The effects of the DC and AC magnetic fields on the phase composition, morphology and distribution of the ternary Al-Fe-Si alloy were investigated. The solidification structures of the alloy solidified with and without the application of magnetic fields were confirmed by DSC and structural measurements. The results showed that, Fe/Si ratio plays an important role in determining the reaction type, which in turn affects the phase composition, morphology. As for the alloy with the Fe/Si ratio 1.2, the elongated needle-like Al3Fe phase was the dominant phase in the dendritic regions with the minor amount of Chinese script-like α-AlFeSi. As for the alloy with the Fe/Si ratio 0.2, the Chinese script-like α-AlFeSi was the dominant phase, accompanied with a small amount of needle-like β-AlFeSi and granular Si. In these Al-Fe-Si alloys, the homogeneous distribution of the intermetallics formed in the interdendritic regions was achieved with the application of the DC magnetic field. However, the intermetallic phases were accumulated towards the sample center with the application of the AC magnetic field. This was attributed to the accumulation of the iron-containing cluster and silicon-containing cluster at the melt center. Furthermore, the amount of Chinese script-like α-AlFeSi was increased remarkably in the former alloy under AC magnetic field, while in the latter alloy, the amount of β-AlFeSi and Si was increased under AC magnetic field.
Ban Chunyan, Liu Na, Wang Na, Han Yi, Ba Qixian, Cui Jianzhong Key Laboratory of National Education Ministry for Electromagnetic Processing of Materials, Northeastern University, Shenyang 110004, China
The phase equilibria and compositions in Mg-rich side at 300 ℃ were investigated in Mg-Zn-Ca ternary system through the equilibrated alloy method by using scanning electron microscopy,electron probe microanalysis,X-ray diffraction and transmission electron microscopy.The results show that two ternary compounds T1 and T2 can be in equilibrium with the Mg-based solid solution in Mg-Zn-Ca system.T1 phase is a linear compound with the composition region(molar fraction) of 15% Ca,20.5%-48.9% Zn and balanced Mg at 300 ℃.Its hexagonal structure parameters decrease with increasing Zn content,i.e.a=0.992-0.945 nm,c=1.034-1.003 nm.T2 phase has hexagonal structure with the composition region of 26.4%-28.4% Mg,63.2%-65.5% Zn and 7.1%-8.4% Ca.At 300 ℃,the solubility of Zn in the Mg-based solid solution increases for the addition of Ca,the maximum solubility of Zn is 3.7%.Three-phase fields consisting of--Mg+Mg2Ca+T1,--Mg+T1+T2,--Mg+T2+MgZn and MgZn+T2+Mg2Zn3 exist in the Mg-Zn-Ca system at 300 ℃.
An isothermal section of the Mg-Nd-Gd ternary system at 723 K was established by diffusion triple technique and electron probe microanalysis (EPMA). Mg3Gd and Mg3Nd form a continuous solid solution (Gd,Nd)3Mg, and a continuous solid solution (Gd,Nd)Mg is also formed between MgGd and MgNd. Mg7Gd, Mg5Gd, Mg2Gd, Mg41Nd5, (Gd,Nd)3Mg and (Gd,Nd)Mg are found in the ternary system. In these intermetallic phases, Mg7Gd has been reported to be a metastable phase in previous literatures. The solubilities of Mg, Gd and Nd in all the phases were detected. Furthermore, four three-phase equilibria, α(Mg)+Mg7Gd+Mg41Nd5, Mg7Gd+Mg5Gd+Mg41Nd5, Mg5Gd+Mg41Nd5+(Gd,Nd)3Mg and (Gd,Nd)3Mg+(Gd,Nd)Mg+Mg2Gd, were identified in the isothermal section.
Based on the available experimental data,the Bi-Ni binary system was optimized thermodynamically by the CALPHAD method.The solution phases,including liquid,fcc_A1(Ni) and rhombohedral_A7(Bi),were described as substitutional solution phases,of which the excess Gibbs energies were expressed with the Redlich-Kister polynomial.The intermetallic compound,BiNi,was modeled using three sublattices(Bi)(Ni,Va)(Ni,Va) considering its crystal structure(NiAs-type) and the compatibility of thermodynamic database in the multi-component systems,while Bi3Ni was treated as a stoichiometric compound.Finally,a set of self-consistent thermodynamic parameters formulating the Gibbs energies of various phases in this binary system were obtained.The calculated results are in reasonable agreement with the reported experimental data.
The phase equilibria in Mg-rich corner of Mg-Ca-Gd and Mg-Ca-Nd ternary systems at 400℃ were determined through the equilibrated alloy method by using XRD, SEM, EPMA and DSC. Partial isothermal sections in Mg-rich corner of Mg-Ca-Gd and Mg-Ca-Nd ternary systems at 400 ℃ were constructed from 13 alloys. A three-phase region of a-Mg, Mg41RE5 and Mg2Ca was determined in both ternary systems. It is formed by a similar ternary eutectic reaction L→a-Mg+Mg2Ca+Mg41RE5 at 499.6 ℃ and 505.6 ℃, respectively. It is found that the maximum solubility of Ca in Mg5Gd is 3.68% (molar fraction) and 3% of Gd can be dissolved in Mg2Ca in the Mg-Ca-Gd system at 400 ℃. While in the Mg-Ca-Nd system, the maximum solubility of Ca in Mg41Nd5 is 3.57% and 1.24% of Nd can be dissolved in Mg2Ca at 400 ℃. Other three-phase equilibria existing in Mg-rich corner of Mg-Ca-Gd system are a-Mg+MgsGd+T and MgsGd+Mg2Ca+T and the three-phase equilibrium in Mg-rich corner of Mg-Ca-Nd system is Mg3Nd+Mg2Ca+ Mg41Nd5.