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.

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.