High Temperature Wear Behavior And Wear Transformation Of Two Heat-resistant Magnesium Alloys

Magnesium alloys have always been called the star material in the metal industry by scholars in the field of metal materials.In today's increasingly serious global energy shortage problem,the in-depth exploration of the field of magnesium alloys has become the mainstream direction of material science research.There are few researches on this aspect.Industrial applications usually have higher requirements on the working environment of magnesium alloys.Usually,magnesium alloys have poor mechanical properties at high temperatures,resulting in less theoretical research on the wear resistance of magnesium alloys in high temperature environments.In order to make magnesium alloys more widely and safely used in future engineering,we selected Mg-RE-Zn ternary alloys composed of Zn elements in Mg-RE alloys,and Mg-Al-Al alloys composed of Si elements in Mg-Al alloys.The wear resistance of Si ternary alloys under high temperature conditions is explored,and the wear transformation map under high temperature conditions is drawn,which provides a solid theoretical basis for engineering applications.In this experiment,a pin-disc wear tester was used to conduct wear tests on Mg97Zn1Y2 alloy at room temperature(20°C)and high temperature(50?200°C).The sliding speed was 2 m/s and the loading range was 5?320 N.The wear rate and friction coefficient were obtained from the wear test,and the curves were drawn to preliminarily determine the wear transition load range.Further in-depth study of the role of Mg97Zn1Y2 alloy and the long-range ordered structural phase(LPSO)in the alloy in the mild-severe wear transition(SWT).At each different test temperature,the changing law of the wear rate curve shows the load characteristics of three stages,namely the gradual rising stage,the slightly higher plateau stage and the fast rising stage.The surface morphology of the worn samples was observed by scanning electron microscope(SEM)and the wear mechanism of the three stages was analyzed.Energy dispersive spectrometer(EDS)was used to analyze the distribution of element content on the worn surface.The first stage was mild wear,and the remaining two stages were confirmed to be heavy wear.Under the high temperature conditions of150 and 200°C,the dendritic LPSO structure phase and the magnesium matrix were elongated into strips along the sliding direction,and the lath-like LPSO structure phase was precipitated.The fiber reinforcement effect and precipitation effect of the LPSO structural phase directly lead to a small difference in the wear rate curves of the first and second stages,that is,there is a masking effect on the SWT.The microstructure of the subsurface was observed by a Zeiss microscope and the microhardness of the subsurface layer was measured by a Vickers hardness tester,which confirmed that the main reason for the occurrence of SWT was dynamic recrystallization(DRX)softening.There is a clear linear correlation between the critical transition load of the SWT and the test temperature,indicating that the SWT is governed by a common critical DRX temperature.Under the same test conditions at 2m/s and 20~200?,the wear rate curves of heat-resistant magnesium alloy AS31 and Mg97Zn1Y2 alloy show an increasing trend with the increase of loading load,but the wear rate curve of AS31 alloy increases faster than that of Mg97Zn1Y2 alloy.During the SWT process of the two alloys,the lath-shaped LPSO phase in the Mg97Zn1Y2 alloy masked the SWT transition point on the wear rate curve,while the Chinese character-shaped Mg₂Si phase in the AS31alloy could not mask the increase in the wear rate curve.The transformation loads of AS31 and Mg97Zn1Y2 alloy at lower temperature(20~50?)are basically the same,but the transformation load curve of AS31 at high temperature(100~200?)is lower than that of Mg97Zn1Y2 alloy,indicating that AS31 alloy has lower resistance slightly-severe Wear transformation ability.