Mazda Motor Corporation has developed what is claims is the world's first direct spot joining technology to join steel and aluminium.

This new technology was first employed in 2003 in the development of the RX-8 sports car that used friction heat to join separate aluminium sheets. The technology has evolved, and will be used to join the boot [trunk] lid and bolt retainer for the latest MX-5.

Up to now, welding two different metals such as steel and aluminium has been a difficult task. However, by optimising the rotating tool shape and joining characteristics, and by using galvanised steel on one side, joining steel and aluminium has been made possible.

The process is similar to that of joining two pieces of aluminium, when a joining gun holds the parts from both sides with a welding tool. The joining tool is then made to spin while force is applied, which in turn generates frictional heat that subsequently joins the aluminium materials to the steel sheet metal. Galvanised steel helps prevent the galvanic corrosion that results from the contact of two different types of metal. Compared with conventional joining techniques such as riveting or clinching, steel and aluminium spot friction welding makes it easier to join materials that are difficult to deform, such as aluminium casting and high tensile steel. Additionally, running costs can be reduced because riveting becomes unnecessary.

This innovative technology makes it simple to join steel and aluminium, and improves the potential of coupling aluminium parts to steel in vehicle bodies, and has other applications in a wide range of industrial uses. The process contributed significantly to vehicle weight reduction efforts during the development of the MX-5, where each gram was counted, as well as lowering costs.

Mazda has applied for over twenty patents related to this technology.