Effect of defocusing distance on laser powder bed fusion of high strength Al-Cu-Mg-Mn alloy

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.