Resistance spot welding between aluminum and steel: A review of process mechanisms and advancement strategies for enhanced joint performance

In this paper, recent advances in resistance spot welding (RSW) process between aluminum and steel are comprehensively reviewed. Aluminum and steel are important materials to achieve lightweight manufacturing in automobile and related industrial occasions. However, it is difficult to use conventional RSW process to join these two types of metal sheets, because the large difference in metallurgical properties between aluminum and steel can induce various welding defects, such as hard and brittle intermetallic compounds (IMCs), which significantly deteriorate welding quality during the process. The paper first considers research related to interfacial phenomena and bonding mechanisms, which focused on fundamental studies of the process such as temperature field and stress variation, double nugget evolution and IMC formation and distribution. Then the work on advances in various Al/steel RSW process optimization methods is comprehensively considered, which include using optimized electrode methods, adding auxiliary materials or using external energy field to assist the Al/steel RSW process and also introducing some hybrid optimization methods which combined other welding or joining processes. Some representative and remarkable works were presented in detail, and corresponding statistic and comparative information of different works using the same type of optimization methods were also provided. In addition, the comprehensive performances of the methods, which include some important criteria, are listed in detail. Although these works can provide optimization approaches to obtain Al/steel spot welded joint with satisfactory quality, the reliable implementation of these methods in high-volume industrial application requires further developments in process robustness and cost reduction. In these various improvement methods, the external energy field assisted method is a promising solution for practical applications because it does not require pre-treatment of the parent metal sheets and may allow convenient online adjustment and control. This paper also pays attention to the quality evaluation and process parameter optimization of the process, and provides a prediction about future trends in these aspects by combining advanced artificial intelligent methods based on a review and comprehensive analysis of some relative works. Furthermore, concluding remarks and suggestions for the future works are provided. This work is expected to provide references and insights for academic research and actual industrial application of Al/steel dissimilar metal RSW related areas.