Papers by Keyword: Superplasticity

Abstract: The texture characteristics and the relationship between texture and tensile properties at room temperature and superplasticity at high temperatures in a hot extruded AZ61 alloy are examined in this paper. After warm extrusion, the alloy exhibits a of refined grains microstructure and a sharp basal {0001} texture. The tensile properties at room and elevated temperatures in extruded with the loading axis oriented at 0°, 45° and 90° to the extrusion direction are tested. It is found that the 45° specimens exhibit has lower yield strength and higher ductility. The possible causes for mechanical anisotropy are also analyzed based on the Schmid factor calculations.

Abstract: An AZ81 magnesium alloy, which was processed by hot extrusion in advance, was tested in the temperature range of 473 ~ 623 K and at various initial strain rates, ranging from 1×10-1 to 1×10-4 s-1. True stress-true strain curves under various temperatures and activation energy within different temperature range were investigated for the analysis of effect of temperature on superplastic behaviors. Elongation of the as-extruded AZ81 alloy increased with temperature when tested at the same initial strain rate. Elongation values, obtained at the same initial strain rate of 1×10-3 s-1, were 94% at 473K and 446% at 623K, respectively. Deformation mechanisms varied with increasing temperature, from the grain boundary sliding (GBS) accommodated by grain boundary diffusion to the GBS accommodated by lattice diffusion, transition temperature was 573 K.

Abstract: Microstructure evolution and superplastic behaviors of ZK40 magnesium alloy were investigated in the temperature range of 473 ~ 623 K. Twinning occurred significantly after being processed by equal channel angular pressing (ECAP) for one pass through the die, the mean grain size was 5.6 µm. Finer grains can be obtained after further processing through ECAP, the average grain size of the alloy processed by ECAP for three passes was as low as 0.8 µm; this alloy exhibited low temperature superplasticity at 473 ~ 523 K, elongations at an initial strain rate of 1×10-3 s-1 were 260 % at 473 K and 612 % at 523 K, respectively. The incompatibility between fine and coarse grains was thought to be unfavorable to the improvement of superplasticity. Low temperature superplasticity of the as-ECAP ZK40 alloy can be attributed to the relatively finer grain size and the homogeneity of microstructure.

Abstract: The superplasticity and microstructure of magnesium alloy ZK40 processed by ECAP for 1 and 4 passes were investigated. Tensile experiments at 523 K showed that the elongation of ZK40 was improved with the increasing passes. The elongation-to-failure of ZK40 processed by ECAP for 4 passes tested at 523 K and strain rate of 1×10-4s-1 was 660%. The microstructural analyses explained these results.

Abstract: Orientation-controlled Mg single crystals were tensile tested at temperatures between 473 K and 673 K at a strain rate of 4.2 x 10-4 s-1 in vacuum. Though all the single crystals showed high ductility compared with that of polycrystals, the ductility of the single crystals strongly depended on the crystal orientation. The [27 -1 -26 1] single crystal showed 0.57 fracture strain, while the [3 8 -11 -1] single crystal showed superplastic behavior of ductility over 1.8 strain. The observed strong orientation dependence of ductility seemed to be caused by orientation dependence of ease occurrence of dynamic recrystallization (DRX) in the single crystals during high-temperature deformation. The orientation dependence of ductility of Mg single crystals will be discussed in detail concerning crystallographical orientations of the single crystals, occurrence of DRX and fracture.

Abstract: In the current four-year term project in Japan, new platform science and technology is proposed as a core concept of research and development of advanced magnesium alloys together with understanding of their intrinsic characteristics. The research fields related to advanced super-light magnesium alloys for 21st Century have been focused to the selected three categories; ecomaterial design and processing, high qualification of mechanical performance, and high performance design and processing in functionality. On the basis of the obtained results, platform science and technology for environmentally benign and high performance magnesium alloys is constructed as an industrial base material for the next generation. As a result, numerous large-scale joint research and development projects on magnesium alloys based on partnerships between industries, academia and government has already started towards practical utilization since last year.