MAZDA Motor Corporation has developed 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 Mazda 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 lid and its hinges for the updated and improved Mazda MX-5 sports car scheduled to go on sale in the UK in late November.

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.