H.C. Liao M. Zhang J.J. Bi K. Ding X. Xi S.Q. Wu
材料科学技术（英文）
Eutectic solidification in near-eutectic Al-13 wt pct Si casting alloys and the effect of trace addition of boron or strontium on it have been investigated using thermal analysis and microstructural characterization. In unmodified alloy, dual eutectic structure has been observed. The coarse eutectic (dendrite-like Al+ coarse Si flakes) is formed above the equilibrium temperature of eutectic (Al+Si) reaction (577°C). The coarse eutectic (CE) grains nucleate from the primary silicon particles formed earlier due to local enrichment of silicon solute and grow in a divorced mode between the dendritic Al phase and large silicon flakes. The fine eutectic (FE) grains nucleate later on other potential sites activated by melt undercooling and grow in coupled-growing mode with the silicon crystals as fine flakes. The formation of the FE grains is favored in the alloys containing boron because of a great number of potential nucleation sites being added from boron-containing particles. Addition of strontium to the alloys restrains completely the formation of primary silicon particles and hence limits the nucleation of the CE. This is because the eutectic point has moved far enough to make the alloy, at this composition (Al-13 wt pct Si), hypo-eutectic. Local cooling rate during solidification has an important influence on competition formation of these two eutectics.
关键词:
Al-Si alloy
,
eutectic
,
solidification
,
dual eutectic grains
,
grain refinement
W.Q. Zhang
,
Q.M. Liu
,
Y.F. Zhu
,
Y.S. Yang and Z.Q. Hu(State Key Laboratory of RSA
,
Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)
金属学报(英文版)
An investigation on electromagnetically-stirred solidification of Al-CuAl2 eutectic system is presented in this paper. With electromagnetic stirring in solidification, structural transition from lamellar to rod-like eutectic has been found in the as-cast structures, and provided strong stirring is applied, proeutectic growth of α-Al phase is enhanced. Moreover, the interphase spacing of eutectic is clearly increased with melt flow intensified. Numerical computation of flow field is also presented, and the effect of stirring on structural formation is discussed.
关键词:
electromagnetic stirring
,
null
,
null
,
null
J. Zhang (Department of Metallurgy
,
University of Science and Technology Beijing
,
Beijing 100083
,
China)
金属学报(英文版)
Based on the facts that cations and anions of molten salts and binary basic oxide solid solutions do not separate from each other as well as that the electric conductivities of mattes are greater than that of salts and basic oxide solid solutions, the calculating models of mass action concentrations for binary and ternary mattes involving eutectic have been formulated. The results of calculation agree well with the values measured;this in turn shows that the calculating models can reftect the structural characteristics of the mattes concerned.
关键词:
matte
,
null
,
null
,
null
刘心刚
,
雷强
,
王莉
,
李相伟
,
钱宝
,
楼琅洪
材料研究学报
通过金相显微镜(OM)、扫描电镜(SEM)和电子探针(EPMA)等手段研究了第三代单晶高温合金DD33在固溶处理过程中组织的演变.结果表明:在第三代单晶高温合金DD33中,枝晶间γ'相在1310℃保温时明显长大,而在1320℃/2 h固溶后完全溶解;(γ+γ')共晶在高于1320℃时显著溶解;MC碳化物在固溶处理过程中发生溶解,由草书体状向颗粒状转变,促进枝晶间y'相的长大;随着固溶温度的提高共晶γ'相中A1、Ta、Cr、Co等元素的偏析加剧,这一现象可能是上坡扩散引起的.
关键词:
金属材料
,
单晶高温合金
,
固溶处理
,
微观组织
,
共晶
