Self-Piercing Riveting of Medium- and High-Strength Al and Mg Alloy Sheets Enabled by In-Process Electric Resistance Heating

Enduring joints of high-strength materials are becoming increasingly important for the manufacturing of highly loaded body-in-white structures, particularly for automobiles, which require structural light-weighting without sacrificing passenger safety. While self-piercing riveting has been proven suitable for various material classes, its application to high-strength, low-ductile materials is hindered by the occurrence of cracks and insufficient penetration. In this work, we demonstrated that these restrictions can be overcome by localized one-sided short-time electric resistance heating. The treatment can be integrated into the riveting process, allowing for short process times. The heating lowers the hardness of the materials to be joined and enables piercing and penetration of the sheets to yield crack-free joints. The local mechanical properties are hardly changed in case of peak-aged sheet material conditions but increase significantly in the close vicinity of the rivet in case of under-aged sheet material conditions. The outstanding static and dynamic mechanical properties of the resulting joints evidence their robustness.