Anisotropic high cycle fatigue property of Sc and Zr-modified Al-Mg alloy fabricated by laser powder bed fusion

This work investigates the defects (pore and lack of fusion), microstructure, and fatigue properties of Sc and Zr-modified Al–Mg alloy on different building directions fabricated by laser powder bed fusion (LPBF). The results showed that transversely deposited (TD) samples exhibited a superior fatigue strength (100.5 MPa) compared to that (57 MPa) of the parallelly deposited (PD) sample, while their tensile and hardness properties were similar. This phenomenon is attributed to two factors: defects and grain/microstructure. For the defects, the lack of fusion resulted in a higher stress concentration in the PD samples than that of the TD samples in the crack initiation stage. For the microstructure, owing to the indistinctive crack deflection and possible cyclic softening of the columnar grains, a decrement in fatigue resistance appears. Thus, the different crack propagation paths led to different columnar grain/equiaxed grain area ratios for the anisotropic fatigue properties. Furthermore, in the TD samples, some grains, with the <110>|| building direction orientation, partly led to a higher fatigue resistance of the TD sample than of the PD sample owing to the exceptional dislocation formation.