本文選題：Mg-4Y-3Nd　切入點(diǎn)：Dy　出處：《哈爾濱工業(yè)大學(xué)》2015年博士論文

【摘要】：鎂合金作為具有高比強(qiáng)度和比剛度的結(jié)構(gòu)材料,在汽車、電子等領(lǐng)域已被大量應(yīng)用,但較低的高溫性能限制了其在航天航空工業(yè)上的應(yīng)用。稀土元素可以明顯提高鎂合金的性能,尤其是高溫拉伸和高溫蠕變性能,因此稀土鎂合金為當(dāng)前世界鎂合金領(lǐng)域的一個(gè)研究熱點(diǎn)。本文在Mg-4Y-3Nd-0.5Zr合金基礎(chǔ)上,添加Dy稀土元素,開發(fā)新型Mg-4Y-3Nd-x Dy-Zr鎂合金。研究了合金中Dy對(duì)合金組織形態(tài)、相組成及結(jié)構(gòu)、室溫及高溫力學(xué)性能等的影響。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3,5)合金鑄態(tài)組織研究表明,合金鑄態(tài)組織由基體a-Mg、存在于晶界的骨狀的共晶相Mg5RE(f.c.c.,a=2.2~2.3nm)和沿骨骼狀相邊緣及其內(nèi)部形成的塊狀相RE17Mg3(f.c.c.,a=0.5~0.6nm)組成。Dy未影響鑄態(tài)相結(jié)構(gòu)類型,但對(duì)相的晶格常數(shù)有微弱影響。隨著合金中Dy含量的增加,骨狀相體積增多,尺寸增大,形貌更加復(fù)雜。在合金凝固過程中,Dy替代了部分Nd析出形成骨狀相,而對(duì)骨狀相中的Y沒有影響。在形成塊狀相時(shí),Dy對(duì)Nd基本沒有影響,塊狀相中Dy/Y隨著合金中Dy含量的增加而不斷增大。在鑄態(tài)組織中Nd主要集中分布在骨狀相中,而Y和Dy在晶界和骨狀相中有微弱的富集。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3,5)合金固溶態(tài)組織研究表明:骨狀相在500℃溫度下結(jié)構(gòu)穩(wěn)定,而在525℃和550℃溫度下快速消融;塊狀相在525℃以下溫度時(shí)相結(jié)構(gòu)穩(wěn)定,Nd從塊狀相中不斷擴(kuò)散到基體中直至與基體中的含量一致,但在550℃固溶處理過程中,塊狀相在緩慢消融,對(duì)晶界的釘扎作用逐漸減弱導(dǎo)致晶�？焖匍L大。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3,5)合金時(shí)效硬化曲線和時(shí)效析出行為研究結(jié)果表明,該系合金具有明顯的時(shí)效硬化效應(yīng),并隨著時(shí)效溫度的升高,合金時(shí)效硬度略有下降。加入Dy大大提高了合金硬度,同時(shí)也使到達(dá)峰時(shí)效提前、析出相更加細(xì)小彌散。在250℃時(shí)效處理過程中,Mg-4Y-3Nd-0.5Zr合金時(shí)效析出順序?yàn)?β″、β′、β。但Mg-4Y-3Nd-0.5Z合金中加入Dy,促進(jìn)了β′相的形核析出,這也是導(dǎo)致峰時(shí)效提前原因。對(duì)Mg-4Y-3Nd-0.5Zr(WN43)合金和Mg-4Y-3Nd-2Dy-0.5Zr(WND432)合金固溶態(tài)的基體固溶體脫溶沉淀析出的轉(zhuǎn)變驅(qū)動(dòng)力進(jìn)行了分析,并計(jì)算得出了在250℃下的WN43DG=-85J/mol,WND432DG=-101J/mol。較低的脫溶沉淀析出轉(zhuǎn)變驅(qū)動(dòng)力促使β￠相的形核析出。Mg-4Y-3Nd-x Dy-0.5Zr(x=0,1,2,3)合金性能研究結(jié)果表明,Dy能顯著提高合金拉伸性能,尤其是高溫抗拉性能。在300℃下,加入3%Dy的Mg-4Y-3Nd-3Dy-0.5Zr合金的抗拉強(qiáng)度和屈服強(qiáng)度分別提高了43.2%和37.6%。但由于合金加入Dy較少,對(duì)合金蠕變性能影響很小,尤其是較低溫度的蠕變性能。Mg-4Y-3Nd-2Dy-0.5Zr合金在蠕變溫度為250℃時(shí),應(yīng)力敏感性指數(shù)為2.3,滑移機(jī)制主要為基面滑移和棱柱面滑移;在蠕變應(yīng)力為40MPa和80MPa時(shí),激活能分別為94k J/mol和195k J/mol。細(xì)小彌散的塊狀相RE17Mg3對(duì)合金具有第二相強(qiáng)化作用,但其強(qiáng)化作用弱于塊狀相中稀土固溶進(jìn)基體后產(chǎn)生的固溶強(qiáng)化作用。
[Abstract]:Magnesium alloys, as structural materials with high specific strength and specific stiffness, have been widely used in automotive, electronic and other fields, but their low high temperature properties limit their application in aerospace industry.Rare earth elements can obviously improve the properties of magnesium alloys, especially the tensile and creep properties of magnesium alloys at high temperature. Therefore, rare earth magnesium alloys have become a research hotspot in the field of magnesium alloys in the world.On the basis of Mg-4Y-3Nd-0.5Zr alloy, a new type of Mg-4Y-3Nd-x Dy-Zr magnesium alloy was developed by adding Dy rare earth element.The effect of Dy on microstructure, phase composition and structure, mechanical properties at room and high temperature.With the increase of Dy content in the alloy, the volume of bone phase increases, the size increases and the morphology becomes more complex.During the solidification of the alloy, Dy replaced some ND precipitates to form bone-like phase, but had no effect on Y in the bone-like phase.Dy/Y in bulk phase increases with the increase of Dy content in bulk phase.In the as-cast microstructure, ND is mainly concentrated in the bony phase, while Y and Dy are weakly enriched in the grain boundary and the bone-like phase.The aging hardening curve and precipitation behavior of Mg-4Y-3Nd-x Dy-0.5Zrd-x Dy-0.5ZrxO0 ~ (2 +) alloy are studied. The results show that the aging hardening effect of the alloy is obvious.With the increase of aging temperature, the aging hardness of the alloy decreases slightly.The addition of Dy can greatly improve the hardness of the alloy, at the same time, the peak aging is advanced, and the precipitate phase is more fine and dispersed.During aging treatment at 250 鈩，

本文編號(hào)：1718851