Solid-State Additive Manufacturing of Alternating Dissimilar Aluminum Layers: Time-Series Events and Co-Evolutional Mechanisms

Nikhil Gotawala, S. Mohammad H. Hojjatzadeh †, Mackenzie E.J. Perry ‡, Greg D. Hahn, and Hang Z. Yu *

Department of Materials Science and Engineering, Virginia Tech, Blacksburg, VA 24061, USA

† Current Address: Department of Mechanical Engineering, University of Memphis, 3720 Alumni Ave, Memphis, TN 38152, USA

‡ Current Address: Naval Surface Warfare Center Carderock Division (NSWCCD), 9500 MacArthur Blvd, West Bethesda, MD 20817, USA

* Corresponding Author: hangyu@vt.edu

Abstract

Additive manufacturing of dissimilar aluminum alloys holds significant promise for industrial applications, enabling lightweight structures with a balance of strength, corrosion resistance, and formability. Fusion-based additive manufacturing, however, often generates undesirable interfacial phases due to high energy input. Here, we present a solid-state approach using additive friction stir deposition to fabricate alternating layers of Al-Cu and Al-Mg-Si alloys, focusing on the time-series evolution of interfacial morphology, grain structure, and precipitates. To investigate the effects of reheating and re-deformation during multi-layer deposition, structures with varying layer counts (one to six) are printed and analyzed. X-ray computed tomography shows asymmetric material distribution, with swirling concentrated on the advancing side of each layer. Successive layer deposition is found to cause local thinning, stretching, bulging, and detachment in the underlying layers due to compression and shear. Continuous dynamic recrystallization is identified as the dominant grain refinement mechanism in both alloys, though Al-Mg-Si exhibits larger grains than Al-Cu, attributed to incomplete recrystallization. Complex precipitate evolution is revealed by comparing the printed Al-Mg-Si in the second layer of two-layer and six-layer structures, as well as the printed Al-Cu in the first layer of these structures. In both cases, reheating during subsequent layer deposition is proven to fully dissolve the initial precipitate phases formed during printing, leading to the development of new precipitate types and morphologies upon cooling. This results in a heterogeneous hardness distribution along the build direction, emphasizing the intricate interplay of thermal and mechanical effects during the printing of alternating dissimilar aluminum layers.

Keywords

Additive friction stir deposition; Multi-layer; Dissimilar Aluminum; Interfacial Morphology; Precipitate evolutions; Reheating effect