The effect of grain boundary structures on the deformation behavior at the grain boundaries in magnesium was examined by the nanoindentation creep test. The results of the nanoindentation creep test ...showed that the dominant deformation mechanism around the grain boundary was grain boundary sliding; however, the occurrence of grain boundary sliding was closely related to the grain boundary energy. The grain boundary with high energy showed high strain rate sensitivity, which was the same tendency as that of the other metallic materials. Furthermore, the addition of aluminum atoms into magnesium tended to prevent the grain boundary sliding due to the decrease in grain boundary energy.
► The grain boundary structures in Mg affected the deformation mechanism. ► The grain boundary with high energy indicated high strain rate sensitivity. ► The addition of Al atoms into Mg decreased the grain boundary energy. ► Mg–Al alloy prevented the grain boundary sliding to compared that with Mg.
The effect of twin boundaries on indentation behavior was investigated in Mg-0.3 at.%X (X = Al, Li, Y and Zn) binary alloys containing preexisting {101¯2} deformation twins. These alloys exhibited ...the highest hardness values reported among both fine- and coarse-grained alloys studied in the literature, irrespective of the alloying elements present. The activation volumes for plastic deformation were found to lie between 18b3 and 60b3, consistent with a rate-controlling mechanism of dislocation slip. These activation volumes were similar to previously reported results for alloys devoid of twins prior to testing, suggesting that although twin boundaries do not affect the dominant deformation mechanism, they lead to an increase in hardness. On the other hand, the activation volumes obtained from indentation tests were different from those obtained by uniaxial compression tests in samples without pre-existing twins, due to the occurrence of microstructural evolution, i.e., deformation twin formation, during plastic deformation.
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•{10–12} twin does not affect deformation mechanism, but leads to enhancing hardness.•Nanoindentation shows greater strain rate dependence than does uniaxial testing.•The activation volumes are obtained to be 18–60 b3 at nanoindentation.•The rate-controlling mechanism is dislocation slip irrespective of twin boundary.
The fracture toughness of extruded pure magnesium increased with grain refinement due to the effect of the plastic zone, which is a sensitive factor related to the mechanical properties of yield ...strength, elongation-to-failure and strain hardening exponent.
The mechanical properties, i.e., strength and toughness, were investigated on five fine-grained Mg–0.3at% X (X=Al, Ca, Sn, Y and Zn) alloys by two different processes: extrusion and caliber rolling. ...The extruded and caliber rolled alloys had the same texture distribution, but different grain boundary structures. The caliber rolled alloys, which had high fraction of low-angle grain boundaries, showed higher toughness and larger void size as compared to those of the extruded alloys, regardless of the alloying elements. The low-angle grain boundaries played a role in suppression of micro-void nucleation site. Thus, the control of grain boundaries is an effective method to enhance the mechanical properties in magnesium alloys, especially toughness. Importantly, the addition of aluminum or zinc elements in the caliber rolled alloys was the most effective in improving the strength and toughness balance among the well-known binary alloying elements.
The effects of temperature and alloying elements on deformation in the high-strain-rate regime were investigated by testing fine-grained magnesium alloys with an average grain size of 2 ∼ 3 μm by a ...nanoindentation technique. The dynamic hardness measurements aligned well with existing quasistatic data, together spanning a wide range of strain rates, 10−3 ∼ 150/s. The high-rate hardness was influenced by various alloying elements (Al, Li, Y and Zn) to different degrees, consistent with expectations based on solid solution strengthening. Transmission electron microscopy observations of the indented region revealed no evidence for deformation twins for any alloying elements, despite the high strain-rate. The activation energy for deformation in the present alloys was found to be 85 ∼ 300 kJ/mol within the temperature range of 298 ∼ 373 K, corresponding to a dominant deformation mechanism of dislocation glide.
In a Mg-Sc system, a bcc (
β
) phase exists in a high-temperature region, and the quenched
β
shows drastic age-hardening and shape-memory properties. In addition to the disordered
β
phase, the ...ordered
β
(B2) phase is reported to exist in a low-temperature region. We report that the quenched
β
phase can be ordered through aging treatment at 573 K. This finding indicates that the mechanical characteristics and shape-memory functionality of
β
-type Mg-Sc alloys can be controlled by ordering the
β
phase.
The cast AZ91 magnesium alloy having excellent mechanical properties, such as high strength and high creep resistance was developed by additional elements of Ca and Sr. From the microstructural ...observations, in order to obtain the fine grained AZ91 magnesium alloys, the optimal concentration of elements, such as Ca and Sr were at least 1.0 and 0.5
wt%, respectively. The present developed cast AZ91 magnesium alloy had fine grain sizes of 19
μm. The tensile strength and elongation at room temperature were 250
MPa and 3.5%, respectively. The strength at an elevated temperature of 448
K on developed AZ91 magnesium alloy was also drastically larger than that on precious cast magnesium alloys.
For the first time, we report here segregation of Zn atoms to twin boundaries formed under 9% compression at room temperature (RT) in a Mg-3Zn-0.5Y (in at%) alloy. The wrought processed (textured) ...alloy was severely plastically deformed (SPD) through high pressure torsion (HPT) at RT. Zn segregation (2 to 4at%) was observed on newly formed boundaries, such as twin boundaries (formed on compression only in HPT), low angle boundaries formed by deformation and grain boundaries due to recrystallization. First principles calculations performed on low angle boundaries shows that Zn atom prefers to segregate to the dislocations in the boundary.
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