その場加熱SPRプロセスで締結したAM50マグネシウム合金板材の接合強度

Abstract

Self pierce riveting (SPR) as mechanical joining is widely used for aluminum alloy, high strength steel or dissimilar materials such as polymer and metal in vehicle structures. The purpose of this study is to evaluate the tensile-shear strength of AM50 magnesium sheets jointed by a newly developed in-situ heating SPR joining system. It is difficult to joint magnesium sheets by riveting due to less ductility from a limitation of slip at room temperature, although there are few studies. In-situ heating SPR joining process has been developed to improve reliability of the joining sheet of magnesium, and to prevent occurrence of cracks which are initiated at beginning of riveting process. AM50 magnesium alloy sheet has 0.8 mm in thickness, and commercial aluminum rivet with 3.3 mm in diameter of the leg and 4 mm in height was used in this process. Cracks occurred in a lower sheet in both as-rolled and annealed AM50 sheet when conventional SPR joining process was applied at room temperature. No cracks are observed during in-situ heating SPR joining process at 250°C. The tensile-shear test was carried out at room temperature in order to estimate an effect of in-situ heating on reliability of the joint. The tensile-shear strength of AM50 joint heated at 250°C is higher than that of the joint from 5052 aluminum alloy with the conventional equipment.