Microstructure and Mechanical Properties of Mg-x%Zn-(Al) Alloy

The microstructure and mechanical properties of Mg-x%Zn(5%,7%,9%,15% and 20%) binary alloys and Mg-7Zn-4Al alloy were investigated by optical microscope(OM),X-ray diffraction(XRD),scanning electron microscope(SEM) and universal testing machine.The results indicate that the microstructures of Mg-Zn binary alloys consist of α-Mg matrix and Mg7Zn3 on grain boundary.The tensile strength of alloys rises first and descends later with increasing the Zn content,while the elongations gradually decrease.The maximum value of tensile strength is 213.3 MPa with addition of 7% Zn;the tensile strength and elongation are significantly decreased when added more than 9% Zn content.Added 4% Al to Mg-7Zn matrix alloy,the microstructures consist of α-Mg matrix and Mg32(Al,Zn)49 ternary eutectic phase.Compared to Mg-Zn binary,the tensile strength of as-cast Mg-7Zn-4Al alloy has declined,but it is enhanced significantly after heat treatment,the value has increased by 57.8% to 305 MPa.Consequently,the addition of Al to Mg-Zn alloy is beneficial to heat treatment strengthening.