Effects of Si on microstructure and mechanical properties of Mg-4Al-1Zn-xSi alloys

Effects of Si content on microstructure and mechanical properties of Mg-4Al-1Zn-xSi(x = 0.5,1.0,2.0,mass%) alloys were investigated by optical microscope(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD) and tensile tests.The results show that the network β-Mg17Al12 phase is continously distributed on grain boundaries for the alloy with higher Si content instead of individual point distribution in the matrix at low Si content.Moreover,the coarse Chinese script type Mg2 Si particles show intergranular and transgranular distribution in the alloy containing higher Si content.The average grain size of α-Mg matrix decreases from 25 μm to10 μm with the increasing of Si content from 0.5% to 2.0%,while the average particles size of Chinese script type Mg2 Si increases from5 μm to 100 μm with the increasing of Si content.The hardness of the alloys increases gradually with increasing of Si content.The ultimate tensile strength,yield strength and elongation of the alloys decreases with increasing content of Si from 0.5% to 1.0% and then increases when increasing Si content to 2.0%.The fracture of the alloy is characterized by quasi-cleavage brittle mode.