La对Al-Cu-Mg合金组织性能及热裂影响
发布时间：2018-11-24 18:44
【摘要】：Al-Cu-Mg系合金在室温和高温下都具有良好的综合性能,一直备受瞩目。但由于Al-Cu-Mg系合金热裂倾向严重,一直限制其在工业生产上的应用和发展。为降低Al-Cu-Mg系合金的热裂倾向,国内外的学者们分别从不同方面进行了许多实验探索。研究表明稀土元素能有效降低Al-Cu-Mg系合金的热裂倾向。本文通过研究稀土元素La对Al-4.4Cu-1.5Mg-0.15Zr合金热裂倾向的影响,并针对热裂的形成机理,探讨La元素的作用机制。通过临界直径法和热敏感系数来表征合金的热裂倾向。研究表明,随着La元素的加入合金的晶粒尺寸呈先减小后增加的趋势,未添加La元素时,合金晶粒表现为粗大的树枝晶,晶界处有连续粗大的网格状第二相分布;当La元素加入量为0.4%时,合金的晶粒形态变为等轴晶,晶界处的粗大网格状第二相开始变得不连续,有亮白色新相生成。对于Al-4.4Cu-1.5Mg-0.15Zr-xLa合金,其热敏感系数Hsc随La元素的加入呈先减小后增加的趋势。未添加La元素时,合金的热裂倾向最高,热敏感系数为1.64;当La元素加入量为0.4%时,合金的热裂倾向最低,热敏感系数为1.05。三种热裂纹形成机理即晶间搭桥理论、液膜理论和凝固补偿理论对于Al-4.4Cu-1.5Mg-0.15Zr-xLa合金同时存在。当稀土元素La加入量小于0.3%时,合金的热裂机理主要为晶间搭桥理论;当稀土元素La加入量大于等于0.3%时,合金的热裂机理主要为液膜理论和凝固收缩补偿理论共同作用。对于Al-4.4Cu-1.5Mg-0.15Zr-xLa合金的热裂抗性,最优La元素的加入量为0.4%。此时,相比于未添加La元素的Al-4.4Cu-1.5Mg-0.15Zr合金,其抗拉强度从173MPa增加到258MPa,伸长率由7.3%增加到8.6%。为改善Al-4.4Cu-1.5Mg-0.15Zr-0.4La合金的综合力学性能,扩大其在实际生产中的应用,本文对Al-4.4Cu-1.5Mg-0.15Zr-0.4La合金热处理工艺进行探究。研究了双极均匀化处理工艺、固溶时间和时效时间对合金组织性能的影响。结果表明,对于Al-4.4Cu-1.5Mg-0.15Zr-0.4La合金的最优热处理工艺为:双级均匀化处理350℃×8h+480℃×16h,固溶处理490±2℃×80min,然后185℃±2℃×12h人工时效处理。合金经热处理后抗拉强度和硬度都大幅度增加,分别由258MPa增加到498MPa、85HV增加到164HV,但合金的伸长率有所下降,从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，
本文编号：2354632
[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，
本文编号：2354632
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