The Effect Of Fe, Si On The Precipitation Behaviors And Recrystallization Process Of Al-Mn Wrought Alloys

Heat exchangers made of three-layer aluminum brazing sheets instead of traditional cooper alloys have been widely used in the automotive industry in order to reduce the weight of vehicle and production costs. Mn concent in solid solution (Mnss) in the core layer was considered as the main factor of recrystallized structure and propertities after brazing, and Fe, Si elements has strong interactions with Mn element. The effects of Fe, Si on the precipitation behaviors during homogenization and recrystallization process duiring annealing within four different alloys which have different Fe, Si content were studied.The effects of Fe, Si on the precipitation behaviors during homogenization were studied. It was shown that the supersaturation of Mnss was decreased greatly with the increasing of Fe, Si content, especially the Si content. Fe, Si also could accelerate the dissolving rate of Mn during homogenization. When annealed at 600 ℃, A1 and A2 alloys precipitate Al12(Mn,Fe)3Si and Al12Mn3Si particles in the early stage and Al12(Mn,Fe)3Si particles resolved with the homogenization time;However, A3 alloy precipitates Al12Mn3Si only. The states show that alloys with high Si content have a small size and high number density of precipitations while the low Si alloy has a larger diameter and lower number density. The particles grow up according to the Parabolic Growth Law when the supersaturation was high enough, and when the supersaturation was close to zero the particles coarsening following the LSW theory in A1 and A2 alloys while A3 alloy was not.The effects of Fe, Si on the recrystallization process were invetgated. The recrystallization was retarded in unhomogenizied alloys as Mnss was high, the precipitation happened before recrystallization and the precipitates distributed along the rolled direction(RD) pinned the dislocations and subgrain boundaries which lead to the growth of the recrystallization grain along the RD. After homogenizied at 600 ℃ for 32h, The recrystallization postpone was weakened as Mnss was dropped significantly. The particles precipitated during homogenization has a certain effect of grain boundary pinning, but not obvious. When the Mnss was 0.5%, obtained by homogenizied at different temperature, the Tc temperature of four alloys was almost the same(475℃), and Fe, Si did not have a directly influence on the recrystallization process.The key factor of structure-control in 3xxx alloys was the content of Mn in the matrix, Fe, Si did’t affect the recrystallization process directly. But it is feasible to control Mnss within a reasonable range in order to obtain a proper structure by using the strong interactions among Mn, Al, Fe, Si during casting and homogenization.