Friction stir welding of aluminum alloys and steels: Issues and solutions

Welding of aluminum alloys and steels by conventional fusion welding technology is difficult because of their different mechanical, chemical, and physical properties. Alternatively, friction stir welding (FSW) could be a solution as materials are joined in a solid state. However, FSW has some issues and drawbacks. The possible formation of brittle Al–Fe intermetallic compounds deteriorates mechanical joint strength. Improper process parameters, such as rotational and welding speed, could generate insufficient and/or inadequate materials intermixing. Therefore, defects like incomplete penetration, tunnel, surface grooves, surface galling, and kissing bond can form. Tool geometry (e.g. tool pin profile and shoulder) drives the uniformity of heat input and intermixing pattern inside weld joint. Tool wear is not capable of producing a homogenous heat and an adequate intermixing, thus voids and/or flashes can occur. To overcome the above-mentioned issues, a proper selection of process parameters, tool geometry and materials should be employed to ensure an adequate heat input and intermixing to join successfully aluminum and steel sheets. This article is a short review about the main issues related to FSW of aluminum and steels sheets and possible solutions.