定向凝固ZA35合金组织模拟和实验研究

发布时间：2018-03-21 20:48

本文选题：ZA35合金　切入点：定向凝固　出处：《辽宁工程技术大学》2015年硕士论文　论文类型：学位论文

【摘要】：锌铝合金具有较高的强度和硬度、良好的耐磨性能,工业上现已有部分锌铝合金制作轴承、轴瓦等耐磨材料来替代传统铜合金。然而由于锌铝合金的结晶温度范围较宽,常规铸造条件下存在偏析严重、底缩等缺陷,运用定向凝固技术可获得优良柱状单晶或多晶组织,能有效改善锌铝合金的力学和物理性能。微观组织数值模拟技术能在晶粒尺度上对溶质分部、晶体形貌、晶粒形核,长大等过程予以模拟研究,进而预测晶粒微观组织的特征。本文采用元胞自动机模型(Cellular Automata)与有限元方法(Finite element method)耦合起来建立的宏观-微观计算的CAFE方法对ZA35合金定向凝固过程进行了微观组织模拟。本文建立了定向凝固下柱状晶向等轴晶转化模型,并通过提高熔炼温度,使固液界面前沿液相处于过热状态,有效抑制了等轴晶的形成,促进了柱状晶的生长,熔炼温度过高会导致羽毛状组织的形成。探讨了模拟过程中铸件凝固端传热系数不同,及抽拉速率不同对定向凝固组织的影响。模拟结果表明：随着传热系数增加,冷却速率加快,铸件激冷区面积增加,中间过渡区面积减小,较快进入稳定期。随着抽拉速度增加,二次枝晶臂间距减小,中间过渡区面积相应减少。采用自制Bridgman水平定向凝固装置进行ZA35合金定向凝固实验,表明随抽拉速率增加,二次枝晶臂间距减小,随磁感应强度增加,二次枝晶粗化加剧。实验结果与模拟结果相符。
[Abstract]:Zn-Al alloy has high strength and hardness and good wear resistance. Some of Zn-Al alloy have been used to make bearing, bearing, bearing and other wear-resistant materials to replace the traditional copper alloy. However, because of the wide crystallization temperature range of Zn-Al alloy, Under conventional casting conditions, there are some defects such as serious segregation and bottom shrinkage. Good columnar single crystal or polycrystalline structure can be obtained by directional solidification technique. The numerical simulation technique of microstructure can simulate the solute distribution, crystal morphology, nucleation and growth of zinc aluminum alloy on the grain scale, which can effectively improve the mechanical and physical properties of Zn-Al alloy. Cellular Automata (CA) coupled with finite element method (finite element method) was used to calculate the microstructure of ZA35 alloy by CAFE method. The transformation model of columnar crystal to equiaxed grain under directional solidification is established. By increasing the melting temperature, the liquid phase at the front of the solid-liquid interface is in an overheated state, which effectively inhibits the formation of equiaxed crystals and promotes the growth of columnar crystals. Too high melting temperature will lead to the formation of feathered microstructure. The effects of different heat transfer coefficient at solidification end of casting and different pulling rate on directional solidification microstructure are discussed in this paper. The simulation results show that the heat transfer coefficient increases with the increase of heat transfer coefficient. With the increase of the cooling rate, the area of the quench zone increases, the area of the intermediate transition region decreases, and the area of the intermediate transition zone decreases, and the secondary dendrite arm spacing decreases with the increase of the pull-out speed. The area of intermediate transition zone is reduced correspondingly. The experiments of directional solidification of ZA35 alloy with self-made Bridgman horizontal directional solidification device show that with the increase of pulling rate, the secondary dendritic arm spacing decreases and the magnetic induction intensity increases. The secondary dendrite coarsening is aggravated. The experimental results are in agreement with the simulation results.
【学位授予单位】：辽宁工程技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.13

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