Formation and growth mechanism of Cu-rich layer at aluminum/steel friction welding interface

Utilizing friction welding to achieve the high-quality bonding of 2219 aluminum (Al) alloy/304 stainless steel dissimilar materials has promising applications in aerospace and other industrial fields. The formation of the Cu-rich layer is a distinctive feature that distinguishes it from other series Al alloy/steel friction welding joints. Currently, a summary of the relevant literature reveals that there are three main possible formation mechanisms for the Cu-rich layer: diffusion mechanism, liquefaction mechanism and strengthening phase accumulation mechanism. In this paper, these three formation mechanisms are denied experimentally. Meanwhile, it is proposed that the formation and growth mechanism of the Cu-rich layer is strengthening phase precipitation-reaction-reprecipitation mechanism. The correctness of this theory has also been proved by experiments. The proposed model can facilitate the improvement of the friction welding process of dissimilar materials and provide a theoretical basis for the regulation of the metallurgical reaction of the friction welding joint.