With the advancement of laser powder bed fusion (LPBF) additive manufacturing, efficient utilization of powders beyond conventional particle distributions (15~53 μm) has become critical for improving raw material efficiency. This study systematically investigates process optimization, microstructure, and mechanical properties of coarse AlMgScZr alloy powders (53~150 μm) in LPBF. The controlled variable method was employed to analyze parameter effects on density, defects, microstructure, and mechanical performance. Results demonstrated that the coarse powder exhibited a narrow process window with high sensitivity to parameter fluctuations. Optimized parameters were identified as layer thickness of 100 μm, laser power of 450 W, and scanning speed of 900 mm/s, achieving relative density of 99.3±0.2 %. Microstructural analysis revealed fine equiaxed grains near fusion boundaries transitioning to columnar grains within molten pools, with no observable secondary precipitates. The as-printed samples showed an average microhardness of 98.8±8.0 HV0.1, tensile strength of 336.5±8.0 MPa, and elongation of 12.7±0.4 %. The findings could provide valuable insights for improving material utilization efficiency and process reliability in LPBF, particularly for expanding applicability of off-size powder in industrial applications.