Experimental Study And Numerical Simulation Of Current-assisted Diffusion Welding Of 5a06 Aluminum Alloy

5A06 aluminum alloys are widely used in the precise manufacturing structures such as liquid-cooled and waveguide components because of high strength,good thermal conductivity and excellent corrosion resistance.In this paper,spark plasma diffusion welding technology is used to realize the joining of 5A06 aluminum alloy.By experimental analysis finite element simulation,the SPS connection mechanism of5A06 aluminum alloy is explored from the perspective of process,structure and metallurgy,laying theoretical foundation for application of SPS diffusion bonding of aluminum alloys.The main research content and results are as follows:SPS diffusion welding experiments are performed at the temperature range of500-540^oC,pressure of 0-8MPa,holding time of 10-30min and vacuum of about 5 Pa.Due to the short holding time,the maximum deformation of welding sample is 0.06%.The optimal parameters are 530^oC,7MPa,and holding time of 10min.The maximum tensile strength is 107MPa.The oxide film will hinder the progress of diffusion,and the oxygen content of the poorly-bonded area is higher than that of the well-bonded area;With the extension of the holding time,a wide range of oxidation zones are found in the fracture,surface.The microhardness of the entire interface is close,the dimple areas are enriched of Mg and Si elements,and the segregation of Fe elements appears in the tear layer area.Furthermore,Al-20Cu-5Si-2Ni(wt.%)brazing filler metal is added as the intermediate layer for welding.SPS welding is performed at the welding temperature of 500-540^oC,pressure of 0-6MPa and holding time of 10-20min.The optimal parameters are temperature of 540^oC,pressure of 6MPa,holding time for 10 minutes.The maximum tensile strength of bonded joint reaches 229MPa.This fracture occurred in the interlayer.The ductile fracture morphologies were observed that agglomerated dimples appeared.The addition of brazing material has a physical film removal effect in the melting stage and inhibits the growth of the oxide film.On the other hand,the brazing melting causes the joint to produce a liquid channel.The diffusion activation energy of the interface is low.The Cu Al₂and fine Si particles in the solder diffuse to the grain boundary and enter the interface from the liquid channel.The Si element and the segregated Mg in the base material react to form Mg₂Si and Mg Si diffusion zones.The diffusion of Cu element leads to the production of Cu₉Al₄.The uniformly distributed Cu Al₂and fine Si particles at the grain boundary hinder the movement of dislocations and improve the mechanical properties of the joint.Hardening phases such as Mg₂Si are generated on the outside of the interface,causing the hardness of the diffusion zone to increase.Al/Ti SPS joint is obtained and analyzed for atomic diffusion analysis.The results show that the diffusion coefficient of atoms is greatly improved under the influence of electric field,and the vacancy defects in the bonding interface have directional movement,which promotes the diffusion of atoms.Based on MSC.MARC software,the thermal-electric-mechanical coupling finite element model of SPS diffusion welding is established.The model can predict the temperature field,electric field and stress and deformation field for the welding system.The influencing factors of the process are studied by defining a single variable,which is electric conductivity,contact electrical conductance and sample assembly while keeping the similar electric current constant for specified welding system.The simulation shows that the temperature in the center of the sample with a smaller resistivity is higher than that of the sample with a larger resistivity.The contact resistance causes the difference in current density inside the sample.While taking the interface contact conductance into account,the current density and temperature in the interface are lower,but the overall temperature of the sample rises.Moreover,there is a suitable value,which can make the sample temperature reach the highest value.The assembly method affects the welding process.When the resistivity of the upper material is high,the current flows from the indenter to the mold and the lower material.In this condition,the average temperature of the welding sample is higher.