Mechanical Performance and Microstructure of Resistance Element Welds of Dissimilar Metals Created with a Headless Rivet

Abstract

Resistance Element Welding (REW) is a novel processing technology developed to join dissimilar materials such as aluminum and steel. It uses an auxiliary steel rivet (element) inserted into an aluminum sheet that forms a resistance spot weld with the steel sheet, and the aluminum work piece is mechanically joined by the interlocking rivet. The versatility and agility of REW is advantageous, especially in the automotive industry. However, the head of the rivet often extends out externally over the work piece, and the misalignment of the electrode with the head can be problematic since inserting the head and the weld are performed in separate stages. In the present paper, we performed REW using a headless rivet which has minimal to no overhanging part above the aluminum surface. The lap-shear strength of REW is higher than self-piercing rivets, which makes REW a promising solution for extending applications of multi-material structures. The microstructure of the joint involves a fusion zone which mainly consists of martensite, and the failure occurs near the heat affected zone. This study finds that the electrode-rivet alignment needs to be optimized to manage the optimal nugget size and to avoid current arcing through the aluminum work piece.

An Overview of Resistance Element Welding with Focus on Mechanical and Microstructure Joint and Optimization in Automotive Metal Joints

“…In addition, an analytical model was also established to predict the critical nugget size of REW using the average SZ hardness and sheet thickness, which well explained the failure mode transition of the existing REW joints. The microstructure of the REW joint which mainly consists of martensite, was reported by Oh et al 26) . It seems that the microstructure of the REW joint is similar to that of RSW, revealing microstructure modifications caused by heating and cooling at a high rate.…”

“…The join-ability of magnesium to stainless steel and the join-ability of aluminium to ultra-high-strength steel are reported in 21,22) , respectively. Oh et al 26) employed a newly designed rivet for bonding between the A365 and SGACC plates, and secured mechanical performance by minimizing the head that protrudes from the aluminum plate. It was difficult, however, to maintain mechanical properties for the misalignment between the rivet and electrodes with a 6mm electrode di-ameter for the rivet.…”

Performance and Interfacial Microstructure of Al/Steel Joints Welded by Resistance Element Welding

“…Second, the upper sheet, lower sheet, and rivet are welded together using RSW. To explore the influence of element shape on joint performance, rivets of various shapes were selected as elements for welding an Al alloy and steel [18,19]. The REW of dissimilar materials can realize a one-step integrated process by optimizing the geometry of the rivet's shank tip [20].…”

Resistance spot weldability of heat-treatable and non-heat-treatable dissimilar aluminium alloys

“…For appropriate material selection for optimised structure, weldability is one of the most crucial characteristics to be considered. While novel joining technologies have been developed to accommodate the weldability of a wider range of material combinations [1][2][3][4], resistance spot welding (RSW) is still extensively used in the automobile production because it stands as the most agile and versatile welding technology [5].…”