Microstructural gradients and associated mechanical properties in the rapid solidification microstructure of hypo-eutectic Al-10at.%Cu obtaining after scanned-laser melting

Scanned-laser surface melting strategies have been developed to establish morphologically graded rapid solidification (RS) microstructures in bulk alloy specimens of hypoeutectic Al-10Cu. Using electron microscopy and instrumented nanoindentation location-specific mechanical properties have been determined for three morphologically distinct RS microstructure regions that are characterisitic of Al-10Cu, i.e., the transition, α-cell and banded-grain zone. RS microstructure and mechanical property evolution in response to isothermal annealing (120 s ≤ t ≤ 480 s; 180˚C < T ≤ 280˚C) are reported and discussed. Melt pools induced by single-pass scans showed evidence of Marangoni-effect driven mixing and uneven composition retained in the melt. Multi-pass scans and using multiple scan speeds, 1 m/s ≤ v b ≤ 4 m/s, produced compositionally more uniform melts before forming RS microstructures exhibiting the three morphologically distinct zones. Nanoindentation hardness of the transition, α-cell and banded-grain zones, increased from 2.7 GPa to 3.3 GPa and up to 3.4 GPa, respectively. Annealing caused an initial hardening response attributed to precipitation reactions, followed by moderate coarsening and up to ∼15 % hardness drop. Since the morphologically distinct RS microstructures zones in Al-Cu alloys form for characteristic composition specific solidification velocities, this study illustrates how properties correlate with solidification microstructure selection maps and assists development of processing schema for tayloring properties in Al–Cu parts prepared by laser melting processes.