Towards Isotropic Properties in Additive Friction Stir Deposition of 7075 Aluminum

Additive friction stir deposition is a solid-state, near-net shape process capable of quickly building forge preforms. As a solid-state, friction stir derivative, the process creates depositions with refined grain structures, capable of forge like microstructures and properties. Recent efforts within the community have focused on eliminating graphite lubricants used in earlier development. Graphite free deposition required significant changes in the process parameters and tooling to effectively print AA7075-T6 material, and these changes led to increased anisotropy in the properties of the depositions. Many researchers show strong performance within a layer (horizontal properties), but have characterized significant challenges between layers (vertical properties). By evaluating the influence of layer heights, tool features, thermal processing regimes, and other process parameters, challenges influencing the bonding between layers becomes more clear, and pathways to achieve greater isotropy in AFSD depositions are defined. The present research both elucidates the challenges that have prevented strong vertical performance in AFSD deposits, and demonstrates how to overcome these same challenges to achieve tensile fractures across layers, and greater uniformity in properties regardless of direction.