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Twinning plays a prominent role in the plastic deformation of low-symmetry crystals such as magnesium alloys. However, the capture of twin nucleation has been challenging since the process is rapid and difficult to predict, making it impossible to observe directly. Because of this, the understanding of the fundamental twinning mechanism through experiments and simulation techniques incorporating twinning has progressed slowly. In this study, a quantitative analysis integrating an in-situ three-point bending experiment and crystal plasticity modeling was conducted on the twin nucleation in AZ31 magnesium alloys with different grain sizes. The threshold for triggering twin nucleation has been quantified. The prediction ability of three widely used criteria for twin nucleation, i.e., geometrically necessary dislocation (GND) density, von Mises stress, and stored energy density, is evaluated. The results suggest that only the stored energy density is able to capture the twin nucleation location accurately in all the considered grain sizes. The critical value exhibits an exponential reduction with the increase in grain size. Based on the quantitative analysis, the mechanism of the grain size effect on twin nucleation is proposed.

The deformation behavior of hot-roll-bonded Mg/Al laminated metal composites (LMCs) is investigated, focusing on the crack formation around the interface. The material demonstrates a positive strain rate sensitivity mainly arising from the Mg matrix. A diffusion layer was formed at the Mg/Al interface with a serrated morphology during the two-pass rolling process, which consists of the Al3Mg2 and Mg17Al12 phases. The mechanical responses of the LMCs are evaluated using uniaxial tension, interfacial debonding tests (in normal and shear modes), and microstructure characterization techniques, which clarify the interfacial heterogeneity. The fracture constants of the interface were calibrated and incorporated in the finite element models to predict the failure modes of heterogeneous Mg/Al interface under three-point bending. With the increased thickness ratio of the Mg layer, the damage accumulation rate decreases at the interface and increases in the Mg matrix. As a result, the failure mode transferred from interface failure to matrix fracture. The findings of the present work provide new insight into the failure mechanism in laminated metal composites under bending conditions and can provide theoretical guidance for the plastic forming of such materials.

It is of significance to reveal the low-cycle fatigue deformation mechanism of titanium alloy with tri-modal microstructure for improving its properties. This work developed a crystal plasticity finite element model based on realistic microstructure to predict the low-cycle fatigue behavior of TA15 titanium alloys with tri-modal microstructure containing primary α (αp), secondary lamellar α (αl) and transformed β (βt). During modelling, plastic strain accumulation (PSA) and energy dissipation were used as the fatigue indicator parameter (FIP) to predict fatigue damage and life. It is found that the fatigue deformation prefers to localize at the interfaces of αp/β, αl/β and at triple junctions, which leads to the initiation of fatigue crack. In addition, the soft geometry of αl will also contribute to the strain localization inside αl grains causing fatigue damage. This is because the local lattice rotation is more prone to occur at these locations due to the tension-compression asymmetry of lattice rotation, which induces the occurrence of the microtexture and aggravates the heterogeneity of the lattice rotation, leading to the localized PSA and the total energy dissipation. And the asymmetry of lattice rotation in each cycle also leads to the tension-compression asymmetry of flow behavior. Both of the two FIPs can effectively predict fatigue life. With the strain amplitude increasing, the PSA-based model shows a relatively higher predictive accuracy of fatigue life than that of the accumulated energy dissipation-based model. The predicted fatigue life is in accordance with the C-M model.

A two-dimensional discrete dislocation plasticity model was used to examine the role of strain rate asymmetry on the Bauschinger effect (BE). A simple single crystal single slip plane model was used first to investigate stress–strain response within high strain rate regimes where the rate sensitivity is mainly governed by dislocation nucleation and the free-flight of dislocations. Both the yield strength and the BE of the specimen showed a strong correlation to the forward and reverse deformation rate. Simulations were also carried out on a single crystal with multiple slip systems. The effect of source and obstacle density on the BE and its rate dependence was investigated. We find that the rate dependence of the BE is enhanced by increasing the source density in obstacle-free specimens and is reduced by obstacles when they are present. At low strain rates, where thermally-activated dislocation escape from obstacles becomes the predominant rate-controlling mechanism, the BE of single crystals is only affected by strain rates if the activation energy is low. Grain boundaries in polycrystalline specimens and obstacles with high activation energies act as barriers to dislocation motion, suggesting that the rate dependence under low strain rate regimes is enhanced by decreasing the grain size or reducing the activation energy associated with dislocation escape from obstacles. The effect mechanisms of strain rate asymmetry on the BE can be fundamentally crucial for multiple industrial applications, including lifetime assessments of aero-engine disks, zirconium cladding of nuclear reactor and the spring-back prediction of metal forming.

The initial texture effect of strain rate sensitivity response in magnesium alloys was studied using the quasi in situ electron backscatter diffraction technique. The strain accumulations, under uniaxial loading of both tensile and compression along the rolling direction, showed strain rate dependency. For the AZ31 magnesium sheets with strong basal texture (max intensity to 11.2), twinning first occurs at the onset of plastic deformation, resulting in macroscopic strain rate insensitivity. With further loading, the strain rate sensitivity significantly increases (with the strain rate sensitivity coefficient m increased from 0.0025 to 0.012), arising from the initiation of slip. For the WE43 alloy sheets with weak basal texture (max intensity to 2.6), the overall deformation is sensitive to strain rate under both tensile and compression. The twinning growth rate and twinned volume fraction have been used to identify whether the process is twin-dominated or slip-dominated during the plastic deformation of a magnesium alloy.

The manufacturing process is inevitably accompanied with the production of scraps, which leads to resource waste and environmental pollution. Recycling and remanufacturing are the most commonly used approaches for metal scraps due to their well-established advantages from economic and environmental perspectives. In this study, spinning experiments with 2195 Al-Li alloy tailor welded blanks produced by friction stir welding from metal scraps were conducted under different process parameter designs. And then the effects of various process parameters on spinning of thin-walled curved surface parts were systematically studied. The results of the corresponding experimental groups show that the roller attack angle, the spinning clearance, and the installation method of tailor welded blanks have the most significant effect on the weld torsion angle. In addition, it was found that along the longitude direction of spun parts, the surface roughnesses of the weld of spun parts were greatly improved under the roller nose radius of 10 mm, the spinning clearance of 1.0 mm, the constant linear velocity, and the installation method of tailor welded blanks (the lower surface of tailor welded blanks is spun by rollers), while the process parameters have little significant effect on the surface roughness along the latitude direction of spun parts. Furthermore, it can be concluded that the forming profiles of spun parts fitted the mandrel well under the roller nose radius of 6 mm, double rollers, the roller attack angle of 30° and 45°, spinning clearance of 1.5 mm, and the installation method of tailor welded blanks (the upper surface of tailor welded blanks is spun by rollers). The research results will provide guidance for the precise spinning of thin-walled curved surface parts with tailor welded blanks. Thereby, it is also beneficial for green manufacturing involving recycling and remanufacturing of metal scraps.