Microstructural Features and Metastable Phase Formation in a High-Strength Aluminum Alloy Fabricated Using Additive Manufacturing

Published

April 25, 2025

Author(s)

Andrew Iams, Jordan Weaver, Brandon Lane, Lucille Giannuzzi, Feng Yi, Darby LaPlant, John Martin, Fan Zhang

Abstract

Additive manufacturing (AM) has captured recent attention for its potential to fabricate high-strength aluminum alloy components. A detailed understanding of the microstructure under the as-fabricated conditions is required to harness its potential. We conducted a thorough, multi-length-scale microstructural and computational analysis of the commercially available, precipitation-hardenable aluminum alloy (AA) 7A77 designed for AM applications. Using the as-fabricated and single pass samples, we determined an unambiguous bimodal microstructure predominantly influenced by the solidification process, with fine, equiaxed grains near the melt-pool boundary and the coarse, elongated grains in the center of the melt pool. Two critical metastable phases were identified: the cuboidal L12 Al3Zr phase within fine grains and the icosahedral Mg32(Al, Zn, Cu)49 quasicrystals predominantly within coarse grains and along grain boundaries. Computational simulations revealed a secondary phase predicted to form at the termination of solidification has a composition favorable for the formation the icosahedral quasicrystals. Our nanoindentation data demonstrate the as-fabricated AA7A77 has a hardness value comparable to that of the peak-aged AA7075 alloy, which leads to the possibility of further improvement through a precipitation-hardening heat treatment of AA7A77. Our study brings new insights into the microstructural characteristics of high-strength AM aluminum alloys and provides a novel pathway for intentionally incorporating quasicrystals for improved mechanical performance.

Citation

Journal of Alloys and Compounds

Pub Type

Journals

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Keywords

additive manufacturing, powder bed fusion, aluminum, microstructure, quasicrystal

Citation

Iams, A. , Weaver, J. , Lane, B. , Giannuzzi, L. , Yi, F. , LaPlant, D. , Martin, J. and Zhang, F. (2025), Microstructural Features and Metastable Phase Formation in a High-Strength Aluminum Alloy Fabricated Using Additive Manufacturing, Journal of Alloys and Compounds, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=956803 (Accessed April 19, 2025)