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.

The strength-ductility trade-off in magnesium alloys remains a critical challenge urgently requiring resolution in their engineering applications. In this study, both mechanical and corrosion properties are enhanced in extruded Mg-Y-Nd-Zr alloys by Sm addition. Sm promotes dynamic recrystallization, activates non-basal slip systems and weakens basal texture intensity, leading to the sub-grain lamellar structure and rare earth texture. The EWS2 alloy exhibits an outstanding combination of high yield strength (328 MPa) and ductility (15.1%). Furthermore, the fragmented second phases in the Sm-containing alloy are uniformly distributed, reducing the subsequent corrosion driving force after micro-galvanic corrosion and facilitating the growth of a more passivating and compact corrosion film. These combined effects contribute to the lowest degradation rate in the EWS2 alloy. This study demonstrates the correlation between microstructure and properties in Sm-containing WE series alloys, providing insights for the design of other high performance magnesium 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.

The effect of different extrusion parameters on the microstructure and mechanical properties of Mg-4Sm-3Gd-2Yb-0.5Zr (SGY2) alloy was investigated. It was observed that under different extrusion parameters, unDRXed grains of SGY2 alloy exhibited a pronounced basal plane texture, specifically <0110>//ED, while the texture of DRXed grains was relatively dispersed. Under the condition of 420 °C and an extrusion ratio of 9.4 (420 °C-ER9.4), the basal plane texture intensity of unDRXed grains in SGY2 alloy was the highest. Furthermore, SGY2 alloy at different extrusion parameters exhibited recrystallization mechanisms mainly characterized by continuous dynamic recrystallization (CDRX), with some DRXed grains and deformed grains experiencing discontinuous dynamic recrystallization (DDRX). Additionally, at the 420 °C-ER9.4, the second phase particles in the as-extruded SGY2 alloy were smaller in size and exhibited a dispersed distribution. Under this condition, a significant amount of dislocation accumulation, dislocation bypassing, and dislocation tangling phenomena were observed in the SGY2 alloy. The primary deformation mechanism of unDRXed grains in the SGY2 alloy at the 420 °C-ER9.4 may involve prismatic plane 〈a〉, pyramidal plane 〈a〉, and pyramidal plane 〈c + a〉 slip, thereby activating a significant amount of dislocations. Compared to other extrusion conditions, this condition is more prone to activate non-basal plane slip. The as-extruded SGY2 alloy exhibited superior mechanical properties, with ultimate tensile strength (UTS) and yield strength (YS) of 332 MPa and 278 MPa, respectively. This is mainly attributed to the extremely fine grains, with many DRXed grains having grain sizes smaller than 1 µm, and higher density grain boundaries produced under this condition. Additionally, the unDRXed grains contain a high density of dislocations with small Schmid factor (SF), thus effectively inhibiting basal plane slip and strengthening the alloy to some extent. Similarly, the increased presence of second phase particles will also contribute to strengthening the alloy matrix through precipitation hardening.