The fracture mechanism of Al–Mg-Sc-Zr alloy with high-Sc content fabricated by wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is one of the most promising technologies for manufacturing large and complex metal components, exhibiting particularly excellent compatibility with Al-Mg-Sc-Zr alloys. However, increasing the Sc content more than 0.60 wt.%, the strength significantly decreased. At present, no studies reported the mechanism of the strength reduction. Therefore, in this work, CMT + Adv was used to prepare Al-Mg-0.72Sc-0.23Zr (wt.%) alloy, and the reasons for the lower strength at high Sc content were deeply discussed. Results indicated that pores aggregated at interlayer zone, with a porosity of about 0.43%. The microstructures were fine equiaxed grains, with an average grain size of approximately 7.64 ± 3.57 μm. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the heat-treated alloy (325 °C - 6 h) were 276 ± 3 MPa, 396 ± 4 MPa, and 17 ± 2% in the horizontal (H) direction, respectively. Solid solution strengthening and precipitation strengthening were the main strengthening mechanisms. However, the performance significantly decreased in the vertical (V) direction, with UTS and EL being about 337 ± 3 MPa and 5 ± 1%, respectively. Results showed that primary micrometer Al 3 (Sc, Zr) phases was the main reason for the alloy fracturing in the H direction. The combination of pores and primary micrometer Al 3 (Sc, Zr) phases with diameter greater than 3 μm led to the alloy fracture in the V direction. This work provided the first explanation for the strength reduction in high-Sc alloys, laying a theoretical foundation for the composition design of high-strength Al-Mg-Sc-Zr alloys.