In this study, dynamic precipitation was observed in ZK60 (Mg-6.0Zn-0.5Zr) alloy during low temperature extrusion. The microstructure and mechanical properties of the alloy were investigated for various extrusion temperatures (400 oC, 350 oC and 300 oC). Decreasing extrusion temperature resulted in an increased dynamic precipitation as well as grain refinement. With decreasing extrusion temperature from 400 oC to 300 oC, the grain size was refined from 9.6 μm to 1.4 μm, and the dynamic recrystallization was changed from a discontinuous mechanism to a continuous one. The low temperature extrusion (300oC) resulted in an increased defect density and a supersaturated Zn in Mg matrix, which promoted the nucleation and potential for precipitation during extrusion process. The dynamic precipitates accelerated the nucleation of new grains during the dynamic recrystallization process. Besides the grain size, the texture intensity was also reduced. Due to the grain refinement and texture weakening during low temperature extrusion, both the mechanical strength and tensile ductility were improved with decreasing extrusion temperature. When extruded at 300 oC, the ZK60 alloy achieved a relatively high tensile yield strength (TYS) of 295 MPa and a remarkably high tensile elongation of 27.7%.

Dynamic precipitation and enhanced mechanical properties of ZK60 magnesium alloy achieved by low temperature extrusion

Effect mechanism of texture orientation on mechanical properties and Hall-Petch relationship of CVCDE AZ31 magnesium alloy via crystal plastic finite element method (CPFEM)

Microstructures and mechanical properties of a hot-extruded Mg−8Zn−6Al−1Gd (wt.%) alloy

Enhancing strength and ductility of low-cost rare earth Mg-5Y-Ni alloy containing LPSO phase fabricated via multi-pass rolling based on dislocation regulation and grain refinement

In this study, the extruded Mg–Zn–Mn–Ce–Ca alloy tube with a weak basal fiber texture, i.e. the {0001} plane is distributed along the TD with 0°∼30° deflection towards ED, was fabricated. The alloy tube exhibits a low mechanical anisotropy in the tensile process at room temperature. To clarify the relationship between the weak texture and the low mechanical anisotropy, the microstructure and deformation mechanism of the alloy tube in the tensile process along the ED, 45ED and TD were studied. The results revealed that during yielding, the deformation in ED sample was governed by predominant prismatic slip, and a portion of additional basal slip and lowest pyramidal <c+a> slip, while predominant basal slip and accompanied by a high fraction of prismatic slip and lowest pyramidal <c+a> slip for both 45ED and TD samples. These relatively high additional slips result from the weak texture, which attenuates the deformation differences among the three samples. After yielding, the three samples underwent similar prismatic slip transition and twin nucleation quantity. Additionally, the {0001} plane displayed to converge towards the RD after tensile fracture, which may be related to the twins and intragranular slip. Especially for 45ED and TD samples, relatively high basal slip may cause their {0001} plane to tend to be parallel to the loading direction. In summary, the similar deformation mechanisms governed by weak texture along the three directions resulted in the low mechanical anisotropic of the alloy tube. 

The influence of initial texture, microstructure and deformation behavior on the low mechanical anisotropy of extruded Mg alloy tube

A weak texture dependence of Hall–Petch relation in a rare-earth containing magnesium alloy

Hall–Petch slope (k), an important parameter in Hall–Petch relation, describes the efficiency of strengthening effect by grain boundaries. Previously, a highly texture dependent k for Mg alloys is frequently reported, but, in the present study, we report a weak texture dependence of k in a rare-earth containing Mg-2Zn-1Gd plate with two peaks of (0002) poles inclining approximately ± 30 ° away from the ND toward the TD. Although there is a strong mechanical anisotropy between tension along the TD and RD, the k for TD-tension (280 MPa μm1/2) is quite similar to that for RD-tension (276 MPa μm1/2). Here, RD, TD and ND refer to the rolling direction, transverse direction and normal direction of the plate, respectively. The weak texture dependence of k is well predicted by the compound use of the activation stress difference between neighboring grains (ΔStress) and the geometric compatibility factor (m′). By analyzing how the texture affects the values for ΔStress and m′, the mechanism for this texture independence of k is ascribed to the activation of a high fraction of additional deformation mode, besides the predominant one for both RD-tension and TD-tension, namely, prismatic slip accompanied by a high fraction of basal slip for RD-tension and basal slip accompanied by a high fraction of prismatic slip for TD-tension. This will lead to multiple deformation transfer modes and, consequently, the effect of texture on the ease of deformation transfer across grain boundaries is weakened. As a result, there is a similar k for TD-tension and RD-tension. 

Solute atom mediated Hall-Petch relations for magnesium binary alloys

Dual-phase Mg–Li alloys exhibit better formability than conventional Mg alloys. However, conventional processing methods, such as rolling and extrusion, usually result in a lamellar structure, which will generate a strong planar anisotropy. In the present study, an as-extruded dual-phase Mg-8Li plate was rolled along two different directions, extrusion direction (ED-rolling) and transverse direction (TD-rolling), with the aim to investigate the effect of rolling path on the microstructure, texture and in-plane mechanical anisotropy. The results show that the lamellar α+β structures in the initial plate well remained after 20% or 50% ED-rolling and subsequent annealing at 250 °C for 4 h. In contrast, this lamellar structure completely disappears after TD-rolling and subsequent annealing. The basal poles of grains close to the TD in α phase in the initial plate slightly rotate from TD towards the normal direction (ND) during ED-rolling, while are largely parallel to the ND after TD-rolling. The variation of rolling path hardly alters the texture of β phase. For both α and β phases, annealing does not change the type of texture, only reduce the maximum intensity of texture. The mechanisms for texture evolution during rolling were studied using visco-plastic self-consistent (VPSC) simulations. It is shown that the main texture features of rolled plates are determined by the activated deformation modes in each phase, while α/β phase boundaries will retard the texture evolution. After ED-rolling, there is an obvious anisotropy in work hardening behavior and elongation for tension along the TD and RD, while this mechanical anisotropy disappears after TD-rolling. The corresponding mechanism were discussed. 

E Aiden

Papers

A weak texture dependence of Hall–Petch relation in a rare-earth containing magnesium alloy

A weak texture dependence of Hall–Petch relation in a rare-earth containing magnesium alloy

Solute atom mediated Hall-Petch relations for magnesium binary alloys

Tailoring the microstructure and texture of a dual-phase Mg–8Li alloy by varying the rolling path