This review consolidates decades of research on hot-deformation processing maps into a single, mechanism-based framework that connects macroscopic stability criteria with high-temperature deformation physics. It traces the evolution of major formulations—including those by Prasad, Murty, and Kim–Jeong—back to their common thermokinetic foundation in creep and dynamic-recrystallization (DRX) kinetics. Through this unified treatment, the review clarifies that power-dissipation efficiency (η) and flow-instability indices are different projections of the same rate-dependent constitutive response, which also dictates transitions between power-law deformation mechanism regimes and the onset of power-law breakdown. The paper is organized to move from theory to application. Early sections reconstruct the mathematical origin and physical meaning of η and instability functions; middle sections benchmark these criteria across published Mg datasets; and later sections provide practical guidance for constructing reliable maps using physics-constrained regression and uncertainty reporting. The review further clarifies—by distinguishing necessity from sufficiency in the DRX–η relationship—why DRX annotations and high-η domains frequently coincide without implying causal equivalence. Collectively, these contributions transform processing maps from empirical contour charts into predictive diagnostic tools and offers a reproducible workflow and interpretive hierarchy adaptable to diverse alloy systems and data qualities.

Ultrathin metallic foils deform under plane-stress conditions, where the absence of through-thickness constraint and a low thickness-to-grain-size ratio (t/d) promote early necking and severely limit uniform elongation. Here, we demonstrate that high-ratio differential speed rolling (HRDSR) mitigates these geometric limitations in Mg–10Li alloy foils by refining grains to the nearly ultrafine regime, thereby increasing t/d and activating grain-boundary–mediated deformation. Foils 100 µm thick with grain sizes of 1.1 µm (t/d ≈ 91) exhibit elongations exceeding 30 % at 10⁻⁵ s⁻¹, whereas coarse-grained counterparts (29.4 µm, t/d ≈ 3.4) of the same thickness fail abruptly with < 1 % uniform strain under identical conditions. Micro-pattern formability tests confirm homogeneous deformation and high surface fidelity in ultrafine-grained foils, in sharp contrast to severe strain localization and pattern collapse in coarse-grained samples. Strain-rate jump tests on the ultrafine-grained foils reveal an elevated strain-rate sensitivity (m ≈ 0.23) and low activation volumes (15–30 b³) at low strain-rates, suggesting that deformation is governed by a combined contribution of grain boundary sliding (GBS) and dislocation climb creep (DCC). A unified constitutive framework captures the transition from DCC at moderate strain-rates to GBS at low rates. The present findings demonstrate that refining Mg–Li alloys to a quasi-ultrafine-grained regime effectively overcomes the intrinsic ductility limitations imposed by plane-stress geometry, thereby enabling their practical application in flexible electronics, bioresorbable implants, and lightweight energy-storage systems.

The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy (LAZ1011) with a grain size of 3.2 µm, primarily composed of the BCC β phase and a small amount of the HCP α phase, were examined in a temperature range of 473 K to 623 K. The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling. The best superplasticity was achieved at 523 K and at strain rates of 10⁻⁴ -5 × 10⁻⁴ s⁻¹, where tensile elongations of 550–600% were obtained. During the heating and holding stage of the tensile samples prior to tensile loading, a significant increase in grain size was observed at temperatures above 573 K. Therefore, it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms. In the investigated strain rate range, the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding, while at high strain rates, lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism. It was concluded that solute drag creep is unlikely to occur. During the late stages of deformation at 523 K, it was observed that grain boundary sliding led to the agglomeration of the α phase, resulting in significant strain hardening. Deformation mechanism maps were constructed for β-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate, stress, temperature, and grain size, using the constitutive equations for various deformation mechanisms derived based on the data of the current tests.

Magnesium (Mg) alloys have several advantages, such as low density, high specific strength and biocompatibility. However, they also suffer weak points, such as high corrosion, low formability and easy ignition, which makes their applications limited. Many studies have been conducted to overcome these disadvantages and further improve the advantages of Mg alloys. Severe plastic deformation (SPD) is one of the most important techniques and has great effects on the microstructure refinement of Mg alloys and improvements in their strength and formability. Several researchers have studied the corrosion behavior of SPD-processed Mg alloys in recent decades. However, these studies have reported some controversial effects of SPD on the corrosion of Mg alloys, which makes the research roadmap ambiguous. Therefore, it is important to review the literature related to the corrosion properties of Mg alloys prepared by SPD and understand the mechanisms controlling their corrosion behavior. Effective grain refinement by SPD improves the corrosion properties of pure Mg and Mg alloys, but control of the processing conditions is a key factor for achieving this goal because texture, dislocation density, size and morphology of secondary phase also importantly affects the corrosion properties of Mg alloys. Reduced grain size in the fine grain-size range can decrease the corrosion rate due to the increased barrier effect of grain boundaries against corrosion and the formation of a stable passivation layer on the surface of fine grains. Basal texture reduces the corrosion rate because basal planes with the highest atomic planar density are more corrosion resistant than other planes. Increased dislocation density after SPD deteriorates the corrosion resistance of the interior grains and thus proper annealing after SPD is important. The fine and uniform distribution of secondary phase particles during SPD is important to minimize the micro-galvanic corrosion effect and retain small grains during annealing treatment for removing dislocations.

Samples of Mg-8.2Gd-3.8Y-1.1Zn-0.4Zr alloy with and without an intragranular lamellae-shaped long period stacking ordered (LPSO) phase were prepared through heat treatment and a series of hot compression tests on these materials were conducted to examine and evaluate the influence of LPSO on the hot compressive deformation behavior and deformation mechanisms at a given alloy composition. The values of activation energy for plastic flow (Q_c) of the solution treated (without LPSO phase) and annealed alloys (with intragranular LPSO phase) were larger than that for pure Mg, indicating that the presence of a high amount of rare earth (RE) elements and LPSO in the Mg matrix significantly increases Q_c. The Q_c value of the annealed alloy was larger than that of the solution treated alloy at all the strain levels (223.3 vs. 195.5 kJ/mol in average) and the largest difference in Q_c between the two alloys was recorded at the smallest strain of 0.1 where precipitation of LPSO during deformation was limited in the solution treated alloy. These observations imply that the formation of LPSO phase out of the RE-rich solid solution matrix during deformation increases Q_c, but the increment is not so large. Analysis of the hot compressive data of the alloys with LPSO phase and the alloys with RE-rich solid solution matrix in literatures indicates the similarity of the effect of the LPSO and RE-rich solid solution matrix phases on Q_c and high-temperature strength.