Research On Low Deformation Diffusion Bonding Process And Mechanism Of 5A06 Aluminum Alloy

Aluminum alloys are widely used in aerospace,power electronics,household appliances and other important structures due to their low density,good thermal conductivity and corrosion resistance.With the rapid development of modern industry and the continuous development of various large-scale high-power equipment,the entire industrial field has put forward higher requirements for radiator parts.6063aluminum alloy is widely used in the manufacture of water-cooled panels for radiator due to its good corrosion resistance and weldability.However,as the power of various equipments continuously increasing,its corrosion resistance requirements cannot meet the increasingly demanding industrial demands.5A06 aluminum alloy has better corrosion resistance and is an alternative material for water-cooled board in the future.At present,the most advanced method for water-cooled plate processing is diffusion bonding,but the 5A06 aluminum alloy has a lower melting point than the 6063aluminum alloy,and it is easy to cause a problem that the low-temperature atomic diffusion power is insufficient and the high-temperature shape variable is too large when diffusion bonding is performed.In response to this situation,by using an intermediate layer,we constructed an element concentration gradient at the interface to reduce the deformation of the process parameters and controlled the deformation by means of a fixture to achieve a dense connection with a deformation rate of less than1%.Various analytical test instruments such as electron probes,metallographic optical microscopes,X-ray diffractometers,thermal dilatometers,high temperature dynamic elastic modulus and damping systems,electronic universal material testing machines,etc.,were used to analyze the microstructure and properties of welded samples under various process parameters.The diffusion pressure of aluminum alloy is generally low,and its deformation mainly comes from creep.Therefore,the creep deformations of 5A06 aluminum alloy under different temperature,holding time and pressure parameters were explored.The results indicated that the process parameters with deformation rate of no more than 1%were T=460°C,t=1 h,and P=2 MPa.And we explored the joint morphology of the5A06 self-connected.In the case of excessive deformation rate,it still failed to form a good joint,indicating that its diffusion connection performance is poor.The diffusion joint of Al/Al+Al?Ag,Mg?/Ag₂Al/Ag/Ag₂Al/Al+Al?Ag,Mg?/Al was obtained by using Ag as the intermediate layer to realize the indirect diffusion bonding of 5A06 aluminum alloy.However,due to the brittleness of the intermetallic compound,microcracks were generated in the joint,and the strength was low,and the highest was 26.8 MPa.In addition,due to the large potential difference between Ag-Al,severe electrochemical corrosion occurred at the interface.Ni,the potential of which is close to the Al was adopted in the improved scheme as an intermediate layer for diffusion bonding of the 5A06 aluminum alloy/Ni/5A06aluminum alloy,and a dense joint with the structure of Al/Al₃Ni/Al₃Ni₂/Ni/Al₃Ni₂/Al₃Ni/Al were obtained.Due to the influence of residual stress,the joint strength was generally low,up to 16.8 MPa.We calculated the kinetic parameters of the formed Al₃Ni₂ reaction layer,and the growth activation energy and pre-exponential factors were 147.374 kJ/mol and 8.954×10^-4m²/s,respectively.The electrochemical corrosion behavior of the joint using Ni as the intermediate layer was significantly improved compared with Ag,but the oxide film formed by the Al₃Ni layer and the oxide film on the base material at the interface were cracked,which was not conducive to the protection of the internal materials by the corrosion products.In order to solve the problem of brittle product formation in heterogeneous interlayers and corrosion caused by potential difference,pure Al was used as the intermediate layer for diffusion bonding,which was the same material as the base material.The concentration gradient built at the interface improved the interface relative to the direct connection,forming a dense joint.However,since the concentration gradient was low and the reaction layer was not formed to achieve indirect connection,the process parameters for forming the dense joint exceeded the deformation rate of 1%.We used the 304 stainless steel with a linear expansion coefficient lower than 5A06 aluminum alloy to closely mount the base material,and used the pressure generated by the difference in expansion between the fixture and the base material during the heating process as the welding pressure.A dense connection was achieved at 475?for 2h or more,and the deformation was less than 1%.The joint strength increased with increasing the welding temperature and holding time.At490?and 3h of heat insulation,the joint shear strength reached 61 MPa,and the fracture had obvious dimple characteristics.