鎂合金板材特殊軋制變形技術(shù)研究

1、學(xué)校代號(hào) 10532 學(xué) 號(hào) B02131015 分 類(lèi) 號(hào) TG .3 密 級(jí) 公開(kāi) 博士學(xué)位論文 鎂合金板材 特殊軋制變形技術(shù)研究培 養(yǎng) 單學(xué) 科 專 研 究 方 論文提交日學(xué)校代號(hào)：10532學(xué) 號(hào)：B02131015密 級(jí)：公開(kāi)湖南大學(xué)博士學(xué)位論文鎂合金板材特殊軋制變形技術(shù)研究學(xué)位申請(qǐng)人姓名： 夏偉軍導(dǎo)師姓名及職稱： 陳振華 教授培專養(yǎng)業(yè)單名位： 材料科學(xué)與工程學(xué)院 稱： 材料加工工程論文提交日期： 2010年3月25日論文答辯日期： 2010年5月31日答辯委員會(huì)主席： 萬(wàn) 隆 教授Research on Special Rolling Techniques of Wrought M

2、agnesiumAlloy SheetbyXIA WeijunB.E.(Centeral South University1993M.S. (Centeral South University2001A dissertation submitted in partial satisfaction of theRequirements for the degree ofDoctor of EngineeringinMaterial Science and Engineeringin theGraduate SchoolofHunan UniversitySupervisorProfessor C

3、HEN ZhenhuaMay ，2010湖 南 大 學(xué)學(xué)位論文原創(chuàng)性聲明本人鄭重聲明：所呈交的論文是本人在導(dǎo)師的指導(dǎo)下獨(dú)立進(jìn)行研究所取得的研究成果。 除了文中特別加以標(biāo)注引用的內(nèi)容外，本論文不包含任何其他個(gè)人或集體已經(jīng)發(fā)表或撰寫(xiě)的成果作品。對(duì)本文的研究做出重要貢獻(xiàn)的個(gè)人和集體，均已在文中以明確方式標(biāo)明。本人完全意識(shí)到本聲明的法律后果由本人承擔(dān)。作者簽名： 日期：年 月 日學(xué)位論文版權(quán)使用授權(quán)書(shū)本學(xué)位論文作者完全了解學(xué)校有關(guān)保留、使用學(xué)位論文的規(guī)定，同意學(xué)校保留并向國(guó)家有關(guān)部門(mén)或機(jī)構(gòu)送交論文的復(fù)印件和電子版，允許論文被查閱和借閱。本人授權(quán)湖南大學(xué)可以將本學(xué)位論文的全部或部分內(nèi)容編入有關(guān)數(shù)據(jù)庫(kù)進(jìn)行

4、檢索，可以采用影印、縮印或掃描等復(fù)制手段保存和匯編本學(xué)位論文。本學(xué)位論文屬于1保密 ，在2不保密。(請(qǐng)?jiān)谝陨舷鄳?yīng)方框內(nèi)打”作者簽名： 日期： 年 月 日導(dǎo)師簽名： 日期： 年 月 日I鎂合金板材特殊軋制變形技術(shù)研究摘 要作為最輕的金屬結(jié)構(gòu)材料，鎂合金被譽(yù)為“二十一世紀(jì)最具發(fā)展前景的綠色工程材料”，特別是變形鎂合金板材以其優(yōu)異的的綜合性能展現(xiàn)出極其廣闊的應(yīng)用前景。但受到鎂合金自身晶體結(jié)構(gòu)的限制，傳統(tǒng)的制備和加工技術(shù)生產(chǎn)鎂合金板材時(shí)存在成本偏高、力學(xué)性能和低溫成形性能不夠理想等局限，從而很大程度上制約了變形鎂合金的發(fā)展。因此，低成本、高性能變形鎂合金板材的研制已成為當(dāng)今材料領(lǐng)域研究的熱點(diǎn)。為提高鎂

