Effect of CoCrNi Interlayer on the Microstructure, Mechanical, and Corrosion Properties of Cold Metal Transfer Al/Steel Joints

Cold metal transfer (CMT) welding is an advanced arc welding technology, which is promising for joining dissimilar materials such as aluminum, magnesium, titanium alloys and steels for automotive and aerospace industries, as their high demands on reliable lightweight structures. Meanwhile, medium entropy alloys (MEAs) are a kind of highly promising new materials because of the excellent functional and mechanical performances. In this work, AA5052 Al/galvanized steel dissimilar joints were obtained by CMT-CS (cycle step) lap welding technology with CoCrNi MEA powder interlayer. When the MEA interlayer was applied, the contact angle reduced from 53.6° to 31.5°, and brazed width increased from 6.1 to 6.9 mm, which improved the wettability and spreadability of the molten filler on the steel substrate. In terms of interfacial microsture, the addition of the MEA layer with Co, Cr, Ni elements promoted the geneation of a relatively ductile Fe-rich Fe-Al IMCs, i.e., FeAl and Fe₃Al, and thus enhanced the mechanical propeties of the laser joints. The maximum tensile load of the joints with interlayer reached 274 N/mm, which was 27.4% higher than that of the joints without interlayer. The introduction of MEA interlayer also improved the corrosion resistance and reduced the corrosion rate of the dissimilar joints.