The Research Of Friction Stir Welding Of Al/Cu Adopting Tooth-Shaped Joint Configuration

In the present study,dissimilar metals of aluminum alloy and pure copper were friction stir butt welded adopting tooth-shaped joint configuration(TJC)to investigate the influence of Al/Cu content in welding bead on the microstructure and mechanical properties of the joint.The Al/Cu content in the weld could be controlled by changing the tooth width.Then,a set of comparative experiments were conducted with the conventional butting joint congratulation(BJC)and TJC to investigate the advantages brought by the latter.Under the optimized parameters,the low heat input was achieved.The length of the tooth was defined as 3mm,smaller than the largest diameter of the pin.Welding experiments were performed with the dimensions of the tooth as variables.With the increase of Cu content,the void defect could be captured due to its high plasticized temperature and poor flowability,which led to the insufficient filling of the space extruded by the pin movement.However,the defect-free joint could be fabricated,when controlling the mixing content of Al and Cu.Activated by the thermal cycle,two sublayers with different elemental content were formed near the Al and Cu sides,respectively.Clearly,the thin interlayer achieved the metallurgical bonding of base metals and benefited the joint performance.Dynamic recrystallization yielded fine grain microstructure because of the combined role of welding heat and stirring force.The mirohardness of the weld nugget was higher than that on the other region owing to the dynamic recrystallization and the occurrence of hard intermetallics.Under the optimal parameters,tensile strength of the joint obtained significant improvement accompanied by the ductile fracture characteristic.For comparison,the friction stir welding of alumimium alloy to copper with BJC was also conducted.Since the temperature distribution plays a vital role in the microstructure evolution,two thermocouples were placed on the advancing side and retreating side respectively to monitor the real-time temperature.The resultant temperature curves are distinctly different on Al and Cu sides.Peak temperature was captured on Cu side about 496℃,which is roughly 60℃ higher than that on Al side,illustrating the low heat input during the processing.Microstructure of the cross section of the joints illustrates that void defect was formed with the BJC,while defect-free joint was produced with the TJC.Besides,there is clear material flow behavior and the onion ring structure could be observed as well under TJC,which confirms the alternated arrangement of base metals is good for the material mixing and flow.Due to the special tooth-shaped structure,plenty of Cu particles were peeled off from the matrix and distributed over the Al matrix,forming the composite-like structure.Undeniably,some of the particles may have transformed into the intermetallic compound because of the metallurgical reaction between Al and Cu.The tensile tests show that the failure load fabricated with TJC is obviously higher than that with BJC.