Experimental Design And Performance Research On Stress Corrosion Resistance Of 7075 Aluminum Alloy Under Different MIG Welding Processes

7075 aluminum alloy is widely used in industrial fields due to its high strength,low density,and strong corrosion resistance.Various complex-shaped load-bearing parts formed by welding processes are also used in power,transportation,aerospace and other fields.Although 7075 aluminum alloy has excellent mechanical properties,due to its large coefficient of linear expansion and fast heat conduction,a large amount of heat is needed for the successful welding.In the non-equilibrium solidification process,the micro-structure and composition of different zones of the joint are quite different,resulting in large welding residual stress,which seriously affects its corrosion resistance and limits the wide use of 7075 aluminum member.In addition,such components often service in a corrosive environment,subjected to the interaction of stress and corrosive media which promotes the stress corrosion.Because the stress is much lower than the yield strength of a material when the stress corrosion occurs,there is no obvious sign before it occurs,which makes its judgment and prediction very difficult.The structural failure caused by stress corrosion often causes huge disasters and economic losses.Therefore,investigating the influence of welding on the stress,microstructure and corrosion resistance of 7075 aluminum alloy,as well as the corrosion resistance is of great significance for the wide application of aluminum alloy in industry.This subject is based on the constant-load stress corrosion cracking test method,and self-designed stress corrosion test device for laboratory use.The single-side/double-side MIG welding was adopted to obtain the 7075 aluminum samples.The microstructure,residual stress and corrosion resistance of the samples were studied.Using a self-designed stress corrosion test device,the stress corrosion behavior of 7075 aluminum alloy in 3.5%NaCl solution was studied,and its corrosion mechanism was discussed.The main conclusions are as follows:(1)A small stress corrosion test device for laboratory use was designed and manufactured.The device has the characteristics of clear stress state,simple test method,relatively short test period.(2)There is little difference in the mechanical properties of 7075 aluminum alloy MIG single/double-side welding.The tensile strength of the double-side welded joint is 250.2MPa and the elongation is 2.0%;the tensile strength of the MIG single-side welded joint is 260.4MPa,The elongation is 2.2%.Compared with single-side welding,the use of double-side MIG welding facilitate to obtain a finer weld microstructure.(3)The corrosion resistance of MIG welds of 7075 aluminum alloy is better than that of the base metal.Electrochemical tests show that the corrosion tendency of the welds is less than that of the base metal.For immersion corrosion,the corrosion resistance of different areas from the...