5、合金板材的成品率并進(jìn)一步改善其室溫塑性，本文采用AZ31鎂合金為研究對(duì)象，提出了通過(guò)細(xì)化晶粒、調(diào)整晶粒取向和控制動(dòng)態(tài)再結(jié)晶及孿生行為等前期處理，從根本上改善鎂合金成形性能，再結(jié)合優(yōu)化的軋制工藝制備高性能鎂合金板材的思想，開(kāi)展了鎂合金板材的系列特殊軋制技術(shù)研究。首先，基于鎂合金初始晶粒取向、動(dòng)態(tài)再結(jié)晶和孿生行為在板材軋制過(guò)程中的重要作用，論文開(kāi)展了AZ31鎂合金鑄錠擠壓坯軋制技術(shù)的研究，分析了擠壓坯的顯微組織特征和壓縮變形行為，研究了軋制溫度、變形量和板坯初始取向?qū)Z31鎂合金板材微觀組織和力學(xué)性能的影響規(guī)律，探討了熱軋過(guò)程中孿晶的演變以及動(dòng)態(tài)再結(jié)晶組織特征和機(jī)制，揭示了板材在退火過(guò)程中的組織

6、、性能的演變規(guī)律，結(jié)果表明：（1）AZ31鎂合金擠壓坯具有很強(qiáng)的（0002）基面擇優(yōu)取向和明顯的室溫各向異性，擠壓坯的軋制成形性能隨基面與軋面之間傾角的增大而明顯改善；隨著道次變形量的增大，板材的晶粒組織細(xì)化，室溫抗拉強(qiáng)度和伸長(zhǎng)率增大；鎂合金熱變形組織對(duì)初始晶粒組織非常敏感，具有較明顯的組織遺傳效應(yīng)；多道次熱軋時(shí)，合理地逐步增大道次變形量有利于獲得細(xì)小均勻的動(dòng)態(tài)再結(jié)晶晶粒組織。（2）拉伸孿晶的界面容易擴(kuò)展，其內(nèi)部主要發(fā)生滑移變形；壓縮孿晶的界面穩(wěn)定，可以作為再結(jié)晶的形核質(zhì)點(diǎn)而細(xì)化晶粒。軋制過(guò)程中的動(dòng)態(tài)再結(jié)晶在低溫時(shí)以基于孿生的再結(jié)晶為主要機(jī)制，其實(shí)質(zhì)為壓縮孿晶內(nèi)的動(dòng)態(tài)再結(jié)晶；中溫軋制時(shí)的動(dòng)態(tài)再

7、結(jié)晶機(jī)制包括基于孿生的動(dòng)態(tài)再結(jié)晶和連續(xù)動(dòng)態(tài)再結(jié)晶；高溫軋制時(shí)為非連續(xù)動(dòng)態(tài)再結(jié)晶。（3）低溫軋制板材在200退火120min 可獲得最佳的晶粒組織，在400以下溫度退火發(fā)生初次再結(jié)晶對(duì)板材織構(gòu)影響不大，在450退火時(shí)發(fā)生二次再 II博士學(xué)位論文結(jié)晶使基面織構(gòu)弱化。其次，基于鑄錠先擠后軋雖可顯著改善鎂合金鑄錠的熱軋開(kāi)坯性能，但擠壓坯常規(guī)軋制時(shí)，板材仍形成強(qiáng)烈的基面織構(gòu)而對(duì)后續(xù)成形極為不利的事實(shí)，以抑制軋制過(guò)程中基面織構(gòu)的形成為目的，論文開(kāi)展了擠壓坯異步軋制技術(shù)的研究，分析了小異速比多道次異步軋制的變形特點(diǎn)和規(guī)律，揭示了異步軋制工藝參數(shù)對(duì)板材組織及性能的影響規(guī)律，結(jié)果表明：（1）小異速比多道次異步軋

