Mechanical properties of AZ91 studied by indentation tests

The present work investigated the microstructure and nanomechanical properties of cast magnesium alloy (AZ91). The microstructural features, particularly the morphology and the distribution of Mg₁₂Al ₁₇ (β phase) precipitates have been studied using electron microscopy, while the nanomechanical properties of the matrix (α-phase) and the β precipitates have been studied using depth sensing nanoindentation technique. The effect of strain rate on the hardness and elastic modulus of the β precipitates has been evaluated. The modulus of the β precipitates has been found to be about 30GPa higher than that of the matrix while the hardness of the β precipitates can be about 3 times of that of the matrix, depending on the loading schemes. The macroscopic strengthening effect caused by the β precipitates will also be discussed in conjunction with the microstructure features.