Printability assessment with porosity and solidification cracking susceptibilities for a high strength aluminum alloy during laser powder bed fusion

Abstract

The rapid development of additive manufacturing requires a large number of printable metallic materials for various engineering applications. In this work, the printability of a high strength aluminum alloy AA2024 was evaluated for laser powder bed fusion (LPBF) with comparisons to the widely used AlSi10Mg. Strikingly different solidification cracking networks were generated when using diverse scanning strategies and overlap rates of adjacent tracks. Depending on the overlap rates, the crack propagation patterns transited from the longitudinal-dominant to the transverse-dominant. The lengths and propagation angles of the transverse zigzag cracks were strongly interdependent and both increased with the overlap rate of adjacent tracks. The characterization results implied that these diverse crack propagation patterns originated from the columnar grain structure, which were produced in the localized solidification conditions determined by the track-wisely moving molten pool. The characteristics of the thermal cycles and solidification conditions of AlSi10Mg and AA2024 were further examined using a comprehensive phenomenological model for a better understanding of the printability of AA2024. The results showed that AA2024 generated smaller molten pool and that AA2024 was more susceptible to lack of fusion defects given the same LPBF process conditions. Supported by the evaluated printability of AA2024, a comprehensive scheme targeting the printing of crack-free LPBF builds was proposed considering the heat input, the overlap rate, and the scanning strategies of the laser beam.