The Preparation And Characterization Of MgCu₂ Type Laves Phase Mg(Cu_1-XAl_X)₂

There is an increasing interest in Laves phase as their excellent physical and chemical properties make them available for potential functional as well as structural applications. Laves phase are classified into the three fundamental structures C14, C15 and C36 which are typified by MgZn₂, MgCu₂ and MgNi₂,respectively. Although they are well known since long, there are still unsolved problems concerning the stability of the respective crystal structures. Some geometric and electronic factors such as the atomic size ratio of the A and B atoms and their valence electron numbers are well known to affect the occurrence of a Laves phase and there exist various simple models based on these factors that aim at a prediction of the stable Laves phase. In addition, deviations from the stoichiometric composition were reported to result in a change of the stable polytype in various systems. The B atoms in the AB₂ were substituted by Al ,Si partially, could improve Structure and stability of Laves phases.In this paper, The majour work of this study is the Cu atoms in the MgCu₂ were substituted by Al partially. the microstructure and property of the test materials were measured. The new opinions as follows were obtained:(1) The mechanochemical effects of 3Cu-2Mg-Al in mechanical milling process are studied with XRD, SEM, and pulverisette5 miller. The result showed that, the crystallite size decreases, the micro strain and effective temperature factor increases, respectively, with the increasing of milling time. The effective temperature factor and micro strain increased with the decreasing of crystallite size, and micro strain increase with the increasing of effective temperature factor. After being milled for 30 hours, the diffraction peak of Mg is vanished completely. when the milling time get 60 hours, the diffraction peak of Al is vanished, also, and the diffraction peak of Cu further broaden, at the same time, its' diffraction angular shift to lower angles. The supersaturated solid solution of Mg and Al in the Cu formed, at this time. 90 hours later, the new phase of Mg₃₂Al₄₇Cu₇ can be found.(2) The AB₂ type Laves Mg(Cu_1-xAl_x)₂(0≤x≤0.35) were prepared by the method of mechanical activation combining with thermal explosion and the products of thermal explosion were analyzed by XRD,EPMA ,SEM and DSC. The result showed that, although the Cu atoms in the MgCu₂ were substituted by Al partially, the structure of the intermetallcs was not changed. And the main phase wasλ₁ phase with a MgCu₂ type structure. At the same time, by the increasing of Al content, the lattice constant and angular shift to lower angles of the total diffraction peaks increased, the compactness improved, the grain size decreases, crystal lattice aberration increased a little. By the increasing of Al content, the melting point ofλ₁ phase present increasing firstly the decreasing later, the melting point of stoichiometric Mg₂Cu₃Al(X=0.25) was about 910℃which was 113℃higher than the counterpart of MgCu₂(about 797℃). This showed that choosing Al of the light and high oxidation resistance as alloying element could make the Laves phase of C15 structure more stable, and could improve various properties of the intermetallics.(3) The Laves Mg(Cu_1-xAl_x)2(x=0, 0. 25) were prepared by the method of mechanical activation combining with hot pressing. Its microstructure and properties were investigated. The result showed that, compared with MgCu₂, compactness improved, hardness and Young's modules increases greatly of C15 Laves phase Mg₂Cu₃Al. Ab initio calculations were performed to calculate the elastic moduli of C15 Laves phase MgCu₂.The calculation was conducted using the method of augmented plane wave plus local orbitals (APW+lo) with the generalized gradient approximation (GGA). The enthalpy of formation for MgCu₂ was obtained by calculating the total energy. The results show that the calculated elastic properties are close to the experimental results.