EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The concept of a combination of severe plastic deformation and precipitation hardening has been studied as a desired route for further mechanical performance improvement of ultrafine grained materials. However, deformation induced defects suppress the nucleation of strengthening phases in most cases. On the other hand, thermal instabilities of severely deformed aluminum alloys exclude conventional procedure of solution treatment followed with ageing.
This study focuses on the heat treatable 6xxx aluminum alloys series. The relatively low content of alloying elements like Si and Mg, enable deformability and give the possibility to nucleate and grow strengthening precipitates. Several thermo-mechanical procedures based on accumulative roll bonding technique and conventional solution treatment and ageing have been applied to 6082 alloy. Inter-layer boundaries are known to improve thermal stability by providing mechanical blockade for grain boundaries motion. For this reason, there are possibilities to maintain fine grain sizes within layers and achieve supersaturated solid solution for the nucleation and growth of strengthening phases during subsequent ageing. EBSD and TEM microstructural studies were performed to check the impact of applied thermo-mechanical routes on deformation-induced defects and strengthening precipitates. The inter-layer boundaries indeed stopped grain growth through the thickness while most of defects were annealed from grain interiors during the solution treatment allowing homogeneous precipitation of strengthening phases. Despite almost defect-free microstructure, the peak ageing condition were shifted when compared to the conventional coarse grain material. Hardness measurements indicate that applied combination of multiple ARB passes and conventional ageing enable to significantly improve mechanical strength of 6xxx series aluminum alloys.