What if they are not weld-able?

Many light metals, such as aluminum and magnesium alloys, are promised to provide significant weight reduction for automobiles. However, the difficulties in welding these metals seriously hinder their large-scale applications. A new, hybrid mechanical joining process is proposed to avoid the inherited metallurgical complications in welding. By spinning and pressing a solid rivet into the metals, a joint is formed with the locking from the rivet, a stirred/mixed zone around the rivet, and solid bonding at the faying interface. This riveting process combines the actions of friction-stir welding in which metals of difierent sheets are mechanically mixed, and self-piercing riveting process which embeds a rivet in the sheets. Experiments have shown that such a friction-stir riveting process can produce joints of comparable strength to those created by other joining means, and can be applied to dififcult-to-weld metals and dissimilar metals, such as aluminum-to-aluminum, magnesium-to-magnesium, and aluminum-to-magnesium.