Microstructure And Properties Of Cu/Al Alloy Welded Joints

In this paper,rolled sheet metal materials of pure copper and pure aluminum with2 mm thickness were welded by friction stir lap welding and resistance welding.The forming,interface structure and properties of the joints under different welding parameters were studied,Analyzed the connection mechanism of two kinds of welding methods.The following content were studied:（1）Aluminum plate placed on copper,were welded by lap fricition stir welding with single-pass and double-pass at rotation speed is 900 r/min and welding speed is30 mm/min,50 mm/min respectively.The forming of Cu-Al joint,mechanical properties and interface organization were analyzed and explained.During the single-pass and double-pass welding,copper particles move into the aluminum side stirring zone;compared with single-pass welding,double-pass welding’s the size of copper particles is reduced and the distribution is more uniform in the weld zone of the aluminum side.The interface of Cu-Al joint undre two kinds of welding procedure existed continuous transition layer which is different from the parent metal,the transition layer of the single-pass joint is composed of a double-layer intermetallic compound,and the transition layer of the double-pass joint is only a single layer intermetallic compound.The tunnel holes in the single-pass weld can be eliminated by double pass welding,the double passes repair welding will not reduce the tensile strength.（2）Friction stir lap welding of dissimilar materials,in addition to the rotation speed and the forward speed of the agitator can affected the performance of the joint,when the plates under different stir lap position and the size of the stirring pin on the influence of interface of Cu/Al joint tissue.The shape and structure of the joint changed significantly with the change of the size of the stirring needle.Under the same welding parameters,when the lap joint location and the selected FSW Tool size is different,the heat input changes.When copper plate on the aluminum plate lap welding,generating Al-Al₂Cu eutectic organization in the aluminum side.（3）In order to investigate the electrical conductivity and mechanical properties were there any improvement of the joints obtained by friction stir welding.The experiment of resistance welding of dissimilar metals of copper and aluminum was designed.It is found that the microstructure of the joint interface by resistance welding is more complex than that of the lap joint during friction stir welding.Theinterface of joints is composed of α-Al-Al₂Cu（near the aluminum side）and intermetallic compounds（IMC）Al₂Cu（intermediate）and Al₄Cu₉（near the copper side）,the IMC’s thickness increases with the increase of heat input.Due to the influence of intermetallic compound and eutectic phase,the resistivity of the joints obtained by resistance welding is obviously greater than that of the joints obtained by friction stir lap welding.Experiment show,Cu and Al two kinds of metals with good electrical conductivity were welded by friction stir lap welding,not only the mechanical properties of the joints are good,more importantly,the electrical properties are excellent.