Al-15wt.%Mg2Si复合材料中二元相的研究

Study in binary phase of Al-15wt.%Mg2Si composite

摘要:

原位内生法制备Al-15wt%Mg₂Si复合材料,其中二元相成分的研究很少,本文通过XRD测试方法,定性和定量的分析材料中的相成分和相含量。利用Reflex模拟Al-Mg-Si系合金的XRD衍射图谱,并与XRD测试结果对比。利用CASTEP中基于密度泛函理论的第一性原理方法,对Al-Mg₂Si复合材料中的Mg₂Si相和Mg₁₇Al₁₂相的平衡晶格常数,热力学参数和弹性性质做了系统的研究,分析两相的稳定性和力学性能。XRD分析结果显示,Al-15wt%Mg₂Si复合材料中仅含有α-Al相和Mg₂Si相,且Mg₂Si相的质量分数为14.9wt.%。模拟与实验中,相同晶面指数的XRD标定值相差很小,实验值验证了模拟值的可靠性。模拟值证实Al-Mg₂Si复合材料中,理论上只形成α-Al相和Mg₂Si相。CASTEP计算结果表明,Al-Mg₂Si复合材料中的Mg₂Si相较Mg₁₇Al₁₂相易于形成,且稳定性较好。Mg₂Si相的弹性模量E,剪切模量G,体模量B均大于Mg₁₇Al₁₂相,Mg₂Si相的力学性能较好,但脆性较大,且塑性较差。

Abstract:

Prepared Al-15wt.%Mg2Si composite by in-situ, little research had been done in binary phase of Al-15wt.%Mg2Si composite. Employed the method of qualitative and quantitative analysis to confirm the phase components and content by XRD test. Simulated the XRD Patten of Al-Mg-Si alloy by Reflex and compared the simulated result with testing result. Lattice constants, thermodynamic parameter and elastic constant of Mg2Si phase and Mg17Al12 phase in Al-Mg2Si composite were investigated by means of first-principle calculations from CASTEP program based on density functional theory, in order to compare the stability and mechanical properties. There are only α-Al phase and Mg2Si phase in Al-15wt.%Mg2Si composite shown in XRD testing result; and the mass fraction of phase Mg2Si is 14.9%. The differences of XRD indices with same crystal plane (h k l) between simulation and test is fractional. Therefore, the simulated result by reflex is reliable. Only α-Al phase and Mg2Si phase are formed in theory shown by simulation. The calculated heats of formation and cohesive energies show that Mg2Si phase is easy to form and the alloying ability is more strong. Mg2Si phase is more stable than Mg17Al12 phase. Elastic modulus (E), shear modulus (G), bulk modulus (B) of Mg2Si phase is better than Mg17Al12 phase. However, the friability of Mg2Si phase is better and the plasticity is lower.