Temperature-dependent mechanical behavior of additively manufactured aluminum alloys

Abstract

Additive manufacturing (AM) enables the fabrication of lightweight, geometrically complex aluminum (Al) alloy components for aerospace, automotive, and energy applications operating across wide temperature ranges. Despite these promises, the temperature-dependent mechanical behavior of AM Al alloys remains insufficiently understood, particularly regarding the combined effects of alloy chemistry, AM process selection, and the resulting microstructure and defect populations on tensile and fatigue behaviors. This dissertation systematically investigates the tensile and fatigue behaviors of five representative AM Al alloys, including AlSi10Mg, F357 (AlSi7Mg), A6061-RAM2, A1000-RAM10, and Scalmalloy, fabricated via laser powder bed fusion (L-PBF) and laser powder direct energy deposition (LP-DED), across a temperature range from cryogenic (-195 °C) to elevated temperatures (up to 400 °C for tensile and up to 200 °C for fatigue). Integrating four peer-reviewed articles, this document encompasses three distinct material classes, i.e., precipitation-hardened Al-Si-Mg systems (AlSi10Mg and F357), particle-reinforced metal matrix composite systems (A6061-RAM2 and A1000-RAM10), and nanoprecipitate-strengthened Al-Mg-Sc-Zr systems (Scalmalloy). For each alloy and AM process combination, micro-/defect-structures have been characterized and correlated with temperature-dependent mechanical behavior. Key findings show that tensile strength generally decreases with increasing temperature due to enhanced dislocation mobility and thermally activated deformation mechanisms, with grain boundary sliding becoming dominant above approximately 200 °C. Conversely, cryogenic temperatures restrict dislocation motion, yielding peak strength values across all alloys. Process-dependent differences are observed, where L-PBF yields finer grain structures and higher tensile strength at low-to-moderate temperatures, and grain boundary sliding accelerates strength degradation at elevated temperatures. Fatigue behavior is governed by a combination of defect characteristics and temperature-dependent cyclic plasticity, with their relative influence varying across fatigue regimes; in the high-cycle regime, fatigue life is primarily controlled by the size and location of crack-initiating defects or particles, whereas in the low-cycle regime, cyclic plasticity plays a dominant role. Overall, this dissertation provides a comprehensive understanding of the relationships among alloy chemistry, processing, microstructure, defect content, and temperature-dependent tensile and fatigue behaviors of additively manufactured (AM) Al alloys. The findings contribute directly to the data and understanding needed to qualify and deploy reliable AM Al components in safety-critical engineering applications.