Microstructure And Properties Of Dissimilar Materials Cu/Ti Lapped Joint By Friction Stir Welding

As a new type of solid-state connection technology, friction stir welding (FSW) has tremendousapplication value in the fields of dissimilar materials connection. Nowadays, there are fewerresearches about friction stir welding of titanium alloys to copper alloys at home and abroad.Firstly, the integrated stir tool and the combined stir tool have been designed and produced whichwere applied for friction stir lap welding (FSLW) of TA2to copper T2. Secondly,2mm thick copperT2sheets were successfully joined by FSLW, which mainly studied the welded process,microstructure and properties of the lap joints. Finally, the lap joints of commercial puritytitanium(TA2) and copper(T2) plates were successfully produced via FSLW. The results shown thatthe sound joints could be obtained under the suitable process parameters (the rotation speed is700~900rpm, the welding speed is20~40mm/min) when used the combined stir tool. The flow oftitanium materials and copper materials at Cu/Ti lap interface were obvious extremely on themacroscopic view, the interface of Cu/Ti joints exhibited the typical bounded texture microstructureof Cu and Ti in the stir zone. Additionally, some local regions existed mechanical interlock betweenCu and Ti. The horizontal hardness distribution on the copper side of the nugget zone of the Cu/TiFSLP joints was irregular specially, the lowest hardnkess value appeared in the advancing side of theheat affected zone of the upper copper sheet. The vertical hardness distribution of nugget zone shownas an “M” shape. The fracture location of the joints which were processed by the combined stir toolwere mostly located in the advancing side of the heat affected zone of the upper copper sheet, thefracture was the mixed fracture. The sound joints could be obtained under the suitable processparameters (the rotation speed is800~900rpm, the welding speed is20~40mm/min) when used theintegrated stir tool. The microstructure of the nugget zone of the Cu/Ti lap joint closed to copper sideexhibits refined equiaxial grains and the thermo-mechanically affected zone exhibits deformed largegrains. A type of diffused intermediate layer was formed in the interface of lap joint, the diffusionvelocity of Cu is faster than that of Ti, and the lap joint of Cu and Ti has formed the metallurgicalbonding. Some joints which were processed by the integrated stir tool were located in the Cu/Ti lapinterface, the fracture was brittle fracture.