Among existing lightweight metals, magnesium (Mg) alloys have garnered significant attention due to their exceptional specific strength. However, their laser welding applications face challenges from porosity, cracking, and grain coarsening defects. Rare earth (RE) elements, leveraging their unique strengthening effects, offer a promising solution for refining weld microstructures and suppressing welding defects. Nevertheless, a systematic review of RE-enhanced mechanisms and defect suppression strategies remains lacking. This paper systematically reviews recent research advancements in Mg alloy laser welding, with a focused elucidation of the governing effects of welding parameters on weld performance, and the core mechanistic roles of RE elements in the welded joint. Furthermore, we discuss key challenges and future directions in process optimization, service performance enhancement, and industrial scalability of RE-modified Mg alloy welding. The findings aim to provide theoretical foundations for designing high-performance welded Mg-RE structures and advance lightweight manufacturing technologies in aerospace, electric vehicles, and other cutting-edge industries.

The hot deformation behavior of magnesium (Mg) alloys is significantly governed by the multi-physics coupling effects of temperature (T), strain rate (ε) and strain (ε), resulting in flow behavior that exhibits pronounced nonlinearity and multi-scale complexity. This study systematically investigates the hot deformation behavior of Mg-Y-Nd-(Sm)-Zr alloys. Sm alloying promotes recrystallization. The flow stress of Sm-containing alloys declines sharply towards a steady state after reaching its peak value. To overcome the limitations of the Arrhenius-type constitutive (AC) model in predicting complex nonlinear flow behavior, the AC and data hybrid informed neural network (ACINN) model is developed. This approach enhances the predictive accuracy and extends the applicability of the traditional AC model. The evolution of microstructure and recrystallization behavior under hot deformation conditions are investigated based on results from electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The relationship between the power dissipation factor (η) and recrystallization behavior is further examined using K-means clustering analysis. The results demonstrate that dynamic recrystallization (DRX) behavior varies with the η value, comprising four distinct regimes: dynamic recovery (DRV), discontinuous dynamic recrystallization (DDRX) dominance, continuous dynamic recrystallization (CDRX) dominance and complete dynamic recrystallization. This analysis presents a new perspective for studying the hot deformation processes of Mg alloys.

In this study, friction stir processing (FSP) was employed to modify the as-cast Mg-14Gd-0.6Ce-0.5Zr alloy, and the effects of texture evolution and distribution of second phases on mechanical properties were systematically investigated. The results show that friction stir processing effectively refined the coarse Mg₅Gd phases into nanoscale second phases uniformly distributed along grain boundaries. The synergistic effect of texture weakening and second phases refinement significantly enhanced the tensile strength and elongation of the FSP-1000-120 alloy to 302.1 MPa and 18.3%, respectively, representing increases of 20.8% and 281.3% compared to the as-cast alloy. The as-cast alloy has a lower corrosion rate in the initial stage due to fewer micro-galvanic corrosion sites. However, the uniform distribution of the second phase in the FSP-treated (FSPed) alloy contributes to the formation of a more complete and dense corrosion product film. After 120 h of immersion, the as-cast alloy forms deep pits due to the continuous dissolution at the second phase-matrix interface, with the average corrosion rate increasing from 0.31 to 0.47 mL/cm²/h. The long-term corrosion rates of FSP-1000-60, FSP-1000-120, and FSP-1200-120 samples are stable at 0.36, 0.43, and 0.50 mL/cm²/h, respectively. Research reveals that FSP regulates texture and second phase distribution to achieve synergistic strengthening of alloy strength plasticity, and the homogenization of second phase distribution is a key factor in improving the long-term corrosion resistance of alloys.

A high-strength magnesium alloy containing Yb was prepared through a simple hot extrusion process. The effect of Yb addition on dynamic precipitation, texture evolution, dynamic recrystallization mechanisms, deformation mechanisms, and strengthening mechanisms in as-extruded Mg-4Sm-3Gd(-2Yb)-0.5Zr (SGY0, SGY2) alloys was systematically investigated. The results indicated that the average grain size decreased from 4.17 µm to 1.48 µm with the addition of Yb. This extreme grain refinement greatly enhances the strength. The addition of Yb significantly facilitated the phase precipitation, but did not change the texture type. The non-dynamic recrystallized (unDRXed) grains exhibited a strong basal plane texture of <0110> parallel to the extrusion direction (ED), while the dynamic recrystallized (DRXed) grains showed a weaker rare earth texture, characterized by <1212> // ED. Moreover, the as-extruded SGY0 and SGY2 alloys predominantly undergo continuous dynamic recrystallization (CDRX), and some DRXed grains exhibit a discontinuous dynamic recrystallization mechanism (DDRX). In addition, the addition of Yb facilitates the activation of non-basal plane slip. The dislocation types in the as-extruded SGY0 and SGY2 alloys include 〈a〉, 〈c〉 and 〈c + a〉 dislocations. However, the SGY2 alloy exhibits a relatively high dislocation density, which contributes to the enhancement of the strength. Extreme grain refinement and the dispersion of nanoscale second-phase particles are key factors in increasing the strength.

We studied the microstructure evolution of Mg-4Y-3Nd-2Sm-0.5Zr alloy by quasi-in-situ electron backscatter diffraction (EBSD) along with several strains under compression tests, which provided direct evidence for the influence of different twin-twin geometric structure on the twinning behavior. The results showed that the mechanical properties of the alloy were higher than traditional magnesium alloys (the maximum compressive strength reaches 402.5 MPa) due to the strengthening effect of Sm and Nd elements addition on solution strengthening, precipitation strengthening, and grain refinement. Combined with the quasi-in-situ EBSD technique, two different twin-twin geometric structures, ‘parallel structure’ and ‘cross structure’, were observed directly in the alloy. In the later stage of deformation, for ‘parallel structure’, residual stress and a large number of dislocations mainly existed in the twin boundary and tip position. For the ‘cross structure’, there was a lot of dislocation density in the interior of twins after fusion. The twin growth rate of ‘parallel structure’ was much faster than that of ‘cross structure’ because the stress of twins was mainly concentrated on the tip of twin. When the movement for the tip of twin was blocked, the growth rate of twin would be obviously decreased. Moreover, the ‘cross structure’ was easy to produce closed space. Due to the constraints of surrounding twins, the confined space was easy to stress concentration, thus inhibiting the growth of twins. At the same time, the ‘cross structure’ of twins needed a more external force to continue to deform, which also served as a strengthening structure.