Abstract
Room- and elevated-temperature wear tests were conducted using a pin-on-disk testing machine to study wear behavior of Mg97Zn1Y2 alloy and role of long-period-stacking-ordered (LPSO) structure phase in mild–severe wear transition (SWT). Variation of wear rate exhibited a three-stage characteristic with load at various test temperatures, i.e., a gradual increasing stage, a slightly higher plateau stage, and a rapid rising stage. The wear mechanisms in the three stages were identified using scanning electron microscope (SEM), from which the first stage was confirmed as mild wear, and the other two stages were verified as severe wear. The interdendritic LPSO structure phase was elongated into strips along the sliding direction with Mg matrix deformation in the subsurface, plate-like LPSO structure phase precipitated at elevated temperatures of 150 and 200 °C. The fiber enhancement effect and precipitation effect of LPSO structure phase resulted in a little difference in wear rate between the first and second stages, i.e., a masking effect on SWT. Microstructure and microhardness were examined in the subsurfaces, from which the mechanism for SWT was confirmed to be dynamic recrystallization (DRX) softening. There is an apparently linear correlation between the critical load for SWT and test temperature, indicating that SWT is governed by a common critical DRX temperature.
Highlights
Mg97Zn1Y2 alloy is a special type of rare-earth (RE) magnesium alloy because it exhibits excellent strength and high thermal stability, and because it contains an extraordinary long-period-stacking-ordered (LPSO) structure phase
During the continuous heating process in differential thermal analysis (DTA), two endothermic peaks appeared successively, the former had an initial temperature of 533.8 ◦C, while the latter had an initial temperature of 602.8 ◦C and a final temperature of 662.7 ◦C, details of which can be found in our previous work [10]
The occurrence of widespread slip deformation in LPSO structure phase implies the loss of fiber enhancement effect in the third stage, while the growth of dynamic recrystallization (DRX) grains suggests the decrease of deformation resistance in Mg matrix
Summary
Mg97Zn1Y2 alloy is a special type of rare-earth (RE) magnesium alloy because it exhibits excellent strength and high thermal stability, and because it contains an extraordinary long-period-stacking-ordered (LPSO) structure phase. Even though conventional Mg-based alloys are not regard as proper alternatives to Al-based alloys in tribological applications owing to their low strength, indifferent ductility and poor thermal stability [8,9], Mg97Zn1Y2 alloy has the potential to make wear components such as bearing, pistons of engine and clutch in automotive industry and low-mediate-load bearing gear in aerospace industry [10,11] To achieve this goal, the room-and elevated-temperature wear performance of Mg97Zn1Y2 alloy should be studied, in which the mild–severe wear transition (hereafter abbreviated as SWT) and the role of LPSO structure phase are two main concerns. The linear correlation between SWT and test temperature was interpreted based on microstructure transformation and property change in surface material and friction heating
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