Al–Mg–Sc–Zr fatigue samples were formed by selective laser melting to study the characteristics of pore defects and effect of pore defects on fatigue properties of aluminum alloy by laser additive manufacturing. The threedimensional characteristics of pore defects in fatigue samples were characterized by X-ray computed tomography (X-CT)

and the number

size and morphology of pore defects were statistically analyzed. The fatigue properties of alloy were tested by fatigue test and fatigue fracture morphology was observed. The results show that pore defects mainly comprise of porosity and lack of fusion (LOF)

in which

the LOF defects are large in size

irregular in shape and mostly flat interlayer unfused defects. The porosity of fatigue samples ranges from 0.004% to 0.102%; the large-size pore defects (with an equivalent diameter 100 μm) account for 0.58% of the total pore defects; the maximum equivalent diameter is 188 μm. The degree of sphericity (DOS) of pore defects is between 0.2 and 0.6 with DOS of large-size pore defects less than 0.4. Fatigue fracture morphology shows that the fatigue cracks originated from LOF defects of the sample surface

moreover

the larger the feature size of the crack source defects

the lower the fatigue life of the sample.