Effect Of Interlayer On Microstructure And Mechanical Properties Of Al/Cu Friction Stir Welded Joints

In recent years,with the continuous improvement of the requirements in the field of engineering and manufacturing,aluminum/copper dissimilar metal welding which takes into account different special properties has been widely used.Since the advent of friction stir welding technology in the 1990s,this new solid-phase connection technology has been widely used in the connection and research of non-ferrous metals,and has achieved good results.The formation of brittle intermetallic compounds is still unavoidable in the actual friction stir welding of aluminum and copper.In order to further inhibit the growth of brittle intermetallic compounds and improve the performance of joints,the interlayers of pure Zn,Zn-15Al-1.2Cu and Zn-15Al-3.0Ag were selected to be placed between Al/Cu lap joints,and the effective joint of aluminium/copper FSW lap joints at ultra-high rotating speed was successfully realized.The experimental results are as follows:compared with the coarse intermetallic compounds produced by direct FSW welding of aluminium/copper joints,when pure Zn foil is used as the interlayer,the thickness of Al2Cu intermetallic compounds decreases significantly,and the structure of aluminium based solid solution-zinc based solid solution-Al2Cu in the joint improves the mechanical properties of the joint.But in the situation of higher welding speed or rotating speed,the formation of a large number of Zn-Al hypoeutectic structures in the interface and the formation of intermetallic compounds at the interface of Cu side,such as CuZn₅ or Al_4.2Cu_3.2Zn_0.7,will directly reduce the mechanical properties of the joints.When Zn-15Al-1.2Cu alloy is used as the interlayer,the addition of Al and Cu elements change the structure of the interface greatly.In spite of the formation of layered solid solution strengthening phases at the interface of aluminium side at different welding speeds,the mechanical properties of the joints are still poor and the shear resistance are generally lower than 2kN,which is caused by the formation of a large number of Zn-Al eutectoid structure at the interface of copper side at lower welding speeds,as well as the presence of bulky rectangular Al₂Cu at the interface at higher welding speeds.When Zn-15Al-3.0Ag alloy is used as the interlayer,a trace amount of Ag element is solid-dissolved into the interfacial aluminium-based solid solution and the intermetallic compounds.The solid solution strengthening effect makes the shear resistance of the joints at different welding speeds higher than 2kN.The mechanical properties are highest among the interlayers of the three components,and the stability of the joint bonding is enhanced.With the increase of welding speed,the Zn-Al eutectoid structure in the interface grows and coarsens,and the mechanical properties of the joint begin to decrease.