基于表面动态再结晶温度准则的耐热镁合金高温轻微-严重磨损转变预测研究

This project is proposed in accordance with the urgent requirement of extending tribological applications of heat-resistant magnesium alloys. It is designed to address the key problems facing the safe operation region boundary for wear components made of heat-resistant magnesium alloys, such as the mechanism for mild to severe wear transition and the corresponding prediction method. We have thoroughly investigated the room-temperature wear behavior of magnesium alloys such as AZ, AS and Mg97Zn1Y2 alloys, and identified that the transformation from the friction-induced deformed to the DRX microstructure in the subsurface caused a thermal softening, resulting in the mild-severe wear transition. We have proposed a dynamic recrystallization (DRX) temperature criterion for judging mild-severe wear transition, i.e. the realization of DRX in subsurface at various sliding speeds is responsible for thermal softening. This criterion has been confirmed in wear tests of AZ31, AZ51, AZ91, AS31 and Mg97Zn1Y2 alloys. In order to further improve and identify our hypothesis under elevated-temperature sliding condition, the project is to be carried out according to the established DRX temperature criterion, and the characterization of the friction-induced thermally activated softening in subsurface is chosen as the breakthrough point, from which the following theoretical innovations will be made. Firstly, establishment of the numerical relationship between contact surface critical DRX temperature and the sliding speed according to thermally activated process kinetics of hot-deformed magnesium alloys. Secondly, development of the numerical model of evaluating high-temperature mild-severe wear transition loads from the critical DRX temperature. The project will create a new theoretical method of predicting the mild to severe wear transition under high-temperature sliding condition for heat-resistant magnesium alloys. This method is simple, practical and clear in physical meaning as compared with previous investigations on wear behavior of magnesium alloys. The proposed project will also provide a new theoretical basis for the tribological applications of heat-resistant magnesium alloys.

本项目聚焦于耐热镁合金在高温摩擦学领域应用的迫切需要，针对界定耐热镁合金高温磨损安全区（轻微磨损区）所涉及到系列理论问题开展研究,如轻微-严重磨损转变机制和预测等关键科学问题。在研究AZ系、Mg97Zn1Y2等镁合金室温磨损行为基础上，我们证实轻微-严重磨损转变机制实质是磨损表层动态再结晶软化所致，首先提出判定轻微-严重磨损转变的表面动态再结晶临界温度准则，建立预测不同滑动速度下轻微-严重磨损转变载荷的模型，并实验证实。本项目拟将我们提出的室温下的表面动态再结晶温度准则，拓展到复杂的高温磨损领域，以摩擦热激活动态再结晶软化为切入点，依据镁合金热变形软化动力学理论，建立磨损表面动态再结晶临界温度与速度的数值关系，建立动态再结晶临界温度和转变载荷预测模型，实现高温条件下的轻微-严重磨损转变的预测，最终达到理论预测耐热镁合金高温磨损安全区边界的目标，为耐热镁合金高温磨损条件下的应用奠定理论基础。

为了满足耐热镁合金在高温摩擦学领域应用的迫切需求，本项目针对高温磨损安全区和危险区的临界转变，即轻微-严重磨损转变机制和预测等关键问题开展研究。以三种具有不同热稳定性的典型耐热镁合金为研究对象，在滑动速度0.2-4.0m/s和50-200oC高温条件下进行滑动摩擦磨损实验，以便揭示高温下耐热镁合金的轻微-严重磨损转变机理。基于动态再结晶动力学理论，在我们提出的表面动态再结晶临界温度准则的基础上，建立高温下轻微-严重磨损转变载荷的预测模型，并予以检验，从而证实表面动态再结晶临界温度准则的高温磨损条件下的适用性，为耐热镁合金在高温摩擦学领域应用提供理论基础。研究结果表明：在轻微-严重磨损转变后，亚表层组织发生动态再结晶转变，其导致的表层材料软化是轻微-严重磨损转变的根本原因。通过热压缩试验获得的动态再结晶激活能，基于动态再结晶动力学理论，计算出不同速度下发生轻微-严重磨损转变所必需的临界动态再结晶温度。结合我们提出的高温下轻微-严重磨损转变载荷的预测模型进行计算，计算值和测量值之间符合很好。以上结果证实了我们提出的表面动态再结晶临界温度准则在高温条件下的适用性。项目的完成解决了长期以来困惑摩擦学领域的轻微-严重磨损转变机制的未解之谜，提出了一种物理概念清晰的判定准则和预测方法，丰富了耐热镁合金摩擦学理论，也能为耐热镁合金磨损部件的安全应用和设计提供参考。