Optimizing microstructures of hypereutectic Al-Si alloys with high Fe content via spray forming technique
Optimizing microstructures of hypereutectic Al-Si alloys with high Fe content via spray forming technique
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DOI：
10.1016/j.msea.2010.06.066
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发表时间：
2010-09-15
期刊：
影响因子：
6.4
通讯作者：
Zhang, J. S.
中科院分区：
文献类型：
--
作者：
Hou, L. G.;Cui, C.;Zhang, J. S.
采用喷射成形技术制备了含铁过共晶Al-Si合金，研究了不同Mn/Cr加入量对合金组织的影响。结果表明，在喷射成形Al-25Si-5Fe-3Cu(wt.%)合金中分别加入2wt.%的Mn/Cr能显著细化Al-25Si-5Fe-3Cu(wt.%)合金中的含铁相，形成大量细小、分布均匀的颗粒状α-Al(Fe，Mn/Cr)Si相，其中以铬的细化效果更好。但喷射成形Al-Si合金中仍存在一些短片状含铁相。然后，在喷射成形Al-Si合金中加入Mn和Cr，使这些短片状含铁相转变为细小的颗粒状α-Al(Fe，Mn，Cr)Si相，促进了几乎单一的α-Al(Fe，Mn，Cr)Si相的出现。提出了两种机制来解释在凝固过程中α-Al(Fe，Tm)Si相(Tm=Mn/Cr/(Mn+Cr))的形成：(1)在添加Mn/(Mn+Cr)合金中由亚稳的-Al(Fe，Tm)Si相转变；(2)在含铬合金中直接从液态析出。由于不同Tm元素之间的强相互作用和类质同象替代，在添加Mn或(Mn+Cr)合金中，亚稳的8-Al(Fe，Tm)Si相(团)可以从液态析出并转变为稳定的三角洲-Al(Fe，Mn，Cr)Si相。Al-Cr-Si系中不存在亚稳的三元金属间化合物，可以从液态中直接析出稳定的α-Al(Fe，Cr)Si相，并可转变为稳定的α-AlCrSi相。Al液中铬的高偏析温度促进了添加铬合金中铬的微观偏析和(AlCrSi)团簇/金属间化合物的形成。结果表明，添加(Mn+Cr)合金中既存在亚稳的-Al(Fe，Tm)Si相(团)，又存在稳定的α-Al(Fe，Tm)Si相(团)。随着进一步的凝固，这些团簇成为形核中心，并不断长大。在液态合金中，β-Al(Fe，Tm)Si相和α-Al(Fe，Tm)Si相核的共存可导致雾化液滴或颗粒中同时存在这两种相。随着雾化液滴或颗粒的不断沉积，预制体表面糊状区的出现促进了亚稳的-Al(Fe，Tm)Si相向稳定的α-Al(Fe，Tm)Si相的转变，特别是导致了以单一的α-Al(Fe，Tm)Si相为特征的理想情况。结果表明，现有过共晶Al-Si合金热稳定性的提高归因于固相线温度的提高和Tm的加入导致了具有较高溶解温度的颗粒状α-Al(Fe，Tm)Si相的存在。(C)2010爱思唯尔B.V.保留所有权利。
By using spray forming technique Fe-contained hypereutectic Al-Si alloys were prepared with different Mn/Cr additions for the study of their effects on the microstructures. The results show that adding 2 wt.% Mn/Cr separately can strikingly refine the Fe-bearing phase in spray-formed Al-25Si-5Fe-3Cu (wt.%) alloy into quantities of fine, uniformly distributed granular alpha-Al(Fe,Mn/Cr)Si phase, and Cr is more effective. But some short-plate Fe-bearing phases still exist in the spray-formed Al-Si alloys. Then, combined addition of Mn and Cr transforms these short-plate Fe-bearing phases into fine, granular alpha-Al(Fe,Mn,Cr)Si phase, promoting the appearance of almost single alpha-Al(Fe,Mn,Cr)Si phase in the spray-formed Al-Si alloys. Two mechanisms are proposed to elucidate the formation of alpha-Al(Fe,TM)Si phase (TM = Mn/Cr/(Mn+ Cr)) during the solidification process: (1) transformed from metastable delta-Al(Fe,TM)Si phase in Mn/(Mn + Cr)-added alloys or (2) precipitated from liquids directly in Cr-containing alloys. Because the strong interactions and isomorphic substitution among different TM elements, the metastable 8-Al(Fe,TM)Si phase (clusters) can be precipitated from the liquids and transformed into stable delta-Al(Fe,Mn,Cr)Si phase in Mn- or (Mn+Cr)-added alloys. The stable alpha-Al(Fe,Cr)Si phase can precipitate directly from the liquids because no metastable ternary intermetallics exist in Al-Cr-Si system and can be transformed into stable alpha-AlCrSi phase. Also the high segregation temperature of Cr in liquid Al melts promotes the microsegregation of Cr and formation of (AlCrSi)clusters/intermetallics in Cr-added alloys. As a result, both metastable delta-Al(Fe,TM)Si phase (clusters) and stable alpha-Al(Fe,TM)Si phase (clusters) can be present in (Mn + Cr)-added alloys. With further solidification, these clusters become the nucleation sites and grow up unceasingly. The coexistence of the nucleus of delta-Al(Fe,TM)Si and alpha-Al(Fe,TM)Si phases in the liquid alloys can induce the simultaneous presence of these two phases in atomized droplets or particles. With continuous deposition of atomized droplets or particles, the appearance of mushy zone on the surface of preforms promotes the transformation of metastable delta-Al(Fe,TM)Si phase into stable alpha-Al(Fe,TM)Si phase, especially inducing the ideal case featured by single alpha-Al(Fe,TM)Si phase. It is concluded that the improvements of the thermal stability of present hypereutectic Al-Si alloys are attributed to the increment of solidus temperatures and the presence of the granular alpha-Al(Fe,TM)Si phase with high dissolution temperature induced by TM addition. (C) 2010 Elsevier B.V. All rights reserved.