Compositional Formulations and Post-Process Heat Treatment Optimization of an Advanced Aluminum Alloy for Additive Manufacturing

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Author:
Sweny, Rebecca Ann
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 24, 2018
Committee Members:
  • Dr. Rich Martukanitz, Thesis Advisor
Keywords:
  • Al-Cu-Ag-Mg
  • Aluminum
  • Alloys for Additive Manufacturing
Abstract:
Traditional aluminum alloys for use in additive manufacturing have been developed from traditional foundry technologies. There is a need for the development of an aluminum alloy which takes full advantage of the benefits additive manufacturing offers, i.e. rapid solidification and cooling. Preliminary research conducted by the Center for Innovative Materials Processing through Direct Energy Deposition (CIMP-3D) in 2016 had shown that Al-Cu-Ag-Mg precipitation-hardenable alloys could achieve hardness exceeding 140 VHN after deposition and heat treatment, compared to the traditional aluminum alloy for additive manufacturing (Al-10Si-0.5Mg) which provided hardness near 100 VHN. A correlated improvement of strength was also seen with the advanced Al-Cu-Ag-Mg alloy, approaching 500 MPa, a typical yield strength for a 7075-T651 alloy. To better refine the target composition for commercialization, three metal powders were used to blend 9 characteristic Al-Cu-Ag-Mg compositions. Manufactured test specimens were printed by multiple deposition tracks using blended experimental powders. Specimen’s surface appearance was examined for porosity, cracks, and lack of fusion. Samples were subjected to post processing precipitation hardening heat treatment cycles to study the effect of aging temperature and time on hardness of samples varying in composition. The peak-aged condition was determined to be ¬¬20 hours at 160°C for alloys with moderate Cu and Ag contents. The alloy demonstrating the most improved hardness was characterized and tested for mechanical properties. The relationships between composition, aging temperature and aging duration were analyzed to determine the optimal parameters for an advanced aluminum alloy.