【摘要】：Al-Cu-Mg系合金在室溫和高溫下都具有良好的綜合性能,一直備受矚目。但由于Al-Cu-Mg系合金熱裂傾向嚴(yán)重,一直限制其在工業(yè)生產(chǎn)上的應(yīng)用和發(fā)展。為降低Al-Cu-Mg系合金的熱裂傾向,國(guó)內(nèi)外的學(xué)者們分別從不同方面進(jìn)行了許多實(shí)驗(yàn)探索。研究表明稀土元素能有效降低Al-Cu-Mg系合金的熱裂傾向。本文通過研究稀土元素La對(duì)Al-4.4Cu-1.5Mg-0.15Zr合金熱裂傾向的影響,并針對(duì)熱裂的形成機(jī)理,探討La元素的作用機(jī)制。通過臨界直徑法和熱敏感系數(shù)來表征合金的熱裂傾向。研究表明,隨著La元素的加入合金的晶粒尺寸呈先減小后增加的趨勢(shì),未添加La元素時(shí),合金晶粒表現(xiàn)為粗大的樹枝晶,晶界處有連續(xù)粗大的網(wǎng)格狀第二相分布;當(dāng)La元素加入量為0.4%時(shí),合金的晶粒形態(tài)變?yōu)榈容S晶,晶界處的粗大網(wǎng)格狀第二相開始變得不連續(xù),有亮白色新相生成。對(duì)于Al-4.4Cu-1.5Mg-0.15Zr-xLa合金,其熱敏感系數(shù)Hsc隨La元素的加入呈先減小后增加的趨勢(shì)。未添加La元素時(shí),合金的熱裂傾向最高,熱敏感系數(shù)為1.64;當(dāng)La元素加入量為0.4%時(shí),合金的熱裂傾向最低,熱敏感系數(shù)為1.05。三種熱裂紋形成機(jī)理即晶間搭橋理論、液膜理論和凝固補(bǔ)償理論對(duì)于Al-4.4Cu-1.5Mg-0.15Zr-xLa合金同時(shí)存在。當(dāng)稀土元素La加入量小于0.3%時(shí),合金的熱裂機(jī)理主要為晶間搭橋理論;當(dāng)稀土元素La加入量大于等于0.3%時(shí),合金的熱裂機(jī)理主要為液膜理論和凝固收縮補(bǔ)償理論共同作用。對(duì)于Al-4.4Cu-1.5Mg-0.15Zr-xLa合金的熱裂抗性,最優(yōu)La元素的加入量為0.4%。此時(shí),相比于未添加La元素的Al-4.4Cu-1.5Mg-0.15Zr合金,其抗拉強(qiáng)度從173MPa增加到258MPa,伸長(zhǎng)率由7.3%增加到8.6%。為改善Al-4.4Cu-1.5Mg-0.15Zr-0.4La合金的綜合力學(xué)性能,擴(kuò)大其在實(shí)際生產(chǎn)中的應(yīng)用,本文對(duì)Al-4.4Cu-1.5Mg-0.15Zr-0.4La合金熱處理工藝進(jìn)行探究。研究了雙極均勻化處理工藝、固溶時(shí)間和時(shí)效時(shí)間對(duì)合金組織性能的影響。結(jié)果表明,對(duì)于Al-4.4Cu-1.5Mg-0.15Zr-0.4La合金的最優(yōu)熱處理工藝為:雙級(jí)均勻化處理350℃×8h+480℃×16h,固溶處理490±2℃×80min,然后185℃±2℃×12h人工時(shí)效處理。合金經(jīng)熱處理后抗拉強(qiáng)度和硬度都大幅度增加,分別由258MPa增加到498MPa、85HV增加到164HV,但合金的伸長(zhǎng)率有所下降,從8.6%降低到6.9%。
[Abstract]:Al-Cu-Mg alloys have been attracting much attention for their excellent comprehensive properties at room temperature and high temperature. However, the application and development of Al-Cu-Mg alloys in industrial production have been restricted because of their serious hot cracking tendency. In order to reduce the hot cracking tendency of Al-Cu-Mg alloys, many domestic and foreign scholars have made many experiments from different aspects. The results show that rare earth elements can effectively reduce the hot cracking tendency of Al-Cu-Mg alloys. In this paper, the effect of rare earth element La on hot cracking tendency of Al-4.4Cu-1.5Mg-0.15Zr alloy is studied, and the mechanism of La element is discussed according to the formation mechanism of hot crack. The hot cracking tendency of the alloy was characterized by critical diameter method and thermal sensitivity coefficient. The results show that with the addition of La element, the grain size of the alloy decreases first and then increases. Without the addition of La element, the grain size of the alloy appears to be coarse dendrite, and there is a continuous coarse second phase distribution at the grain boundary. When the addition of La element is 0.4, the grain morphology of the alloy becomes equiaxed, and the coarse mesh-like second phase at the grain boundary begins to become discontinuous, and a new bright white phase is formed. For Al-4.4Cu-1.5Mg-0.15Zr-xLa alloys, the thermal sensitivity coefficient (Hsc) decreases first and then increases with the addition of La elements. When La element was not added, the hot cracking tendency of the alloy was the highest, the thermal sensitivity coefficient was 1.64, and when the amount of La element was 0.4, the hot cracking tendency of the alloy was the lowest and the thermal sensitivity coefficient was 1.05. Three kinds of hot crack formation mechanisms, I. e., intergranular bridging theory, liquid film theory and solidification compensation theory, exist simultaneously for Al-4.4Cu-1.5Mg-0.15Zr-xLa alloys. When the amount of rare earth element La is less than 0.3, the hot cracking mechanism of the alloy is mainly the theory of intergranular bypass. When the amount of rare earth element La is greater than 0.3, the hot cracking mechanism of the alloy is mainly composed of liquid film theory and solidification shrinkage compensation theory. For the hot cracking resistance of Al-4.4Cu-1.5Mg-0.15Zr-xLa alloy, the optimum addition amount of La element is 0.4. Compared with the Al-4.4Cu-1.5Mg-0.15Zr alloy without La element, the tensile strength of the alloy increased from 173MPa to 258 MPA, and the elongation increased from 7.3% to 8.6%. In order to improve the comprehensive mechanical properties of Al-4.4Cu-1.5Mg-0.15Zr-0.4La alloy and expand its application in practical production, the heat treatment process of Al-4.4Cu-1.5Mg-0.15Zr-0.4La alloy is studied in this paper. The effects of bipolar homogenization process, solution time and aging time on the microstructure and properties of the alloy were studied. The results show that the optimal heat treatment for Al-4.4Cu-1.5Mg-0.15Zr-0.4La alloy is as follows: double stage homogenization treatment 350 鈩，

本文編號(hào)：2354632