本文選題：超聲波輔助振動 + 微擠壓　； 參考：《深圳大學(xué)》2017年碩士論文

【摘要】：鎂合金是目前最輕的金屬結(jié)構(gòu)材料,然而鎂合金為密排六方晶格結(jié)構(gòu),在常溫下獨立滑移系較少導(dǎo)致塑性變形困難,探索新的鎂合金微成形工藝對于促進其在汽車材料等領(lǐng)域的應(yīng)用有重要意義。由于傳統(tǒng)微成形工藝遇到許多技術(shù)難題,本文提出一種新工藝,將超聲振動應(yīng)用于ZK60鎂合金微成形。目前關(guān)于超聲振動輔助金屬塑性變形的理論并不成熟,其應(yīng)用于微成形領(lǐng)域的研究就更少,本文在室溫下對ZK60鎂合金進行了一系列超聲波輔助振動微擠壓變形實驗并做了相應(yīng)的有限元分析,對微成形件的微觀結(jié)構(gòu)及力學(xué)性能進行相關(guān)測試與分析,實驗結(jié)果表明:在常溫下,傳統(tǒng)擠壓的ZK60鎂合金晶粒大小基本不變,但在晶粒內(nèi)部可以觀察到大量的形變孿晶;在超聲波波輔助振動振幅為33μm時,在樣品中心部分開始出現(xiàn)了細小的動態(tài)再結(jié)晶晶粒,因此與傳統(tǒng)擠壓相比,變形應(yīng)力顯著減小。當振幅為39μm和42μm時,ZK60鎂合金完全發(fā)生了動態(tài)再結(jié)晶,晶粒尺寸從原始的192μm細化到了13μm,變形應(yīng)力減小,成形能力提高。在超聲波輔助振動微擠壓中鎂合金最大應(yīng)力降低約為80%左右。根據(jù)表面原理,當擠出直徑為0.3mm或0.5mm時(原始晶粒尺寸0.192mm),則變型腔平均包含1至3個晶粒,這意味著所有的晶粒都位于自由表面上,則在不同振幅下的變形應(yīng)力降低幾乎相同;但是當擠出直徑為0.7mm時有一部分晶粒在內(nèi)部,內(nèi)部晶粒受到約束導(dǎo)致應(yīng)力減小量變小,發(fā)生了尺寸效應(yīng)現(xiàn)象。隨著超聲波輔助振動振幅的增加,ZK60鎂合金的硬度增加,當振幅達到39μm時,由于完全發(fā)生了動態(tài)再結(jié)晶現(xiàn)象,硬度值達到最大;在42μm時晶粒有所長大,則硬度也略微降低。通過有限元模擬發(fā)現(xiàn),超聲波輔助振動微擠壓的應(yīng)力分布得到改善,大應(yīng)力區(qū)域明顯減少,大應(yīng)力主要分布在擠壓孔附近。常規(guī)擠壓試樣表面發(fā)生塑性變形,在超聲波擠壓中塑性變形主要發(fā)生在擠出部分,振幅越大等效應(yīng)變最大值越大�？傊�,將超聲波輔助振動應(yīng)用于ZK60鎂合金的微成形,對于提高其微成形制件的成形能力、機械性能有著重大的意義。
[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.
【學(xué)位授予單位】：深圳大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG379;TG663

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