Research On Elevated-temperature Wear Behavior Of Mg97Zn1Y2 Alloy

Magnesium alloys have attracted much attention for their excellent performance,and have significant effects on achieving material lightweighting and reducing energy consumption.Traditional magnesium alloys such as AZ and AM systems are widely used in front-end fields such as automobiles and aerospace,but their poor wear resistance and high temperature performance have largely limited the scope of application of magnesium alloys.Studies have shown that the addition of rare earth elements effectively improves high temperature performance and creep resistance of magnesium alloys.Mg97Zn1Y2 alloy has present high temperature strength and creep resistance,and it now has become the research hotspots in rare earth magnesium alloys.Based on previous studies,this article studies the dry sliding wear behavior of Mg97Zn1Y2 alloys under elevated-temperature conditions.A pin-disk wear tester was used to perform an elevated-temperature wear test on the Mg97Zn1Y2 alloy.The sliding speed was selected as 0.5 m/s.The test temperature was selected as 20^oC,50 ^oC,100^oC,150^oC and 200^oC,and the applied load was within10 to 320 N,wear sliding distance is 565.2 m.Based on the test results,the friction coefficient-load curve and wear rate-load curve were plotted,from which the mild-severe wear transition loads determined,and the wear mechanisms were identified based on the SEM morphologies of the worn surfaces and the chemical element analysis of worn surfaces by EDS.A wear mechanism transition map of the alloy was established.According to the division of the wear mechanism,the relationship between the subsurface microstructure evolution and the hardness change was established for the wear samples before and after mild-severe transition,and the main reason for the mild-severe wear transition was explored.The wear mechanism of Mg97Zn1Y2 alloy in the mild wear stage included:abrasive wear+oxidative wear,delamination wear+surface oxidation,delamination wear+slight plastic deformation+surface oxidation.Among them,when the test temperature was higher than 100^oC,abrasive wear+oxidative wear mechanism disappeared,when the test temperature was higher than 150^oC,the wear surface underwent slight plastic deformation.The wear mechanisms in the severe wear stage included:severe plastic deformation+oxidation layer spallation,surface melting.When the test temperature was higher than 150^oC,the surface oxidation mechanism disappeared.In the range of 20-200℃,the mild-severe wear transition load of Mg97Zn1Y2 alloy decreased with increasing temperature,and the transition loads are as follows:20^oC,220 N;50 ^oC,200 N;100℃,160 N;150℃,120 N;200℃,80 N.Through the microstructure observation and hardness change analysis of the alloy sample,it was found that the range of the friction-affected zone deepened as the load increased,and the subsurface hardness curve had a corresponding relationship with the microstructure.The frictional heat-affected zone（FAZ）at the mild wear stage was mainly a plastic deformation zone and a mechanically mixed layer.The work hardening caused by plastic deformation and the combined action of the mechanically mixed layer improve the wear resistance.In severe wear stage,FAZ was composed of dynamic recrystallization zone（DRX）and plastic deformation zone,and solidification zone was formed near the wear surface under large loads.The appearance of the DRX region softens the subsurface tissue,that is,dynamic recrystallization is the main reason for the mild-severe abrasion transition,and the accumulated frictional heat makes T_S≥T_DRX.Through fitting,it is found that the mild-severe wear transition load decreases linearly with increasing temperature,and the wear transition of the alloy at 20²00°C is still conformed to the surface dynamic recrystallization temperature（SDT）criterion,so the criterion can be used to predict the alloy’s mild-severe wear transition load.At a sliding speed of 2 m/s,it was determined through analysis of the wear mechanism that 40N at 100°C and 25 N at 200°C were mild-severe wear transition loads.The wear rule of the alloy in the sliding speed range of 0.5⁴ m/s is summarized,and the slightness at the temperature of 0.8 m/s,2.0 m/s,3.0 m/s,4.0 m/s at 100℃and 200℃The severe wear transition load should be verified by the surface dynamic recrystallization（SDT）criterion.The calculation of the mild-severe wear transition load calculated from the surface dynamic recrystallization temperature criterion is in good agreement with the measured value,indicating that the dynamic recrystallization temperature criterion of the worn surface Judgement of mild-severe abrasion transitions at high temperatures still has good applicability.