Effects Of Aging Process On Microstructure And Corrosion Properties Of 7N01 Alloy

China's development in the field of rail transit is very rapid,and the demand for Al-Zn-Mg alloys continues to increase due to the increase in the mileage of high-speed rails and the continuous increase in speed.This means that it is necessary to obtain an aluminum alloy with high light corrosion resistance and after hot rolling.Al-Zn-Mg alloys also need to be further aging to improve the strength of the material,improve the material's structure and corrosion resistance to meet the needs of practical applications.Therefore,research on the aging processing,microstructure,strength and corrosion resistance of Al-Zn-Mg alloy is of great significance.In this paper,7N01 alloy was heat treated by different aging techniques.The changes of precipitation phase in the alloy were studied by means of transmission electron microscopy and DSC.The strength,hardness,electrical conductivity and corrosion performance of the alloy were analyzed.Different aging processes were discussed.The influence of the precipitation phase change of the post alloy on the strength and corrosion resistance of the alloy.The hardness variation of 7N01 alloy in the single-stage aging process shows that the hardness of the alloy increases first and then decreases with the aging time,and reaches the peak at 120 ?/24 h.The hardness value is 109 HB,and the conductivity value increases continuously.In the different regression process,the hardness of the alloy first decreases to the valley value with the extension of the regression time,then decreases after rising to a certain value,and the hardness value after the aging is significantly increased,but the regression process for 210 ? and The hardness values of the regression and reaging are relatively close,and continue to decrease with time.The conductivity value is always increasing,and the higher the regression temperature,the greater the maximum conductivity,up to 40.17% IACS.The intensity of the partial regression process parameters after re-aging is higher than the strength of the alloy T6 state,up to 403.5MPa,which is more than 27% stronger than the T6 state.However,the strength after 210? regression and aging is significantly lower than that of the alloy T6.The strength of the state is therefore favorable for the strength of the alloy to be 180 ? and 190 ?.The precipitation strengthening phase in the T6 state 7N01 alloy is mainly the GP zone and the ?' phase.During the subsequent regression treatment,the precipitation phase dissolution less than the critical size and the growth of the precipitation phase larger than the critical size occur.With the extension of the regression time,The average size of the precipitated phase gradually increases,and the higher the regression temperature,the larger the average size of the alloy and enters the Ostwarld ripening stage.After the reaging alloy,due to the nucleation of the new phase,the GP region coherent with the matrix is re-formed in the crystal,the semi-coherent ?' phase and the non-coherent ? phase.When the precipitated phase of the alloy is a dispersed GP zone and a small part of the semi-coherent phase precipitates the phase,the precipitation strengthening effect is obvious,so the strength value of the alloy is improved.When there is a ? phase in the precipitated phase in the alloy crystal,the strength value of the alloy is low.After the polarization curve was measured,the corrosion current of the alloy was the smallest after returning to 190 ? for 50 min.The test results of the intergranular corrosion performance were consistent with those of the polarization curve test.The intergranular corrosion depth of the T6 alloy was the deepest,reaching 110 ?m.The corrosion performance of the re-aged alloy is better than that of the T6 state,and the corrosion depth of the section is significantly smaller than that of the T6 alloy section.The results of exfoliation corrosion indicate that the alloy will first pitting at the position of the inclusion phase,then bubbling.After bubbling breaks,a layer of floc is formed on the surface of the alloy and then peeled off.Finally,the surface of the alloy peels off,and the surface after peeling can be corroded.The crack propagates along the grain boundary of the alloy and passes through the grain,and the corrosion process continues to develop toward the depth of the alloy.The improvement of the corrosion performance of the alloy is attributed to the coarse ? phase with intermittent grain boundaries and large spacing,and the Cu element is enriched at the grain boundary.