Masters Theses

Date of Award

12-2025

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

Bradley Jared

Committee Members

Bradley Jared, Brett Compton, Eric Lass

Abstract

Development of an aluminum metal-metal multi-material (MM) is achieved through robotic wire arc additive manufacturing (WAAM) and additive friction stir deposition (AFSD). Using both additive processes enables the deposition of two distinct alloys to create one monolithic component. The interface formed by combining these two additive processes, represents an unexplored region. A comprehensive understanding of the microstructural characteristics and mechanical behavior is necessary to evaluate its influence on the performance of the bimetallic interface. AFSD is a solid-state additive manufacturing (AM) process that plastically deforms the feedstock material, enabling deposition layer-by-layer. Robotic WAAM uses a gas metal arc welding (GMAW) torch, attached to the end effector of a robotic mechanism, to fuse material together, layer-by-layer. AFSD has higher deposition rates and can deposit alloys that are traditionally known as unweldable, specifically aluminum alloy 6061, which is prone to solidification cracking. Current AFSD machines are limited to 3-axis deposition, which limits capabilities within the printing process. Robotic WAAM has multi-axis deposition capabilities but must use aluminum filler wire, such as aluminum alloy 4943, that is less susceptible to solidification cracking. Printing with AFSD and WAAM sequentially, facilitates printing of complex geometries, where material versatility and deposition capability can be utilized from both AM processes. The resulting deposits are composed of multiple materials with discrete interfaces. Using AFSD, Al6061 is deposited, subsequently, WAAM Al4943 is deposited on the AFSD surface with varying orientations. The AFSD Al6061 and WAAM Al4943 interface is investigated through metallographic analysis in conjunction with mechanical testing. Results are then compared to the parent alloys as well as a wrought Al6061-T6 counterpart. Al6061 deposited via AFSD and Al4943WAAM both exhibited an overaging effect in the as-deposited (AD) condition. This is attributed to the repeated thermal cycles during the deposition processes. Strengthening precipitates coarsen, diminishing the deposited material’s mechanical performance. The discrete interface demonstrated superior mechanical performance compared to the weaker parent alloys, the AFSD Al6061. Under post T6 heat treatment, both alloys exhibited homogeneity, allowing strengthening mechanisms to develop, resulting in improved mechanical properties. Uniformity along the interface region was also observed, where the mechanical performance exceeded the Al6061 AFSD region. Characterization of the interface in both the as-deposited and heat treatment conditions, indicate that this region will not initiate failure, proved by its sufficient structural integrity. Such performance suggests the further use of aluminum MM developed through sequential AM of AFSD and WAAM without failure at the interface.

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