Sn-6Bi合金熔体结构转变对凝固组织的影响

Melt Structure Changes of Sn-6Bi Alloy and its Effects on the Solidification Behavior and Microstructure

通过研究Sn-6Bi合金熔体电阻率随温度的变化规律,发现在不同的温度区间合金发生了两种不同类型的液液结构转变,即高温阶段(890～1095℃)不可逆转变和低温阶段(645℃)的可逆液液结构转变。分析认为可逆的液液结构转变是由四面体结构的Sn-Sn共价键团簇的打破和重聚引起的,而不可逆液液结构转变是由(Bi)n原子集团、亚稳态的Sn原子团簇引起的。根据这一结果进行凝固试验,发现当熔体经历过温度诱导结构转变后会使凝固过冷度增大,凝固时间延长,凝固过程中释放的凝固潜热略微减少,凝固组织明显细化。

Through investigating electric resistivity-temperature curves of Sn-6Bi alloy melt,two kinds of liquid-liquid structure transition（LLST） were irreversible LLST at high temperature stage（890~1 095 ℃） and reversible LLST at low temperature（645 ℃） were observed at different temperature zone.The irreversible LLST is attributed to the transition of metastable Sn SROs and（Bi）n SROs,while the tetrahedral Sn-Sn SROs can be broken or dissolved into smaller ones during heating cycle,and to be rebuilt during subsequent cooling process,which is responsible for the reversible LLST.Based on the observation,the solidification experiments were carried out.With the melt experienced LLST from temperature induction,the solidification undercooling is increased,and solidified time is postponed with the slightly decrease of solidification latent heat,refining evidently solidification microstructure.