Microstructure and nano-scale mechanical behavior of Mg-Al and Mg-Al-Ca alloys

A regression analysis of the experimental nanoindentation data reveals a linear correlation between the contact stiffness and the penetration depth for all the tested alloys. The established correlations were used to calculate the continuous hardness and the composite modulus. Both the experimental and calculated data show that hardness values exhibit peak load dependence, i.e. indentation size effect (ISE) on all the tested alloys, while composite modulus was insensitive to peak load. Upon reaching a peak value of hardness at the beginning of the indentation test, the hardness of all the tested alloys decreases considerably by six times from around 1.2 to 0.2 GPa with increasing the penetration depth during the course of testing. However, the composite modulus of the alloy is much less dependent on the penetration depth only changing from 35 to 25 GPa during the tests. The comparison of the calculated results with experimental measurements indicates that they are in good agreement.