AZ80镁合金负重轮疲劳性能研究

发布时间：2018-04-09 03:19

本文选题：AZ80镁合金　切入点：负重轮　出处：《中北大学》2017年硕士论文

【摘要】：负重轮作为履带车辆的主要组成部件,对履带式车辆的安全性、舒适性、平稳性起着决定性作用,因此可以通过降低负重轮的重量来达到武器系统轻量化设计的目的,镁合金因其优越的性能作为生产负重轮的首选材料。在行驶过程中负重轮受到多种交变载荷的作用,而这种载荷的作用易引起构件疲劳失效,所以提高镁合金负重轮的疲劳性能、增加其疲劳寿命是促进负重轮广泛应用的必要前提,而成形工艺直接影响着负重轮的性能,因此针对提出的径向-反向复合挤压工艺,系统分析研究该工艺成形的AZ80镁合金负重轮的疲劳性能,对成形工艺的改进以及促进镁合金负重轮的应用具有显著的实际意义。本文首先简单介绍了成形负重轮的新工艺——径向-反向复合挤压工艺的工艺流程,其次在负重轮壁部和底部平行挤压方向截取试样,使用ZEISS金相显微镜观察其显微组织,利用INSTRON 3382试验机进行拉伸试验。最后在负重轮的壁部沿挤压方向截取试样,采用INSTRON 8801试验机进行高周疲劳试验和裂纹扩展速率试验,测试其疲劳强度和断裂韧性,并利用SU5000扫描电镜对疲劳裂纹断口形貌进行分析。AZ80镁合金负重轮壁部和底部的晶粒细小呈等轴状,壁部第二相析出呈点状、棒状和片层状,底部第二相析出呈颗粒状。壁部试样抗拉强度为301Mpa,延伸率为9.8%,底部试样的抗拉强度为285Mpa,延伸率为9.3%。结果表明壁部强度偏大、塑性较好,相差百分比分别为5.3%、5.1%。说明该新工艺成形的负重轮实现了壁部和底部的组织性能均匀化。高周疲劳试验结果表明:绘制S-N曲线和利用公式计算后均可得负重轮壁部的疲劳强度值约为102Mpa,与曾荣昌等的研究相比,疲劳强度值提高10Mpa左右,说明径向扩-收复合挤压工艺可以改善负重轮的疲劳强度。从断口形貌可知:裂纹萌生于试样表面;扩展区存在疲劳辉纹、二次裂纹、解理台阶及羽毛状花样形貌;瞬断区存在二次裂纹、韧窝、解理及准解理台阶和撕裂棱形貌。裂纹扩展试验结果表明:采用COD法测定的试样断裂韧性值KIC=10.01MPa。从da/dN-ΔK曲线可得,过时效处理使负重轮抵抗裂纹扩展的能力降低。从断口形貌可以看出:疲劳断口呈多源萌生,过时效试样的预制裂纹源区呈光滑平整形貌,峰值时效试样呈河流状类解理形貌;与峰值时效试样相比,过时效试样扩展区的疲劳条带扩展痕迹间隔较大,瞬断区的韧窝少且浅,说明过时效处理后负重轮的疲劳寿命降低。
[Abstract]:As the main component of tracked vehicle, load-bearing wheel plays a decisive role in the safety, comfort and smoothness of tracked vehicle, so the lightweight design of weapon system can be achieved by reducing the weight of load-bearing wheel.Magnesium alloys are the preferred materials for the production of load-bearing wheels because of their superior properties.In the course of driving, the load bearing wheel is subjected to many kinds of alternating loads, and this kind of load can easily cause fatigue failure of the components, so the fatigue performance of the magnesium alloy bearing wheel can be improved.Increasing its fatigue life is a necessary prerequisite to promote the wide application of load-bearing wheels, and the forming process directly affects the performance of the load-bearing wheels.The fatigue properties of the AZ80 magnesium alloy bearing wheel formed by this process are analyzed systematically. It is of great practical significance to improve the forming process and promote the application of the magnesium alloy bearing wheel.In this paper, the new technology of radial reverse composite extrusion for forming load-bearing wheel is introduced briefly. Secondly, the specimen is intercepted in the wall and bottom of the wheel, and the microstructure is observed by ZEISS metallographic microscope.Tensile test was carried out with INSTRON 3382 tester.Finally, the specimens were cut off from the wall of the load-bearing wheel along the extrusion direction. High cycle fatigue tests and crack growth rate tests were carried out with INSTRON 8801 tester to test their fatigue strength and fracture toughness.The fracture morphology of fatigue crack was analyzed by SU5000 scanning electron microscope. The fine grains in the wall and bottom of the wheel of AZ80 magnesium alloy were equiaxed, the second phase in the wall was punctate, the second phase was in the shape of rod and lamellar, and the second phase in the bottom was granular.The tensile strength of the wall specimen is 301 Mpaand the elongation is 9.8. The tensile strength of the bottom specimen is 285 Mpaand the elongation of the bottom specimen is 9.3.The results show that the strength of the wall is larger, the plasticity is better, the difference percentage is 5.3% and 5.1% respectively.The results show that the new process can homogenize the structure and properties of the wall and bottom.The results of high cycle fatigue test show that the fatigue strength of the wall of the load-bearing wheel can be obtained by drawing S-N curve and calculating by the formula. Compared with Zeng Rongchang and so on, the fatigue strength is increased by about 10Mpa.It is shown that the fatigue strength of the load wheel can be improved by the radial expansion-retraction composite extrusion process.The fracture morphology shows that the crack originates on the surface of the specimen, the fatigue ripple, the secondary crack, the cleavage step and the feather pattern in the propagating zone, and the secondary crack, dimple, cleavage, quasi cleavage step and tearing edge in the transient fracture zone.The results of crack growth test show that the fracture toughness of the specimen determined by COD method is 10.01 MPa.From the da / dN- 螖 K curve, it is found that aging treatment reduces the resistance of the load-bearing wheel to crack growth.From the fracture morphology, it can be seen that the fatigue fracture surface is multi-source initiation, the prefabricated crack source area of overaged specimen is smooth and smooth, and the peak aging specimen has fluvial cleavage morphology, compared with the peak aging specimen,The fatigue bands in the overaging specimens have a large spread trace interval, and the dimples in the transient fracture zone are small and shallow, which indicates that the fatigue life of the load-bearing wheel decreases after aging treatment.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.22

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