input and resulted in thicker IMCs layer and cracking in the weld seam.