Wear behavior of copper and stainless steel butt joints fabricated by laser oscillation welding

Bi-metal heat exchangers were fabricated by butt welding C1100 pure copper and SUS 304 stainless steel plates using two fiber laser oscillation methods (zigzag and circular). The microhardness, microstructure, and wear resistance of the weld zone were analyzed for both methods. The effects of adding single Ni, Ti, and Co interlayers and double Ni/Co interlayers to the welded joint were also investigated. The wear depth of the welded joint prepared using the circular oscillating mode was lower than that of the joint fabricated using the zigzag oscillating mode, which are 22 mu m and 27 mu m, respectively. Moreover, the zigzag oscillating mode increased the porosity of the weld area and hence lowered the wear resistance. The addition of a Ti interlayer prompted the formation of intermetallic compounds (IMCs) and thus enhanced the microhardness of the welding area. The sample with a pure Ti interlayer shows both the highest microhardness (> 400 HV) and the lowest wear depth (< 8 mu m) and thus has the highest wear resistance. For both the single Co interlayer and the double Ni/Co interlayer, the average copper content in the weld zone increased. Among all of the interlayer welds, that containing a Ti interlayer has the highest microhardness (400 HV), the highest Cu content (51 wt%), and the lowest wet kinetic friction coefficient (0.15). As a result, it has the best wear resistance among all the samples with an interlayer. The resulting reduction in the kinetic friction coefficient improved the overall wear resistance of the weld zone.