Research On Sliding Wear Behavior Of Mg-10Gd-1.4Y-0.4Zr Alloy

Magnesium alloys as one of the lightweight metal materials have good room temperature properties and wide applications.But the properties reduce at higher temperatures,and they are main disadvantages for practical use.Rare earth heat-resistant magnesium alloys are potential magnesium alloys.They show better high-temperature properties than the traditional magnesium alloys.The Mg-Gd-Y-Zr heat-resistant magnesium alloys have good comprehensive performance,but the study on the wear behavior of the alloys is limited so that the tribological applications of the alloys in many fields are rare.For example,pistons,transmission parts and other automotive components are required good wear resistance.So,it’s necessary to study the wear performance of Mg-Gd-Y-Zr magnesium alloys.In the present experiment,the friction and wear properties of Mg-10Gd-1.4Y-0.4Zr alloy were investigated at room temperature.The load is increased from 20 N to 380 N and the sliding speed range is 0.2-4.0m/s and the sliding cycles are 3000.The friction conterface is high carbon chrome steel with a hardness of 57 HRC.The wear surface of the specimens were observed by scanning electron microscopy(SEM)to analyze the wear mechanism and establishe the wear transformation diagram by combining the friction coefficient curves and the wear rate curves.The near-surface and subsurface microstructures of the samples was observed by confocal laser scanning microscopy to study the microstructural evolution before and after the transition loads.The hardness of the subsurface is tested to study the change induced by microstructural transformation.The experimental results show that the friction coefficient of Mg-10Gd-1.4Y-0.4Zr alloy decreases gradually with the influence of the sliding speed,the load and the wear mechanism.The wear rate is proportional to the load and increases rapidly upon mild to severe wear transitis.The growth trend of wear rate is closely related to the wear mechanism in the wear process.There are six wear mechanisms in Mg-10Gd-1.4Y-0.4Zr alloy friction process including abrasive wear,oxidation wear,delamination wear,thermal softening and surface melting.The first three are in mild wear regime and the latter two are in severe wear regime.Transition loads at 0.2m/s and 0.5m/s are 100 N,and increasing the sliding velocity in the range of 0.785m/s to 4.0m/s resultes in a decrease in transition load from 140 N to 40 N.When mild wear behavior turns into sever wear behavior,the subsurface microstructure changes under the influence of stress and temperature.In mild wear regime,the plastic deformation occurs in the subsurface is acompanied by the second phase breaking and twins forming in the near worn surface region,and the hardness will be increased obviously.The degree of deformation and hardness is proportional to the load and is inversely proportional to the depth.In severe wear regime,the subsurface is dynamicaly recrystallized,resulting in formation of recrystallized grains.The wear surface is melted at high load or high speed.There are small grains produced by melting-solidification and no sign of twins is found there.The secondary phase in the near worn surface region is dissolved,and consequently the hardness is lower than that before the transition.In the wear process,the hardness of the worn surface reaches the peak near the transition load.In the mild wear regime,the hardness of the worn surface is affected by the deformation hardening,and the hardness exceeds the hardness of the as-cast and increase with the increase of the load.In the severe wear regime,even though the hardness of the worn surface is reduced by the influence of the dynamic recrystallization grains and the grains produced by the melting-solidification,it is still higher than the hardness of the as-cast.