Research On Fatigue And Corrosion Properties Of Extruded 6061 Aluminum Alloy Profile Used In New Energy Automobile

With rapid growth of the quantity of automobile,the environmental pollution and energy crisis have become a critical problem to be solved for the whole world.And one of the important solutions to this problem is increasing the use of aluminum alloy in automobile to reduce the weight of vehicle.As a typical heat-treatable alloy,6061 aluminum alloy has medium strength,excellent formability and good corrosion resistance,and therefore it has been widely used in automobile production.Automotive components often work under cyclic loading,which may make the components fail through fatigue fracture.What's more,automobiles always work in complex atmospheric environment and the atmospheric corrosion may cause it's performance degradation.Therefore,when we select the automobile component material,the fatigue and corrosion properties must be taken into consideration.In this study,extruded profiles of 6061aluminum alloy,which has been used to make battery bracket for new energy vehicle,was selected as the base metal.The impact of the artificial aging treatment on microstructures,mechanical or corrosion properties were studied and the fatigue properties of 6061-T6aluminum alloy were investigated.Firstly,the effect of artificial aging on microstructure and mechanical properties of the alloy was investigated.The precipitation sequence for alloy aged under 180?can be described as:super-saturated solid solution????G.P.zone?metastable^???metastable^?and^??stable?and Q.In the alloy aged for 5h,^??phase,the mainly strengthing phase,precipitate from the matrix,thus the microhardness and the tensile strength of the peak-aged alloy reach the maximum value 122 HV and and tensile strength rise to 327 MPa,respectively,while the elongation drop to 11.9%.According to the analysis of tensile fracture,the under-aged alloy's fracture mechanism is ductile fracture,while peak-aged alloy fails through brittle and ductile fracture.Secondly,the high frequency fatigue behaviors of 6061-T6 aluminum alloy were tested to determinate the S-N curve on middle and long fatigue life range.At room temperature,with the decrease of loading stress,the fatigue life increases continuously and the conditional fatigue limit of the tested material is 127 MPa.The microstructure observations of fatigue fracture indicate that:the cracks initiate from the impure phases,second phases and persistent slip band?PSB?,and the width of fatigue striation grows as the loading stress increases.The fatigue crack growth was analyzed by EBSD,the results show that the model of crack growth is a mixture of intergranular and transgranular fracture with the main crack growth plane of{111}plane.The deflection and bifurcation,both of which depend strongly on the orientations of grains,take place with the propagation of fatigue cracks.At last,the effect of artificial aging time on corrosion behavior of the studied alloy was investigated.The electrochemical and neutral salt spray tests both show that the corrosion properties sequence of the extruded 6061 aluminum alloy are as follows:the alloy aged for 5h,17h,11h,1h,1h aged specimen is the best.After removal of corrosion products,the peak-aged alloy is found to be most sensitive to the intergranular corrosion?IGC?.Because the peak-aged alloy has continuous distribution precipitates on the grain boundary,favoring the electrochemical corrosion in these regions.The main corrosion form found in the over-aged alloy is pitting corrosion and the pitting susceptibility grows with aging time.