Study On The Interface Structure And Properties Of Al/Interlayer/Cu Friction Stirring Brazed Lap Joint

During the high-speed friction stir lap welding process,the direct welding of Al/Cu plates will form a continuous layer of Al-Cu intermetallic compound at the interface,and the presence of this brittle hard compound will greatly reduce the strength of the joint.In this project,Zn x Al（x=0,2,5,8）solder was added between the 1mm thick 6061 aluminum alloy and the 1mm thick T2 copper,and the solder was melted and flowed through the high speed friction stir of the stirring head,thus forming Zn-Al solid solution on the Al side and Cu-Zn compound on the Cu side,completing the effective connection of the Al/Cu lap joint,and inhibiting the generation of Al Cu intermetallics.The effect of Al element content in solder on the microstructure and mechanical properties of joints was studied,and the experimental results are as follows:The difference in melting temperature of solder leads to different degrees of superheat during the stirring process.The higher the superheat,the better the fluidity of the intermediate layer,and the better the joint performance.The research results on the wettability of solder in Al and Cu plates indicate that with the increase of Al content,the wettability of the intermediate layer continuously increases.In the process of friction stir brazing,Zn Al solder with different Al content was added as the interlayer.Through the study of the microstructure and composition of the joint interface,it can be seen that there was an obvious delamination phenomenon at the interface.From the Al side to the Cu side,there were Al based Solid solution,Zn Al hypereutectic,Al based Solid solution,Zn based Solid solution,and Zn Al eutectic structures,in which Zn Al eutectic structure was the main structure,accounting for most of the area.The addition of Al element in Zn-Al solder results in the formation of double layer intermetallic compounds at the fracture interface.Compared with the Cu Zn₅structure produced by using pure Zn solder as the interlayer,the grain size of the newly produced Al Cu-Zn Ternary compound is smaller.The addition of Al element has a fine grain strengthening effect on the joint structure,and the joint performance has been improved.The highest shear strength is obtained by adding 5%Al content.The research results show that when the welding heat input is sufficient,the liquid solder is squeezed to both ends of the solder.When the welding heat input is insufficient,the unmelted solder at both ends of the intermediate layer hinders the flow of the central liquid solder,and is ultimately squeezed into the instantaneous cavities on the forward and backward sides,resulting in the phenomenon of solder flowing into the base metal,which improves the performance of the joint.