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

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

https://www2.nsysu.edu.tw/MSE/research/Two_column.pdf

Recent progress in metallic glasses in Taiwan

The effect of adding Sn to an extruded Mg–8Al–2Zn (AZ82 alloy) was investigated by analyzing its microstructural characteristics before and after extrusion, and by conducting tensile and compressive tests with 2, 4, and 6 wt% Sn addition. This revealed that although second phases formed during solidification are nearly fully dissolved by homogenization treatment in AZ82 alloy with 2 wt% Sn, numerous Mg2Sn particles remain in AZ82 alloys with 4 and 6 wt% Sn due to this concentration being over the solubility limit. All of the extruded alloys were found to have a fully recrystallized structure, yet the addition of 6 wt% Sn created a considerable quantity of large, banded Mg2Sn particles oriented along the extrusion direction. The tensile and compressive yield strength gradually increased with Sn content mainly due to a decrease in the size of recrystallized grains and an increased amount of fine Mg2Sn precipitates, though this came at the expense of a decrease in elongation. It was also found that the ultimate tensile strength improves with Sn addition of up to 4 wt%, but deteriorates beyond that point due to premature fracture caused by crack initiation at large particles.

Influence of Sn addition on the microstructure and mechanical properties of extruded Mg–8Al–2Zn alloy

On the amorphous and nanocrystalline Zr-Cu and Zr-Ti co-sputtered thin films

In this study, a powder metallurgy processing technique combined with rapid microwave sintering was used to synthesise carbon nanotubes (CNTs) filled AZ61 magnesium alloy composites under ambient conditions, without recourse to any secondary process. In order to determine the appropriate amount of CNTs for taking full advantage of the AZ61/CNTs composite, a powder mixture of the CNTs, in varying volume fractions of 1–3%, and the AZ61 alloy was prepared through a mechanical milling process. The optimized milling intensity allowed for reducing the powder size for effective microwave absorption, and thus improved the dispersion of the CNTs in the Mg alloy matrix without reducing the structural integrity of CNTs. In addition to the incorporation of the CNTs with the dual role of mechanical reinforcement and microwave susceptor, microwave sintering was achieved in only 8 min by using a synergetic combination of graphite and silicon carbide as microwave susceptors in a microwave furnace. The sintered samples, whose porosity ranged between 4 and 6%, were characterised for microstructural, hardness, compressive and fracture properties. The results of hardness and compression tests indicated that these properties of all the composites were significantly improved compared to the monolithic samples. The highest microhardness value (∼105% increment) was recorded for the composite with 3.0% volume fraction of CNTs, while the composite sample with 1.0% volume fraction of CNTs had the highest ultimate compressive yield strength and 0.2% offset yield strength with approximate increments of 59% and 127%, respectively. The failure mechanisms of the composites as compared with the monolithic samples were discussed.

Rapid microwave sintering of carbon nanotube-filled AZ61 magnesium alloy composites

The gradual nanocrystallization and amorphization mechanisms in various Zr-X alloys during accumulative roll bonding (ARB) are explored. The effects of strain accumulation, the relative initial hardness of the elemental foils, the enhanced diffusion, and the critical nano size for the sudden transformation from the nanocrystalline phase to the amorphous state are examined. For elemental foils with compatible initial hardness, the nanocrystallization and amorphization rates appear to be higher. The estimated diffusion rates during ARB are higher by several orders of magnitude than the lattice diffusion in bulk materials. When the nano grains are refined down to around 3 nm, sudden transformation into the amorphous phase would occur.

/pdf/nanocrystallization-and-amorphization-mechanisms-in-zr-x-2nnjs5lbs1.pdf

Nanocrystallization and Amorphization Mechanisms in Zr-X Alloys during the ARB Process

The strengthening mechanisms and bending toughness of the AZ61 Mg based composites reinforced by nano SiO 2 particles are examined. The composites were prepared either by spray forming, ingot metallurgy, or powder metallurgy, followed by severe hot extrusion. The spray formed composites exhibit the best nano particle distribution and toughness, but the volume fraction of the nano particles that can be inserted is limited. The nano composites fabricated through the powder metallurgy method possess the highest strength due to the extra strengthening effect from the MgO phase. Strengthening analysis based on the Orowan strengthening mechanism can predict well the composite strength provided that the nano particles are in reasonably uniform dispersion. For composites containing higher nano particle volume fractions greater than 3%, the experimental strength data fall well below the theoretical predictions, suggesting poor dispersion of the reinforcement.

/pdf/strengthening-and-toughness-of-az61-mg-with-nano-sio2-2e6kw0oaek.pdf

Strengthening and toughness of AZ61 Mg with nano SiO2 particles

The current study applies the inclusion of thermally stable ceramic nano powders into the light weight AZ61 Mg base alloys via spray forming plus extrusion The combination of spray forming and severe extrusion provides a new processing route for fabricating nano composites, with uniform distribution of the nano fillers Parallel tries using the PM route followed by the same severe extrusion can also yield sound composites but the dispersion of the nano SiO2 appears to be less uniform The processed composites are characterized in terms of microstructure examination, thermal analysis, phase identification, and mechanical testing

/pdf/az61-mg-with-nano-sio2-particles-prepared-by-spray-forming-4bt6phbulu.pdf

Y. P. Hung

Papers

Nanocrystallization and Amorphization Mechanisms in Zr-X Alloys during the ARB Process

Strengthening and toughness of AZ61 Mg with nano SiO2 particles

AZ61 Mg with Nano SiO2 Particles Prepared by Spray Forming plus Extrusion