The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal <c+a> slip to accommodate plastic strain. In the present study, however, a quantitative analysis reveals ...that Li-addition can only slightly stimulate the activation of pyramidal <c+a> slip under compression along the normal direction of a hot-rolled Mg-4.5 wt.% Li plate, with a relative activity of approximately 18%. Although the limited activity of pyramidal <c+a> slip alone cannot accommodate a large plastic strain, it effectively reduces the number of {101¯1}−{101¯2} double twins, which are believed to be favorable sites for crack initiation. The evidently reduced activity of double twins leads to a lower cracking tendency, and therefore improves ductility.
In the present study, a comparative study about the hardening effect of solute segregation at {101¯2} twin boundaries (TBs) on a {101¯2} twinning predominant deformation and a detwinning predominant ...one was carried out. The influence of the pre-straining and subsequent annealing conditions on mechanical behavior was systematically addressed. Our results show that solute segregation at TBs can occur even at 100°C. The annealing at 100°C for 20min induces a partial segregation at TBs, while that at 150°C or higher temperature for 20min can induce a complete solute segregation. The annealing conditions and pre-strain levels generate quite different effects on deformation by twinning and that by detwinning. Both annealing hardening and annealing softening might happen during the twinning predominant recompression. Annealing hardening occurs only with pre-strains of 3.0% and 5.5% after annealing at 100°C for 6h. A higher pre-strain or a higher annealing temperature or a longer annealing time generate a higher annealing softening effect. However, during the detwinning predominant recompression, all used annealing treatments generate hardening effect in all the pre-strained samples. With a complete solute segregation at TBs, a hardening of about 11–25MPa is generally achieved. It is also found that solute segregation at TBs reduces the strain hardening rate of deformation by TBs migration.
In the present study, several composite twin structures containing different fractions of {101−2} primary twins (PTs) and {101−2}-{101−2} secondary twins (STs) were prepared from a rolled sheet by a ...pre-compression along the transverse direction (TD) and a subsequent recompression along the rolling direction (RD). Mechanical properties under tension and compression along the TD, RD and normal direction (ND) were systematically studied, along with an in-situ EBSD experiment, to disclose the exact deformation mechanisms of various composite twin structures under different loading paths. Our results show that the composite twin structures can effectively harden the materials in three dimensions, while the hardening effect is highly dependent on the loading paths and the pre-straining conditions. With a constant TD pre-strain, a higher RD pre-strain can achieve a better hardening, while counterbalance the contribution to mechanical anisotropy. Deformation mechanisms in the composite twin structure vary with the changes in the loading conditions, but are also affected by the grain structure. It is also found that in some cases detwinning of the STs back to the PTs can also take place. However, in grains in which the parent PT is almost invisible or completely transformed into a ST, nucleation of new {101−2} twins followed by detwinning rather than direct detwinning of this ST takes place under the loading condition that would favor detwinning of STs. Similarly, in grains in which the matrix of PTs is totally consumed, nucleation of {101−2} twins followed by detwinning will occur under the loading condition that generally starts detwinning of PTs. As nucleation of new twins has a higher activation stress than detwinning of the pre-existing twins, the mechanical properties can be improved.
•A new wave-shaped interface rolling method was proposed to tailor the basal texture.•The as-proposed rolling method can largely incline basal poles.•A texture gradient exists in the as-rolled and ...annealed plate.
In this study, a new rolling method, wave-shaped interface rolling (WIR), was proposed to tailor the strong basal texture of a hot-rolled Mg AZ31 plate. Microstructure and texture of the WIRed and annealed plate were investigated and the mechanism for texture variation was discussed. The results show that the waved interface can effectively rotate the basal poles away from the normal direction toward the rolling direction at both the regions near and far from the waved interface. Different inclination angles of 〈0002〉 away from the normal direction occur at different regions in the rolled plates and a maximum inclination around 30° can be obtained.
The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension, compression and plane strain compression (PSC) tests were ...performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress (CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening. Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.