8、制不僅能有效地獲得大剪切應(yīng)變積累，而且等效應(yīng)變分布比大異速比軋制時(shí)更為均勻。（2）小異速比多道次異步軋制時(shí)，隨著道次變形量的增大，形成傾轉(zhuǎn)基面織構(gòu)的能力減弱，成形性能降低；隨著總變形量的增大，基面織構(gòu)的強(qiáng)度有所減弱；隨著異步軋制溫度的升高，新晶粒的形成機(jī)制逐漸由動(dòng)態(tài)再結(jié)晶轉(zhuǎn)變?yōu)樾纬勺冃螏?，基面織?gòu)強(qiáng)度逐漸降低；沿D 路徑軋制時(shí)可以獲得最佳的綜合力學(xué)性能和成形性能。對(duì)異步軋制板材在300下經(jīng)60min 退火處理后，基面織構(gòu)強(qiáng)度顯著降低，板材的室溫成形性能進(jìn)一步提高。（3）采用優(yōu)化工藝制備的異步軋制AZ31鎂合金板材的室溫伸長(zhǎng)率達(dá)31.7%，比普通軋制的提高了約49%；室溫Erichsen 值高達(dá)

9、6.14mm ，比普通軋制的高出3倍。第三，基于先擠后軋技術(shù)在制備大尺寸板材時(shí)的局限性，以及軋制成形受坯件顯微組織和晶粒取向影響的認(rèn)識(shí)，同時(shí)針對(duì)傳統(tǒng)鑄造鎂合金晶粒組織粗大、易于在晶界析出粗大片狀共晶相等對(duì)板材軋制的不利影響，以控制鑄錠微觀組織特別是晶粒取向?yàn)槟康?，論文提出了鎂合金定向凝固坯軋制技術(shù)，研究了不同定向凝固方式下AZ31鎂合金鑄錠的晶粒組織、晶粒取向、熱壓縮和熱軋制變形特點(diǎn)，建立了定向凝固鑄件熱壓縮變形本構(gòu)方程，制定了定向凝固坯熱軋工藝規(guī)程，結(jié)果表明：（1）定向凝固能有效抑制傳統(tǒng)鑄造坯晶界脆性相的析出，在平面定向凝固鎂合金中同時(shí)存在（）、（）棱柱面和（）、（）錐面擇優(yōu)取向。（2）定向

10、凝固AZ31鎂合金熱壓縮時(shí)的應(yīng)變速率敏感指數(shù)m 值為0.19，明顯大于文獻(xiàn)報(bào)道的普通鑄錠的0.14，并且與擠壓態(tài)的相當(dāng)。（3）定向凝固坯軋制技術(shù)能明顯改善鎂合金的熱軋成形性能，縮短軋制工藝流程，減小開(kāi)裂傾向，提高板材成品率。關(guān)鍵詞：AZ31鎂合金板材；異步軋制；定向凝固；織構(gòu)；顯微組織；成形性能；孿生；動(dòng)態(tài)再結(jié)晶。III鎂合金板材特殊軋制變形技術(shù)研究AbstractBeing the lightest metallic structural materials, magnesium alloys are considered as the environment-friendly engine

11、ering material with the greatest prospects for development in the 21st century. Especially, wrought magnesium alloy plates have broad application prospects due to their excellent combined properties. However, magnesium alloy plates prepared by the traditional preparation & plastic processing tec

12、hnologies always exhibit high fabrication cost, undesirable mechanical properties and forming ability at low temperatures due to the intrinsic close-packed hexagonal crystal structure and thus their devolpment is restricted to a great extent. Therefore, research and development of wrought magnesium

13、alloy plates with low cost and high performance is a hot topic in the field of materials research today.The thought that improving the forming ability of magnesium alloys can be fundamentally achieved by grain refinement, grain orientation modification and control of dynamic recrystallization &

14、twinning and the high-performance magnesium alloy plates can be prepared by the optimum rolling process in the combination with the pretreatment mentioned above is proposed to improve the rate of finished products and their ambient temperature plasticity. The AZ31 magnesium alloy is selected for the

15、 study on the special rolling technologies of magnesium alloy plates in the present study.Firstly, the conventional rolling technique of the extrusions prepared from the AZ31 ingots is studied in the consideration that the crystal orientation of original grains, dynamic recrystallization and twinnin

16、g play the important role during the rolling process of magnesium alloy plates. The microstructural feature and the compression deformation behavior of the as-extruded AZ31 magnesium alloy are analyzed. The effects of the rolling parameters such as rolling temperature, reduction in each pass and cry

17、stal orientation of the original plate on the microstructure and mechanical properties of the AZ31 plate are also investigated. Moreover, the evolution of twinning during the hot rolling process as well as the microstructural feature and the mechanism of dynamic recrystallization is explored. In add

