Effect of aging prior to extrusion on the microstructure and mechanical properties of Mg–7Sn–1Al–1Zn alloy

Improved strength of Mg alloy extruded at high speed with artificial cooling

“…5e and f, yet it has been reported that dynamically precipitated Mg 2 Sn usually has a spherical shape in extruded MgeSn binary [13,14] or MgeSneAleZn alloys [10,12,15e17]. However, in these previous studies, a small amount of lath-like Mg 2 Sn precipitate was observed in TAZ711 extruded at a relatively low temperature of 250 C and a high speed of 8 mm/s [10]. In this study, the non-cooled sample extruded at 350 C and 9 mm/s has only spherical precipitates, while the artificially cooled samples extruded under the same conditions contain both spherical and lath-like precipitates; the latter being extensively dispersed within the large non-DRXed grains (Fig.…”

“…It is known that thermally stable Mg 2 Sn particles are dynamically precipitated from a supersaturated a-Mg matrix during extrusion in high-Sn containing Mg alloys such as Mge8Sne1Ale1Zn [6] and Mge9.8Sne1.2Zne1.0Al [12], and that the amount in weight percent of these precipitates generally increases with decreasing extrusion temperature due to a rapid reduction in Sn solid solubility [10]. The SEM images in Fig.…”

“…A previous study [10] has revealed that homogenized TAZ711 alloy has an equiaxed structure with an average grain size of 340 mm, and although it contains a very small amount of Al 3 Fe or Al 8 Mn 5 inclusions with a negligible effect, any coarse Mg 2 Sn phases formed during solidification are fully dissolved by homogenization. The microstructure and inverse pole figure map of the extruded samples shown in Fig.…”

“…That is, given the fact that the effect of crystal defects and precipitates on the electrical resistivity of extruded Mg alloy is negligible [15], any drop in electrical resistivity after extrusion can be assumed to be related to the dynamic precipitation of Mg 2 Sn [10]. A previous report has demonstrated that a decrease in electrical resistivity of 4.87 nUm in TAZ711 alloy corresponds to the formation of 1 wt.% Mg 2 Sn [10], and so the decrease in electrical resistivity seen in Fig. 7 from 131.1 nUm in the homogenized billet to 124.8 nUm without cooling, and to 114.5 and 113.9 nUm with Water 2 and Water 5, respectively, correlates to 1.29, 3.41 and 3.53 wt.% of Mg 2 Sn precipitates.…”

Improving mechanical properties of extruded Mg–Al alloy with a bimodal grain structure through alloying addition

“…Significantly, although complete DRX occurs throughout the entire sample during extrusion, a bimodal microstructure of fine and relatively coarse DRXed grains can be generated by the uneven distribution of dynamic precipitates. It is the micro-segregation of alloy elements dissolved within the a-Mg matrix of a homogenized billet that is responsible for localized precipitation during hot deformation, which eventually leads to the formation of fine DRXed grains in regions where precipitates are concentrated due to their grain-boundary pinning effect [1,9]. At the same time, coarse DRXed grains are formed in precipitate-free regions through enhanced grain growth.…”