Investigation Of Refill Friction Stir Spot Welding Process And Atomic Diffusion Behavior Of Al/Cu Dissimilia Materials

In order to use our scarce resources reasonably and save the costs,the joining of aluminum/copper dissimilar materials has developed rapidly in recently years.Refill friction Stir Spot Welding（RFSSW）is a solid-state joining technology,which has a series of advantages that include good sealing performance,simple process,small thermal deformation,high quality joint and etc.In this paper,RFSSW technology was adopted to joining1.8mm-thickness AA1060 aluminum and 2mm-thickness C11000 copper and the atomic diffusion behavior of the joint was also investigated.The study include the following aspects.Firstly,BBD method was adopted to optimizing welding parameters.It was found that the rotating speed is main factor affecting the joint property,followed by the plunge depth,and the welding time has the smallest influence.The three optimum welding process parameters were 2500 r/min,1.7 mm and 6 s,respectively.Secondly,the control variable method was adopted to research the effects of welding parameters on the microstructure,mechanical properties and atomic diffusion behavior of the joints.Surface defects such as flash and material adhesion and inner defects such as void and incomplete refilling were formed during the welding process when the welding parameters were not selected properly.Besides,it was also found that the hardness value of the Stir zone（SZ）decreases with increasing the welding time.The maximum hardness（125 HV）can be obtained when the plunge depth is 1.6 mm.Both the tensile shear failure load and the cross tensile failure load of the joints first increase and then decrease with the increase of welding time,plunge depth and rotating speed.And the maximum values of the tensile shear failure load and the cross tensile failure load are 4.65 KN and 0.59 KN,respectively.Lastly,diffusion bonding was formed in the lap interface because the rotating tool didn’t plunge into the lower sheet.Therefore,a diffusion layer and intermetallic compound layers which includes CuAl₂ were formed in the lap interface.It was found that the thickness of the diffusion layer and intermetallic compound layer are increase with the increase of rotating speed,plunge depth and welding time.And the maximum values of the diffusion layer and intermetallic compound layer are 18.1μm and 2.3μm,respectively.