18、ition, the evolution regularities of the microstructure and mechanical properties of the as-rolled AZ31 plates are revealed during the subsequent annealling. The results show that:(1 The as-extruded AZ31 magnesium alloy exhibits a strong (0002 basal IV博士學(xué)位論文preferential orientation and an obvious am

19、bient-temperature anisotropy and its rolling ability is evidently improved as the angle between the basal plane and the rolling surface increases. Grain refinement, higher ambient-temperature ultimate tensile strength and higher elongation are achieved with the increasing reduction in each pass. The

20、 hot-deformed microstructure of the AZ31 alloy is very sensitive to the original microstructure and exhibits rather an obvious microstructure hereditary effect. The properly gradual increase of reduction in each pass is beneficial to achieve the fine, homogenous dynamic recrystallization grains duri

21、ng the multiple pass hot rolling.(2 through dislocation slip is dominant within these twins. The interfaces of the as the nucleation sites of dynamic recrystallization. The twin-induced dynamic recrystallization is dominant during rolling at low temperatures. In essence, it is twin-induced dynamic r

22、ecrystallization in the combination with the continuous dynamic recrystallization is dominant during rolling at medium temperatures, while the non-continuous dynamic recrystallization is dominant during rolling at high temperatures.(3 The AZ31 plates rolled at low temperatures exhibit the best micro

23、structure afterannealing at 200 for 12min. Annealing below 400 brings about the primary recrystallization and the latter has no obvious influence on the basal textures. However, annealing at 450 induces the secondary recrystallization and the latter weakens the basal textures.Secondly, the different

24、 speed rolling technique of the extrusions prepared from the AZ31 ingots is studied to prohibit the formation of the basal rolling textures since the conventional rolling brings about the severe basal texture and the latter is harmful to the subsequent plastic processing. However, extrusion before r

25、olling can improve the hot rolling ability of the AZ31 ingots. The deformation features and regularities of the different speed rolling with a small differece in the rolling speed and multiple passes are also analyzed. Moreover, the effects of the different speed rolling parameters on the microstruc

26、ture and mechanical properties of the as-rolled plates are also disclosed. The results show that:(1 The different speed rolling with a small differece in the rolling speed and multiplepasses can not only achieves the bigger accumulation of shear strain effectively, V鎂合金板材特殊軋制變形技術(shù)研究but also the equiv

27、alent strain distribution is more uniform than that of the highly different speed rolling.(2 The rotation ability of the basal textures is weakened and the forming ability isreduced with the increasing reduction in each pass during the different speed rolling with a small differece in the rolling sp

28、eed and multiple passes. The intensity of the basal textures is weakened with the increasing total strain. The formation mode of new grains is varied from dynamic recrystallization to the deformation band and the intensity of the basal textures is reduced gradually. The best mechanical properties an

29、d forming ability can be achived by rolling along theD path. The intensity of the basal textures of the as-rolled plate is obviously reduced after annealing at 300 for 60min and thus its forming ability at ambient temperature is further improved.(3 The AZ31 plates prepared by the optium different sp

30、eed rolling process exhibitsthe elongation at ambient temperature up to 31.7%, about 49% higher than that of the plate prepared by conventional rolling. Its Erichsen value at ambient temperature is high up to 6.14mm, about 3 times higher than that of conventional rolling.Thirdly, the rolling techniq

31、ue of the directionally solidified AZ31 ingot is developed on the basis of the understanding of the influences of the microstructure and the grain orientation of the ingot on the rolling deformation to modify the microstructure especially the grain orientation of the ingot since the conventional rol

32、ling after extrusion exhibits the limitation for the preparation of the large-size plates and the traditional magnesium alloy castings are characteristic of coarse grains and coarse plate-like eutectics along the grain boundaries, which have a detrimental effect on the rolling. The microstructure, g

33、rain orientation, hot compression and hot rolling deformation features of the AZ31 ingots prepared under the different directional solidification conditions are investigated. On the basis of the understanding mentioned above, the constitutional equation of the directionally solidified AZ31 ingot dur

