Effect of bottom blowing argon flow on temperature and solidification of molten metal during casting
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摘要: 采用低熔点Pb18Sn12In21Bi49（质量分数）合金，在不锈钢的锭模中进行浇铸过程底吹氩试验。利用热电偶测定模内不同位置的温度，并采用扫描电镜（SEM）对凝固试样进行铸态相组织观察，研究了浇铸过程底吹氩对合金液温度与合金凝固相组织的影响。试验结果表明，浇铸过程无底吹时，水平方向中心测温点的温度下降很缓慢，浇铸结束后该点的温度骤降到凝固等温平台温度。当浇铸过程底吹氩时，中心点温度以较快的温降速率降低到凝固温度。无底吹氩时，在竖直方向，合金液从下自上依次开始凝固，而底吹氩时，各监测点几乎同时开始凝固。在相同的冷却条件下，浇铸过程底吹氩显著延迟模型下部的开始凝固时间。无底吹氩时检测截面上富Sn相平均直径在2.58 μm，当进行底吹氩时，可以有效改善凝固相组织粒径分布，细化合金铸态相组织，截面上富Sn相平均直径约为1.89～2.20 μm, 较无底吹时降低了26.7%～14.7%。Abstract: The low melting point Pb18Sn12In21Bi49 alloy (mass fraction) in a stainless steel ingot mold during casting with bottom argon blowing was used to investigate the effects of bottom argon blowing on the temperature of the molten alloy and the microstructure of the solidified phase during casting by measuring the temperature at different positions in the mold by thermocouples and observing the microstructure of the solidified phase by scanning electron microscope (SEM). The experimental results showed that the temperature of the central temperature measurement point in the horizontal direction decreased slowly in the casting process without bottom blowing, and the temperature dropped sharply to the isothermal platform temperature after casting. The central point temperature decreased to solidification at a faster drop rate in the casting process with bottom argon blowing. When there was no bottom blowing argon during casting, the liquid alloy was solidified from bottom to top in the vertical direction, while with the bottom argon blowing, the solidification began at all monitoring points almost simultaneously. Under the same cooling conditions, bottom argon blowing noteworthy delayed the solidification start time at the lower part of the model during the casting process. The average diameter of the Sn-rich phase on the detection cross-section was 2.58 μm without bottom argon blowing. In contrast, with bottom argon blowing, the particle size distribution of solidified phase can be effectively improved, the microstructure of as-cast alloy can be refined, and the average diameter of the Sn-rich phase on the cross-section was about 1.89～2.20 μm, which was reduced by 26.7%～14.7% compared with that without bottom blowing.
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图 3 不同底吹流量下水平方向上的温度变化
Figure 3. Variations of temperature at the horizontal direction with different bottom argon flow rates
图 4 不同底吹流量下竖直方向上温度的变化
Figure 4. Variations of temperature at the vertical direction with different bottom argon flow rates
图 5 模型内各监测点的开始凝固时间对比
Figure 5. Comparison of solidification start time at each monitoring point
图 6 不同底吹流量下截面中心处的Bi49 In21Pb18Sn12低熔点合金的背散射图像
图中的黑色相为富Sn相，深灰色区域为InBi相，白色区域为PbBi相
Figure 6. SEM backscattered electron images of Bi49In21Pb18Sn12 low-melting-point alloy at the center of the cross section and bottom gas flow rates
（a）q=0 mL/min；（b）q=120 mL/min；（c）q=200 mL/min；（d）q=300 mL/min
图 7 不同底吹流量下富Sn相的粒径分布与平均直径
Figure 7. Particle size distribution and average diameter of Sn-rich phase with different bottom gas flow rates
表 1 铸模模型的尺寸
Table 1. Main size of casting mold
mm 高度 上部长边 上部短边 底部长边 底部短边 合金液入口直径 230 154 94 114 54 4 
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