Study On Ultrasonic Welding Of Aluminum And Copper And The Evolution Of Joint Compounds

As a low-energy,non-pollution and high-efficiency solid-state welding method,ultrasonic welding applies to joining the aluminum-copper（Al-Cu）parts in lithium batteries and capacitor.At present,many researches has focused on the ultrasonic welding process of Al/Cu two-layered joints and the mechanism of welded joint,while the studys on the joining of three-layered sheets and the relationship between the intermetallic compounds and the joint properties are relatively few.For these problems,ultrasonic welding of Al1199 pure aluminum and T2 pure copper was carried out in this paper.The effect of welding energy,welding pressure and welding amplitude on the peak load of Al and Cu welded joints was discussed by orthogonal test.The results indicated that the optimum process parameters of two-layered sheets were welding energy of 600 J,welding pressure of 40 PSI and welding amplitude of 45μm,and that welding energy produced the biggest influence on the peak load of Al/Cu welded joints.Then,the effect of welding energy on the linear bonding density,interface temperature and the microstructure of welded joints was focused on.As welding energy increased,the linear bonding density of Al/Cu joints gradually increased to 94%,while the effective thickness slightly decreased.At 600 J,Al and Cu were well welded,and the atom diffusion layer was formed at the interface.When welding energy increased to 800 J,a thin thickness Al₂Cu compounds layer was formed at the Al/Cu joints.Next,the heat treatment method was used to accelerate the evolution of Al/Cu intermetallic compounds,and the effect of the intermetallic compounds on the joints properties were investigated.The results showed that when heating temperature was150℃,Al/Cu joints hardly formed the compounds At 300℃,Al/Cu welded joints gradually formed Al₂Cu and Al₄Cu₉ compounds layers.At 400℃,the joints generated four types of Al/Cu intermetallic compounds.In addition,the peak load of Al/Cu joints could decrease rapidly when the total thickness of Al/Cu compounds layers exceeded1.40μm.Owing to the high microhardness,the formation of AlCu was very bad for the joints properties,leading to the occurance of interfacial fracture of joints.Finally,based on the joining of two-layered joints,the three-layered sheets of Al and Cu were welded together,and the lapped modes of Al/Al/Cu and Al/Cu/Cu were mainly investigated.The peak load of Al/Al/Cu I-type joints had the biggest values,and the joint fracture mode was the interface fracture with tear.Moreover,the peak load of Al/Cu/Cu Ⅲ-type joints reached 2927 N,and the fracture mode was base-metal fracture.In addition,as welding energy increased,the peak load of Al/Al/Cu I-type joints increased first and then decreased,while the peak load of Al/Cu/Cu Ⅲ-type joints showed little change.