Research On Wear Behavior Of Mg97Zn1Y2 Magnesium Alloy

Magnesium alloys have excellent comprehensive properties at room temperature,with the rapid development of aerospace and automobile industry in our country,a higher requirement of the comprehensive performance and application area of magnesium alloy has been put forward.Traditional commercial magnesium alloys(AZ series)have been used in die castings and body forming components in automobile industry,however the poor wear and heat resistance of this kind of magnesium alloys in tribological application fields has become an important obstacle,so it can't be made as piston,sliding bearing and cylinder liner wear parts that used to be made from aluminum alloy,which required a higher working condition.Therefore,magnesium alloys with excellent wear resistance and heat-resistant need developing to expand its wide applications.The tribological properties of Mg97Zn1Y2 alloy were investigated using a pin-on-disk wear configuration within a load range of 20-380 N and a sliding speed of 0.2-4.0m/s,morphologies and oxygen contents of worn surfaces were examined,and wear rates were measured.Maps of transition load and wear rate under different sliding velocity were plotted,microstructural evolution of the subsurface were investigated.The microstructure evolution before and after mild-sever transition were analyzed,variation of hardness in subsurfaces was examined,the results revealed the reason behind the mild-severe wear transition and led to the following conclusions:There are two wear regimes found in the process of friction and wear: mild wear and severe wear.Mild wear regime consisted of oxidation+abrasive wear,serious oxidation and delamination,delamination.Severe wear regime included severe plastic deformation,severe plastic deformation accompany oxidation,surface melting.Mild wear has a low wear rate because of the oxidation layer and mechanically mixing layer has a better wear resistance,when mild wear transformed into severe wear,the accumulation of frictional heat exceeds dynamic recrystallization temperature of the alloy,leading to the severe plastic deformation or melting of the wear surface and decrease of the surface hardness,thus cause the wear rate rising.So the reason behind mild-sever wear transition is the realization of dynamic recrystallization in subsurface.The microstructure changed during the transformation from mild to severe wear in the near surface.Plastic deformation happened even at a low load of 20 N,in the mild wear regime,the depth of the plastic deformation zone increased with the applied load,after transition into severe wear regime,the frictional heating had a more significant effect on the near surface material,microstructure changed from the plastic deformed to the dynamically recrystallized,increasing load and sliding speed further eventually caused surface melting of the alloy.Therefore,the near-surface microstructure evolution sequence is: plastic deformation-dynamic recrystallization--surface melting and solidifying.Plastic deformation in the near-surface of the wear sample occurred before the mild-severe wear transition,strain hardening effect of the worn surface and the subsurface resulted in a high level of hardness when the applied load was in a low range,and the hardness increased with the applied load.Thus strain hardening suppressed the rapid increase of the wear rate.After the mild-severe wear transition,the accumulation of frictional heating caused the worn surface temperature rising over the dynamic recrystallization temperature of the material(TDRX),then the wear surface started softening,which overwhelmed the effect of work hardening by plastic deformation,consequently the hardness of the surface and subsurface dropped,and the wear rate rose.This suggests that the wear of Mg97Zn1Y2 alloy enters a severe wear stage.