Research On Vacuum Diffusion Bonding Technology Of 6061 Aluminum Alloy

Aluminum alloy has the characteristics of low density,high specific strength and excellent machining performance.It has been widely used in aeronautics and astronautics,automobile manufacturing,power electronics and other fields.The proportion of aluminum alloy welded structural parts in these fields is increasing.However,it is difficult to meet the quality requirements of aluminum alloy cooling plates and microchannel radiators by using traditional welding technology.Diffusion bonding technology is a solid phase welding method,which has unique advantages in realizing the welding of complex structure precision parts.Therefore,it is important to study the diffusion bonding of aluminum alloy.Taking 6061 aluminum alloy as the research object,diffusion welding of 6061 aluminum alloy without interlayer and with micron powder and pure silver foil as the interlayer respectively was carried out.Optical microscope(OM),scanning electron microscope(SEM)and energy spectrum analyzer(EDS)were used to observe bonding surface welding,microstructure evolution and element diffusion,and shear performance of welded joints were tested.The influences of surface treatment of aluminum alloy,welding temperature,welding pressure and holding time on joint welding rate,deformation rate and mechanical properties were analyzed.At the same time,the shear section morphology of the joint was observed by SEM and the fracture types were analyzed.The results show that,The surface treatment of aluminum alloy by chemical cleaning is more advantageous to the joint formation.With the increase of welding temperature,welding pressure and holding time,the gap at the welding interface decreases and the welding rate increases,meanwhile the grain size in the joint and the deformation rate of the joint increase and the shear strength of the joint increases firstly and then decreases.When T=540℃,P=4MPa,T=120min,welded rate of joint is 94%,the shear strength is 72 MPa and the fracture mode is ductile fracture.However,the deformation rate of joint is as high as 22%,farly exceeding the specified value.When micron powder is used as the interlayer,no intermetallic compounds are generated in the joint,and no diffusion reaction layer occurs because the main element of micron powder is the same as the main element of the matrix.With the increase of welding temperature,welding pressure and holding time,the thickness of the interlayer decreased,the more the micron powder diffused,and the shear strength of the joint increased.Under the technological parameters of T=465 ℃,P=5MPa,T=120min,welded joint rate is nearly 100%,joint fracture occurs in the bonding surface of micro powder and aluminum alloy,the shear strength of joint is 77 MPa and the deformation rate is only8.9%.It has achieved the established indicators in this topic.When pure the interlayer is silver foil,an obvious diffusion layer appears at the joint,because silver atoms enter the matrix and combine with aluminum and magnesium atoms of the matrix to form compounds.With the increase of welding parameters,the diffusion layer is thicker,the distribution of compounds is more uniform.The silver foil decreased until it completely disappeared,and the joint strength increased continuously.When T=500℃,P=3MPa,T=90min,joint is welded entiredly,the deformation rate was 11.5% and the shear strength of joint is 89 MPa.Fracture location is on the bonding surface of the silver foil and substrate and types fracture is plastic.Therefore,when silver foil is used as the interlayer,aluminum alloy diffusion welding joints can be obtained as well.