Study On The Correlation Between Local Corrosion,Aging Degree And Electrochemical Properties Of Al-Zn-Mg Alloys

Al-Zn-Mg alloys have been widely employed in the production of components with harsh load environments and extremely high material performance requirements.However,Al-Zn-Mg alloys exhibit high susceptibility to localized corrosion,which have limited their application range.In this paper,in-situ corrosion is used to prove the difference of the second phase with different composition and size in the as-rolled Al-Zn-Mg alloy during the corrosion process,as well as the precipitation characteristics of the second phase and grain boundary in the 7050aluminum alloy with different aging treatment.effect on its corrosion performance and establish a correlation with electrochemical performance by electrochemical impedance spectroscopy.The purpose is to explore the corrosion mechanism of Al-Zn-Mg alloys and improve their corrosion resistance.The main conclusions obtained are as follows:（1）The Fe-containing phase on the surface of the 7050 aluminum alloy sample is the second phase of Al₇Cu₂Fe type,and the larger the phase size,the smaller the Cu/Fe.For the 7050 aluminum alloy samples aged at120℃ for 24 h,60 h and 120 h,the Al₇Cu₂Fe phase in the size range of1.5～3.5μm has the largest number and the largest area ratio,accounting for 79.10%,87.96%,87.06%.（2）Compared with A7N01 and 7050,it is found that the presence of Cu element in the Fe-containing phase can reduce the potential difference with the matrix and slow down the corrosion rate of Al-Zn-Mg alloys.During the pitting corrosion process of the Al₇Cu₂Fe e phase,the surrounding matrix is preferentially corroded,and then the Al element in the phase is selectively dissolved to form Cu and Fe-rich clusters.The larger the phase size,the faster the surrounding matrix corrodes and the faster the formation of rich clusters.（3）With the increase of aging degree,the grain orientation dispersion of 7050 aluminum alloy which is prone to intergranular corrosion is gradually weakened,and the resistance to intergranular corrosion is enhanced.The intergranular corrosion depths of 7050 aluminum alloy samples aged at 120℃ for 24 h,60 h,and 120 h were 68.23μm,39.46μm,and 18.11μm,respectively,and the electrical conductivity was42.1%IACS,41.67%IACS,and 46.37%IACS,respectively.（4）In the intergranular corrosion solution,the aluminum matrix is preferentially corroded in the early stage of corrosion,and the corrosion performance of the sample decreases significantly.The pitting corrosion of the as-rolled 7050 aluminum alloy continued to work within 0～1.5 h.The pitting corrosion of the 7050 aluminum alloy aged at 120℃ for 24 h mainly occurred within 0～1.5 h,and the pitting corrosion of the 60 h and 120 h aging mainly occurred in the 0～1.5 h.within 1 hour.During the pitting corrosion,the corrosion resistance of the alloy continued to decrease,and after the effect reached the maximum value,the corrosion resistance of the sample gradually improved.