Evolution of near-equiaxed microstructure in the semisolid state
Evolution of near-equiaxed microstructure in the semisolid state
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DOI：
10.1016/s0921-5093(00)00908-4
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发表时间：
2000-09
期刊：
影响因子：
6.4
通讯作者：
E. Tzimas;A. Zavaliangos
中科院分区：
文献类型：
--
作者：
E. Tzimas;A. Zavaliangos
通过快速淬火和等温均热实验，研究了喷射铸造、磁流体力学(MHD)铸造和应力诱导熔体激活(SIMA)工艺制备的近等轴显微组织在半固态短时间内的演化规律。淬火实验揭示了高体积分数和中等体积分数液体的固相形态和分布。在中等液态含量时，喷射铸造和SIMA合金的显微组织由分散的等轴晶均匀弥散分布在液相中，而MHD-铸造合金的组织由不完全球化的颗粒组成。从晶向偏差的角度讨论了半固态中固相连接性和固相骨架的形成。等温浸泡实验研究了半固态浸泡时间和含液量对晶粒长大和球化程度的影响。结果表明，与SIMA和喷射铸造合金相比，即使在半固态保温5min后，MHD铸造组织的等轴化程度也较低。研究还表明，喷射铸造合金的晶粒长大速率小于SIMA合金。还讨论了聚结的作用和合金元素的影响。
The microstructure of alloys with a near-equiaxed microstructure, produced by spray casting, magnetohydrodynamic (MHD) casting and the stress induced, melt activated (SIMA) process, as it evolves within short times in the semisolid state, is examined by rapid quenching and isothermal soaking experiments. Quenching experiments reveal the morphology and distribution of solid phase at high and medium volume fractions of liquid. At medium liquid content, the microstructure of spray-cast and SIMA alloys consists of discrete equiaxed grains uniformly dispersed in the liquid phase, while the corresponding microstructure of MHD-cast alloys exhibits extensive agglomerates consisting of incompletely spheroidized grains. The connectivity of solid phase and the formation of a solid skeleton in the semisolid state are discussed in terms of grain misorientation. Isothermal soaking experiments investigated grain growth and degree of spheroidization as a function of soaking time and liquid content in the semisolid state. Results demonstrated that MHD-cast microstructures are less equiaxed compared with SIMA and spray-cast alloys even after 5 min of soaking in the semisolid state. It is also shown that the grain growth rate is smaller in spray-cast alloys than in SIMA alloys. The role of coalescence and the effects of alloying elements are also discussed.