Magnesium (Mg) alloys are the lightest metallic structural materials, holding significant potential for automotive, aerospace, electronic, and biomedical applications. However, their broader adoption is impeded by inherent drawbacks, including low strength, limited ductility, and poor corrosion resistance. High-pressure torsion (HPT) has proven effective in generating ultrafine-grained (UFG) Mg alloys, resulting in substantial property enhancements. This review critically assesses the microstructure evolution of HPT-processed Mg alloys covering not only grain refinement but also solute segregation, texture evolution, dissolution and precipitation of second phases, allotropic transformation, crystal-to-amorphous transition and nanocrystallization. In particular, it elucidates the impact of these microstructures’ evolutions on mechanical properties, including yield strength, hardness and superplasticity. Additionally, the review discusses the improvements in the addresses the functional augmentation of HPT-processed Mg alloys, specifically corrosion behavior, hydrogen storage capabilities, and biomedical performance.

This study presents a proposed interdisciplinary framework for developing ignition-resistant magnesium alloys and analyzing their combustion behavior. It focuses on both commercial AZ31, AZ91, WE43 and formulated Mg-Gd-Y-Zn-Zr alloys with various rare earth elements (REEs) contents. The research integrates experimental methods, heating rate simulations, advanced image processing, and machine learning (ML) techniques to identify key mechanisms that enhance ignition resistance, particularly for aerospace and other industrial applications. A novel alloy composition, Mg-8Gd-6Y-0.6Zn-0.6Zr, demonstrated exceptional non-combustibility in air. The study is systematically to classifies the combustion process into distinct phases and surface morphologies by leveraging supervised and unsupervised learning models based on unseen heating rate features. Advanced image processing techniques reveal dynamic surface morphology changes, including thermal deformation, melting spots, gas bubble formation, and transformations during saturation and post-melting phases, while unsupervised ML models also validate these outstanding predictions of surface morphology features. Additionally, the research highlights the synergistic effects of REEs in forming dense, protective oxide layers, refining microstructures, and delaying ignition. This phase-based analysis provides the combustion behavior of magnesium alloys, which is crucial for evaluating their performance in industrial fire scenarios.

The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered (LPSO) phase during tension and compression was investigated by in-situ synchrotron diffraction. The micro-yielding, macro-yielding, tension-compression asymmetry and strain hardening behavior of the alloys were explored by combining with deformation mechanisms. The micro-yielding is dominated by basal slip of dynamic recrystallized (DRXed) grains in tension, while it is dominated by extension twinning of non-dynamic recrystallized (non-DRXed) grains in compression. At macro-yielding, the non-DRXed grains are still elastic deformed in tension and the basal slip of DRXed grains in compression are activated. Meanwhile, the LPSO phase still retains elastic deformation, but can bear more load, so the higher the volume fraction of hard LPSO phase, the higher the tensile/compressive macro-yield strength of the alloys. Benefiting from the low volume fraction of the non-DRXed grains and the delay effect of LPSO and γ′ phases on extension twinning, the as-extruded alloys exhibit excellent tension-compression symmetry. When the volume fraction of LPSO phase reaches ∼50%, tension-compression asymmetry is reversed, which is due to the fact that the LPSO phase is stronger in compression than in tension. The tensile strain hardening behavior is dominated by dislocation slip, while the dominate mechanism for compressive strain hardening changes from twinning in the α-Mg grains to kinking of the LPSO phase with increasing volume fraction of LPSO phase. The activation of kinking leads to the constant compressive strain hardening rate of ∼2500 MPa, which is significantly higher than the tensile strain hardening rate.

A Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr (wt.%) alloy is processed by solution treatment and high pressure torsion (HPT) at room temperature to produce a nanostructured light material with high hardness. The stability of this alloy is subsequently tested through isochronal annealing for 0.5 h at 373 K to 673 K. The results reveal a thermal stability that is vastly superior to that of conventional Mg-based alloys processed by severe plastic deformation: the grain size remains at around 50 nm on heating to 573 K, and as the temperature is increased to 673 K, grain growth is restricted to within 500 nm. The stability of grain refinement of the present alloy/processing combination allowing grain size to be limited to 55 nm after exposure at 573 K, appears to be nearly one order of magnitude better than for the other SPD processed Mg-RE type alloys, and 2 orders of magnitude better than those of SPD processed RE-free Mg alloys. This superior thermal stability is attributed to formation of co-clusters near and segregation at grain boundaries, which cause a thermodynamic stabilization of grain size, as well as formation of β-Mg₅RE equilibrium phase at grain boundaries, which impede grain growth by the Zener pinning effect. The hardness of the nanostructured Mg-Gd-Y-Zn-Zr alloy increases with increasing annealing temperature up to 573 K, which is quite different from the other SPD-processed Mg-based alloys. The high hardness of 136 HV after annealing at 573 K is mainly due to solute segregation and solute clustering at or near grain boundaries.

Mg-1.0Al-1.0Ca-0.4Mn (AXM1104, wt.%) low alloy was extruded at 200 ℃ with an extrusion ratio of 25 and different ram speeds from 1.0 to 7.0 mm/s. The influence of extrusion rate on microstructure and mechanical properties of the AXM1104 alloy was systematically studied. With the increasing of extrusion rate, the mean dynamically recrystallized (DRXed) grain size of the low alloy and average particles diameter of precipitate second phases were increased, while the degree of grain boundary segregation and the intensity of the basal fiber texture were decreased. With the rising of extrusion rate from 1.0 to 7.0 mm/s, the tensile yield strength (TYS) of the as-extruded AXM1104 alloy was decreased from 445 MPa to 249 MPa, while the elongation to failure (EL) was increased from 5.0% to 17.6%. The TYS, ultimate tensile strength (UTS) and EL of the AXM1104 alloy extruded at the ram speed of 1.5 mm/s was 412 MPa, 419 MPa and 12.0%, respectively, exhibiting comprehensive tensile mechanical properties with ultra-high strength and excellent plasticity. The ultra-high TYS of 412 MPa was mainly due to the strengthening from ultra-fine DRXed grains with segregation of solute atoms at grain boundaries. The strain hardening rate is increase slightly with increasing extrusion speed, which may be ascribed to the increasing mean DRXed grain size with rising extrusion speed. The higher strain hardening rate contributes to the higher EL of these AXM1104 samples extruded at higher ram speed.