Investigation On Wear Behavior Of Mg-3Al-0.4Si Alloy At Elevated Temperatures

As an important type of lightweight structural metal material,magnesium alloys have received widespread attention due to their high specific strength and excellent casting properties.And they have broad prospects in the aerospace and automotive industries,the magnesium alloy auto parts can reduce the body weight,reduce exhaust emissions,save resources and so on.However,with the further research of magnesium alloys,their shortcomings as a structural metal material are also clearly recognized,such as poor mechanical properties and creep properties at high temperatures,poor wear resistance and so on.Due to these disadvantages,magnesium alloys are limited in high-temperature areas,like automobile engine pistons.Therefore,researching and developing the heat-resistant magnesium alloys with better wear resistance is an important way to solve the current issues.In this paper,the wear tests of Mg-3Al-0.4Si alloy were carried out under different temperatures,sliding speeds and loads by dry friction and wear.The temperature range was selected from 50 to 200?,and the range of sliding speed was0.785-4.0 m/s,the loading range was 10-280 N.The wear mechanism transition and wear behavior transition were judged by observing the surface of the sample,analyzing chemical element content and comparing with development trend of wear rate after wear testing.An empirical wear transition map has been established to delineate the effects of applied load and test temperature on wear mechanisms in the mild and severe wear regimes.Then the subsurface microstructure evolution and hardness changes were studied to further analyze the causes of the mild-severe wear transition.After investigation,the following conclusions were obtained:The wear behavior of Mg-3Al-0.4Si alloy can be divided into two main categories: mild wear and severe wear.The mild wear mainly includes abrasive wear,oxidative wear,delamination,delamination accompanied by surface oxidation,whilesevere wear includes thermal softening,surface melting and oxidation+surface melting.The mild-severe wear transition load tends to be smaller with the sliding speed or the test temperature increasing.The fundamental reason for the wear transition of the material is dynamic recrystallization beneath the surface,so when the accumulated frictional heat reaches the dynamic recrystallization temperature of the material,the material enters a severe wear stage.Subsurface microstructure also evolves during the mild-severe wear transition.At 50-200?,the microstructure experienced the transition from plastic deformation to dynamic recrystallization.The plastic deformation of subsurface materials produces work-hardening effect,recrystallization softens the surface layer,and these changes were confirmed by hardness tests.At 200?,the structure of the friction-afected zone(FAZ)is quite different from that at 50-150 ? because of the test temperature exceeds the static recrystallization temperature of the alloy.In the mild wear regime,the FAZ is composed of plastic deformation sub-zone,static recrystallization sub-zone and plastic deformation+static recrystallization sub-zone.In the severe wear regime,the FAZ is composed of dynamic recrystallization(DRX)sub-zone,static recrystallization sub-zone and plastic deformation sub-zone.In the range of 50-200?,the mild-severe wear transition still follows the contact surface recrystallization temperature criterion,which can be used to predict the transition load at a given temperature.