Self-Piercing Riveting (SPR) of Magnesium High Pressure Die Casting and Dissimilar Materials

Solid state joining processes are attractive for magnesium alloys as they can offer robust joints without the porosity issue typically associated with welding of magnesium and dissimilar materials. Among these techniques, Self-Piercing Riveting (SPR) is a clean, fast and cost-effective method widely employed in automotive industry for aluminum alloys. While SPR has been proven effective for joining aluminum and steel, it has yet to be successfully adapted for magnesium alloy castings. The primary challenge in developing magnesium SPR technology is the cracking of the magnesium button, which occurs due to magnesium's low formability at room temperature. Researchers and engineers approached this issue with several techniques, such as pre-heating, applying rotation to rivets, using a sacrificial layer and padded SPR. However, all these methods involve the employment of new equipment or introduction of extra processing steps. The aim of this work is to develop a SPR technique which adapts current SPR machines with minimal changes to existing processes to create crack-free joint between magnesium and dissimilar materials. In the current study, feasibility of joining coupons of typical structural materials including high strength steel, aluminum alloys and composite to magnesium high pressure die casting (HPDC) was investigated. It was demonstrated that a joint is achieved which is crack-free both internally and externally. Also, the lap shear strength of the joints was investigated. Given its flexibility in material selection and compatibility with existing SPR process lines, this method holds significant potential to facilitate more applications on materials with limited ductility.