Vacuum Diffusion Welding Of Aluminum Matrix Composites With Microstructure And Properties Analysis

Aluminum matrix composites have special properties, such as high specific strength, wear and corrosion resistance, low thermal expansion coefficient, good dimensional stability, so they have large quantities of application. Because of the chemical and physical properties' difference between reinforcement and matrix, fusion welding and laser induced reaction welding would induce defects in the welding zone of the composites, while friction stir welding have serious tool wear in bonding these composites. This paper systematically investigated the vacuum diffusion welding of aluminum matrix composites (Al-5wt.%Si-Al2O3), studied the theory and mechanism of diffusion welding, which can provide theoretical evidence and technical support to bond the composites.Power metallurgy method was applied firstly in this paper to in situ fabricate Al-5wt.%Si-Al2O3composites using the raw materials of about5um Al powder and SiO2nanopowder, through HIP with the processing parameters of700℃x50MPax1h. The composites'microstructure was uniform with Si and Al2O3dispersing in the matrix, and their relative density reached98.88%, and had good compression and shear strength. The fabricated composites were used as the raw materials for vacuum diffusion welding, and the welding samples were put in vacuum hot pressed sintering furnace to carry out vacuum diffusion welding. Orthogonal test was utilized in the experimental to optimize diffusion welding parameters, choosing welding temperature, pressure and hold time as three factors with three values. Effect of diffusion welding parameters on welding joint microstructure and properties as well as significance of effect was analyzed and the optimal processing parameters (555℃x50Mpax3h) in orthogonal test were confirmed. The estimated shear strength can reach36.61MPa, while the verification result was34.44MPa, and the confidence coefficient came to70%.Further investigation on orthogonal test results was studied by extension experiment, and it was found the shear strength of welding joints increased with the increase of welding pressure, while shear strength increased slightly when welding time was increased if it have already reached3hours. At the same time Al powder was used as interlayer to bond Al-5wt.%Si-Al2O3composites by diffusion welding. The contact surfaces between reinforcements have turned into that between reinforcement and matrix, and Si in the composites diffused into Al interlayer with some Si particles pining on the joint surface, which have largely increase the joints" shear strength(96MP. increased178.7%when compared with the optimal parameters in orthogonal test.