Study On Interface Microstructure And Properties Of Cu-Al Dissimilar Metal Friction Stir Welding Joint

Friction stir welding(FSW)as a high-efficiency,environmental welding method has the characteristics of the low heat input,small deformation and high quality,applied to aerospace,ships and track vehicles.Based on the features of the FSW,it was regarded as the ideal way to join the dissimilar materials.In this paper,the Cu-Al dissimilar materials lap joints were treated as the main researching objects to study the welding characteristic,micro-structure evolution and alloy elements reinforce systematically.The FSW process characteristics for Cu-Al lap joint were studied and the effect of the plates position,welding speed and rotation speed on the weld appearance were investigated.The results show that the overheat appeared on the weld surface as the excessive heat input.There are difference in the phenomenon of overheating of the different plate positions,when the aluminium plate is the upper,the adhesion and great flash appeared on the weld surface,and when the copper plate is upper,the fibrous substance appeared on the weld surface.The "liquid region" can be seen in the Al side when the copper plate was upper,from the micro-structure.In this region,the eutectic reaction occurred between the liquid aluminum and the copper,forming the dendrite eutectic structure.The Intermetallic Compounds(IMCs)layer formed at the Cu-Al bonding interface,and the IMCs layer consists of two layer structures,which was effected by the welding parameters,the thickness of the layer increase with the increase of the heat input.The IMCs layer growth mechanism is revealed through the IMCs layer of the Cu-Al lap joint with annealing treatment analysis.The result show that IMCs layer grown once again during the annealing process,and the IMCs layers growth behaviors were different under different annealing conditions,only the original structure of the IMCs layer grew under the lower annealing temperature and holding time;the original structure of the IMCs layer grew again and a new layer structure appeared in the middle of the original structure under the high annealing temperature and holding time.The strengthening effect of the Sn alloy elements on the lap joint was investigated.The results show that Sn elements are mainly distributed at the Cu-Al interface.The tensile test show that the stress of the joint adding Sn element is similar to that of plastic fracture and the elongation increased to a certain extent.The strength of the joints with Sn are higher than the joints without Sn when the heat input is lower,and the strength of the joints with Sn is reduced when the heat input is too large.