Metal inclusions in the seams and fracture of the tool during friction stir welding of aluminium alloys

It is shown that the appearance of foreign metal inclusions in the seams of aluminium alloys created by friction stir welding is a consequence of the interaction of the working tool with the metal being welded, as well as the tool wears itself. Working tool fracture occurs when a tribological layer is formed on the tool surface as a result of the welded metal diffusion interaction and the tool material. The formation of the tribological layer is accompanied by the formation of aluminium penetration tongues along the grain boundaries into the steel from which the tool is made. Foreign metal inclusions are an intermetallic iron-aluminium particles of the FeAl3 type, which are detached from the tool surface and get mixed in the weld metal. It was found that tool wears increases with an increase in the temporary resistance of the welded aluminium alloy and with the presence of reinforcing ceramic particles SiC in its structure. © 2021 Informa UK Limited, trading as Taylor & Francis Group.