本文選題：鎂合金 + 形變熱處理�。� 參考：《重慶大學(xué)》2016年博士論文

【摘要】：鎂合金作為最輕的金屬結(jié)構(gòu)材料,具有比強(qiáng)度高、比剛度高且易于回收利用等優(yōu)點(diǎn),在汽車、航空和電子產(chǎn)品領(lǐng)域得到廣泛應(yīng)用。但是,鎂合金具有密排六方晶體結(jié)構(gòu),具有的獨(dú)立滑移系較少,室溫變形能力較差。而且,鎂合金在塑性變形過(guò)程中極易產(chǎn)生孿生變形,導(dǎo)致屈服強(qiáng)度低和拉壓屈服不對(duì)稱等。這些缺點(diǎn)都嚴(yán)重限制了鎂合金的廣泛使用。目前,鎂合金的主要研究方向有:制備高強(qiáng)度鎂合金、改善拉壓屈服不對(duì)稱性和提高室溫塑性變形能力等方面。本課題選用常用的AZ31和ZK60鎂合金作為研究對(duì)象。本文的一個(gè)主要研究?jī)?nèi)容就是研究形變熱處理工藝對(duì)鎂合金的微觀組織和力學(xué)性能的影響;另一個(gè)主要研究?jī)?nèi)容就是研究扭轉(zhuǎn)變形對(duì)鎂合金的微觀組織和力學(xué)性能的影響。通過(guò)金相顯微分析(OM)、X射線衍射分析(XRD)、電子背散射衍射技術(shù)(EBSD)、掃描電鏡(SEM)、透射電鏡(TEM)等對(duì)試樣微觀組織進(jìn)行表征,對(duì)相關(guān)機(jī)理進(jìn)行深入分析,取得的主要結(jié)論如下:(1)低溫退火處理(170℃)能夠提高預(yù)孿生化AZ31鎂合金試樣的壓縮屈服強(qiáng)度。由于溶質(zhì)原子在孿晶界偏聚,阻礙孿晶界擴(kuò)展,增加了孿生長(zhǎng)大的激活應(yīng)力,從而導(dǎo)致預(yù)孿生化試樣的壓縮屈服強(qiáng)度增高。(2)時(shí)效處理(180℃)可以有效地降低預(yù)孿生化ZK60鎂合金試樣的拉壓屈服不對(duì)稱性。在預(yù)孿生化ZK60鎂合金的{1012}拉伸孿晶內(nèi)觀察到三種形貌的析出相:(0001)_(_(twin))板狀、[11-20]_(twin)條狀和[0001]_(twin)棒狀,分別由Mg4Zn7相或Mg Zn2相組成。由于在預(yù)孿生化ZK60鎂合金的基體和孿晶內(nèi)具有不同的析出行為,而且溶質(zhì)原子在孿晶界偏聚,阻礙孿晶界擴(kuò)展,導(dǎo)致時(shí)效處理試樣的后續(xù)拉伸(退孿生變形機(jī)制)和壓縮(孿晶長(zhǎng)大機(jī)制)屈服強(qiáng)度增量不同。(3)扭轉(zhuǎn)變形可以有效地降低擠壓態(tài)AZ31鎂合金試樣的拉壓屈服不對(duì)稱性。試樣的壓縮屈服強(qiáng)度隨著扭轉(zhuǎn)應(yīng)變量的增大而升高;但拉伸屈服強(qiáng)度基本不受扭轉(zhuǎn)應(yīng)變量的影響。當(dāng)試樣經(jīng)受的切應(yīng)變量較低時(shí)(γ0.35),其塑性變形主要以位錯(cuò)滑移為主;當(dāng)試樣經(jīng)受的切應(yīng)變量較高時(shí)(γ0.52),其塑性變形除了位錯(cuò)滑移之外,還會(huì)產(chǎn)生大量的{1012}拉伸孿晶。(4)扭轉(zhuǎn)變形速度對(duì)擠壓態(tài)AZ31鎂合金試樣的流變曲線具有重要影響。扭轉(zhuǎn)變形速度越快,則流變曲線就越高。扭轉(zhuǎn)變形使試樣橫截面產(chǎn)生梯度組織,而且能夠提高試樣的硬度。扭轉(zhuǎn)變形產(chǎn)生的梯度應(yīng)變是試樣橫截面產(chǎn)生梯度組織的主要原因。位錯(cuò)密度、硬度和孿晶面積分?jǐn)?shù)沿試樣橫截面的半徑方向逐漸增加。硬度的提高主要?dú)w因于位錯(cuò)強(qiáng)化機(jī)制,而織構(gòu)強(qiáng)化和細(xì)晶強(qiáng)化的作用微乎其微。(5)熱扭轉(zhuǎn)變形也會(huì)使擠壓態(tài)AZ31鎂合金試樣在橫截面上產(chǎn)生梯度組織。在橫截面邊緣處產(chǎn)生的動(dòng)態(tài)再結(jié)晶晶粒多,而心部產(chǎn)生的動(dòng)態(tài)再結(jié)晶晶粒少。隨著變形溫度升高和切應(yīng)變量增大,動(dòng)態(tài)再結(jié)晶晶粒的面積分?jǐn)?shù)也逐漸增加。熱扭轉(zhuǎn)變形試樣的壓縮屈服強(qiáng)度增高主要是由細(xì)晶強(qiáng)化(動(dòng)態(tài)再結(jié)晶)引起的。
[Abstract]:Magnesium alloy is the lightest metal structural material, has high strength, high stiffness and advantages, easy recycling in the automotive, aerospace and electronic products are widely used in the field. However, magnesium alloy has close packed crystal structure with six party, the independent slip systems at room temperature is less, poor deformation capacity. Moreover, magnesium alloy is easy to produce deformation twinning during plastic deformation, resulting in low yield strength and tension compression asymmetry. These disadvantages seriously limit the widespread use of magnesium alloy. At present, the main research direction of magnesium alloys: preparation of high strength magnesium alloy, improve the tension compression asymmetry and improve ductility at room temperature deformation capacity and so on. This paper selected the commonly used AZ31 and ZK60 magnesium alloy as the research object in this paper. One of the main research content is the study of heat treatment process on Microstructure and mechanical properties of magnesium alloys. Ring; another main research content is to study the influence of torsion deformation on the microstructure and mechanical properties of magnesium alloy. By metallographic micro analysis (OM), X ray diffraction (XRD), electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) were used to characterize the microstructure of the specimen, in-depth analysis of relevant mechanism, the main conclusions are as follows: (1) annealing temperature (170 DEG C) can improve the biochemical twin of AZ31 magnesium alloy with compression yield strength. Due to segregation of solute atoms in the twin boundary, hinder twin boundary expansion, increase the twin growth activation of stress thus, the pre twin biochemical samples compressive yield strength increased. (2) (180 C) aging treatment can effectively reduce the twin biochemical ZK60 magnesium alloy pre tension compression asymmetry. In the pre twin biochemical ZK60 magnesium alloy {1012} tension twin gold was observed within three The morphology of precipitated phase: (0001) _ (_ (twin)) plate, [11-20]_ (twin) and [0001]_ (twin) strip rod, respectively by Mg4Zn7 or Mg Zn2 phases. Due to different precipitation behavior in pre twin biochemical ZK60 magnesium alloy matrix and twin, and segregation of solute atoms in the twin boundary, hinder twin boundary expansion, leading to subsequent tensile aging treatment samples (back twinning mechanism) and compression (twin growth mechanism) yield strength increment is different. (3) can effectively reduce the torsional deformation of extruded AZ31 magnesium alloy specimen tension compression asymmetry. The compression yield strength. With the increase of torsional strain; but the tensile yield strength did not reverse the effects of strain. When the specimen is subjected to shear strain is low (gamma 0.35), the plastic deformation is dominated by dislocation slip; when the specimen is subjected to high shear strain (gamma 0.52), the plastic deformation In addition to form dislocation slip, will produce a large number of {1012} twinning. (4) the torsional deformation speed has an important influence on the rheological curves of extruded AZ31 magnesium alloy. The torsional deformation speed more quickly, while the rheological curve is higher. The torsional deformation of cross section of the specimen has the gradient structure, but also can improve the hardness of the sample. Torsional strain gradient deformation is the main reason for the cross section of the specimen to produce gradient tissue. The dislocation density along the radius direction of cross section of the specimen hardness and twinning area fraction increases gradually. The increase in hardness is mainly attributed to the dislocation strengthening mechanism, and strengthening the role of very little texture and fine grain strengthening. (5) hot torsion deformation the extruded AZ31 magnesium alloy samples have the gradient structure in cross section. In the cross section at the edge of the dynamic recrystallization grain, and the core of dynamic recrystallization grain with less. With the increase of deformation temperature and shear stress, the area fraction of dynamic recrystallized grain also increases. The increase of compressive yield strength is mainly caused by fine-grained strengthening (dynamic recrystallization).

【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG146.22;TG166.4

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