Investigation of microstructural and mechanical properties in AA2024-T351 multi-layer friction surfacing

This study on multi-layer friction surfacing (MLFS) as a process for additive manufacturing focuses on the influence of process parameters on the resulting microstructural properties for the precipitation-hardenable Al-Cu-Mg alloy AA2024. The energy input, which is determined by the process parameters, is correlated with the process temperature, which has a direct influence on the microstructure and mechanical properties. At higher process temperatures, e.g. at 450.1^∘C, larger average grain sizes, i.e. 2.5 μm, were observed in the deposited material compared to lower temperatures, i.e. 1.2 μm at 380.6^∘C. At the same time, hardness (109.2 HV0.1 ↔ 115.7 HV0.1) and ultimate tensile strength (360.8 MPa ↔ 423.3 MPa) were lower at higher temperatures, in particular due to a pronounced overaging. In terms of overall mechanical behavior, the interfaces between the first layer and the substrate are the weak points of MLFS, as they exhibit lower tensile strength compared to the interfaces between the layers. Within the MLFS, the interfaces have a slightly higher hardness, which can be attributed to locally smaller grains.