Residual mechanical performance and microstructural changes of 6061-T651 aluminum alloy after fire

The use of aluminum alloys in transport, aerospace, and structural applications continues to grow due to their exceptional strength to weight ratio, corrosion resistance, and formability. Nonetheless, as a result of their post-fire performance, aluminum alloys pose a higher risk to structural safety. Consequently, to assess these risks, a combined experimental and analytical study was carried out. The experimental program consisted of tensile tests on 31 coupons. These coupons were then subjected to fire-simulated temperatures of up to 550 °C with subsequent cooling to room temperature via water, natural air, and foam cooling. In the analytical phase, the response of AA6061-T651 to other properties such as yield strength, ultimate tensile strength, hardness, and elastic modulus based on temperature was integrated into a new set of empirical expressions. These models were compared with the experimental data which are available in the literature. The proposed models allow a generalized framework to be created in evaluating the post-fire performance of the 6xxx series aluminum alloys, which can be used for structural safety assessments and fire-resistant designs. Microstructural investigations confirmed that no new phase transformations occurred after fire exposure, while SEM and EDS analyses revealed grain coarsening, precipitate coarsening/dissolution, and recrystallization at temperatures above 300 °C.