【作者】 孙克庆；

【导师】 司乃潮；

【作者基本信息】 江苏大学 ， 材料加工工程， 2005， 硕士

【摘要】 本文在大量试验的基础上建立了Al-Cu合金熔体结构物理模型,研究了熔体过热处理对Al-Cu合金熔体结构的影响;在温度梯度、抽拉速率一定的条件下,研究了熔体过热处理（熔体过热温度T_s、熔体过热时间ts和低温保持时间t_h）对Al-4.7%Cu合金定向凝固组织形态及一次枝晶间距的影响;在电子万能试验机上测出经不同过热处理后定向凝固试样的应力—应变曲线;用扫描电镜分析了Al-4.7%Cu合金定向凝固试样拉伸后的断口形貌;用XRD分析了不同熔体过热处理定向凝固的晶体取向;探讨了熔体过热处理影响最终组织、性能及晶体取向的内在机制,以期能够丰富凝固理论、指导生产实践。 研究结果表明:Al-Cu合金过热熔体不可逆微观不均匀区主要包括不可逆类固型原子团簇、可逆类固型原子团簇、可逆类液型原子团簇和短程序;Al-Cu合金熔体过热处理会使熔体结构状态发生不可逆变化,使熔体的结构敏感物性参数如粘滞系数η和溶质扩散系数D_L出现滞后效应表现出滞回现象,并使形核过冷度ΔT增加;熔体过热处理对Al-4.7%Cu合金定向凝固组织及力学性能有显著影响,经过950℃和1050℃过热处理的一次枝晶间距λ₁比在750℃无过热直接定向凝固的减小了30%以上;Al-4.7%Cu合金非定向凝固试样失效形式为脆性断裂,而经不同熔体过热处理后Al-4.7%Cu合金定向凝固试样失效形式则表现为韧性断裂,定向凝固试样力学性能比非定向凝固的要好,强度提高了近60%,延伸率提高了近一倍;通过熔体过热处理的Al-4.7%Cu合金定向凝固试样,其富Cu相明显减少,韧窝数量显著增加;Al-4.7%Cu合金枝晶沿择优方向<100>生长,而且随着熔体过热温度的提高,（100）晶面衍射强度减弱,表明晶面取向产生分支现象;熔体过热处理之所以对Al-4.7%Cu合金定向凝固组织、力学性能及晶体取向有显著影响,是因为熔体过热处理改变了熔体的结构状态,液态金属结构的改变直接影响了最终的组织、性能及晶体取向。更多还原

【Abstract】 Firstly, the physical models of Al-Cu based alloy melts were put forward through many experiments, and then the paper studied the influence of melt superheat treatment on Al-Cu alloy melt. Under the constant given conditions of technological parameters, as thermal gradient, withdraw velocity, etc; the influence of melt superheat treatment （including superheating temperature T_s, superheating time t_s, and low temperature holding time t_h） on the solidification microstructure and the primary dendrite arm spacing of directionally solidified Al-4.7%Cu alloy was studied. The stress-strain curves of directionally solidified specimens after different superheat treatment were measured by electronic universal material tester, their fracture morphology was analyzed by SEM and their crystal orientation was analyzed by XRD. We discussed the inner mechanism of the influence of melt superheat treatment on solidification structure, property and crystal orientation in order to enrich solidification theory and instruct practice.The result shows that the heterogeneous phenomenon of irreversible solid-like clusters, reversible solid-like clusters, reversible liquid-like clusters and short procedure may be present simultaneously in the Al-Cu alloy melts. The superheat treatment of Al-Cu alloy can make melt configuration state change irreversibly, the sensitive material property parameter such as viscous coefficient η and solute diffusion coefficient D_L shows hysteresis effect and crystallization undercooling △T. decreases. The melt superheat treatment can influence the directionally solidified structure and mechanical property obviously, the primary dendrite arm spacing λ₁ of the sample treated by superheat temperature 950℃ and 1050℃ decreases by more 30% than that of the sample treated by superheat temperature 750℃. The inactivation form of Al-4.7%Cu alloy sample that is not directional solidification is brittle fraction while that of directionally solidified Al-4.7%Cu alloy sample treated by different superheat treatment is tough fracture. The mechanics property of directionally solidified sample is better than that of none directionally solidified sample, the strength of the former increases by 60% and the elongation increases by nearly 100%. The directionally solidified Al-4.7%Cu alloy sample after treated by superheat treatment, its Cu-rich phase decreases obviously and its dimple number increasesobviously. The dendrites of Al-4.7%Cu alloy grow along with preferred orientation <100>. The diffraction intension of crystal face （100） lowers with the increase of superheat temperature, which shows that the branches of the crystal face orientation happen. The reason why superheat treatment can influence the microstructure, mechanics property and crystal orientation obviously is that superheat treatment changes the melt structure state and the change of the liquid metal structure is response to the influence.更多还原