【作者】 苑玉婷；

【导师】 徐瑞；

【作者基本信息】 燕山大学 ， 材料学， 2011， 硕士

【摘要】 目前,人们对凝固理论的研究大多集中于以二元铝合金为材料的定向凝固,而对于三元或多元铝合金定向凝固的研究却一直很少有人触及。因此,本文选取Al-Cu-Ni三元合金进行下拉式定向凝固,从而研究原始组织和定向凝固组织相组成以及形貌变化的情况。实验选取的合金成分为:Al-18 wt%Cu-5 wt%Ni。将熔炼后的Al-Cu-Ni三元合金进行定向凝固,选取的温度梯度为5 K/mm,下拉速率分别为1 mm/min、5 mm/min、10 mm/min、20 mm/min。利用金相显微镜、高分辨冷场发射、X射线衍射等方法初步了解了该Al-Cu-Ni三元合金原始铸态组织的形貌以及横纵截面的相组成情况。利用Material-Studio模拟软件结合X射线衍射分析结果最终确定该Al-Cu-Ni三元合金生成的三元相,而且准确得出各生成相的晶体结构。利用差热分析、高分辨冷场发射、能谱分析、X射线衍射等方法初步确定了到该Al-Cu-Ni三元合金定向凝固的生成相及其元素组成,又进一步确定了该Al-Cu-Ni三元合金生成相晶体的择优取向。本实验还详细分析了下拉速率对该Al-Cu-Ni三元合金定向凝固组织形貌的影响。利用金相显微镜和高分辨冷场发射对定向凝固试样的横纵截面进行低、高倍的组织形貌观察,结果发现,该Al-Cu-Ni三元合金定向凝固后组织获得了统一的生长方向即热流方向。在温度梯度相同时,随着下拉速率的增加,凝固组织排列越均匀有序,组织实现了由胞状晶向柱状晶转变,且组织越来越细密。更多还原

【Abstract】 Nowadays, the investigation of the solidification theory is mainly focused on the directional solidification which is based on binary aluminous alloy. But the researcher rarely studied the directional solidification of ternary or multiple aluminum alloys. In this paper, ternary Al-Cu-Ni alloy was chosen with down-drawing directional solidification. We studied the effects of different down-drawing rate on the directionally solidified microstructure.The alloy composition selected was Al-18wt%Cu-5wt%Ni. The temperature gradient which was the experiment conditions of directionally solidified Al-Cu-Ni alloy after smelted was 5 K/mm. The down-drawing rates were 1 mm/min, 5 mm/min, 10 mm/min, 20 mm/min. Optical Microscope (OM) and Field Emission Scanning Electron Microscope (FESEM) were used to preliminarily understand the as-cast microstructure and the phase composition of the ternary Al-Cu-Ni alloy on the cross section and the longitudinal section. X-Ray Diffractomer (XRD) which was combined with the method of Material-Studio simulative software was used to eventually determine the ternary phase of the ternary Al-Cu-Ni alloy and conclude the crystal structure of each generating phase. Differential Scanning Calorimeter (DSC), FESEM, Energy Dispersive Spectrdmeter(EDS) and XRD were used to preliminarily determine the generating phases and the element composition of the directionally solidified ternary Al-Cu-Ni alloy and further determine preferred orientation of the crystal in the generating phases.The experiment also detailedly analyzed the effects of different down-drawing rates on the directionally solidifide microstructure. OM and FESEM were used to observe the microstructure on the cross section and the longitudinal section of directionally solidified samples. The results showed that the growth of the microstructrue in the directionally solidified alloy is in the same direction as heat flow. At the same temperature gradient, the array of the directionally solidified microstrutures is more symmetrical and well-regulated with the decrease of down-drawing rates, and the structures are changed from the celluler to the dendrite, and the microstructure is increasingly refined.更多还原