高强铝合金中间相Al2 Cu,Al2 CuMg和MgZn2性能的第一性原理计算

采用第一性原理平面波赝势方法,计算Al-Zn-Mg-Cu系高强铝合金主要中间相Al2 Cu,Al2 CuMg和MgZn2的结合能、形成焓、弹性常数及态密度。计算结果表明：3相结合能按MgZn2>Al2 CuMg>Al2 Cu顺序递减；形成焓按MgZn2>Al2 Cu>Al2 CuMg顺序递减；Al2 Cu具有很高的弹性模量,同时具有一定的塑性,可以作为合金的强化相；Al2 CuMg是典型的脆性相,并表现出明显的各向异性,容易诱导产生裂纹；MgZn2具有良好的塑性,同时熔点较低,是合金的主要强化相；3相中均存在离子键的相互作用,提高了结构稳定性；通过适当降低Cu,Mg含量,提高Zn的含量,有利于生成MgZn2相,进一步提高合金的综合性能。

First-principle Calculations of Mechanical Properties of Al2 Cu,Al2 CuMg and MgZn2 Intermetallics in High Strength Aluminum Alloys

Structural stabilities, mechanical properties and electronic structures of Al2 Cu, Al2 CuMg and MgZn2 intermetallics in Al-Zn-Mg-Cu aluminum alloys were determined from the first-principle calculations by VASP based on the density functional theory. The re-sults show that the cohesive energy ( Ecoh ) decreases in the order MgZn2 > Al2 CuMg > Al2 Cu, whereas the formation enthalpy (ΔH) decreases in the order MgZn2 > Al2 Cu > Al2 CuMg. Al2 Cu can act as a strengthening phase for its ductile and high Young’ s modulus. The Al2 CuMg phase exhibits elastic anisotropy and may act as a crack initiation point. MgZn2 has good plasticity and low melting point, which is the main strengthening phase in the Al-Zn-Mg-Cu aluminum alloys. Metallic bonding mode coexists with a fractional ionic in-teraction in Al2 Cu, Al2 CuMg and MgZn2 , and that improves the structural stability. In order to improve the alloys’ performance fur-ther, the generation of MgZn2 phase should be promoted by increasing Zn content while Mg and Cu contents are decreased properly.