| Higher demand for light weight of components has been proposed in aviation, aerospace, automobile,3C electronic products and other areas on the background of respecting environmental conservation, reducing energy consumption and creating a green earth. Mg-Li alloy is considered as the lightest metal structure material. But the strength and toughness of the Mg-Li alloy are not as high as Al alloy, which greatly limits the application of Mg-Li alloy. Therefore, taking various measures to improve the strength and toughness of the Mg-Li alloys has become the most effective method to promote a very wide application of Mg-Li alloys, while alloying is the most effective method to improve the strength and toughness of the Mg-Li alloys. During many methods on prediction of material's properties and exploration of the experimental mechanism, the first-principle is more and more widespread because it is not dependent on any empirical parameters, but only related to the five basic physical quantities and can ensure the credibility of the calculation results. In this paper, strenghening and toughening mechanisms of alloying elements in Mg-Li-X alloy were studied based on the first-principles. The main contents are as follows. (1) Structural stability and mechanical properties of the two basic phases a and P in Mg-Li binary alloy were studied. The results show that the formation ofβis easier than that of a phase and the thermodynamic and kinetic properties of a phase andβphase are both stable. Solid solution of Li in Mg can help improve the toughness of a phase. The tensile simulation was carried out on the grain boundary and phase boundary models of a andβ. The results show that the solid solution of Li in Mg and the solid solution of Mg in Li both can improve the binding capacity of the interfaces of pure Mg and Li, and increase the bonding strength of the interface of Mg and Li.(2) The results of analysis on the formation enthalphy, bulk modulus and other physical quantities of the solid solution of Al, Zn, Cd dissolved in Mg-Li show that Zn and Cd dissolved in the P phase can improve its strength, and the strengthening effect of Cd is more obvious than that of Zn, furthermore, Al dissolved in theβphase can improve its toughness.(3) The effect of binding capacity of Si, Ge, Ca, Al, Zn, Cd and other alloying elements at the phase boundary and the grain boundary in Mg-Li alloy was studied. The results show that Cd can increase the bonding strength and tensile strength of Mg/Mg interface, and Zn can increase the bonding strength of theα/βphase boundary, while Si, Ge, Al and Ca reduce the binding capacity of theα/βinterface.(4) Bulk modulus, shear modulus and other physical quantities of the intermetallic compounds formed by Al, Zn, Cd, Si, Ge, Ca, Sn, Gd, Y and Mg were studied. The results show that Mg2Si, Mg2Ge, Mg2Sn, MgZn2 and Mg17Al12 have high bulk modulus, shear modulus and Young's modulus, and they all can play a significant precipitation strengthening role in alloy. The modulus descends in the following order: Mg2Si>Mg2Ge> MgZn2>Mg17Al12> Mg2Sn. The ratio of bulk modulus to shear modulus indicates the toughness of Mg3Gd, Mg7Gd, Mg24Y5 and MgZn2 is better, furthermore, the toughness descends in the following order: Mg3Gd>Mg7Gd>Mg24Y5>MgZn2.(5) The comprehensive analyses of the effect of various alloying elements on the strength and toughness of Mg-Li alloy indicate that Mg-Li-Zn-Si-Ge-Cd is a more suitable high-strength Mg-Li alloy and Mg-Li-Al-Gd-Y-Ca could become a lightweight, high strength and superplastic magnesium alloy.
|
PDF Full Text Request