Optimization of Mechanical and Electrical Properties in Age-Hardened Aluminum Alloy through HPTE Processing

Aluminum alloys are commonly used due to their versatility and tunability of properties through addition of solutes and heat treatments. This study focuses on age-hardenable Al-Mg-Si alloys, which are lightweight and extensively used in the electrical industry. Precipitate hardening is the way to improve strength in this alloy system, where the size of precipitates depends on temperature and aging time.
However, the presence of solute atoms is problematic as it degrades electrical conductivity (EC) by reducing the mean free path of conducting electrons. This inherent trade-off between strength and electrical conductivity presents significant challenges for industrial applications, where both properties are crucial for optimal overall performance.
This bottleneck serves as the primary motivation for this study, focusing on simultaneous improvement of strength and EC. In this study, we introduce an approach that combines severe plastic deformation with subsequent heat treatment to optimize both strength and conductivity. Despite the proven efficacy of severe plastic deformation in strengthening materials, previous studies in this direction
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have predominantly operated in a limited scope of laboratory scale. Our research aims to bridge this gap by exploring the application of high-pressure torsion extrusion (HPTE) as a viable method for implementing these techniques at a larger scale. Mechanical properties were evaluated by microhardness and tensile testing. The results showed a remarkable improvement in strength while EC remained unchanged. Furthermore, modeling of strength and EC, based on microstructural
characterization, revealed good agreement with experimental values.
The second objective is to conduct an atomic-level investigation of the precipitates formed under conditions of extreme deformation and subsequent annealing. Advanced microscopy and EDX microanalysis demonstrated that the material processing led to the development of various hardening phases with distinct morphologies and compositions. The high density of defects induced by HPTE deformation resulted in a predominantly disordered structure for most particles. The particles exhibit a set of orientation relations with the Al matrix, which differ from those established for the studied alloy.
Furthermore, a considerable number of nanometer-sized precipitates exhibit a core-shell structure or evidence of simultaneous co-precipitation of several secondary phase particles. These observations lead to the conclusion that nucleation and growth of hardening precipitates occur in non-equilibrium conditions.