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 ℃) 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 ℃ and reached the optimum conditions after 2–4 h at 400 ℃. However, the dispersoids coarsened with increasing holding time at temperatures above 450 ℃. After the peak precipitation treatment at 400 ℃ for 2 h, the yield strength at 300 ℃ 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 ℃ for up to 1000 h holding owing to its relative high precipitation temperature (350–400 ℃), 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 PZ 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