The Research On Grain Refinement And Mechanism Of Pure Tin

Grain refining can improve the strength of material, at the same time can significantlyimprove its mechanical properties, so make it the most important and basic method to controlthe organization of metal materials.The grain refining is essential process in production process of many metals and alloys,especially in aluminum and its alloy. But there is no satisfactory theory model about themechanism of the grain refining. Our research is adding particleTiB₂, TiC, Cu powder, CeO₂directly to the pure tin, contrasting and analyzing the change of grain size in different amountof additives, discussing mechanism of grain refinement. Take it a model to study the refiningmechanism, to explore the intercommunity of refining by adding various refining agent, andprovide the theory basis for preparation of agent and refinement process.The results show that, adding TiB₂and TiC powder directly into molten pure tin has acertain degree of refinement, but the effect is not stable and efficiency is not high. Pressingdifferent amount of TiC, TiB₂, Cu powder, CeO₂with the pure tin powder into piecesrespectively, then smelting, the result is that pure tin have different levels of refined effect.For the first three refining agent, refining effect unceasingly strengthens with the increasedaddition amount. When the amount of TiC is0.8%, the grain size of pure tin reduced from135μm to43μm; the amount of TiB₂is0.6%, the grain size reduced to57μm.When theamount of Cu powder is0.8%, it decreases from225μm to80μm. CeO₂also has refined effect,but different from the former, when the amount is0.4%, the average grain size reduced from225μm to171μm, and then with the increased amount, grain size doesn’t decrease. The TiC,TiB₂, CeO₂distributed in grain interior, almost not gathered together in grain boundary. Theyall have high melting point, high stability and can exist in the stability of the melt, as a stableof inhomogeneous nucleation core, promote the crystallization. In addition, the crystalstructure of TiC, CeO₂are close to pure tin. This is helpful for nucleation, but TiB₂is not so,this influences the refined effect.Cu powder distributed in interior and grain boundaries. Thelatter has side effect for grain growth. Cu particles as core, promote nucleation, structuralsimilarity of Cu and Sn and good wetting of Cu contribute to the refining.The main mechanism of grain refining is as flollows: the interface correspondence theory,composition under cooling theory and growth inhibition theory, segregation coefficient theoryand so on. Comprehensive consideration of all theories, analyzing the results of theexperiment qualitatively, but haven’t put a systemic、qualitative and quantitative theoreticalexplanations.