Author ORCID Identifier
https://orcid.org/0000-0002-4577-1939
Date Available
12-11-2025
Year of Publication
2025
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Engineering
Department/School/Program
Materials Science and Engineering
Faculty
Paul Rottmann
Faculty
Matthew Beck
Abstract
The processing of certain metals and alloys under magnetic fields presents a promising yet underexplored frontier for controlling microstructure alongside improving physical and mechanical properties. Magnetic fields can be strategically applied at different stages of materials processing, from melting and solidification to subsequent heat treatments to achieve targeted properties in materials. Although magnetic fields have been found to aid changes in microstructural evolution and phase equilibria in ferrous materials, there is limited application of this technique in non-ferrous material systems. This dissertation aims at contributing to the understanding of the influence of magnetic field on the mechanical properties and solid-state diffusion in different non-ferrous metallic systems.
The first section of this dissertation investigates the mechanical properties and precipitate evolution in a conventionally peak-aged 7075 aluminum alloy. Peak-aged 7xxx series possess ultra-high strength, a property derived from two complementary factors: thermomechanical processing and a high density of nanoscale precipitates formed during aging. While laboratory-scale samples often achieve a uniform distribution of these strengthening phases, this homogeneity is frequently lost in large-scale industrial plates, leading to a gradient of properties. For this study, the through-thickness of a 32-mm thick hot rolled 7075 aluminum alloy was investigated. The alloy exhibited a complex M-shaped mechanical strength profile through the thickness of the plate as opposed to a parabolic trend that would be expected for a simpler system. The influence of varying cooling rate and non-uniform plastic deformation was taken into account in modelling the evolution of precipitates and strength profile. A computational model coupled with experimental data enabled quantification of the contribution of both heterogenous cooling rate and varying nucleation site density in the evolution of properties through the thickness of the 7075 aluminum alloy plate.
The second section of this dissertation provides fundamental understanding on the effect of magnetic field annealing on the mechanical properties and precipitate evolution in three (3) 7xxx aluminum alloy; 7075, 7085 and 7056 at time steps below the peak ageing condition. The main strengthening-precipitate-forming alloying element in these 3 different alloys are Zn and Mg, however in varying compositions. This work demonstrates the influence of alloy composition in the susceptibility of the different 7xxx aluminum alloys to magnetic field treatment while being aged for 1, 2 and 4 h under 0 and 3 Tesla. With magnetic field, the 7xxx aluminum alloys showed improved yield strength (up to 27 MPa) and microhardness (up to 10 HV). The solute supersaturation which is correlated to the total Zn and Mg content in these 7xxx alloys proved to be a driving force for the extent to which the alloys were susceptible to magnetic field treatment. This section heralds a novel processing route for enhancing the properties of non-ferrous metals such as aluminum alloys.
The third section of this dissertation underscores the contribution of magnetic field annealing to the solid-state diffusion of a coupled Al-Mg-Zn system. In this work, binary alloys are being coupled together with thermal compression bonding technique at suitable temperature, strain and compressional force without magnetic field. The solid-state bonded systems were then annealed without (0T) and with magnetic field (3T) at different temperatures. The results seek to elucidate the mechanisms that give rise to increased strength and precipitation kinetics observed for Mg- and Zn-containing Al alloys arising from the application of an external magnetic field during annealing.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2025.592
Funding Information
This research was supported by DEVCOM Army Research Laboratory (Award No. W911NF-21-2-0075). This work was performed in part at the U.K. Electron Microscopy Center, a member of the National Nanotechnology Coordinated Infra-structure (NNCI), which is supported by the National Science Foundation (NNCI-2025075).
Recommended Citation
Alewi, Damilola David, "Understanding the influence of applied magnetic field on aluminum alloys: Implications on strength, precipitate development and diffusion of solutes" (2025). Theses and Dissertations--Chemical and Materials Engineering. 185.
https://uknowledge.uky.edu/cme_etds/185
