【作者】 薛峰；

【导师】 周仲荣；

【作者基本信息】 西南交通大学 ， 材料学， 2008， 硕士

【摘要】 目前,动态冲击载荷及介质腐蚀并存条件下镁合金的表面损伤情况还未见报道。本实验以去离子水为介质,探讨AZ91D镁合金在冲击载荷作用下的损伤行为,并与干态下的损伤情况做出对比,讨论了镁合金在干态与去离子水介质中,冲击条件下的损伤机理,并探讨影响冲击磨损性能的因素,具有重要的实际意义和理论意义。本文采用实验室自制冲击磨损试验机,对AZ91D镁合金在干态及去离子水介质下的冲击磨损行为进行了实验研究。系统考察了冲击载荷(20N和40N)及冲击次数(1×10~4～5×10~5)对磨损行为的影响;采用光学显微镜(OM)、激光共焦显微镜(LCSM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDX)及台阶仪等对冲击磨痕进行分析,探讨了冲击磨损机理,得出如下主要结论:1.干态下,AZ91D镁合金的冲击磨损表现出疲劳作用机制。磨损深度及面积随冲击次数的增加而缓缓增加。AZ91D镁合金磨损初期的主要损伤形式为塑性变形,塑变深度增加较快;随着冲击次数的增加,表层产生加工硬化,材料表现出粘着磨损和小块剥落损伤,深度增加速率减缓;后期表层材料塑变耗竭,萌生疲劳裂纹,裂纹扩展相交后导致材料发生大块疲劳剥层失效。2.去离子水介质下,AZ91D镁合金冲击磨损表现出疲劳剥层与腐蚀侵蚀的相互促进机制。磨损深度及面积随冲击次数的增加而快速增加。AZ91D镁合金磨损初期表面主要产生塑性变形和粘着磨损,后期表面萌生疲劳裂纹,裂纹出现后,水介质的腐蚀作用增强,液态介质渗入裂缝中,一方面去离子水本身对镁合金具有腐蚀作用,另一方面去离子水可引起点腐蚀,材料呈现深层脆性剥落的特征;同时,镁合金表面会生成一层腐蚀作用膜,冲击作用下,这层膜可能被持续破坏与生成,表现出深度的增加。总之,冲击力和水介质腐蚀共同作用加速了裂纹增殖和扩展,使AZ91D镁合金损伤严重。3.本试验两种冲击载荷下,去离子介质中AZ91D镁合金的磨损深度及面积均大于干态下的情况,并且增速也比干态下的快。去离子水介质中AZ91D镁合金的抗冲击磨损性能下低,去离子水介质并没有起到润滑或降低冲击磨损的作用,反而引起了材料表面的腐蚀,冲击磨损与表面腐蚀相互促进,加速了材料的损伤和失效。更多还原

【Abstract】 Up to present, the surface damage of magnesium alloy under the conditions of both dynamic impact load and medium corrosion has not reported yet. In this study, the impact wear behaviors of AZ91D magnesium alloys in dry condition and de-ionized water were contrastively investigated, and the damage mechanisms were discussed. Further, the factors of influencing the impact wear properties were discussed. Therefore, the study has both practical significance and academic valueThe impact wear tests of AZ91D magnesium alloy in dry condition and de-ionized water had been performed by the impact tester. The influences of load (20 N and 40 N) and impact number (1×10~4 to 5×10~5) on impact wear behavior had been systemically investigated. The impact wear spots were measured and analyzed by means of optical microscope (OM), laser confocal scanning microscope (LCSM), X-ray diffraction (XRD), scanning electrical microscopy (SEM), energy dispersive spectroscopy (EDX) and surface profiler. Main conclusions are drawn as follows:1. In dry condition, the impact wear mechanism of AZ91D magnesium alloy was fatigue. The depth and area of the wear scar increased slowly with increasing impact number. The damage of AZ91D magnesium alloy at the initial stage was characterized by cyclic plastic deformation, then the phenomenon of adhesive wear and bit delamination appeared because of work-hardening of surface layer. The rate of depth increment was depressed. Finally, the plastic of surface layer exhausted and fatigue crack occurred, the spreading and joining of cracks would cause the failure of the material as big delamination.2. In de-ionized water, the wear mechanism showed as the mutual accelerating of fatigue delamination and corrosion. The depth and area increased rapidly with increasing impact number. At the initial stage, the wear damage of AZ91D magnesium alloy was characterized by cyclic plastic deformation and adhesive wear. With the increase of impact number, fatigue cracks occurred in the surface and sub-surface. The corrosive wear of the material became heavier after the crack appeared. The de-ionized water penetrated into the cracks, on one hand, it had an corrosion effect upon the AZ91D magnesium alloy, on the other hand, it could cause point corrosion, and thus the wear material was characterized by deep brittle spalling; meanwhile, a film appeared on the surface, but it would be destroyed and created circularly by the impact load, and thus the wear depth increased significantly. In a word, the cracks proliferated and spread rapidly by the impact load together with corrosion, , and the damage of AZ91D magnesium alloy was severe.3. Under the impact load of 20 N and 40 N, the wear depth and area and its growth rate of AZ91D magnesium alloy in de-ionized water were larger than that in dry condition. The impact wear resistance of the AZ91D magnesium alloy decreased in de-ionized water. De-ionized water did not play a role of lubricating and reducing the wear degree, contrastly, it brought corrosion mechanism on the worn surface, the impact wear and surface corrosion promoted mutually and accelerated the wear damage and failure of material.更多还原