An Overview of the Effect of Grain Size on Mechanical Properties of Magnesium and Its Alloys

Abstract

Recent studies show significant advances in improving the mechanical properties of magnesium and its alloys. While many papers deal with different alloy compositions, it is apparent that grain size plays a key role in the mechanical behavior of these materials. The ability to produce samples with very fine grain sizes leads to observations of high strength and/or high elongations. There are recent reports of exceptional elongations of over 100% in pure magnesium and a few alloys. These recent findings are critically reviewed in the present study. The experimental data from over 300 papers are collected, and trends between flow stress, elongation, strain rate sensitivity, and grain size are identified. The role of alloy content is examined.The data clearly shows a transition in the flow stress vs. grain size relationship which is attributed to a change in deformation mechanism from twinning controlled in coarse grained to slip controlled in fine and ultrafine grained samples. The slip controlled deformation agrees with the model of grain boundary sliding, which has shown good agreement with multiple metallic materials. It is shown that the elongations display a maximum in the grain size range in which there is a transition in the deformation mechanism. Three strategies are described for achieving high strength, high ductility, and good strength-ductility combination.

An Overview on the Effect of Severe Plastic Deformation on the Performance of Magnesium for Biomedical Applications

“…The effect of grain size on the mechanical properties of magnesium and its alloys has been recently reviewed, and some trends were revealed [ 44 ]. Experimental data on flow stress and elongation from over 300 papers were collected and then plotted as a function of the grain size.…”

“…The experimental data of flow stress of magnesium alloys were also plotted as a function of the elongation in tension to evaluate the strength–ductility relationship [ 44 ]. It was reported that grain refinement improves the mechanical properties of magnesium alloys, leading to a significant expansion of range in flow stress, σ, vs elongation plots.…”

“…This is shown in Figure 9 , in which the data from coarse-grained magnesium ( d > 20 μm) and fine-grained ( d < 2 μm) are plotted with different symbols. Fine-grained magnesium can display higher strength, a better combination of strength and ductility and exceptional ductility compared to their coarse-grained counterparts [ 44 ]. Accordingly, the trends revealed in this analysis show that SPD processing can significantly improve the mechanical properties of magnesium and its alloys due to its ability to promote grain refinement.…”

“… Flow stress and elongation in tension of multiple magnesium alloys plotted as a function of the grain size [ 44 ]. …”

“… Flow stress (σ) of magnesium alloys plotted as a function of the elongation in tension for samples with different grain size ranges [ 44 ]. …”