Study On The Failure Behavior Of Aluminum Alloy Under The Coupling Of Marine Environmental Factors And Stress Loads

Aluminum alloys are widely used in aerospace,marine engineering and many other fields for their light weight,high strength,corrosion resistance and other excellent properties.Corrosion of aluminum alloy is a complex process.Due to the strength,cost,corrosion resistance and many other reasons,aluminum alloy is inevitably combined with other materials in practical use,resulting in galvanic corrosion and affecting the safety of engineering structures.In addition,aluminum alloy structural members are bound to be subjected to stress load during service.Therefore,the galvanic effect and stress load become the main causes of aluminum alloy failure.In the marine environment,the special high temperature,high salt,high humidity and other environmental factors coupled with the galvanic effect and stress load undoubtedly intensify the test of the performance of aluminum alloys.Through stereomicroscope,X-ray diffraction(XRD),scanning Kelvin probe(SKP),electrochemical workstation and other experimental equipment,the effect of temperature on the failure behavior of 5083 aluminum alloy/Q235 steel couple and the effect of the coupling of marine environmental factors and stress load on the failure behavior of 7050aluminum alloy have been studied in this paper from the aspects of mechanics,electrochemistry and material microanalysis.The main results are as follows:at 25℃,35℃and 45℃,the current density of 5083 aluminum alloy/Q235 steel couple is 19.407?A·cm~2,36.688?A·cm~2and 57.465?A·cm~2respectively.The increase of temperature accelerates the corrosion rate of the couple.In the galvanic couple,5083 aluminum alloy is used as anode due to its relatively negative corrosion potential,and the corrosion rate is accelerated.While Q235 steel with higher corrosion potential is protected as cathode.The results of corrosion morphology show that the corrosion of Q235 steel is not obvious under the protection of 5083 aluminum alloy at the early stage of galvanic corrosion.The closer to the coupling connection,the more serious the corrosion of 5083 aluminum alloy.There are corrosion products of 5083 aluminum alloy on the surface of Q235 steel,which inhibit the corrosion rate of Q235 steel.With the polarization curve fitting parameters as the boundary condition,the potential and current density distribution of 5083 aluminum alloy/Q235 steel couple on the model surface are simulated by finite element method.The simulation results are basically consistent with the experimental results.A self-made stress loading device was used to apply constant tensile stress to 7050aluminum alloy specimens in order to study the effect of the coupling of marine environmental factors(temperature,salinity,p H)and stress load on the failure behavior of7050 aluminum alloy.The results show that the higher the tensile stress,the higher the corrosion rate of 7050 aluminum alloy.Under constant tensile stress,the higher the concentration of H~+in solution,the higher the corrosion rate of aluminum alloy;the corrosion rate of 7050 aluminum alloy in solution with different salinity shows2%Na Cl<3.5%Na Cl<6.5%Na Cl<5%Na Cl and that in 5%Na Cl solution at different temperatures reveals 25℃<45℃<35℃<55℃.The results of surface morphology show that at the initial stage of corrosion,due to the difference of electrochemical properties between the second phase on the aluminum alloy surface and the substrate,corrosion pits preferentially occur at the intersection.With the extension of corrosion time,under the interaction of stress and corrosion environment,the corrosion pits gradually expand and finally form cracks.The effect of different tensile stress on the stress and strain,cathodic/anodic surface potential and current density at the corrosion defect of aluminum alloy specimens was simulated by finite element method.The simulation results show that the greater the tensile stress,the greater the stress at the bottom of the corrosion defect.With the increase of the applied stress,the corrosion potential at the corrosion defect gradually moves negatively and the corrosion current density gradually increases.The application of stress accelerates the dissolution of aluminum alloy,thus accelerating the corrosion rate.