ZK60镁合金超声波辅助振动微挤压变形研究及有限元模拟分析

发布时间：2018-06-17 22:37

本文选题：超声波辅助振动 + 微挤压　；参考：《深圳大学》2017年硕士论文

【摘要】：镁合金是目前最轻的金属结构材料,然而镁合金为密排六方晶格结构,在常温下独立滑移系较少导致塑性变形困难,探索新的镁合金微成形工艺对于促进其在汽车材料等领域的应用有重要意义。由于传统微成形工艺遇到许多技术难题,本文提出一种新工艺,将超声振动应用于ZK60镁合金微成形。目前关于超声振动辅助金属塑性变形的理论并不成熟,其应用于微成形领域的研究就更少,本文在室温下对ZK60镁合金进行了一系列超声波辅助振动微挤压变形实验并做了相应的有限元分析,对微成形件的微观结构及力学性能进行相关测试与分析,实验结果表明:在常温下,传统挤压的ZK60镁合金晶粒大小基本不变,但在晶粒内部可以观察到大量的形变孪晶;在超声波波辅助振动振幅为33μm时,在样品中心部分开始出现了细小的动态再结晶晶粒,因此与传统挤压相比,变形应力显著减小。当振幅为39μm和42μm时,ZK60镁合金完全发生了动态再结晶,晶粒尺寸从原始的192μm细化到了13μm,变形应力减小,成形能力提高。在超声波辅助振动微挤压中镁合金最大应力降低约为80%左右。根据表面原理,当挤出直径为0.3mm或0.5mm时(原始晶粒尺寸0.192mm),则变型腔平均包含1至3个晶粒,这意味着所有的晶粒都位于自由表面上,则在不同振幅下的变形应力降低几乎相同;但是当挤出直径为0.7mm时有一部分晶粒在内部,内部晶粒受到约束导致应力减小量变小,发生了尺寸效应现象。随着超声波辅助振动振幅的增加,ZK60镁合金的硬度增加,当振幅达到39μm时,由于完全发生了动态再结晶现象,硬度值达到最大;在42μm时晶粒有所长大,则硬度也略微降低。通过有限元模拟发现,超声波辅助振动微挤压的应力分布得到改善,大应力区域明显减少,大应力主要分布在挤压孔附近。常规挤压试样表面发生塑性变形,在超声波挤压中塑性变形主要发生在挤出部分,振幅越大等效应变最大值越大。总之,将超声波辅助振动应用于ZK60镁合金的微成形,对于提高其微成形制件的成形能力、机械性能有着重大的意义。
[Abstract]:Magnesium alloy is the lightest metal structure material at present. However, magnesium alloy is a dense hexagonal lattice structure, and less independent slip system at room temperature leads to the difficulty of plastic deformation. It is very important to explore new microforming process for magnesium alloy to promote its application in automotive materials and other fields. Due to many technical problems encountered in the traditional microforming process, a new technology is proposed in this paper, in which ultrasonic vibration is applied to micro forming of ZK60 magnesium alloy. At present, the theory of ultrasonic vibration assisted metal plastic deformation is not mature, and its application in the field of microforming is even less. In this paper, a series of ultrasonic assisted vibration micro-extrusion deformation experiments on ZK60 magnesium alloy were carried out at room temperature and the corresponding finite element analysis was made. The microstructure and mechanical properties of the micro-formed parts were tested and analyzed. The experimental results show that the grain size of the traditional extruded ZK60 magnesium alloy is almost unchanged at room temperature, but a large number of deformation twins can be observed in the grain interior, and the ultrasonic wave assisted vibration amplitude is 33 渭 m. Fine dynamic recrystallization grains began to appear in the central part of the sample, so the deformation stress decreased significantly compared with the traditional extrusion. When the amplitude is 39 渭 m and 42 渭 m, the dynamic recrystallization of ZK60 magnesium alloy occurs completely, the grain size is refined from 192 渭 m to 13 渭 m, the deformation stress decreases and the forming ability is improved. The maximum stress of magnesium alloy is reduced by about 80% in ultrasonic assisted vibration micro extrusion. According to the surface principle, when the extrusion diameter is 0.3mm or 0.5mm (original grain size is 0.19mm), the variable cavity contains an average of 1 to 3 grains, which means that all the grains are located on the free surface, and the deformation stress decreases almost the same at different amplitudes. However, when the extrusion diameter is 0.7mm, a part of the grain is in the interior, the internal grain is restrained and the stress decreases and the size effect occurs. With the increase of ultrasonic assisted vibration amplitude, the hardness of ZK60 magnesium alloy increases. When the amplitude reaches 39 渭 m, the hardness of ZK60 magnesium alloy reaches its maximum due to the complete recrystallization, and the hardness decreases slightly when the grain grows at 42 渭 m. By finite element simulation, it is found that the stress distribution of ultrasonic assisted vibration micro-extrusion is improved, the large stress region is obviously reduced, and the large stress distribution is mainly near the extrusion hole. Plastic deformation occurs on the surface of the conventional extruded specimen. In ultrasonic extrusion, the plastic deformation occurs mainly in the extruded part, and the maximum equivalent strain increases with the increase of the amplitude. In a word, the application of ultrasonic assisted vibration to the microforming of ZK60 magnesium alloy is of great significance for improving the forming ability of the micro-forming parts.
【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG379;TG663

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