Engineering precipitates via novel hybrid additive manufacturing enables effective hydrogen trapping

Abstract

This work shows that novel manufacturing routes combining wire arc additive manufacturing (WAAM) and in situ deformation enable control of size, shape, and particle/matrix interface characteristics. To this end, precipitation of the Al3Sc phase in aluminum alloys was studied in specimens fabricated by as-built (W), as-built and thermally post-processed WAAM, as well as in specimens produced by WAAM combined with in-process rolling (HR-W). The experimentally determined equilibrium shape of Al3Sc precipitates in HR-W specimens is a large, elongated ellipsoid with coherent interfaces, a morphology not previously reported for this phase. No Al3Sc particles were detected in W specimens, whereas P-W specimens exhibited the conventional rhombicuboctahedral precipitates with semi-coherent interfaces. Theoretical calculations, together with positron annihilation spectroscopy, confirm that excess vacancies drive this morphological transition. The combination of atom probe tomography, density functional theory, and thermal desorption spectroscopy revealed that coherent Al3Sc∥Al interfaces trap H, whereas a semi-coherent boundary does not trap hydrogen. These findings highlight the interplay between non-equilibrium processing, defect dynamics, and hydrogen trapping, offering a more fundamental understanding of hydrogen behavior in aluminum alloys.