Friction And Wear Behavior Of Mg-10Gd-1.4Y-0.4Zr Alloy At Elevated Temperatures

Magnesium alloys as one of the 21st century green materials have a significant role in achieving weight reduction,energy saving and environmental protection.Conventional magnesium alloys(AZ,AS)have been widely used to produce parts of aircrafts and automobiles,but the poor wear resistance and high-temperature resistance of magnesium alloys seriously impede their further development.Research shows that addition of the rare earth elements in magnesium alloys can improve high-temperature properties and creep resistance.Mg-Gd-Y-Zr alloy as a new type of heat-resistant magnesium alloy has aroused the concern of researchers.Adding rare earth elements of Y and Gd canimprove the strengthening effect and the heat stability of magnesium alloy.Therefore,this article studies the dry sliding wear properties of Mg-10Gd-1.4Y-0.4Zr alloys at high temperatures.In this experiment,the wear performance of Mg-10Gd-1.4Y-0.4Zr heat-resistant magnesium alloy at high temperatures was studied usinga pin-disc wear device at a sliding velocity of 0.79 m/s.Experimental temperatures were 20?,50?,100?,150?,200? and loads in the experiment were at 20-260N.From the friction coefficient curves and the wear rate curves,mild-severe wear transition load can be initially determined.At the same time,in order to analyze wear mechanisms,the surface morphologies of wear samples were observed by scanning electron microscopy(SEM)combined with Energy Dispersive Spectrometer(EDS),then draw the wear mechanism map and wear transition map at different temperatures.Subsequently,the wear surface characteristics and subsurface microstructure were correlated with hardness change,revealing the underlying causes of mild-severe wear and further evaluating the mild-severe wear transition load at various temperatures,and coming to the following conclusions:There are two wear regimes:mild wear and severe wear.In mild wear,it includes abrasive wear and oxidative wear,surface oxidation and delamination wear,partial spallatioan of the oxide layer and slight plastic deformation.In severe wear,it includes the spallatioan of oxide layer,severe plastic deformation and surface melting.The wear rate increases slowly in the mild wear regime due to strain hardening or the presence of oxide layer.However,the rate of wear increased sharply in the severe wear regime,owing tothe accumulation of frictional heat leading to the severe plastic deformation even melting of the wear surface.By studying the sub-surface microstructure evolution at 100? and 200?,it was found that the near-surface layer microstructure was dominated by the plastic deformation zone in the mild wear regime,and the deformation zone became deeper as the load increased.In the severe wear regime,the accumulation of friction heat exceeds the recrystallization temperature or even the melting temperature,so that the near-surface microstructure gradually transformed from the plastic deformation zone to the recrystallization zone until the melting-solidification zone.By observing the changes of the surface and sub-surface hardness,it was found that the strain hardening in the plastic deformation zone caused the increase of hardness within a certain range,and the recrystallization zone caused the hardness to decrease within a certain range.Combining the effects of strain hardening and recrystallization,the hardness curve showed a V-shaped or plateau region.The combination of the microstructure and the hardness also revealed that the reason for the mild-severe wear transition was dynamic recrystallization.