Friction stir welding of accumulative roll-bonded commercial-purity aluminium AA1050 and aluminium alloy AA6016

Ultrafine-grained sheets of the commercial-purity aluminium AA1050 and the aluminium alloy AA6016 were processed by accumulative roll bonding. As-received, conventionally grained and ultrafine-grained aluminium sheets with an average grain size ranging from 20 μm to 30 μm and 200 nm, respectively, were successfully joined by friction stir welding, and the microstructure and the mechanical properties of the welded zone were investigated. Ultrafine-grained materials showed softening in the nugget, although the hardness remained comparable to the as-received, conventionally grained aluminium sheets.