Investigation On Elevated-temperature Friction And Wear Behavior Of An Mg-Gd-Y-Zr Alloy At High And Low Sliding Speeds

Since 21 st century,with the rapid development of industries,the requirements for lightweight and envirmental protection are increasingly emphasized.Magnesium alloys are effective in these two aspects because they have lower density and higher specific strength than aluminum alloys,and are considered to be the next generation lightweight alloy structural materials.In addition,they also have high processing quality,good castability and recyclability.In particular,magnesium alloys are expected to be more widely used in aerospace,aviation,automobile,communication and other industries.However,because the elevated-temperature mechanical properties of Mg-Al(AZ and AM)alloys are not ideal,but Mg-Gd-Y-Zr series alloys are expected to break through the obstacles due to the addition of rare earth elements,therefore,this article dealed with the dry sliding wear performance of a Mg-Gd-Y-Zr alloys at elevated temperatures.In the present study,the wear performance of Mg-10.1Gd-1.4Y-0.4Zr heat-resistant magnesium alloy at high temperatures was studied using a pin-disc wear device at a sliding velocity of 3.0m/s and 0.5m/s.Experimental temperature was within 20-200°C and applied load was within 5-380 N.The wear rates were measured and were plotted against applied load at each test temperature.At each test temperature,there was a turning point on the curve of wear rate versus load.It corresponded to a mild to severe wear transition.The morphologies of the wear surfaces were observed by SEM and the composition was measured by EDS to confirm the wear mechanisms.An elevated-temperature wear mechanism transition map was drawn,indicating the regions of mild and severe wear.The differences in microstructure and microhardness of the subsurface layer between the samples worn in two different regions were compared.The final conclusions are as follows:The wear mechanisms in the mild wear stage at 3.0m/s included delamination wear and surface oxidation,slight plastic deformation + surface oxidation,slight plastic deformation and slight surface oxidation;the wear mechanisms in the severe wear stage were severe plastic deformation + oxide layer spallation,severe plasticdeformation and surface melting.The wear mechanisms in the mild wear stage at0.5m/s were abrasive wear + oxidative wear,delamination wear + surface oxidation,slight plastic deformation + slight surface oxidation;the wear mechanisms in the severe wear stage were severe plastic deformation + surface oxidation,severe plastic deformation + spallation of the oxide layer,severe plastic deformation,and surface melting.The dynamic recrystallization(DRX)softening of the surface material was found to be responsible for the transition from mild to severe wear.The subsurface microstructure in the friction-affected zone(FAZ)before and after the transition was different.The FAZ was a single plastic deformation zone during the mild wear stage.The FAZ was composed of the plastic deformation zone and the dynamic recrystallization zone during the severe wear stage.A V-shaped hardness curve appeared,and an approximately linear relationship was found between the transition load and the test temperature,which indicates that the mild to severe wear transition of the alloy still follows the surface temperature criterion even at high temperatures.The critical surface temperature was considered to be the DRX temperature of the alloy.The linear fitting analysis of the test temperature at a sliding speed of 3.0m/s according to the transient load-test temperature curve showed that the dynamic recrystallization temperature of Mg-10.1Gd-1.4Y-0.4Zr alloy was about 279.3℃.