Phosphorus in Al-Si cast alloys: Thermodynamic prediction of the AlP and eutectic (Si) solidification sequence validated by microstructure and nucleation undercooling data
Phosphorus in Al-Si cast alloys: Thermodynamic prediction of the AlP and eutectic (Si) solidification sequence validated by microstructure and nucleation undercooling data
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DOI：
10.1016/j.actamat.2014.02.042
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发表时间：
2014-06-15
期刊：
影响因子：
9.4
通讯作者：
Schmid-Fetzer, Rainer
中科院分区：
文献类型：
--
作者：
Liang, Song-Mao;Schmid-Fetzer, Rainer
建立了Al-Si-P三元体系的自洽热力学描述。在此基础上，计算了第一个实验支持的一致Al-Si-P相图。p阈值-排除在共晶（Si）之前形成的强效AlP核-使用正常Scheil和平衡凝固模拟阐述。其定量依赖于合金的Si含量，并从这些热力学计算中预测了一个沉淀序列图，涵盖了与Al-Si铸造合金相关的所有Si和P成分。通过对亚共晶Al-Si合金的独立实验研究，验证了预测图的正确性，并与显微组织观察和过冷量测量结果相吻合。此外，应用约束Scheil凝固模拟技术预测了清洁非均相形核条件下的过冷，所得数据与夹带液滴技术的专门实验观察结果完全一致。即使在极低的p含量和较大的过冷度下，（Si）也不会在初生（Al）上直接成核，而是在清洁条件下由AlP的形成触发。P阈值不是微不足道的，因为对于亚共晶合金，它从0到7.4 ppm P不等，这正好在或低于常规Al-Si铸造合金的商业纯度范围内。(C) 2014材料学报Elsevier Ltd.出版。版权所有。
A self-consistent thermodynamic description of the Al-Si-P ternary system was developed. Based on that, the first consistent and experimentally supported Al-Si-P phase diagram was calculated. The P-threshold - excluding the formation of potent AlP nucleants before eutectic (Si) - was elaborated using both normal Scheil and equilibrium solidification simulation. Its quantitative dependence on the Si content of the alloy was determined and a precipitation sequence map, covering all Si and P compositions relevant for Al-Si cast alloys, was predicted from these thermodynamic calculations. The predicted map was validated by independent experimental studies on hypoeutectic Al-Si alloys and it is in perfect agreement with microstructure observation and undercooling measurements. Moreover, a constrained Scheil solidification simulation technique was applied to predict the undercooling under clean heterogeneous nucleation conditions and these data are in perfect agreement with dedicated experimental observations from the entrained droplet technique. Even for extremely low P-content and large undercooling the direct nucleation of (Si) on primary (Al) does not occur but is triggered by the formation of AlP under clean conditions. The P-threshold is not trivial since it varies from zero to 7.4 ppm P for hypoeutectic alloys, which is just in or below the commercial purity range of regular Al-Si cast alloys. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.