Microstructure and mechanical properties of AZ91 polycrystals

Most magnesium alloys have ratios of tensile strength to density and of yield stress to density that are comparable to those of other common structural metals. AZ91 is a typical alloy which can be solution and precipitation heat treated. Mechanical properties depend on thermal treatment i.e. on the microstructure of alloys. Mechanical properties were studied in tension test. Samples were deformed at temperatures from room temperature up to 300 degreesC with the initial strain rate of 8.3 x 10(-5) s(-1). Both the yield stress and the ultimate stress decrease with increasing temperature for temperatures higher than 100 degreesC. Dynamic recrystallisation has been observed at temperatures between 150 and 300 degreesC. Microstructure of deformed samples has been studied by means of optical and scanning electron microscopy. Possible deformation mechanisms and microstructure changes are discussed.