Improvement of elevated-temperature strength and recrystallization resistance via Mn-containing dispersoid strengthening in Al-Mg-Si 6082 alloys

The precipitation behavior of Mn-containing dispersoids in Al-Mg-Si 6082 alloys with different Mn contents (0, 0.5 and 1.0 wt%) during various heat treatments (300-500 degrees C) was investigated. The effects of dispersoids on elevated-temperature strength and recrystallization resistance during hot-rolling and post-rolling annealing were evaluated. The results showed that the dispersoids in the Mn-containing alloys (0.5 and 1.0%) began to precipitate at 350 degrees C and reached the optimum conditions after 2-4h at 400 degrees C. However, the dispersoids coarsened with increasing holding time at temperatures above 450 degrees C. After the peak precipitation treatment at 400 degrees C for 2 h, the yield strength at 300 degrees C increased from 28 MPa (base alloy free of Mn) to 55 MPa (alloy with 0.5% Mn) and 70 MPa (alloy with 1% Mn), respectively, demonstrating a significant dispersoid strengthening effect at elevated temperature. In addition, the dispersoids were thermally stable at 300 degrees C for up to 1000 h holding owing to its relative high precipitation temperature (350-400 degrees C), leading to the superior constant mechanical performance at elevated temperature during the long service life. During hot rolling and post-rolling annealing, the presence of a large amount of dispersoids results in the higher Zener drag P-z compared with base alloy and then significantly improved the recrystallization resistance. The alloy containing 0.5% Mn exhibited the highest recrystallization resistance among three experimental alloys studied during the post-rolling process, likely resulted from the lower coarsening rate of dispersoids and the lower dispersoids free zone. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.