【作者】 王朱恩；

【导师】 卫英慧；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2008， 硕士

【摘要】 镁合金作为一种工程材料,具有比重轻、高比强度、高比刚度及良好的电磁屏蔽性能、良好的铸造性能等一系列优点,广泛用于3C产品和汽车产业。镁合金产品的制造方式大多采用压铸制程,尽管压铸理论及设备已基本完善,但压铸制程中仍会出现许多问题,如模具失效。此外,塑性成形以及触变成形镁合金由于其特殊的加工工艺和产品性能,近年来也受到市场的青睐。本课题结合镁合金的实际生产,利用OM、XRD、SEM及TEM等测试手段,对挤压态AZ31产品的组织和性能进行分析;分析了触变成形与高压压铸AZ91D镁合金性能的差异;研究了压铸模具镶块的失效问题,得出以下主要结论:1、挤压态AZ31镁合金沿挤压方向侧面和截面的微观组织中发现了大量的孪晶;其拉伸变形具有明显的动态再结晶特征;SEM结果表明拉伸断口为典型的韧窝聚合型断口,是一种韧性断裂断口;TEM观测可见,其晶粒内存在着孪晶,也存在着一些析出物;极化试验显示表面的腐蚀电位比侧面和截面高,腐蚀电流小,耐腐蚀能力略强于侧面和截面。2、触变成形铸件在415℃固溶处理时β相溶解入α-Mg固溶体溶解速度比高压压铸的快,固溶处理时,通过合金元素的重新分布促使微观组织的演变。触变成形与高压压铸AZ91D时效处理时,金相显微组织显示,β相存在连续析出和不连续析出两种方式。3、用失重法来衡量腐蚀速率,触变成形AZ91D镁合金的腐蚀速率比高压压铸AZ91D镁合金要小得多。其主要原因是由于触变成形AZ91D镁合金被腐蚀的阳极的表面积比高压压铸AZ91D镁合金的要小;此外,触变成形AZ91D镁合金比高压压铸AZ91D镁合金因为气孔率小得多,这也是其腐蚀速率较小的原因之一。4、模具镶块的断裂是镁液对镶块连续的高温高速冲击引起的。避免断裂最主要是在模具设计时尽量避免在充型时压铸金属液冲击镶块;其次是改善镶块的热处理工艺,提高镶块的力学性能。更多还原

【Abstract】 Magnesium alloys have potential as structural materials for aerospace, 3C and other transport applications due to their high specific properties, low density and high damping capacity. Currently, magnesium alloy products are mainly made by die-casting process. Though the theories and facilities of die-casting process are comparatively perfect, there are always many problems in the process of manufacture, such as the die failure. In addition, due to special processing and performance of the products, the magnesium products manufactured by plastic formation and thixomolding are more and more popular in the market. In this work, combined with practice, a series of problems in magnesium alloy were studied by many testing means including OM, SEM, XRD, TEM, and so on. Microstructures and performances of extruded AZ31 Mg alloy were studyed; The failure problem of embedded lump in the die was tried to analyse; The difference of performance of AZ91D Mg alloy produced by high pressure die-casting and Thixomolding were discussed. The main conclusions are as follows:1. It can be seen that the side plane and cross-section along extrusion direction have many compound twinings from the optical micrograph. The tensile deformation of specimens indicated that they were of dynamic recrystallization. SEM results revealed that the tensile fractures belong to dimple fracture. The microstructures from TEM observation showed the twining and precipitate interior grains. Polarization tests indicated that the corrosion potential of surface was higher than those of cross-section and side plane; however the corrosion current was lower. The corrosion resistant of surface was appreciably better than that of cross-section and side plane.2. Solution treatment of the thixomolding AZ91D alloy at 415℃caused theβ-phase to dissolve intoα-Mg solid solution at a faster dissolution rate than that in the same alloy prepared by high pressure die-casting. During the solution treatment of the Thixomolding AZ91D alloy, the microstructural evolution was accompanied by redistribution of the alloying elements. Both discontinuous and continuous precipitates of the p-phase were observed during the aging treatment.3. The experiment results indicated that the corrosion rate of the thixomolding AZ91D alloy was lower than high pressure die-casting AZ91D alloy by analysing the relationship between weight loss and corrosion time. The main reason was that the surface area of anode of thixomolding AZ91D alloy was smaller than that of high pressure die-casting AZ91D alloy. In addition, the porosity of thixomolding AZ91D alloy was lower than high pressure die-casting AZ91D alloy. It was another reason why thixomolding AZ91D alloy had lower corrosion rate.4. The failure of embedded lump in the die was caused by the continuous impact of the high-temperature and high-velocity molten metal liquid on the die. To avoid the problem, it was very important not to make the metal liquid plumb impact on the embedded lump. It was also efficient to advance mechanical property of the embedded lump by improving heat treatment technology.更多还原