Towards Improved Plasticity in Cold-Sprayed Amorphous/Nanocrystalline Aluminum Alloy Deposits: The Role of Heat Treatment on the Microstructure and Mechanical Anisotropy

Amorphous/nanocrystalline aluminum alloys (Al-Ni-Y-Co-Sc) have potential for high-strength cold spray deposits, but their limited plasticity restricts thick deposit formation. This study explores a composite deposit using a 1:1 weight ratio of Al-Ni-Y-Co-Sc and Al-6061, focusing on microstructural tailoring through heat treatment at 320 and 380 °C. Heat treatment induced crystallization in Al-Ni-Y-Co-Sc splats, forming Al₃Ni and Al₃Sc precipitates, while Al-6061 regions showed grain growth and dislocation recovery. This resulted in a bimodal elastic modulus distribution, with Al-Ni-Y-Co-Sc regions exhibiting higher stiffness (80–110 GPa) compared to Al-6061 (65–75 GPa), while fine grains and precipitates in the microstructure yielded a microhardness of 261 HV, which decreased by 33 and 40% at 320 and 380 °C, respectively. Anisotropy in mechanical behavior, assessed by indentation techniques, reduced with heat treatment due to stress relaxation and grain growth. The ultimate tensile strength decreased from 298 to 260 MPa, with ductility increasing slightly from 0.3 to 0.5%. Although failure occurred through crack propagation in brittle Al-Ni-Y-Co-Sc splats, the crack propagation rate decreased from 61 to 16 ms⁻¹ after heat treatment, indicating improved crack resistance. Further optimization of the Al-Ni-Y-Co-Sc/6061 ratio and heat treatment is recommended to mitigate brittle failure in these deposits.