流动条件对Pb-Sn合金定向凝固过程雀斑形成的作用  

Effects of Flow on the Freckle Formation in Directionally Solidified Pb-Sn Alloys

作　　者：尚金金[1] 沈军[1] 王灵水[1] 刘林[1] 

机构地区：[1]西北工业大学凝固技术国家重点实验室,陕西西安710072

出　　处：《铸造技术》2010年第7期877-881,共5页Foundry Technology

基　　金：国家自然科学基金No.50827102;凝固技术国家重点实验室项目No.28-TP-2009的资助

摘　　要：研究了不同流动条件下Pb-Sn合金进行定向凝固时,试样中雀斑的形成特征。结果表明:在温度梯度为57 K/cm,抽拉速率为6μm/s的条件下,石墨套厚度为15 mm时,在直径为7、12和20 mm的3种试样出现了中心雀斑;石墨套厚度为10 mm时,直径7 mm和12 mm的试样出现边缘雀斑,直径20 mm试样仍然是中心雀斑;在石墨套厚度为5 mm时全部试样均未出现雀斑;这说明强自然对流条件下试样中易出现大的中心雀斑;当加入弱强迫对流后,尺寸大的中心雀斑消失,而出现少量的边缘雀斑;在加入较强的强迫对流后,所有雀斑消失。The freckle formations under different fluid flow during directional solidification of Pb-Sn alloys were investigated. The results show that, the central-freckles appeared in samples 07, o12, 020 respectively, which were under the conditions with 57 K/cm in temperature gradient, 6 um/s in velocity, 15 mm in the thickness of graphite heater. While the thickness of graphite heater changed to o10, results were different-the central-freckles appeared in sample 020 while edge-freckles appeared in sample 07 and sample o12. Furthermore, those freckles disappeared while the thickness of the graphite heater changed to 5 mm. It is concluded that, central-freckles would form with strong natural-convection, while few edge-freckles would emerge with the disappearance of big central-freckles under weak forced-flow. Moreover, all these freckles would disappear completely with strong forced-flow.

关 键 词：Pb—Sn合金 定向凝固 流动 雀斑 

分 类 号：TG244[金属学及工艺—铸造]