Analysing The Effect Of Element Y、Sn On Mg-Al Alloy Properties By Valence Electron Theory

In this work, we calculate the valence electron structures of solid solution phases、second phases、phase interfaces which formed by the Mg-Al alloy added the Y or Sn alloying element, and calculate the covalence bond energy of second phases on the base of Yu’s solids and molecules empirical electron theory (EET theory). Based on the result, we can analyse the relationships between valence electron structures and solid solution strengthening, second phases strengthening, interface strengthening. Research conclusion is summarized as follows:1. We calculate the valence electron structures, covalence bond energy and the phase structure factor ρvC of pure Mg, α-Mg, Mg-Al-Y. Among the nA value (valence electron pairs on the strongest bond) and Ea value (bond energy on the strongest bond), the biggest value of α-Mg is nAS-S=0.11199and EAS-S=10.47317kJ/mol, the biggest value of Mg-Al-Y is nAS-S=0.11325and EAS-S=10.66495kJ/mol, which are bigger than that of pure Mg(nAMg-Mg=0.10992, EAMg-Mg=10.24306kJ/mol). The ρVC value of α-Mg or Mg-Al-Y is ρVC=65.6806%or ρVC=66.0907%, they are bigger than that of pure Mg(ρVC=65.1100%). According to the phase structure factors of nA、EA and ρVC, we could analyse the microscopic mechanisms on which alloying element improves the Mg substrate’s intensity.2. The valence electron structures, covalence bond energy of second phases Al2Y and Mg2Sn are calculated. The biggest value of Al2Y is nAY-Y=0.39773and EAY-Y=51.47456kJ/mol, the biggest value of Mg2Sn is nAMg-Sn=0.37685and EAMg-Sn=34.06651kJ/mol, which are bigger than that of α-Mg(nAS-S=0.11199, EAS-S=0.47317kJ/mol). The phase of Al2Y or Mg2Sn enormously hinder the dislocation movement of α-Mg, which improves the alloy intensity.3. We calculate the FV value of Al2Y and Mg2Sn. The FV value of Al2Y is FV=103.6748, the FV value of Mg2Sn is FY=46.9049. Comparing with that of γ-Mg17Al12, both of the Fy value of Al2Y and Mg2Sn are greater than γ-Mg17Al12’s(FV=44.22). Al2Y and Mg2Sn can effectively block dislocation movement and the producing of slip under high temperature condition. And they can improve the high temperature creep properties of Mg-A1alloy.4. The interface electron structures of (1121)α-Mg//(111) Al2Y、(0001) α-Mg//(111) Mg2sn are calculated and interface conjunction factors of Δρmin、σ are acquired under the first approximation. Comparing the minimum electron density difference, that of (1121) α-Mg//(111) Al2Y is bigger(Δρmin=148.64%) than that of (0001) α-Mg//(111) Mg2Sn. The interface electron density contrast generated by strengthening phases and substrate is greater, the result of interface enhancement is better and the resistance of grain boundary sliding is bigger, which availably raise the strengthening of Mg-Al alloy. The Δρmin value of (0001) α-Mg//(111) Mg2Sn is Δρmin=7.14%<10%, the a value is σ=1327, which shows great continuity, small interface stress, good interface stability, strong interface bonding in (111) surface of Mg2Sn phase and (0001) surface of α-Mg substrate.