Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 149762

149762 - Process-Structure-Property Relationships in Additively Manufactured Alnico Permanent Magnets 

As the United States strives to achieve net-zero carbon emissions by 2050, the demand for permanent magnets is expected to grow. These magnets are critical for the energy sector in wind turbines, hydroelectric power generators, and electric vehicles [3]. Neodymium-iron-boron and Samarium-Cobalt magnets are currently the strongest commercially viable magnets; however, they contain rare-earth elements that suffer from market volatility and geopolitical instability and require hazardous mining practices [3]. Among the possible alternatives for rare-earth magnets, Alnico alloys (so-called by their majority composition of aluminum, nickel, iron, and cobalt) are attractive as they demonstrate high saturation magnetization and high-temperature performance with small magnetic remanence temperature coefficient (-0.025%/°C) and positive coercivity temperature coefficient (+0.01%/°C) up to 550 ̊C, as well as resistance to corrosion effects [3].

Alnico alloys consist of periodically distributed and crystallographically oriented ferromagnetic (Fe-Co)-rich nanostructures embedded in an (Al-Ni)-rich matrix formed by spinodal decomposition. With current manufacturing, producing Alnico magnets requires a complex routine of casting, melting, and controlled heat treatment at high temperatures in the presence of a strong magnetic field[1]. During these processes, the magnet is prone to brittleness, oxidation, porosity, and mediocre gain development, leading to lower performance and thus limiting device applications [1]. To overcome these challenges, this study focusses on fabricating Alnico magnets using Direct Energy Deposition (DED) - a metal 3D printing approach characterized by non-equilibrium solidification conditions (large temperature gradients, high cooling rates, and cyclic reheating) that inherently produce directionally aligned grains and metastable precipitates that are novel and cannot be realized through conventional casting [4].

In this study, gas-atomized pre-alloyed Alnico-3 powders (Al 0.121–Ni 0.255–Cu 0.034–Fe0.589) were built into cube-shaped samples (~5x5mm) using a laser-based deposition system equipped with sensors for real-time monitoring of the printing process. The laser operating parameters (power P, speed ν, beam radius D) and the powder mass flow rate during printing was varied systematically in three experimental builds, resulting in a library of ~90 samples. Results indicate that scanning strategies and heat treatment conditions strongly influence the structural and magnetic properties of the 3D-printed magnets. In particular, the size of the columnar grains and the coercivity (H_c) of the as-printed magnets increase monotonically a function of the energy density (E) during deposition (Note: . Select specimens were heat treated in a vacuum at 835 °C for 10 minutes to solutionize the alloy and then slow-cooled to 560 °C for annealing for a prolonged period of four hours. Following heat treatment, samples deposited with E <1.1 J·s/kg·mm³ demonstrate an increase in H_c, while those deposited with E >1.1 J·s/kg·mm³ show a distinct decrease. Structural characterization using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and x-ray diffraction (XRD) indicate that the magnetic properties of the DED-processed Alnico magnets are closely correlated to the crystallographic texture, morphology, and spatial dimensions of the spinodal decomposed phases. Initial investigation reveals that lower laser power produces smaller grains than higher laser power due to the lower quenching times of a build area. However, annealing is still required for precipitate growth which has not been observed in the as-printed samples. Additional process-structure-property correlations in the additively manufactured permanent magnet composites will be discussed comprehensively to provide insight into the interplay between chemical composition, microstructure effects, and magnetic properties in Alnico alloys. 

Acknowledgment: This work is supported by the U.S. National Science Foundation (Award No. 2310234)

[1] - Zhang, C., Li, Y., Han, X. H., Du, S. long, Sun, J. bing, & Zhang, Y. (2018). Structure and magnetic properties of Alnico ribbons. Journal of Magnetism and Magnetic Materials, 451, 200–207. https://doi.org/10.1016/j.jmmm.2017.11.045

[2] - Svetlizky, David, et al. "Directed energy deposition (DED) additive manufacturing: Physical characteristics, defects, challenges and applications." Materials Today 49 (2021): 271-295.

[3] - Coey, J. M. D. "Perspective and prospects for rare earth permanent magnets." Engineering 6.2 (2020): 119-131.

[4] Cui, Jun, et al. "Manufacturing processes for permanent magnets: Part I—sintering and casting." Jom 74.4 (2022): 1279-1295.

Presenting Author: Anthony Duong Virginia Commonwealth University

Presenting Author Biography: Anthony is a 3rd year Doctoral Graduate Student at Virginia Commonwealth University under Dr. Radhika Barua. He works closely with research partners at The Commonwealth Center for Advanced Manufacturing on projects focused on finding Process-Structure correlations in Direct Energy Deposition additive manufacturing of different magnetic compounds.

Authors:

Anthony Duong Virginia Commonwealth University
Ian Smith Virginia Commonwealth University
Kyle Snyder Commonwealth Center for Advanced Manufacturing
Omar Bishop Virginia Commonwealth University
Everett Carpenter Virginia Commonwealth University
Radhika Barua Virginia Commonwealth University