مورفولوژی mg2si

Although Mg-Si alloys have promising potential applications in various industries, their mechanical properties are challenged by the presence of coarse primary and eutectic Mg2Si particles and their heterogeneous distribution in the microstructure. To address this issue, several methods have been employed to refine the microstructure and improve the mechanical properties. This study examines the effects of equal channel angular pressing on the microstructural evolution and shear strength of an as-cast Mg-2Si alloy. The alloy was initially extruded at 350 °C and then underwent four passes of equal channel angular pressing at 200 °C. Microstructural analysis was conducted using optical and scanning electron microscopy. Shear strength was assessed using the shear punch test. The obtained results indicated that the equal channel angular pressing process led to a more homogeneous distribution of the Mg2Si particles within the microstructure compared to the as-cast alloys, significantly improving the shear strength. In particular, ultimate shear stress  showed a significant increase from 87 MPa in the as-cast condition to 122 MPa after equal channel angular pressing, corresponding to 40 % improvement.

The effect of 0.2, 0.5 and 1.0 wt% Ca additions on the microstructure and creep behavior of an Mg‒6Al‒1Zn‒0.7Si cast alloy was investigated by indentation creep test under constant loads of 5 and 15 N and at temperatures in the range of 448–523 K. The microstructural examination of alloys was conducted using electron microscopy (SEM), and X‒ray diffraction (XRD). Results showed that addition of Ca enhances hardness and the thermal stability of the alloys. It was found that AZ61‒0.7Si‒1.0Ca had the best creep resistance among three tested alloys. The main cause of enhancing mechanical properties of Ca-containing alloys was the change in the morphology of Mg2Si phase from Chinese script to polygonal shape, with formation of CaSi2 and CaMgSi phases. Stress exponents of all alloys showed two different regimes in creep tests. In the low stress regime, n-values of about 4–7 and activation energies of about 95 kJ/mol, introduce pipe-diffusion-controlled dislocation viscous glide as the controlling creep mechanism. In the high stress regime, however, stress exponents of about 11–14 and activation energies of about 135 kJ/mol, suggest that deformation mechanism is dislocation climb with some sort of back stress, similar to those noted in dispersion strengthening alloys.