34、ing hot compression deformation and its hot rolling procedure are established. The results show that:(1 Directional solidification can inhibit the precipitation of the brittle phases alongthe grain boundaries in the traditional castings. The preferential orientations of the existent in the planar di

35、rectionally solidified AZ31 ingots.(2 The strain rate sensitivity exponent m of the directionally solidified AZ31 ingot VI博士學(xué)位論文during hot compression is 0.19, much higher than that of the traditional casting reported in the literature (0.14 and comparable to that of the as-extruded state.(3 The rol

36、ling technique of the directionally solidified ingot can improve the hotrolling ability of the AZ31 alloy, shorten the process flow of rolling, lower the tendency of cracking and increase the rate of the finished AZ31 plate.Keywords: AZ31 magnesium alloy plate; microstructure; different speed rollin

37、g; directional solidification; texture; forming ability; twinning; dynamic recrystallizationVII鎂合金板材特殊軋制變形技術(shù)研究目 錄學(xué)位論文原創(chuàng)性聲明和版權(quán)使用授權(quán)書(shū). I 摘 要. II Abstract .IV 插圖索引.XI 附表索引. XIV第1章 緒 論. 11.1 前言. 11.2 變形鎂合金概述. 21.3 特殊軋制變形技術(shù)的研究與發(fā)展現(xiàn)狀. 61.4 鎂合金定向凝固坯軋制技術(shù)的提出與設(shè)計(jì)思想. 121.5 研究目的、意義和主要內(nèi)容. 16第2章 試驗(yàn)過(guò)程. 172.1 試驗(yàn)材料. 17

38、2.2 工藝流程. 172.3 試樣的制備. 17VIII博士學(xué)位論文2.4 組織性能檢測(cè)與分析. 20第3章 AZ31鎂合金擠壓坯軋制技術(shù)研究. 233.1 前言. 233.2 AZ31鎂合金擠壓坯的組織特征與變形行為. 243.3 軋制工藝參數(shù)對(duì)板材組織與性能的影響. 273.4 熱軋過(guò)程中孿晶的演變規(guī)律. 373.5 熱軋過(guò)程中的動(dòng)態(tài)再結(jié)晶機(jī)制. 413.6 退火處理對(duì)板材組織與性能的影響. 473.7 本章小結(jié). 56第4章 AZ31鎂合金異步軋制技術(shù)研究. 584.1 引言. 584.2異步軋制有限元模擬. 584.3 AZ31鎂合金板材異步軋制工藝研究. 65IX鎂合金板材特殊軋制

39、變形技術(shù)研究4.4 退火處理對(duì)異步軋板組織性能的影響. 974.5 AZ31鎂合金小異速比異步軋制工藝優(yōu)化. 1024.6 本章小結(jié). 104第5章 AZ31鎂合金定向凝固坯軋制技術(shù)研究. 1055.1 引言. 1055.2 定向凝固AZ31鎂合金板坯的微觀組織特征. 1055.3 定向凝固AZ31鎂合金的壓縮變形行為. 1125.4 定向凝固AZ31鎂合金板坯的軋制變形行為. 1235.5 本章小結(jié). 129 結(jié) 論. 130 參考文獻(xiàn). 132 致 謝. 145 附錄A 攻讀博士學(xué)位期間已發(fā)表或待發(fā)表的學(xué)術(shù)論文與著作. 146X博士學(xué)位論文插圖索引圖1.1 Conshearing連續(xù)剪切工藝示意圖. 8圖1.2 ECAR裝置和模具示意圖. 9圖1.3 常規(guī)軋制和異步軋制時(shí)的變形區(qū)及摩擦力分布. 10圖2.1 試驗(yàn)所采用的工藝流程簡(jiǎn)圖. 17圖2.2 軋制路徑示意圖（從上至下分別為A 、B 、C 和D 路徑）. 19圖2.3 分段式定向凝固裝置示意圖. 20圖2.4 定向凝固模組裝結(jié)構(gòu)示意圖. 20圖2.5 室溫拉伸試樣尺寸. 21圖2.6 室溫杯突試驗(yàn)?zāi)＞呓Y(jié)構(gòu)示意圖. 22圖3.1 鑄態(tài)和擠壓態(tài)AZ31鎂合金的金相組織.