Recrystallization Of Mg Research Articles

Flow softening behavior during dynamic recrystallization in Mg–3Al–1Zn magnesium alloy

The flow softening behavior of Mg–3Al–1Zn magnesium alloy in the temperature range 325–500 °C is quantified using plane strain compression. The flow softening ratio, defined as the steady-state stress at 0.6 strain to the peak stress, shows a linear relationship with the Zener–Hollomon (Z) parameter and varies from 45 to 70%. Higher levels of flow softening at high Z are associated with fully recrystallized structures, whereas lower flow softening levels at low Z exhibit a mix of large recrystallized and fine non-recrystallized grains.

On the deformation, recrystallization and texture of hot-rolled Mg–2.9Y and Mg–2.9Zn solid solution alloys—A comparative study

Abstract The microstructure and texture evolution during hot rolling (350 °C) and subsequent annealing are compared in Mg–2.9Y and Mg–2.9Zn (in wt%) solid solution alloys. It is shown that Y in solid solution, unlike Zn, suppresses dynamic recrystallization. Nevertheless, the two alloys exhibit similar, strong basal textures. Upon isothermal annealing of the rolled material at 400 °C, the texture is weakened only in the Mg–2.9Y alloy. The texture weakening is attributed to static recrystallization in basal parent grains. During rolling of Mg–2.9Y, basal parent grains store a high amount of basal dislocations that are organized in a very fine substructure. Such a highly energetic configuration gives rise to fine recrystallized grains with a wide orientation spread during annealing. On the other hand, off-basal parent grains with c-axes close to the RD–TD plane develop coarser substructure accommodating prismatic slip during rolling. The energy stored in these grains is significantly lower than that in basal ones (∼20 times smaller). Static recrystallization at off-basal parent grains leads to coarse new grains and involves rotations about c-axis. The texture weakening induced by static recrystallization in Mg–2.9Y was found to result in higher ductility and lower anisotropy when compared to Mg–2.9Zn.

Thermal and electromigration effects of electropulsing on dynamic recrystallization in Mg–3Al–1Zn alloy

The effect of electropulsing tension (ET) on the elongation to failure, microstructure and fracture behavior of Mg–3Al–1Zn (AZ31) alloy was investigated. It was found that electropulsing increased the plasticity significantly at a high strain rate of 2.5 × 10 −2 s −1 and the mechanism was based on dynamic recrystallization (DRX). The calculated temperature of the ET sample indicated that ET dramatically accelerated DRX at a relatively lower temperature, compared with conventional warm deformation. Based on the flux of vacancies contributed by the thermal and electromigration effects of ET, a model for simulating DRX under ET was established. The interplay between the two effects and a comparison with conventional warm deformation were also discussed.

Effect of homogenization on the hot-deformation ability and dynamic recrystallization of Mg–9Gd–3Y–0.5Zr alloy

Two states of Mg–9Gd–3Y–0.5Zr (wt.%) (GW93) alloy, as-cast (note as F state) and homogenized (note as T4 state), were hot compressed at strain rate of 0.1 s −1 and temperatures range from 623 K to 723 K. The stress-strain curves were established and volume fractions of dynamic recrystallized (DRX) grains were determined using point counting method. The results show that flow stresses are sensitive to the compression temperature and pretreatment state. Comparing with as-cast alloy, T4 state alloy has a higher flow stress and strain hardening rate θ, more complicated deformation microstructures, a smaller dynamic recrystallization rate and Avrami exponents. The phenomena are the results of the difference of initial nucleation sites and eutectic particles stimulated nucleation (EPSN) of two states. The initial nucleation sites of as-cast alloy include the original grain boundaries and eutectic particles, but as for T4 alloy, only original coarse grain boundaries can be act as nucleation sites.

Influence of KOH on the hydrothermal modification of Mg(OH) 2 crystals

Magnesium hydroxide (Mg(OH) 2) particles were synthesized and modified via a reaction-hydrothermal process using Ca(OH) 2 and MgCl 2 as precursors. The influence of KOH mineralizer on the hydrothermal modification of Mg(OH) 2 was investigated. X-ray diffraction, scanning electron microscopy, thermogravimetry and specific surface area analyses indicated that KOH played a key role in the recrystallization of Mg(OH) 2. It was found that the morphology and dispersion of Mg(OH) 2 particles improved significantly with an increase of KOH concentration from 1 to 4 mol/l.

Dynamic recrystallization of Mg and Mg–Y alloys: Crystallographic texture development

Pure magnesium and three binary Mg–Y alloys (0.23, 0.84 and 2.71 wt%Y) have been deformed in plane strain compression under conditions where dynamic recrystallization (DRX) is observed. The development of crystallographic texture during deformation has been determined for both the parent and DRX grains. In all but the highest Y alloy, the texture of the DRX grains was found to follow that of the parent grains closely in all alloys, implying that the DRX texture is dominated by the deformation conditions, rather than preferred nucleation or growth. In the highest Y alloy, the DRX texture is randomized, which also suggests that preferred nucleation or growth is not responsible for texture formation in this alloy. A transition in macrotexture development was observed in going from pure Mg deformed at 250 °C, to Mg–2.71 wt%Y deformed at 450 °C. This can be attributed to activation of additional slip modes, and a concomitant decrease in the contribution of twinning to deformation.

Superplastic forging with dynamic recrystallization of Mg–Al–Zn alloys cast by thixo-molding

Grain refinement during forging was found to be due to dynamic recrystallization of four kinds of Mg–x wt.%Al–1 wt.%Zn (x = 3, 4, 5, 6) alloys with grain sizes of ∼30 μm, which were cast using a thixo-molding machine. Superplastic forming combined with forging was successfully performed at a low temperature (473 K) and high-strain rate (3.3 × 10−2 s−1).

Deformation behavior and dynamic recrystallization of a Mg–Zn–Y–Zr alloy

Dynamic recrystallization (DRX) of Mg–Zn–Y–Zr alloy had been investigated using hot compression test. It was studied that the onset of DRX process occurred before the peak of the stress–strain flow curves. The critical condition of the onset of DRX process was following as ((∂/∂ σ)(−∂ θ/∂ σ)) = 0. The microstructure evolution of the alloy during the hot compression at various temperatures and strain rates had been studied. It suggested that the conventional DRX, i.e. the bulging out of part of the serrated grain boundaries firstly occurred on the original boundaries during the hot compression at 623 K. As further deformation was carried out, the continuous DRX had occurred inside the original grains. As the testing temperature increased, the DRX grain size became larger and larger. It is due to that the high temperature improved the migration of DRX grains boundaries. With increasing strain rate, the DRX grain size for the alloy deformed at the same strain became smaller and smaller. It is due to that the dislocation density of the alloy at high strain rate was higher. Finer subgrains and DRX grains were formed and more dislocations were absorbed into high-angle boundaries in the alloy deformed at high strain rate.

Thermal and structural investigation of (Sn<Subscript>1-x</Subscript>Ti<Subscript>x</Subscript>)O<Subscript>2</Subscript> obtained by the polymeric precursor method

Mg 2 TiO 4 was synthesized by the polymeric precursor method, was doped with 1 molp of Mn 2+ , Fe 2+ or Co 2+ . The powder precursors were characterized by TG/DTA methods. The mass loss took place in three steps. In the first one water and adsorbed gases were released while the second and third step were representative to the decomposition of the organic substance. The DTA experiments indicated the combustion as well as the decomposition and recrystallization of Mg 2 TiO 4 between 800 and 1200°C. XRD results indicated that spinel (AB 2 O 4 ) which have been observed at 600°C transformed to ilmenite (MgTiO 3 ) over 800°C.