In modern material science, the development of alloys with improved properties is a priority task. Aluminum-based alloys doped with nickel, copper and iron have attracted attention due to their potential use in aerospace, automotive and other industries. The objective of this study is to improve the microstructure, mechanical properties and thermal stability of Al-Ni-Cu-Fe powder alloy through thermomechanical treatment (TMT) and recrystallization.
Powder metallurgy enables the production of alloys with high homogeneity and control over the microstructure. TMT, which includes deformation and subsequent annealing, allows control of grain size, dislocation density, and phase distribution. Recrystallization, the process of formation of new, defect-free grains, also plays an important role in the formation of the final microstructure and properties.
The experimental part included mixing Al, Ni, Cu and Fe powders in specified proportions, followed by pressing and sintering to obtain compact samples. The obtained samples were subjected to TMT, which included rolling with different degrees of deformation and annealing at different temperatures and times. Microstructural studies were carried out using optical and electron microscopy. Mechanical properties such as tensile strength, yield strength and relative elongation were determined using tensile tests. Thermal stability was assessed using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).
Al-Ni-Cu-Fe alloys produced using powder metallurgy (PM) technologies are of considerable interest as materials for lightweight and high-temperature-resistant components in automotive and industrial applications. However, their widespread application is hampered by structural inhomogeneity and phase separation. In this paper, an innovative three-step post-processing process comprising T4 heat treatment, thermomechanical treatment by hot rolling, and T6 aging is developed to overcome these limitations.
The T4 heat treatment promoted grain growth and reduced elemental segregation, thereby improving the alloy’s processability. The hot rolling thermomechanical treatment stimulated dynamic recrystallization, providing a more uniform distribution of secondary phases. Subsequent T6 aging refined the grain to an equiaxed structure and reduced the texture induced by the rolling process.
The resulting alloy exhibits tensile strength exceeding 280 MPa, ductility of approximately 7%, and maintains high thermal stability at temperatures up to 200 °C. The strengthening is primarily due to grain boundary pinning, contributions from the Al9FeNi and Al3(Zr, Sc) hard phases, as well as nanoscale Al2Cu precipitates and thermally stable quasi-crystalline phases. These quasi-crystalline phases form semi-coherent boundaries with Al9FeNi and the matrix, acting as stress buffers to stabilize grain boundaries and enhance overall thermal stability. Together, these synergistic effects highlight the alloy’s potential for high-temperature applications and provide new directions for the development of high-temperature aluminum alloys.
The results showed that TMT and recrystallization have a significant effect on the microstructure, mechanical properties and thermal stability of the Al-Ni-Cu-Fe powder alloy. Optimization of TMT and recrystallization parameters allows obtaining an alloy with a fine-grained microstructure, increased strength, ductility and improved thermal stability. The results obtained open up prospects for further development and application of Al-Ni-Cu-Fe alloys in various fields of technology.
Author: Kai-Chieh Chang, Chi-Fong Miu, Fei-Yi Hung
Institute: Department of Materials Science and Engineering, National Cheng Kung University, Tainan, 701, Taiwan