Mg97Zn1Y2镁合金摩擦磨损行为研究

发布时间：2018-05-24 17:22

本文选题：镁合金 + 摩擦磨损　；参考：《吉林大学》2017年硕士论文

【摘要】：镁合金在室温下具有优良的综合性能,随着我国航空航天和汽车工业的迅速发展壮大,对镁合金的综合性能和应用范围提出了更高的要求。传统的商用镁合金(AZ系等)已经在汽车工业中用于制造压铸件和车身成形组件,然而较差的耐磨性和抗高温性能成为该类镁合金在摩擦学领域应用的一个重要障碍,不能如铝合金那样用于制造较高工况要求的活塞、滑动轴承、缸套等磨损部件。因此,发展具有优良耐磨性能的耐热镁合金及其复合材料是解决限制镁合金在摩擦学领域应用的一条重要途径。本论文在室温干滑动磨损状态下采用销-盘式磨损装置对Mg97Zn1Y2耐热镁合金进行研究,在滑动速度0.2-4.0m/s、加载载荷20-380N的范围内对合金的磨损形貌、表面氧含量和磨损率进行分析测量,绘制了不同滑动速度下的转变载荷图和磨损转变图,深入研究了表层及亚表层组织的演变过程。结合硬度的变化情况,详细分析了轻微-严重磨损转变过程中的组织演变,揭示了磨损过程中引起转变的本质原因,得出了如下结论:Mg97Zn1Y2合金在摩擦磨损的过程中存在轻微磨损和严重磨损两种行为,轻微磨损区包括氧化磨损+磨粒磨损机制、严重氧化的剥层磨损机制和剥层磨损机制,严重磨损区包括严重塑性变形机制、伴有氧化层剥落的严重塑性变形机制和表面熔化磨损机制。轻微磨损时氧化层和机械混合层的出现抑制了磨损率的快速上升,进入严重磨损阶段之后,摩擦热的累积使得近表层的温度超过动态再结晶的温度,导致磨损表面发生严重塑性变形或者熔化,表层硬度迅速降低,磨损率快速上升,表面动态再结晶的出现是造成轻微-严重磨损转变的根本原因。近表层组织随着轻微磨损向严重磨损过渡的过程中也逐渐发生变化,在加载载荷20N时即发生了塑性变形,在轻微磨损阶段载荷的逐渐增加使得变形区域深度进一步增大,过渡到严重磨损阶段时,摩擦热引起的高温对近表层材料的影响更为严重,从塑性变形转变到动态再结晶软化,进一步增大载荷和滑动速度使材料表面发生熔化,近表层区域的组织演变顺序为:塑性变形-动态再结晶-表面熔化再凝固。轻微-严重磨损转变之前,磨损试样近表层发生塑性变形,加工硬化产生的效果使得磨损表面硬度在较低的载荷范围内即上升到较高的区间并随着载荷的增加而逐渐增大,亚表层区域的硬度值也整体随着加载载荷的增加而增大,同时硬度的增加也阻止了磨损率的快速上升。轻微-严重磨损转变之后,摩擦热的累积超过了材料的动态再结晶温度(TDRX),磨损表面发生软化,抵消了塑性变形带来的加工硬化效果,因此硬度下降,磨损率上升,发生了严重磨损,亚表层材料的整体硬度值也逐渐下降。
[Abstract]:Magnesium alloys have excellent comprehensive properties at room temperature. With the rapid development of aerospace and automobile industry in China, the comprehensive properties and application scope of magnesium alloys are required to be higher. Traditional commercial magnesium alloys, such as AZ series, have been used in the automobile industry to manufacture die castings and body forming components. However, poor wear resistance and high temperature resistance have become an important obstacle in the application of this kind of magnesium alloys in the field of tribology. It can not be used to manufacture wear parts such as piston, sliding bearing, cylinder liner and so on. Therefore, the development of heat-resistant magnesium alloys with excellent wear resistance and their composites is an important way to limit the application of magnesium alloys in the field of tribology. In this paper, Mg97Zn1Y2 heat-resistant magnesium alloy was studied by pin-disc wear device under dry sliding wear condition at room temperature. The wear morphology, surface oxygen content and wear rate of the alloy were measured in the range of sliding speed of 0.2-4.0 m / s and loading load of 20-380 N. The transition load diagram and wear transition diagram at different sliding velocities were plotted, and the evolution process of surface and subsurface microstructure was studied. Combined with the change of hardness, the microstructure evolution in the process of mild to severe wear transition is analyzed in detail, and the essential cause of transformation in wear process is revealed. It is concluded that there are two behaviors of slight wear and serious wear in the friction and wear process of Mg97Zn1Y2 alloy. The slight wear zone includes the wear mechanism of oxidized abrasive wear, the mechanism of serious oxidation delamination and the mechanism of delamination wear. Serious wear zone includes serious plastic deformation mechanism, serious plastic deformation mechanism with oxide layer flaking and surface melting wear mechanism. The appearance of oxidized layer and mechanical mixed layer inhibited the rapid increase of wear rate. After entering the serious wear stage, the accumulation of friction heat caused the temperature of near surface layer to exceed the temperature of dynamic recrystallization. As a result of serious plastic deformation or melting of the worn surface, the hardness of the surface decreases rapidly, the wear rate increases rapidly, and the appearance of dynamic recrystallization of the surface is the root cause of the slight to severe wear transition. In the process of transition from slight wear to severe wear, the near surface microstructure changes gradually, and plastic deformation occurs at loading load of 20N, and the depth of deformation area increases further with the increasing of load at slight wear stage. During the transition to the serious wear stage, the high temperature caused by friction heat has a more serious effect on the near surface material, which changes from plastic deformation to dynamic recrystallization softening, and further increases the load and sliding speed to make the material surface melt. The order of microstructure evolution near the surface is: plastic deformation, dynamic recrystallization, surface melting and solidification. Before the mild to severe wear transition, plastic deformation occurs near the surface of the wear specimen, and the effect of work hardening causes the hardness of the worn surface to rise to a higher range in the lower load range and increase gradually with the increase of the load. The hardness of the subsurface area also increases with the increase of loading load, and the increase of hardness also prevents the wear rate from rising rapidly. After the mild to severe wear transition, the accumulated heat of friction exceeds the dynamic recrystallization temperature of the material TDRX, and the worn surface softens, which counteracts the work hardening effect caused by plastic deformation, so the hardness decreases and the wear rate increases. Serious wear occurs and the hardness of the subsurface material decreases gradually.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22

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