Effect of reverse dual rotation process on properties of friction stir welding of AA7075 to AISI304
(1. Department of Materials Engineering, Babol Noshirvani University of Technology, Shariati Avenue, Babol, Iran;
2. CEMUC, Department of Mechanical Engineering, University of Coimbra, Rua Luís Reis Santos, 3030-788 Coimbra, Portugal)
2. CEMUC, Department of Mechanical Engineering, University of Coimbra, Rua Luís Reis Santos, 3030-788 Coimbra, Portugal)
Abstract: The friction stir lap welding of AISI304 stainless steel to AA7075 aluminium alloy was investigated using the conventional friction stir welding (C-FSW) and the reverse dual rotation friction stir welding (DR-FSW) processes. In order to reduce the heat input, a dual rotation tool with a lower shoulder rotating speed was used. The results showed that both processes provide welds with excellent appearance and free of internal defects. The use of the DR-FSW process with the tool shoulder rotating reversely at low speed results in larger grain refinement in the nugget and less change in the microstructure of the aluminium alloy than using the C-FSW. The use of DR-FSW process at low speed of rotation allows to reduce the amount of intermetallic compounds in the welding interface, but does not prevent their formation. Although DR-FSW welding exhibits tensile strength superior to that achieved with the conventional process (C-FSW), both exhibit brittle behaviour with fracture at the weld interface.
Key words: dual rotation tool; dissimilar friction stir welding; AA7075; AISI304; microstructure; mechanical properties