本文選題：AZ31鎂合金 + 退火預(yù)處理　； 參考：《太原理工大學(xué)》2017年碩士論文

【摘要】：鎂合金是高性能輕質(zhì)結(jié)構(gòu)材料,各類(lèi)工業(yè)產(chǎn)品中廣泛采用鎂合金為原料。尤其在大力提倡環(huán)保、可持續(xù)的今天,鎂合金諸多優(yōu)點(diǎn)更為突出。但也有些特點(diǎn)導(dǎo)致其焊接性能較差,焊接接頭容易產(chǎn)生粗晶組織、熱裂紋等質(zhì)量缺陷,已成為限制其更廣應(yīng)用的主要原因。恒溫超塑性焊接是一種新型簡(jiǎn)單固態(tài)焊接技術(shù),能有效減輕裂紋及氣孔等傳統(tǒng)焊接缺陷,并利用材料的超塑狀態(tài)特點(diǎn),大大減少焊接時(shí)間,節(jié)約能源,并可與成型同步。目前,此技術(shù)僅在鋼材、銅合金與鎢合金中應(yīng)用研究并看到明顯效果,并未見(jiàn)將其應(yīng)用在鎂合金上展開(kāi)研究。另外,在此焊接技術(shù)中恒溫超塑性壓縮發(fā)揮著關(guān)鍵作用,研究鎂合金壓縮的超塑性能對(duì)恒溫超塑性焊接具有必不可少的指導(dǎo)意義。AZ31鎂合金是本文的研究材料,首先對(duì)其采用退火預(yù)處理來(lái)細(xì)化晶粒、均勻組織,然后對(duì)經(jīng)預(yù)處理后的材料進(jìn)行壓縮超塑性能探究,最后根據(jù)超塑性能規(guī)律及各因素影響結(jié)果進(jìn)一步探究鎂合金的恒溫超塑性焊接。退火預(yù)處理的結(jié)果顯示,在300℃下經(jīng)30 min退火后晶粒達(dá)到較好細(xì)化效果,晶粒尺寸由最初的20.79 um細(xì)化至12.15μm,細(xì)化率為40.7%左右。在250℃至480℃溫度下及1×10~(-4) s~(-1)至1×10~(-2) s~(-1)的初始應(yīng)變速率范圍內(nèi)壓縮,試樣的外緣圓周伸長(zhǎng)率都在200.42%之上,均實(shí)現(xiàn)了良好的壓縮超塑性。在超塑壓縮過(guò)程中組織展現(xiàn)了動(dòng)態(tài)再結(jié)晶特征,真實(shí)的應(yīng)力-應(yīng)變曲線符合動(dòng)態(tài)再結(jié)晶型曲線,流變應(yīng)力、壓縮后的晶粒狀態(tài)及動(dòng)態(tài)再結(jié)晶程度均受初始應(yīng)變速率和壓縮溫度的共同影響,應(yīng)變速率敏感指數(shù)m值在0.18-0.24之間,并隨壓縮溫度升高,其平均值略有增大。經(jīng)退火處理后的AZ31鎂合金在預(yù)壓應(yīng)力30 MPa、溫度450℃、應(yīng)變速率為1×10~(-4) s~(-1)的條件下,經(jīng)13 min恒溫超塑性壓接,接頭剪切強(qiáng)度達(dá)到42.08 MPa。恒溫超塑性焊接過(guò)程中的應(yīng)力-應(yīng)變曲線及焊后焊縫處顯微組織均體現(xiàn)出超塑性特征。在主要影響因素中溫度對(duì)恒溫超塑性固態(tài)焊接接頭強(qiáng)度影響較大、時(shí)間的影響其次、應(yīng)變速率的影響相對(duì)較小。相比擴(kuò)散焊,恒溫超塑性焊接能在更省能源、省時(shí)間的條件下,達(dá)到與之相當(dāng)?shù)慕宇^剪切強(qiáng)度。
[Abstract]:Magnesium alloy is a light structure material with high performance. Magnesium alloy is widely used as raw material in all kinds of industrial products.Especially in the promotion of environmental protection, sustainable today, magnesium alloy many advantages are more prominent.However, there are also some characteristics which lead to poor weldability, and the quality defects such as coarse grain structure and hot crack are easy to be produced in welded joints, which have become the main reasons restricting its wider application.Constant-temperature superplastic welding is a new simple solid-state welding technology, which can effectively reduce the defects of traditional welding such as cracks and pores, and make use of the characteristics of superplastic state of materials, greatly reduce the welding time, save energy, and can synchronize with molding.At present, this technology is only applied in steel, copper and tungsten alloys and has obvious effect, but it has not been applied to magnesium alloys.In addition, constant temperature superplastic compression plays a key role in this welding technology. The study of superplasticity of magnesium alloy compression has an essential guiding significance for isothermal superplastic welding. AZ31 magnesium alloy is the research material of this paper.First of all, annealing pretreatment was used to refine the grain and uniform microstructure, and then the pretreated material was studied by compression superplasticity.Finally, the superplastic welding of magnesium alloy at constant temperature is further explored according to the superplastic energy law and the influence of various factors.The results of annealing pretreatment showed that the grain size was refined from 20.79um to 12.15 渭 m after annealing at 300 鈩，

本文編號(hào)：1741989