Evolution of microstructure and elevated-temperature properties during hot rolling and post-rolling annealing process in Al-Mg-Si 6082 alloys

摘要

In the present work, the hot rolling at 400°C and post-rolling annealing at 500°C were applied on heat-treated Al-Mg-Si 6082 alloys with different Mn contents to study the evolution of microstructure and elevated-temperature properties. During the pre-heat treatment before rolling (400°C/2h), a number of fine rod-like dispersoids formed in Mn-containing alloy while only high volume of larger Mg_(2)Si particles was observed in the matrix of base alloy free of Mn. After hot rolling, the morphology of dispersoids was transferred from rod-like to spherical with finer size and increased number density while the dispersoids gradually coarsened during post-rolling annealing in Mn-containing alloy. The full recrystallization was completed after 1-2 h during annealing in the base alloy, while only partial recrystallization was observed in Mn-containing alloy. The micro-hardness at room temperature and the tensile yield strength at 300°C firstly increased from as-rolled condition to the initial stage of annealing (1 h) for both alloys, which was likely attributed to the dissolution of Mg_(2)Si during the beginning of annealing. With further increasing annealing time (2-8 h), both the microhardness at room temperature and the elevated-temperature strengths of the base alloy remained similar, while they were slightly decreased in Mn-containing alloy owing to the partially recrystallization and coarsening of dispersoids. However, the elevated-temperature strengths were always higher in Mn-containing alloy than the base alloy while their differences between two alloys was reducing with prolonging the post-rolling annealing time. The tensile fracture surface was observed to be ductile for all the conditions of both alloys but the dimples in Mn-containing alloy were finer and much more uniformly distributed.