The influence of the defocusing distance on melt pool morphology, defect, microstructure and mechanical properties of the laser powder bed fusion (L-PBF) of high strength Al–Cu–Mg–Mn alloy was studied. It is found that because of the different laser energy distribution, the defocusing distance has significant effects on melt pool morphology, defects, microstructure and mechanical properties of the L-PBF parts using same process parameters and laser spot size. When defocusing distance in the range of −3.0 to 0 mm, specimens with cracks, fine grains and keyhole or transition melt mode are obtained. When defocusing distance is positive or −3.0 mm, specimens with no cracks, columnar grains and conduction mode are obtained. The best mechanical properties are obtained when defocusing distance is 1.0 mm in this experiment. This paper provides a novel method for tailoring the microstructure and mechanical properties of L-PBF parts.

研究了散焦距离对高强度Al–Cu–Mg–Mn合金的激光粉末床熔合（L-PBF）的熔池形态，缺陷，微观结构和力学性能的影响。研究发现，由于激光能量分布的不同，在相同的工艺参数和激光光斑尺寸下，散焦距离对L-PBF零件的熔池形态，缺陷，微观结构和力学性能有显着影响。当散焦距离在-3.0至0 mm范围内时，会获得带有裂纹，细小晶粒和锁孔或过渡熔融模式的样品。当散焦距离为正值或-3.0 mm时，获得的试样无裂纹，柱状晶粒和导电模式。在本实验中，当散焦距离为1.0 mm时，可以获得最佳的机械性能。