Inhomogeneity Of Interfacial Microstructure And Properties In Radial Direction Of Aluminum/Copper Friction Welded Joints

Using other materials to replace copper is a good method for solving the shortage of copper resources.Aluminum is an expected material which also has excellent electrical and thermal conductivities.Using aluminum to replace copper not only can reduce the production cost,but also reduce the weight of the structural component.And it is inevitably invove the joint of aluminum and copper.Due to the large difference in thermo physical and chemical characteristics between aluminum and copper,solid state joining methods are usually used for joining them.Rotary friction welding is a common and effective joining technology in welding aluminum and copper.However,the rotary friction welding has the characteristic of inhomogeneity microsturcture at interface.And this could influence the integrity and apply of Al/Cu joints.So it is necessary to study the inhomogeneity of microstructure and properties intensively.Type AA1060 pure aluminum and T2 pure copper were selected as base metals to finish weld in rotary friction welding method.And the joints were heat treated at different temperatures with different time.Scanning electron microscope,energy dispersive X-ray soectrometer,electron probe micro-analyzer,X-ray diffractometer,universal tensile testing machine and DC double armed bridge were used to analyse the the inhomogeneity of microstructure and properties.The main results are listed as follows:The integral joints test showed that aluminum and copper were joined successfully using rotary friction welding method,and the sound joints were produced after heat-treated at 100 oC for 2h with tensile strength of 91 MPa and bending angle of more than 90 o.With the increase of heat treatment temperature,the thickness of intermetallic compounds increased and the mechanical properties of joints decreased.The inhomogeneity of as-welded joints showed that the center position had the best mechnical properties,which fractured on aluminum side with tensile strength of 88 MPa and elongation of 20.2%.The tensile strength and elongation decreased with the increase of thickness of intermetallic compounds along the radial direction.After heat treatment at 100 oC and 250 oC for 2h,the tensile strength and elongation of center position of joints decreased but they increased of edge position.After heat treatment at 400 oC,the samples of center and 1/2R positions fractured during machine process,and the tensile strenghth and elongation of edge position decrease dramaticly.Joints had the lowest resistivity after heat treatment at 100 oC for 2h.Heat treatment at lower temperature,such as 100 oC and 250 oC,could relise the residual stress of joint and reduced the resistivity of it.However,both of micro-cracks and intermetallic compounds caused the resistivity of joints to increase,after heat treatment at 400 oC.The thermodynamic and kinetics of interfacial reaction showed that the growth rates of intermetallic compounds were controlled by diffusion.And the growth rates of intermetallic compounds were the fastest in edge position,while they were the slowest in 1/2R position.Comparing the growth rates of different intermetallic compounds,it was found that Al4Cu9 had the fastest growth rate and Al Cu had the slowest growth rate.The activation energies of total intermetallic compounds layer,Al2 Cu,Al Cu and Al4Cu9,which were calculated by the Arrhenius relotionship,were 121.40 k J/mol,92.24 k J/mol,55.59 k J/mol and 146.92 k J/mol,respectively.