【作者】 赵素彦；

【导师】 李荣德；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 本文研究了金属型铸造条件下，Ni、Cr、Mg及Cr和Mg等合金元素对过共晶Al-5％Fe合金组织形态的影响；并对合金元素的作用机理进行了探讨；同时研究了采用液淬技术，过共晶Al-5％Fe二元合金中Al₃Fe相在熔体中的溶解特性。在过共晶Al-5％Fe中加入一定量的Cr后，由于Cr原子在Al₃Fe相中固溶度较大，Cr原子向Al₃Fe相扩散势必会与Fe原子的扩散存在竞争，阻碍Fe原子的扩散，减缓了Al₃Fe相沿择优生长方向的生长，从而使之细化。加入Mg后，Mg在初生相中固溶度很小，在合金熔体结晶凝固的过程中易于在凝固前沿造成Mg的轻微富集，于是在一定程度上抑制了Fe原子向结晶前沿的长程扩散，阻碍了Al₃Fe相在择优方向上的长大。Cr和Mg的加入改变了Al₃Fe的形貌：1)Mg的加入在相的周围富集，造成成分过冷，形成粗糙平面，出现的细小突起易于向过冷区发展，在Al₃Fe相主干的左右方向出现突起，长成鱼骨状；若某些地方Mg不均匀分布，将出现缩颈，严重缩颈将在熔体对流的作用下离开主干，而使得相游离出来变成块状。2)Cr的固溶占据了固液界面的有利位置，降低了Fe原子的沉积几率，阻碍Fe原子的扩散，减缓了Al₃Fe相沿择优生长方向的生长，使未加入合金元素的针状Al₃Fe相不易沿针状方向生长，而横向生长，容易长成鱼骨状。加入Ni后，Ni在Al₃Fe相中大量固溶，且Ni原子在固溶的（Ni原子也需要从液相中扩散过来）同时还会与Fe原子的扩散存在竞争，阻碍Fe原子的扩散，两者都使Al₃Fe相的生长受到了抑制，使得相不能长大从而变得较为细小。采用液淬技术，研究了过共晶Al-5％Fe二元合金中Al₃Fe相在熔体中的溶解特性。本试验最高温度为1000℃小于Al₃Fe的熔点（1147℃），因此在Al₃Fe由针状转变为规则的块状与针点状的过程是溶解过程。随着保温时间的延长，液淬组织由粗大的针片状和针状，转变为大小不一的不规则块状最后转变为细小规则的块状和针点状。保温时间短时，Al₃Fe相比较粗大遗传性比较明显；保温时间越长，Al₃Fe相组织越细小，溶解特性越明显。随着温度的升高，液淬组织由粗大的针状与针片状转变为比较细小的块状与针点状，Al₃Fe相的遗传性逐步减弱。更多还原

【Abstract】 The effects ofNi, Cr, Mg, Cr and Mg on the structure in hypereutectic A1-5%Fe alloy by metal-mould casting were investigated. The mechanisms of these elements on the microstructure in A1-Fe alloys with various contents were also investigated on the base of the experimental results. The hypereuteetic A1-5%Fe alloy, adopted liquid quench technology and Solution characteristics of Al₃Fe phase in molten mass was investigated.Cr was added in hypereutectic A1-5%Fe alloy. Because the solid solubility of Cr atom in Al₃Fe phase is rather large, Cr atom diffused and deposited in Al₃Fe phase will compete with Fe atom in the process of diffusion; these would hinder diffusion of Fe atom down and slow Al₃Fe phase growth in preferred orientation. The solid solubility of Mg atom in Al₃Fe phase is rather minor, which makes Mg enriched in solidifying front edge of molten mass of alloy. So in a given extent, Mg rejects primary phase to grow up in a preferred orientation. When Cr and Mg was combinadly added, pattem of Al₃Fe phase is modified: 1) Mg added isbeneficiated around the phase, and causes, super-cooling and result in coarse interface. Fine tubercle which move into super-cooling area to grow up to herringbone like; If Mg distributs at certain location, necking down would appear. If necking down is severe, this would leave off trunk stem in the effect of melt convection, and make the phase change into block like. 2) The solid solubility of Cr colonizes solid liquid interface favorable position, reduces Fe atom deposition probability and slow up primary phase grow up in preferred orientation. These would make needle-like phase into herringbone like. When Ni is added, the solid solubility of Ni atom in Al₃Fe phase is rather large and at the same time the diffusion of Ni atom compete with Fe, so the diffusion of Fe is rejected. Both aspects reject the growth of Al₃Fe phase, thus make the primary phase finer。The solubility of Al₃Fe in hypereutectic Al-5%Fe alloy melted is researched by liquid quenching technology. The maximum test temperature is 1000℃which is less than the melting point of Al₃Fe （ 1147℃） . So the changing process of Al₃Fe from needle like into regular chunk-like and needle-dot like is a solution process. As the holding time prolongs, the structure of liquid quenching change from coarse needle-sheet like and needle like into irregular chunk like, needle-dot like regular fine chunk-like and needle-dot like in the end. When holding time is short, microstructure is coarser and heredity is more obvious; when holding time is long, the structure of Al₃Fe phase is finer and Solubility is more obvious. As the temperature ascends, microstructure changed from needle-sheet like and needle like into finer chunk like and needle-dot like, the heredity of microstructure weakens step by step.更多还原