Hot-pressing Sintering Of Laves Phase Mg(Cu_1-xAl_x)₂ And Investigation Of Its Properties

Laves phase inter-metallic compounds make it as a new type of structural materials and functional materials for their unique properties.But the Laves phase inter-metallic compounds are brittle at room temperature,this limits its development. The method of alloying may resolve the brittleness of Laves phase,raise the stability and influence the mechanical property of Laves phase.However,the theory of Laves lattice distortion,the character of combination bond,microstructure and properties had made little progress about Laves phase.Therefore,it is necessary to study this issue in system.In this paper,this major work of study is the Cu atoms in the MgCu₂ effect the microstructure and properties of Laves phase,further reveals the fact alloying effects the properties of Laves phase by use of the crystallology and alloy electron theory.The working process,microstructure and mechanical property of the test materials were measured.The primary content as follows was obtained.1.The MgCu₂ type Laves phase Mg(Cu_1-xAl_x)₂ were prepared by the method of mechanical activation combining with vacuum sintering and the product were analyzed. In addition of Al,the crystal structure was not changed,and the main phase was the C15 structure(MgCu₂ type) Laves phase.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.2.The C15 struture Laves phase Mg(Cu_1-xAl_x)₂(x=0,0.15,0.25,0.35) were prepared by the method of mechanical activation combining with hot pressing.By the increasing of Al content,the lattice constant and angular shift to lower angles of the total diffraction peaks increased,the lattice distortion and grain size also increased,the hardness and Young's modulus of Laves phase Mg(Cu_1-xAl_x)₂ increased orderly,the density of products also improved,but the compressive strength increased first and then decreased,the numerical value of compressive strength was maximum at x=0.25.The fracture surface of Laves phase Mg(Cu_1-xAl_x)₂ in macrostructure was cleavage brittle fracture.By the increasing of Al content,the fracture surface in microscopy was from cleavage fracture to quasi-cleavage fracture.At the same time, there existed a small amount of toughness-tearing ridge on the fracture surface,the toughness improved.After adding Al element,the corrosion resisting property of the samples reduced. 3.The discussion is that the alloying influnce the various properties of Laves phase Mg(Cu_1-xAl_x)₂.1) By the view of the formation enthalpy in Thermodynamics,the atomic radius ratio effects the formation and stability of Laves phase.By addition of AI element,the equivalence atomic radius ratio is near the 1.225,the 1.225 is the ideal atomic radius ratio;the melting point is higher than that of MgCu₂ Laves phase;the stability improved.2) In the sight of crystal structure analysis,by addition of Al,the state in bond of Laves phase is changed.The covalent bond plays a major role on the mechanical property in C15 struture Laves phase.Adding of Al,the covalent bond energy between Cu-Al are larger than that between Cu-Cu,To some extent there is improved in the mechanical property.3)From the standpoint of electron theory of alloys, the electronic structure of Laves phase is discussed in order to comprehend the relationship between electronic structure and mechanical property.The density of state of MgCu₂ in Fermi level is mainly from the Cu provided d orbit.In the electron density distribution,Cu-Cu atoms form a highly directional covalent bond,its bond energy is much larger than that of Mg-Cu atoms.In addition of Al substituted Cu position,the bond energy between Cu-Al atoms is greater than that between Cu-Cu.So,by the increasing of Al content,the stability of Laves phase is improved,the mechanical properties are enhanced.