In the present study, three types of bimetal composites, Al 6082 sleeve/Al 6082 core, Mg AZ31 sleeve/Mg AZ31 core and Al 6082 sleeve/Mg AZ31 core, were fabricated by drilling and assembling. The rule ...of mixtures (ROM) for the flow curves and yield strengths during compressive test were addressed. Our results show that the ROM can predict well the experimental flow curves and yield strengths of bimetal composites without bonding, irrespectively of the different strain hardening behavior between the two components.
Based on the heat transfer analysis in the primary cooling region of large-size magnesium alloy flat ingot Direct-chill (DC) casting, a novel crystallizer structure for flat ingot electromagnetic DC ...casting was put forward, in which the primary cooling can be controlled independently from the secondary cooling, and the circumferential control of the primary cooling can be realized synchronously. The design and optimization of the inner sleeve material and thickness and the distribution of the primary cooling were also carried out. For the AZ31B flat ingot with a cross-section size of 1200 × 400 mm, the copper inner sleeve material was selected, and it is beneficial to control temperature gradient and mushy zone shape in flat ingot DC casting. A uniform temperature distribution can be obtained when the cooling intensity ratio of the wide and narrow faces is 1:1/3. Furthermore, the influence of casting process parameters on the mushy zone characteristic of 1200 × 400 mm flat ingot was studied by orthogonal planning of process parameters and numerical simulation methods. Simultaneously, the casting process parameters of other flat ingot sizes were determined, and AZ31B alloy DC casting flat ingots with section sizes of 750 × 440 mm, 1200 × 400 mm, and 1600 × 400 mm under industrial conditions were carried out, and the crack-free preparation of the above billets was successfully achieved.
In the present study,the influence of solute atoms together with dislocations at {101^-2} twin boundary（TB） on mechanical behavior of a detwinning predominant deformation in a Mg alloy AZ31 plate was ...systematically studied.The results show that a large number of {101^-2} twins disappear during recompression along the normal direction.Both the TB-dislocation interaction and TB-solute-dislocation interaction can greatly enhance the yield stress of the recompression along the normal direction（ND）.However,the solute segregation at {1012} TBs with an intensive interaction with 〈a〉 dislocations cannot further enhance the yield stress of ND recompression.The samples with TB-dislocation interaction show a similar working hardening performance with that subjected to a TB-solute-dislocation interaction.Both the TB-dislocation interaction and TB-solute-dislocation interaction greatly reduce the value of work hardening peaks during a detwinning predominant deformation.
Grain growth can modify the texture orientation and the fraction of different texture component. The thermal stability of two texture component in an extruded magnesium AZ31 alloy was investigated. ...Three types samples with different texture distribution were prepared. The results show that normal grain growth takes place in the magnesium AZ31 alloy during annealing at 300 °C and 450 °C. But the grain growth does not lead to the strengthening of either texture component. Both the ⊥ED texture and //ED texture components show good thermal stability, without influence of the texture volume fraction. The two different texture component possess comparable boundary migration ability, so grains of the two texture component consume indifferently the other grains, or are equally consumed during annealing.
The Mg–8Li dual phase alloy was deformed by multi-directional compression with different passes. Microstructure evolution of deformed Mg–8Li alloy was analyzed by electron backscatter diffraction. ...X-ray diffraction profile was used to calculate the dislocation density in α-Mg and β-Li phase to reveal the quantitively change trend under different compression passes. The mechanical properties were assessed through tensile and compressive tests. The Mg–8Li alloy exhibited optimal mechanical properties when compressed with 12 passes (sample 12MDC), with a compression yield strength of 183.1 MPa and a tensile yield strength of 124.2 MPa. The improved mechanical properties in sample 12MDC were attributed to an increase in {10 1‾ 2} twin and {101‾ 3}-{101‾ 2} double twin boundaries, along with the presence of sub-grain boundaries and a reduced grain size in the α-Mg phase. Additionally, the inconsistent results between microhardness and dislocation density calculation manifests the uneven distribution of dislocations in β-Li phase. Broken α-Mg phase brings more phase interface to relieve the strain in β-Li phase, which results to a decreased dislocation density in sample 12MDC (1.19 × 1011/m2). Results show that weaken tension-compression yield asymmetry and more even distribution of dislocation in both phases could be achieved when the compression passes increases to 12.
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