Study On Structure And Properties Of Mg₂Si/AZ31 Composite Fabricated By In-Situ Synthesis Technique

Magnesium (Mg) alloys have been recently recerived considerable attention due to their excellent properties such as light weight, high specific strength and stiffness, machinability and recyclability. These advantages make Mg alloy very attractive as structural materials in a wide variety of application, in particular, as components for aeroplanes or vehicles, in which saving weight extremely important. But in many predominant industries, the application of Mg alloy is limited because of the low strength, so to research and develop high strength magnesium alloy materials is the key to widen the application of Mg in aeroplane and vehicle industries. Recently, plenty of technic have been used to fabricate Mg matrix composite including casting, stir casting, squeeze casting, powder metallurgy, and melting infiltration. The Mg matrix composite fabricated by repeated plastic deformation has excellent mechanical properties due to good interface between reinforcement and Mg matrix which was formed by the in-situ solid state reaction. This article investigated the structure and mechanical properties of Mg2Si/AZ31 composite fabricated by repeated plastic deformation; discussed the effect of repeated plastic deformation time and Mg2Si content on the microstructure and mechanical properties; investigated the strengthen mechanism and factors to influence elongation and discussed the in-situ reaction mechanism of Mg+Si→Mg2Si.Mg2Si/AZ31 composite had been fabricated by repeated plastic deformation via solid state reaction and hot extrusion. The composite consists ofα-Mg and Mg2Si, Al and Zn elements existent as solid solute, and slight MgO was found in the composite. Mg2Si phase distributed in the composite homogeneously and the interface between Mg2Si phase and matrix is very good. As the increase of repeated plastic deformation time, the Mg2Si distributed in the composite more homogeneously and the size of Mg2Si decrease significantly.Mg2Si/AZ31 composite fabricated by repeated plastic deformation have excellent properties, and the composite after 200 plastic deformations have greatest properties, the ultimate strength, yield strength and elongation are 367MPa,302MPa and 6.4%, respectively. The composite with 5wt.%Si addition have the great properties among the composite with different Si addition, and the ultimate strength, yield strength and elongation are 345MPa,267MPa and 5.9%, respectively.Following is the strengthen mechanism of Mg2Si/AZ31 composite fabricated by repeated plastic deformation: grain refining by repeated plastic deformation and conventional extrusion; reinforce of Mg2Si reinforcement. The main factors to influence the plasticity including: grain refining; the fragile caused by reinforcement; the reason of the existence of texture.Using non-isothermal methods to calculate the activation energies of Mg+Si→Mg2Si, and using Coats-Redfern Equation to estimate theconversion function. The activation energies is 410.3kJ/mol using Avrami function (A6) g(α) =[-ln(1-α)]1/2 is 410.3kJ/mol. It can be concluded that the non-isothermal reaction is controlled by nucleation and growth process.