On the strength and strain to failure in particle-reinforced magnesium metal-matrix nanocomposites (Mg MMNCs)

The addition of nanoparticulate (NP) reinforcements to magnesium (Mg)-based materials is considered a promising technique in improving mechanical properties beyond what can be achieved through alloying and grain refinement. In this work, we have comprehensively collected the currently available experimental data for magnesium metal-matrix nanocomposites (Mg MMNCs) and performed analyses to determine the contribution of any Orowan-type strengthening, which is thought to be a primary mechanism in simultaneously improving both strength and ductility. Although studies are numerous, it was found that most of the individual reports in the literature do not provide sufficient data points to make quantitative conclusion on which mechanisms may be active. Of those that do, the analyses show that, in most cases, the enhanced strength can be accounted for by grain refinement and/or dislocation production through mechanical post-processing, such as hot-rolling, with little indication of Orowan strengthening. A comparison with hot-rolled Mg AZ31 alloy specimens demonstrates that the degree of grain refinement in Mg MMNCs is comparable to that achieved by traditional processing routes. In Mg MMNCs with higher yield strength than the AZ31 specimens of comparable grain size, the MMNC typically demonstrated significantly lower ductility indicating that yield strength improvements by mechanical post-processing have resulted in the expected decrease in ductility that accompanies increased dislocation density.