Microstructures refinement and mechanical properties enhancement of aluminum and magnesium alloys by combining distributary-confluence channel process for semisolid slurry preparation with high pressure die-casting
Microstructures refinement and mechanical properties enhancement of aluminum and magnesium alloys by combining distributary-confluence channel process for semisolid slurry preparation with high pressure die-casting
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DOI：
10.1016/j.jmatprotec.2020.116800
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发表时间：
2020-11-01
影响因子：
6.3
通讯作者：
Chen, Junchen
中科院分区：
文献类型：
--
作者：
Qi, Mingfan;Kang, Yonglin;Chen, Junchen
开发了一种简单高效的半固态浆料制备技术，称为分流汇流通道（DCC），用于制备高质量的铝和镁合金半固态浆料。 DCC工艺与高压压铸（HPDC）机的使用相结合，成功实现了近净成形，并通过流变高压压铸（Rheo-HPDC）对各种铝和镁合金铸件实施了生产应用。通过数值模拟研究了采用 DCC 技术制备浆料过程中熔体流动状态和物理场的变化。讨论了DCC过程中初生晶粒的形核机制和长大规律。研究了 DCC Rheo-HPDC 制备的铝镁合金的显微组织、孔隙率和力学性能。结果表明，通过DCC可以制备出含有大量平均尺寸<50μm、形状因子>0.8且均匀分散在液体基质中的初级颗粒的半固体浆料。模拟结果表明，熔体在 DCC 的上部和下部表现出相反的速度矢量。而且在汇合处相遇碰撞产生对流，有利于获得均匀的熔体温度、成分场、晶核剥落和球状生长。随机颗粒跟踪模拟结果表明，DCC工艺改善了浆料的成分场。 DCC工艺通过使用多通道激冷和增加成核面积来促进熔体成核。熔体流动过程中产生的自搅拌使熔体内部产生大量的自由核。球形初生晶粒的形成背后存在两种主要机制。一是爆炸成核和球状生长的机制，二是枝晶臂颈缩、熔融、晶粒成熟和圆化的机制。此外，通过比较传统 HPDC 和其他 Rheo-HPDC 工艺生产的相同合金铸件，DCC Rheo-HPDC 铸件具有更细、更圆的晶粒、更低的孔隙率和更高的机械性能。
A simple and efficient semisolid slurry preparation technique, called distributary-confluence channel (DCC), was developed to prepare high-quality semisolid slurries of aluminum and magnesium alloys. The DCC process was coupled with the use of a high pressure die-casting (HPDC) machine to successfully achieve near-net forming and implement production applications with rheological high pressure die-casting (Rheo-HPDC) for various Al and Mg alloy castings. The changes in the flow state and in the physical field of the melt during the slurry preparation via the DCC technique were investigated by numerical simulations. The nucleation mechanism and the growth law of the primary grain during the DCC process were discussed. The microstructures, porosities, and mechanical properties of the aluminum and magnesium alloys prepared via DCC Rheo-HPDC were studied. The results show that semisolid slurries containing a large amount of primary grains with an average size < 50 mu m, a shape factor > 0.8, and uniformly dispersed in the liquid matrix can be prepared via DCC. The simulation results indicate that the melt exhibits opposite velocity vectors on the upper part and on the lower part of the DCC. Moreover, it encounters and collides at the confluence to generate convection, which is beneficial to obtain uniform melt temperature, composition fields, nuclei exfoliation, and spherical growth. The random particle tracking simulation results show that the DCC process improves the composition field of the slurry. The DCC process facilitates the melt nucleation by using multi-channel chilling and increasing the nucleation area. The self-stirring generated during the flow of the melt produces a large amount of free nuclei inside the melt. There exist two main mechanisms behind the formation of the spherical primary grains. The one is the mechanism of explosive nucleation and spheroidal growth, the other is the dendrite arm necking, fusing, grain ripening, and rounding. Furthermore, by comparing identical alloy castings produced via traditional HPDC and other Rheo-HPDC processes, the DCC Rheo-HPDC castings present finer and rounder grains, a lower porosity, and more performant mechanical properties.