Study On The Effect Of Alloying Element For Mg-Al Alloy Mechanical Properties With Valence Electron Theory

It is essential to study the alloying behaviors of alloying elements and discuss the effect on the Mg-Al alloy mechanical properties from the electron level. In this article, on the base of Yu's empirical electron theory of solids and molecules(EET) and Cheng's improved TFD theory, the valence electron structures of solid solution phase,sencond phase and phase interfaces which formed by the main alloying element melting in the Mg-Al alloy are calculated and the relationships between valence electron structures and solid solution strengthen,sencond phase strengthen,interfaces strengthen,grain refinement are analyzed. Main results are given below:1. The valence electron structures of Mg-Al-Y,Mg-Al-Nd solid solution phase are calculated and the microscopic mechanisms on which alloying elements improve the substrate's intensity are pointed out in accoding to the phase structure factor n_A andρ_V^C.2. The valence electron structures of main strengthening phases are calculated and the key network are analyzed. Among the n_A value(valence electron pairs on the strongest bond), the biggest is s_A^Al4Ce =0.69694, the smallest is n_A^Mg₂Ca =0.30245, which are bigger than that ofα-Mg's( nAα?Mg=0.11233). The second phases enormously hinder the dislocation,phase boundary and crystal boundary's movement, which enhancs the alloy intensity.3. A new phase structure factor, the total bond-forming ability in unit volume FV, is defined, by which the total bond-forming ability in a structural unit can be measured and the stability of alloying system can be estimated. Compared the FV value ofγ-Mg17Al12 (γ-Mg17Al12FV =44.22), Al3Nd is the biggest, which enable dislocation movement to be blocked under high temperature condition and is advantageous to improves the high temperature performance of Mg-Al alloy.4. The interface electron structures of Al2Ca(111)//α-Mg( 112 1),Mg2Ca(001)//α-Mg(0001),Mg3Sb2(001)//α-Mg( 101 0),γ-Mg17(Al,Sb)12(110)//α-Mg(0001) are calculated and interface conjunction factor ofρ,Δρ,σare obtained. The interface electronic density contrast formed by strengthening phases and substrate is greater, and the result of interface enhancement and grain refinement is better, which effectively raises the operation temperature of Mg-Al alloy.5. The microscopic mechanisms of grain refinement are preliminarily analyzed, and it can be supposed that earth element enhance bonding strength of atoms Neighbored to it in the liquid state alloy, Which causes its key-formed atom to be unable to participate in other crystal growth processes, and the process itself growing up also slow down because of other atomic fetters. This processes, therefore, increase the substrate's nucleation rate, slow down the crystal growth speed, then refine the grain size.