In situ investigation into temperature evolution and heat generation during additive friction stir deposition: A comparative study of Cu and Al-Mg-Si

Abstract Additive friction stir deposition is an emerging solid-state additive manufacturing technology that enables site-specific build-up of high-quality metals with fine equiaxed microstructures and excellent mechanical properties. By incorporating machining, it has the potential for creating large-scale complex 3D geometries as a hybrid technology. Still early in its development, a thorough understanding of the thermal process fundamentals, including temperature evolution and heat generation mechanisms, has not been established. Here, we aim to bridge this gap through in situ monitoring of the thermal field and material flow behavior using complementary infrared imaging, thermocouple measurement, and optical imaging. Two materials challenging to print via beam-based additive technologies, Cu and Al-Mg-Si, are investigated. During additive friction stir deposition of both materials, we find similar thermal feature trends (e.g., the trends of peak temperature T P e a k , exposure time, and cooling rate) with respect to the processing conditions (e.g., the tool rotation rate Ω and in-plane velocity V ). However, there is a salient quantitative difference between Cu and Al-Mg-Si; T P e a k exhibits a power law relationship with Ω / V in Cu but with Ω 2/ V in Al-Mg-Si. We correlate this difference to their distinct interfacial contact states that are observed through in situ material flow characterization. In Cu, the interfacial contact between the material and tool head is characterized by a full slipping condition, so interfacial friction is the dominant heat generation mechanism. In Al-Mg-Si, the interfacial contact is characterized by a partial slipping/sticking condition, so both interfacial friction and plastic energy dissipation contribute significantly to the heat generation.