Magnesium (Mg) alloys have attracted considerable attention in the automotive and aerospace industries due to their exceptional lightness, high specific strength, and excellent castability. However, their susceptibility to fatigue failure poses significant challenges for the long-term service under cyclic loading. This review systematically explores the precipitation behavior in the representative rare-earth containing magnesium (Mg-RE) alloys and examines the critical role of precipitates in influencing fatigue behavior. The alloying elements and heat treatment play a pivotal role in affecting the precipitation behavior of the Mg-RE alloys. Notably, the β′, β″, and 14H long-period stacking ordered (LPSO) phases serve as primary strengthening precipitates in the Mg-Gd (Y), Mg-Nd, and Mg-RE-Zn based alloys, respectively. The size, quantity, and distribution of these precipitates can be finely controlled through the optimization of aging treatment parameters. Based on the fundamental principles for enhancing fatigue resistance, this review offers a detailed analysis of the effects of precipitates on fatigue behavior, addressing key aspects such as crack initiation, propagation, and fatigue failure under high-cycle fatigue (HCF) conditions. Besides, the effects of precipitates on the cyclic stress response, cyclic deformation characteristics, and fatigue life under low-cycle fatigue (LCF) conditions are systematically summarized. The influence of precipitates on fatigue behavior of Mg-RE alloys is primarily attributed to the mechanisms such as dislocation pinning, crack path deflection, precipitation strengthening, and the suppression of twinning. This review highlights the significance of precipitation behavior in optimizing fatigue resistance and provides valuable insights into future research directions for advancing Mg-RE alloys in the fatigue-critical structural applications.

A low rare-earth containing ZEK100-O magnesium alloy was welded to AA1230-clad high-strength AA2024-T3 aluminum alloy via solid-state ultrasonic spot welding (USW) to evaluate the microstructure, tensile lap shear strength, and fatigue properties. The tensile strength increased with increasing welding energy, peaked at a welding energy of 1000 J, and then decreased due to the formation of an increasingly thick diffusion layer mainly containing Al₁₂Mg₁₇ intermetallic compound at higher energy levels. The peak tensile lap shear strength attained at 1000 J was attributed to the optimal inter-diffusion between the magnesium alloy and softer AA1230-clad Al layer along with the presence of ‘fishhook’-like mechanical interlocks at the weld interface and the formation of an indistinguishable intermetallic layer. The dissimilar joints welded at 1000 J also exhibited a longer fatigue life than other Mg-Al dissimilar joints, suggesting the beneficial role of the softer clad layer with a better intermingling capacity during USW. While the transverse-through-thickness (TTT) failure mode prevailed at lower cyclic loading levels, interfacial failure was the predominant mode of fatigue failure at higher cyclic loads, where distinctive fatigue striations were also observed on the fracture surface of the softer clad Al layer. This was associated with the presence of opening stress and bending moment near the nugget edge despite the tension-tension lap shear cyclic loading applied.

Strain-controlled cyclic deformation behavior of a high-strength low-alloy (HSLA) Mg-1.2Zn-0.1Ca alloy fabricated via low-temperature extrusion at 150 °C was investigated at different strain amplitudes. Due to the partial dynamic recrystallization (DRX) during extrusion, the extruded HSLA magnesium alloy consisted of a unique heterostructure containing coarse unDRX grains and ultra-fine DRX grains of 0.8 µm, leading to a high tensile yield strength of 374 MPa and an elongation of 14%. The HSLA magnesium alloy exhibited cyclic stabilization at strain amplitudes of ≤0.4%, while cyclic hardening occurred at strain amplitudes of ≥0.6%. In contrast, the homogenized alloy with a uniform coarse-grained microstructure showed a strong cyclic hardening characteristic. Compared with the homogenized alloy, the HSLA magnesium alloy had a significantly higher cyclic stress level at all strain amplitudes, along with a longer fatigue life at lower and intermediate strain amplitudes owing to its higher monotonic strength. However, the homogenized alloy showed a longer fatigue life at a high strain amplitude of 0.8 % due to its better ductility and stronger capacity of storing deformation. While {10–12}<10−11> extension twinning occurred in both the homogenized and HSLA samples at high strain amplitudes, twins were primarily formed in the coarse unDRX grains in the compressive phase during cyclic deformation due to the c-axes of unDRX grains perpendicular to the loading direction, with twinning in the ultra-fine DRX grains being suppressed. The low-cycle fatigue life of both the homogenized and HSLA samples can be well predicted through an accumulative damage model based on the strain-energy density calculation and intrinsic fatigue toughness concept.