Jong Un Lee

Grain-Refined AZ92 Alloy with Superior Strength and Ductility

Grain-refined AZ92 (GR-AZ92) alloy with superior tensile properties is developed by adding 1xa0wt% Zn and a very small amount of SiC (0.17xa0wt%) to commercial AZ91 alloy for enhancing the solid-solution strengthening effect and refining the crystal grains, respectively. The homogenized GR-AZ92 alloy with an average grain size of 91xa0μm exhibits a tensile yield strength (TYS) of 125xa0MPa, ultimate tensile strength (UTS) of 281xa0MPa, and elongation of 12.1%, which are significantly higher than those of AZ91 alloy with a grain size of 420xa0μm (TYS of 94xa0MPa, UTS of 192xa0MPa, and elongation of 7.0%). The peak-aging time of GR-AZ92 alloy (8xa0h) is significantly shorter than that of AZ91 alloy (32xa0h) owing to a larger amount of grain boundaries in the former, which serve as nucleation sites of Mg17Al12 precipitates. A short-aging treatment for less than 1xa0h of the GR-AZ92 alloy causes an effective improvement in its strength without a significant reduction in its ductility. The 30-min-aged GR-AZ92 alloy has an excellent combination of strength and ductility, with a TYS of 142xa0MPa, UTS of 304xa0MPa, and elongation of 8.0%.

Effects of {10–12} Twins on Dynamic Torsional Properties of Extruded AZ31 Magnesium Alloy

Effects of initial twins on dynamic torsional properties of extruded AZ31 alloy were investigated by introducing {10–12} twins into it through precompression to 3 and 6% strains along the extrusion direction and performing torsional testing at a strain rate of 1.4xa0×xa0103xa0s−1 using a torsional Kolsky bar system. The as-extruded sample without twins showed higher dynamic torsional properties than the precompressed samples with many initial twins; the maximum shear strength and fracture shear strain decreased with increasing amount of initial twins. In the as-extruded sample, twinning occurred vigorously throughout the gage section of the tubular specimen during high-strain-rate torsional tests, resulting in heavily deformed morphology, many macrocracks, and rough fractured surfaces. The increased amount of initial twins suppressed the twinning behavior and localized the applied torsional deformation; this resulted in an almost unchanged sample shape, no secondary cracks, and a flat fracture plane, thereby deteriorating the dynamic torsional properties of the extruded alloy.

Extruded Mg-Sn-Al-Zn Alloys with Superior Tensile Properties

This study investigated the microstructure and tensile properties of three indirectly extruded Mg-Sn-Al-Zn alloys: Mg-11Sn-1Al-1Zn (TAZ1111), Mg-8Sn-4Al-1Zn (TAZ841), and Mg-8Sn-1Al-4Zn (TAZ814). The investigation results revealed that in all the alloys, Mg2Sn particles formed during solidification were not fully dissolved by homogenization treatment. These undissolved particles enhanced the dynamic recrystallization behavior through a particle-stimulated nucleation phenomenon. As a result, all the extruded alloys exhibited a fully dynamically recrystallized microstructure. The tensile yield strength (TYS) of the extruded alloys was in the following order: TAZ1111 > TAZ841 > TAZ814. In contrast, the elongation of the alloys was in the opposite order: TAZ814 > TAZ841 > TAZ1111. The highest TYS of the TAZ1111 alloy was attributed mainly to the smaller grain size and more abundant Mg2Sn precipitates resulting from a higher Sn content. However, the ultimate tensile strengths of all the extruded alloys were nearly the same because the Al or Zn atoms dissolved in the TAZ841 and TAZ814 alloys improved the strain hardening rate during plastic deformation.