Study On The Law Of Element Migration In The Process Of Tin-based Alloy Smelting And Condensing

At present,the melt condensation method is one of the most effective means to treat solder,tin-lead,Tin-Lead-Bismuth and other alloys.It has the advantages of large capacity,simple operation,high metal recovery and low operating cost.Therefore,this paper mainly focuses on the migration of elements and their thermophysical properties in the process of melting and condensation of tin-based alloys.The process of melting and condensation of tin-based alloys was studied experimentally.The effects of temperature field and number of melting and condensation on the distribution of elements in liquid matrix and solids were investigated.The migration and interaction mechanism of Pb,Sb,Bi,Cu and Ag in tin melt were obtained.The difference of thermophysical properties of tin-based binary alloys with temperature and composition was studied experimentally.The effects of the viscosity and surface tension of tinbased binary alloys on the migration of elements in the process of melting and condensation were obtained.The main conclusions are as follows:(1)The static experiment results of tin-based binary alloy show that the migration direction of Pb and Bi is from high temperature end to low temperature end,and the migration direction of Sb,Cu and Ag is from low temperature end to high temperature end.With the increase of Pb,Bi,Sb,Cu and Ag content,the total migration of Pb,Bi,Sb,Cu and Ag decreased slightly,which reduced the migration rate of the above elements in tin.In the static crystallization experiment of tin-based multi-alloys,Sb,Bi and Ag have no effect on the migration of Pb,but the presence of Pb slows the migration of Ag,Pb and Bi affect the migration of Sb,and Bi is the main factor.In the continuous crystallization experiment of tin-based binary alloy,Pb,Sb,Cu,Ag and Bi all migrated to the vicinity of 232 °C.With the increase of time,the total migration of Pb,Sb,Cu and Ag increased,and As the temperature rises,the migration rate increases.In the continuous crystallization experiment of tin-based multi-alloys,Pb,Sb,Cu and Ag all migrated to the vicinity of 183 °C,Bi migrated to the vicinity of 138 °C,and the migration rate increased with the increase of temperature.(2)The viscosities of Sn-Pb,Sn-Sb and crude tin alloys were measured experimentally.The results show that the Sn-10wt%Pb alloys exhibit structural changes at 400 and 650 ?,resulting in the formation of intermetallic compounds with high melting points,leading to phase transformation of the metal alloys.The structural change temperature nodes of Sn-20wt%Pb alloys are 850 ? and 1150 ?.It shows that Sn and Pb have higher melting points with the increase of Sn content.Intermetallic compounds.The melt structure of Sn-10wt%Sb did not change at 250 ~1250 ?.Sn and Sb existed as metal alloys.(3)The surface tension of Sn-Pb,Sn-Bi,Sn-Sb,Sn-Ag and Sn-Cu binary alloys was calculated by Butler model.The results show that the surface tension of Sn-Pb,Sn-Bi and Sn-Sb binary alloys decreases with the increase of temperature.With the increase of temperature,the disorder degree of elements in the alloy increases,which is conducive to the migration of elements.The surface tension value of Sn-Cu and SnAg binary alloys increases first and then decreases with the increase of temperature.When the molar ratio of Sn to Cu or Ag is greater than 1:1,the surface tension value decreases with the increase of temperature.When the molar ratio of Sn to Cu or Ag is less than 1:1,the surface tension value increases first and then decreases with the increase of temperature.When the molar ratio of Sn to Cu or Ag is close to 1:1,the surface tension value basically remains unchanged.With the increase of copper or silver content,the increasing rate of surface tension increases.Adding copper or silver to tin increases the surface activity of tin.The higher the content of copper or silver,the slower the migration rate of elements.