Study Of The Effect Of Elastic-plastic Compressive Stress On The Corrosion Behavior Of Mg-RE Alloys

Compared with traditional magnesium alloys,magnesium rare earth alloys have good heat resistance,high specific strength and relatively good corrosion resistance,which are widely used in the fields of aerospace,national defense science and technology.However,due to the low corrosion potential,the corrosion resistance of magnesium rare earth alloys is relatively poor,which restricts its application.At the same time,often used as a structural material,in the service process will not only be affected by the corrosive environment,but also can not avoid the external load stress effect,and in this mechanical-chemical synergy,so that the magnesium alloy corrosion behavior changes,greatly affecting the corrosion resistance of magnesium alloy,so the study of stress on the corrosion behavior of magnesium alloy influence mechanism has great value of engineering applications.However,the current research on the corrosion behavior of magnesium alloys mainly focuses on tensile stress,the research on compressive stress is less,especially the influence of elastic-plastic compressive stress on the corrosion behavior of magnesium rare earth alloys is not clear,so the study of the influence of elastic-plastic compressive stress on the corrosion behavior of magnesium rare earth alloys is of great significance.In this paper,the Mg-Gd-Y alloy was studied by applying different elastic and plastic compressive stresses to the Mg-Gd-Y alloy through a self-researched compressive stress loading device,observing and analyzing the microstructure and phase composition,microscopic morphology and corrosion behavior of the Mg-Gd-Y alloy by full immersion weightlessness method,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and X-ray diffractometer（XRD）.corrosion behavior,and then the corrosion resistance and corrosion susceptibility of Mg rare earth alloy under different elastic-plastic compressive stress loading conditions were investigated by electrochemical workstation.The conclusions are as follows:（1）The Mg-Gd-Y alloy is mainly composed ofα-Mg grains,bone-like Mg₂₄Y₅ phase,a small amount of massive Mg₅Gd phase and 14H-type parallel needle-like LPSO phase(Mg₁₂Y₁Zn₁).Among them,the Mg₂₄Y₅ phase is distributed at theα-Mg grain boundaries,the Mg5Gd phase is distributed around the Mg₂₄Y₅ phase in a scattered pattern,and the LPSO phase extends from the Mg₂₄Y₅ phase to the interior of theα-Mg grains.（2）In the stress-free state,the Mg-Gd-Y alloy first corrodes at the grain boundaries and extends along the grain boundaries,followed by corrosion inside theα-Mg grains,and thereafter around the LPSO phase.Under elastic compressive stress,the Mg-Gd-Y alloy corrodes mainly within the grains and then along the LPSO phase toward the grain boundaries.Under plastic compressive stress,intense corrosion occurs at the grain boundaries of the Mg-Gd-Y alloy,especially at the Mg₂₄Y₅ phase-Mg-Gd-Y alloy grain boundaries.The analysis suggests that the elastic compressive stress leads to the reduction of atomic spacing inside the alloy,resulting in the reduction of electrode potential difference between Mg₂₄Y₅ phase andα-Mg;the plastic compressive stress causes a large number of dislocations near the organization of LPSO phase and Mg₂₄Y₅ phase,and dislocation plugging and dislocation climbing occur at theα-Mg grain boundary,resulting in stress concentration at the grain boundary,which accelerates the corrosion at the grain boundary.（3）Electrochemical test results show that the elastic compressive stress,with the increase of loading stress,magnesium rare earth alloy self-corrosion current density I_coor is always increasing,self-corrosion potential E_coor,charge transfer resistance Rt and corrosion product resistance Rp show a trend of first decreasing and then increasing.However,when the elastic compressive stress reaches 0.7σs,the second capacitive resistance loop appears in the low frequency of EIS,indicating that the elastic compressive stress accelerates the growth of corrosion product film,and the alloy surface has a more complete corrosion product film at this time.Plastic compressive stress,Mg rare earth alloy Rt and Rp show monotonically decreasing,indicating that the degree of electrochemical corrosion of Mg rare earth alloy increased.（4）Mg-Gd-Y alloy in the elastic-plastic compressive stress will not change the corrosion product film phase composition;corrosion of the early stage,the elastic compressive stress（0.5σs,）will make the corrosion product film part of the grain becomes smaller,the corrosion product film carrier concentration and the number of defects is reduced,the growth of corrosion product film on theα-Mg surface in the grain to promote the role.Plastic compressive stress（1.5σs）will destroy the integrity of the corrosion product film,but the film still has a certain protective effect on the substrate during the pre-corrosion period.However,as the number of crack defects at the grain boundaries increases with corrosion time,the stability of the corrosion product film decreases,and the protection of the substrate gradually decreases.