Abstract
Evolution of microstructure in a binary Al-Cu system (Al-4.3Cu) and a commercially alloyed Al-Cu system (A205) during solution heat treatment was investigated using optical microscopy (OM), scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy (WDS), and differential scanning calorimetry (DSC). The diversified coarseness of the microstructure was initiated by controlling the solidification rate. Different solution treatment temperatures were applied to identify a proper solutioning temperature. The larger microstructural scale required an increased solutioning temperature and prolonged holding time to obtain homogenized solutes in the α-Al matrix. The diffusion of Cu primarily controlled the solution heat treatment process. A diffusion-based model was applied and calibrated to determine the dissolution rate of an Al2Cu particle in the matrix. The model operates on a similar time scale with the experimental results for the Al-4.3Cu and A205 alloys with various microstructural scales, different chemical compositions, and at different solution treatment temperatures. Three-dimensional (3D) reconstructed images from SEM images and energy dispersive spectroscopy (EDS) map of elements showed that TiB2 particles shield the Cu-rich phases in the boundaries of α-Al grains, presumably acting as a physical barrier to the diffusion of Cu solutes toward α-Al grains. The model also suggests that the effective diffusion coefficient of Cu in Al, in the presence of TiB2 particles, reduced by a factor of 2.0–2.5 in the A205 alloy compared with the binary Al-Cu alloy.
Highlights
Aluminum has been utilized in the aerospace industry, primarily due to its high strength-to-weight ratio
We investigate whether a diffusion-based solution heat treatment (SHT) numerical model can be applied to describe the homogenization kinetics of Cu solute over time, at different SHT temperatures and microstructural scales, for both Al-4.3Cu and A205 alloys
scanning electron microscopy (SEM) micrographs of the Al-Cu alloys are shown in Figure 3a,b, which were cast at solidification
Summary
Aluminum has been utilized in the aerospace industry, primarily due to its high strength-to-weight ratio. Alloys of 2xxx class are Al-Cu based cast alloys, which can retain strength and hardness at temperatures up to 250 ◦ C [1,2]. Alloys in this class rely on a combination of solid solution strengthening, precipitation hardening by θ” and θ’ precipitates, together with dispersion hardening by Al2 Cu intermetallics [3]. The A205 alloy claimed to have the highest tensile strength among the 2xxx class of alloys, is employed in aerospace industries to satisfy the demand for lightweight and high-performance material [5].
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