Bi-Sn-In控温易熔合金的设计与性能

Design and properties of Bi-Sn-In ternary fusible alloys

在Bi-Sn、Bi-In、Sn-In二元相图的基础上,设计出系列Bi-Sn-In控温易熔合金,并对合金的熔点、相组成和钎焊接头的力学性能进行了研究。结果表明:低铟含量的Bi-Sn-In合金由Bi、-βSn和InBi相组成;随Sn、In含量的增加,易熔合金的相组成向BiIn、BiIn2和γ(InSn4)转化;合金的固相线、液相线随Bi含量或Bi/In的增大而提高,且当Sn含量(质量分数)为17%时合金的液相线最低;易熔合金的硬度随Bi含量或Bi/In的增加而线性增大,但随Sn含量、In含量的增加而降低;提高合金的Sn含量和Bi/In,可使合金钎焊接头的剪切和抗拉强度得到明显的改善;42.6Bi-17.0Sn-40.4In合金的熔点、熔程和钎焊接头的力学性能与50.0Bi-25.0Pb-2.5Sn-12.5Cd伍德合金相当,符合72℃自动灭火洒水喷头感温元件的要求。

Series of Bi-Sn-In ternary fusible alloys were designed based on Bi-Sn, Bi-In and Sn-In phase diagrams, and the melting temperature, phase composition and mechanical properties of these alloys were measured and determined. The results show that Bi-Sn-In ternary fusible alloy with low content of indium consists of Bi,β-Sn and InBi phases. With increasing content of indium and tin in fusible alloy, the phase components turn to BiIn, BiIn2 and γ （InSn4） phases. The solidus and liquidus of alloys increase linearly with increasing content of bismuth or the ratio of Bi to In, and there is a minimum solidus at 17% Sn（mass fraction）. Fusible alloys with higher content of bismuth or higher ratio of Bi to In have a higher hardness, whereas the contents of indium and tin have opposite effect. Meanwhile the shear and tensile strengths of soldering joints can be improved by the promotion of tin content and the Bi/ In ratio in Bi-Sn-In alloy. The melting temperature and mechanical properties of 42. 6Bi-17. 0Sn-40.4In alloy are comparable to those of 50.0Bi-25.0Pb-12.5Sn-12.5Cd Wood alloy, and can be used as the material for 72 ℃ thermal actuator in automatic sprinkler instead of Wood alloy.