Additive manufacturing (AM) has significant application value in the aerospace field due to its characteristics of free-forming and rapid production. However, the fatigue dispersion of materials produced by AM is considerable, and accurately assessing the fatigue life has become an important challenge in aerospace applications. SLM Al-Mg-Sc-Zr alloy exhibits high strength and low density. This paper establishes a fatigue life analysis method based on the mechanisms of crack initiation and propagation for this material. First, a rapid stress intensity factor (SIF) analysis model was developed for cracks with varies sizes and locations based on finite element analysis. Subsequently, the crack propagation life was evaluated using the NASGRO model, and a defect-based crack initiation life model was established. Ultimately, a two-stage fatigue life analysis encompassing both crack initiation and propagation was developed. The analysis results were compared with fatigue test data from TD (transverse build direction) and PD (parallel build direction) samples. The results indicate that the fatigue life experiment results generally fall within the twofold error band, validating the effectiveness of the proposed method. Crack initiation is primarily influenced by the defect geometric characteristics, while crack propagation is mainly governed by the microstructure. This method provides a scientific basis and means for fatigue life assessment of AM materials. Finally, prospects for future research directions were presented.
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