Date of Award


Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

Committee Chair/Advisor

Dr. Enrique Martinez Saez

Committee Member

Dr. Garret Pataky

Committee Member

Dr. Sun Cheng


Aluminum-copper (Al-Cu) alloys are widely used in the aerospace industry due to their favorable strength-to-weight ratio, good fatigue resistance, and corrosion resistance. These properties make Al-Cu alloys an excellent choice for aircraft structural components that require high strength and low weight. Additive manufacturing (AM), also known as 3D printing, has emerged as a promising processing method for Al-Cu alloys in aerospace manufacturing. AM enables the production of lightweight optimized geometries difficult to manufacture through conventional subtractive methods. AM also reduces material waste by only depositing material where needed in the part geometry. The rapid solidification conditions in AM processes motivate further study of solid-liquid interface properties in Al-Cu alloys. This work examines the solid-liquid interface using molecular dynamics (MD) simulations and the capillary fluctuation method (CFM). CFM facilitates quantitatively determining key interfacial characteristics like stiffness, energy, and anisotropy. Simulations were performed under both equilibrium conditions and applied thermal gradients to replicate AM processes. Applying a thermal gradient across the interface led to an augmentation in stiffness and interfacial free energy while preserving the constancy of anisotropic characteristics. This phenomenon was theoretically elucidated by employing a Taylor expansion of the interfacial free energy function. The equations representing the relationships are: for energy and for stiffness, where G represents the thermal gradient. The present study involved simulations on Al-Cu alloys containing varying concentrations of copper, specifically 2%, 3.58%, and 5.065% Cu. These simulations were conducted at different temperatures, 905K, 888K, and 874K, respectively. A total of eight unique interface orientations were investigated. The obtained results were consistent with the proposed theoretical relationships, thereby confirming the presence of anisotropy independent of the gradient and the validity of the first-order Taylor expansion. This study provides fundamental insights into interfacial phenomena during Al-Cu alloy solidification, which can help optimize AM processes by reducing defects. The calculated parameters have significant implications for larger scale computational models of AM by improving accuracy compared to experiments when incorporating non-equilibrium conditions.



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