本文關(guān)鍵詞： 鎂合金 碳納米管 復(fù)合材料 伸長(zhǎng)率 熱壓縮 動(dòng)態(tài)再結(jié)晶　出處：《湖南大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：金屬鎂及其合金具有一系列優(yōu)異的性能,是一種極具前途的輕質(zhì)金屬結(jié)構(gòu)材料。近年來,隨著各行業(yè)的不斷發(fā)展,對(duì)鎂合金材料的性能提出了越來越苛刻的要求,并相繼發(fā)展了高強(qiáng)鎂合金、阻燃鎂合金和耐熱鎂合金等高性能鎂合金。與此同時(shí),很多領(lǐng)域要求材料兼顧強(qiáng)度、塑性、耐熱及耐蝕等多方面的綜合性能。因此,研制和開發(fā)具有優(yōu)異綜合性能的新型鎂合金及其復(fù)合材料具有重要意義。本文以進(jìn)一步改善鎂合金的綜合性能為目標(biāo),選擇具有較佳綜合性能的Mg-Mn-Ce-Zn四元合金為基體,用攪拌鑄造法制備碳納米管(CNTs)增強(qiáng)鎂基復(fù)合材料。采用金相觀察、電子能譜、斷口掃描、透射電鏡、差熱分析及電化學(xué)分析和熱模擬等手段,較系統(tǒng)地研究了復(fù)合材料的微觀組織、力學(xué)性能、耐蝕性能及熱變形行為,并對(duì)復(fù)合材料的強(qiáng)韌化機(jī)理、耐蝕機(jī)理、斷裂機(jī)制及熱變形過程中的組織變化規(guī)律進(jìn)行了探討和分析。首先,研究了CNTs/Mg-1.3Mn-1.0Ce-4.0Zn復(fù)合材料的顯微組織、力學(xué)性能、時(shí)效行為及耐蝕性能。對(duì)顯微組織和力學(xué)性能的研究發(fā)現(xiàn),添加CNTs后基體合金的晶粒組織得以細(xì)化,晶粒形貌及第二相的分布特征發(fā)生改變,鑄態(tài)晶粒組織逐漸由等軸狀轉(zhuǎn)變?yōu)闃渲?晶內(nèi)第二相的數(shù)量增加。隨著CNTs添加量的增大,復(fù)合材料的室溫強(qiáng)度和伸長(zhǎng)率均呈先增大后減小的趨勢(shì)。當(dāng)CNTs添加量為0.5%時(shí),復(fù)合材料的性能最佳,其鑄態(tài)下的室溫抗拉強(qiáng)度和斷后伸長(zhǎng)率分別達(dá)212.2MPa和21.1%,與基體合金相比分別增加了8.5%和37.5%。對(duì)時(shí)效行為的研究表明,添加CNTs后基體合金的峰值時(shí)效硬度提高,并且達(dá)到峰值時(shí)效硬度所需的時(shí)間縮短。電化學(xué)極化曲線結(jié)果顯示,添加CNTs后基體合金的自腐蝕電位升高、電流密度降低,其耐蝕性能得到改善。其次,在Gleeble-3500熱模擬試驗(yàn)機(jī)上對(duì)0.5%CNTs/Mg-1.3Mn-1.0Ce-4.0Zn復(fù)合材料進(jìn)行了熱壓縮實(shí)驗(yàn)。對(duì)復(fù)合材料熱變形行為的研究發(fā)現(xiàn),變形溫度和應(yīng)變速率是影響其流變應(yīng)力的關(guān)鍵因素,該材料在熱變形過程中的流變應(yīng)力模型可以用含Z(Zener-Hollomon)參數(shù)的雙曲正弦方程表示,其中應(yīng)變硬化指數(shù)n值和變形激活能Q值分別為9.23和207.19kJ/mol。對(duì)不同熱變形條件下復(fù)合材料微觀組織的研究表明,變形溫度和應(yīng)變速率對(duì)復(fù)合材料的熱變形組織形貌及晶粒尺寸均具有重要影響。在較低溫度(200～250℃)下壓縮時(shí),形變組織以纖維組織和孿晶為主,孿晶之間的交錯(cuò)程度隨應(yīng)變速率的增大而增強(qiáng)；在較高溫度(300-400℃)下壓縮時(shí)發(fā)生連續(xù)動(dòng)態(tài)再結(jié)晶,再結(jié)晶程度隨應(yīng)變速率的增大而加劇,晶粒尺寸隨應(yīng)變速率的增大而減小,當(dāng)變形溫度為400℃和初始應(yīng)變速率為10s-1時(shí),復(fù)合材料具有細(xì)小均勻的動(dòng)態(tài)再結(jié)晶晶粒組織。
[Abstract]:Metal magnesium and its alloys have a series of excellent properties, and they are a kind of light metal structural materials with great prospect. In recent years, with the development of various industries. High strength magnesium alloys, flame retardant magnesium alloys and heat resistant magnesium alloys have been developed. At the same time, the strength of materials is required in many fields. Plastic, heat and corrosion resistance and other aspects of the comprehensive properties. It is of great significance to develop new magnesium alloys and their composites with excellent comprehensive properties. This paper aims to further improve the comprehensive properties of magnesium alloys. Carbon nanotubes (CNTs) reinforced magnesium matrix composites were prepared by agitation casting with Mg-Mn-Ce-Zn quaternary alloy with better comprehensive properties. Metallographic observation and electron spectroscopy were used. The microstructure, mechanical properties, corrosion resistance and thermal deformation behavior of the composites were systematically studied by means of fracture scanning, transmission electron microscopy, differential thermal analysis, electrochemical analysis and thermal simulation. The strengthening and toughening mechanism, corrosion resistance mechanism, fracture mechanism and microstructure change during hot deformation of the composites were discussed and analyzed. The microstructure, mechanical properties, aging behavior and corrosion resistance of CNTs/Mg-1.3Mn-1.0Ce-4.0Zn composites were studied. After the addition of CNTs, the grain structure of the matrix alloy was refined, the grain morphology and the distribution of the second phase changed, and the as-cast grain structure gradually changed from equiaxed to dendritic. With the increase of CNTs content, the room temperature strength and elongation of the composites increased first and then decreased. When the content of CNTs was 0.5%. The tensile strength at room temperature and the elongation after break of the composites were 212.2 MPA and 21.1% respectively. Compared with the base alloy, the aging behavior of the alloy increased by 8.5% and 37.5, respectively. The results show that the peak aging hardness of the matrix alloy increases with the addition of CNTs. The electrochemical polarization curve showed that the corrosion potential of the matrix alloy increased, the current density decreased, and the corrosion resistance was improved after the addition of CNTs. The thermal compression experiments of 0.5 CNTs / Mg-1.3 Mn-1.0Ce-4.0 Zn composites were carried out on a Gleeble-3500 thermal simulator. The study of formalism found. Deformation temperature and strain rate are the key factors affecting the flow stress. The rheological stress model of the material during hot deformation can be expressed by the hyperbolic sinusoidal equation with ZAZener-Hollomon parameters. The strain hardening exponent n and the deformation activation energy Q are 9.23 and 207.19kJ / mol, respectively. The deformation temperature and strain rate have an important effect on the morphology and grain size of the composites. When the deformation temperature is 200 ~ 250 鈩，

本文編號(hào)：1485010