Zn对Sn-Pb-Ag合金中Ag富集规律的影响

Effect of Zn addition on enrichment of silver in Sn-Pb-Ag alloy

以Sn-36.6%Pb-1%Ag为研究对象,采用扫描电子显微镜(SEM)、X线能谱仪(EDS)和化学成分分析等手段,对Sn-Pb-Ag中加入Zn后Ag与Sn,Zn反应的热力学、浮渣含银量及Ag-Zn化合物的组成、形貌及分布进行研究。研究结果表明:Ag更易与Zn生成Ag-Zn金属间化合物;浮渣含银低于1%(质量分数);体系上部、中部和底部均存在3种金相:富锡相(Sn-12.21%Pb-0.52%Ag-2.42%Zn)、富铅相(Pb-31.34%Sn-1.89%Zn)和Ag-Zn化合物相(Zn-27.30%Ag-10.87%Sn-3.70%Pb),Ag-Zn化合物相不发生偏析,且体系中不存在分层区域。原因可能是Sn-36.6%Pb-1%Ag的密度仅比Ag-Zn化合物密度大0.35 g/cm^3;Sn-36.6%Pb-1%Ag为富锡基体系,富锡基中不存在双液相分层区。但是在Sn-Pb-Ag体系中加入Pb,不仅能增大体系的密度,当铅的质量分数大于60%时液相将存在双液相分层区,使得加锌富集Sn-Pb-Ag中的银成为可能。

The reaction thermodynamic of Ag and Sn or Zn, the mass fraction of Ag in the dross, and the composition, microstructure and distribution of Ag-Zn intermetallic compound（IMC） were studied by using scanning electron microscope（SEM）, energy dispersive spectrometer（EDS） and chemical composition analysis when Zn was added into the Sn-36.6%Pb-1%Ag（mass fraction） system. The results show that the formation of Ag-Zn IMC is easier than that of Ag-Sn IMC. The content of Ag in the dross is less than 1%. There are three phase regions, which are rich Sn region（Sn-12.21%Pb-0.52%Ag-2.42%Zn）, rich Pb region（Pb-31.34%Sn-1.89%Zn） and Ag-Zn IMC region（Zn-27.30%Ag-10.87%Sn-3.7%Pb）. The three phase regions are distributed in the top, middle and bottom of the system, and they are not layered. No segregation of Ag-Zn IMC region can be seen in the system. The reasons for these phenomena can be attributed to the fact that the density of Sn-36.6%Pb-1%Ag is only 0.35 g/cm^3 larger than that of Ag-Zn IMC, and that Sn-36.6%Pb-1%Ag is rich tin-based system in which dual-phase stratified region could not exist. Nevertheless, when thePb was added into the Sn-Pb-Ag system, the density of system increased, and dual-phase stratified region occurred in liquid phase when the mass fraction of Pb was more than 60%, which made it possible to enrich Ag by adding Zn into the Sn-Pb-Ag alloy.