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Magnesium AZ31 alloy sheets were rolled at 100 °C at two speeds: (i) 1000 m/min and (ii) 15 m/min. The rolled specimens were annealed at temperatures from 200 °C to 500 °C for increasing intervals of time. The recrystallization kinetics were analyzed in terms of the Johnson-Mehl-Avrami-Kolmogorov model and found to involve two sequential annealing stages, characterized by two different Avrami exponents. Stage 1 is associated with recrystallization in the high stored energy regions, such as these containing shear bands and twins, while stage 2 concerns the recrystallization of some of the low stored energy regions. Nevertheless, in the specimens subjected to low reductions (<30%) and annealed at 200 °C for long time periods, some of the elongated grains remained unrecrystallized. This is attributed to the relative lack of formation of twins in these grains during rolling, i.e. to the very low stored energies in these regions. There was no significant difference in the microstructure evolution and recrystallization kinetics of the materials rolled at the two speeds. This is interpreted in terms of the Zener-Hollomon parameter, similar values of which applied to the two types of rolling and therefore to the microstructures produced. [ABSTRACT FROM AUTHOR]

Two different amounts of tin (Sn) were added to a Mg–3 wt% Al binary alloy to form different amounts of precipitates during hot deformation. The thermodynamic modeling software, FactSage ™ , was used to calculate the amounts of Sn to generate the desired relative levels of precipitation. The alloys were deformed at four different temperatures and three different strain rates to generate different amounts of precipitates. The objective was to study the effect of these precipitates on dynamic recrystallization. The results indicated that the formation of strain-induced precipitates is a function of deformation temperature, strain, and strain rate. The findings also revealed that higher amounts of precipitates reduced the volume fraction of dynamic recrystallization and refined the dynamically recrystallized grain size. [ABSTRACT FROM AUTHOR]

In this work, the effect of built direction on the small-scale mechanical properties and microstructure of a novel maraging stainless steel (SS-CX) manufactured through the selective laser melting (SLM) process was studied. Advanced electron microscopy and nanoindentation techniques were utilized to evaluate retained austenite fraction and micro-mechanical properties, respectively. Different thermal histories caused by the change of the built direction resulted in microstructures with different volume fractions of retained austenite and grain morphology. Furthermore, the slower cooling rates in the vertically built sample was found to result in the formation of large elongated grains and lower hardness values during the nanoindentation experiments. • The building direction changes the microstructure of selective laser melting product. • Changing the building direction resulted in different volume fractions of retained austenite. • The thermal history of the product depends on the printing orientation. • The laser scan path changes the static and dynamic recovery processes. [ABSTRACT FROM AUTHOR]

MagnesiumAZ31alloy sheets were rolled at a high speed of 1000 m/min(HSR) and a low speed of 15 m/min(LSR) at 100 °C to a reduction of 30%. The as-rolled microstructures were heavily twinned and shear banded at both speeds. Annealing was performed on the as-rolled sheets at three different temperatures (200, 350 and 500 °C) for increasing time intervals. Texture weakening was achieved after annealing of both HSRed and LSRed sheets due to static recrystallization (SRX) on twins and shear bands. This, in turn, greatly improved the ductility of the sheets. It was found that the intensities of the basal texture of the HSRed specimens were lower than those of the LSRed specimens at as-rolled and all annealed conditions. This is related to the higher amount of contraction twins and more slips activated during HSR. Correlation of the maximum intensity of the basal texture with softening/recrystallization fraction was found to be involved in two weakening stages. During the first stage, nucleation on twins and shear bands was the dominant mechanism for texture weakening, while growth of the non-basal grains was responsible for the second stage of texture weakening. Interestingly, it was found that the weakest texture was attained after annealing at 500 °C for 5 min in the HSRed specimen, which can be related to thermal activation of more random nucleation sites and preferential grain growth of the non-basal oriented grains. [ABSTRACT FROM AUTHOR]

Improving the magnetic properties of non-oriented electrical steel (NOES) through the optimization of crystallographic texture has been an on-going research activity for decades. However, using traditional rolling and annealing procedures, the obtained final textures were usually very similar, i.e., exhibiting the {111} (γ) and <110> (α) fibres, which were not the desired {001} texture (θ-fibre) for optimal magnetic quality. In the current work, a 1.8 wt% Si NOES was processed using a new sheet metal deformation method, i.e., repetitive bending under tension (R-BUT), also known as continuous bending under tension (C-BUT), to modify the texture of the electrical steel. The hot-rolled and annealed NOES plates were repeatedly bent and unbent when they were pulled under tension. The deformed plates were then heat treated at different temperatures for various times. Neutron diffraction and electron backscatter diffraction (EBSD) characterisation of the macro- and micro-textures proved that the R-BUT process significantly reduced the undesired {111} texture while promoting the {001} texture. The cube texture, which rarely formed after conventional rolling and annealing, was also seen in the R-BUT samples after annealing. It was shown that, the shear plastic deformation (induced by R-BUT) played a significant role in promoting the desired textures. In addition, the results indicated that the NOES processed by R-BUT could be deformed beyond its common formability limit, which may provide a method to address the poor workability challenge of high silicon electrical steels. [ABSTRACT FROM AUTHOR]