The effect of iron and manganese on the recrystallization behavior of hot-rolled and solution-heat-treated aluminum alloy 6013

The influence of manganese and iron additions on the recrystallization behavior of a hot-rolled Al-Mg-Si-Cu alloy has been investigated. In the as-cast ingot, some manganese remains in supersaturated solid solution and, during the preheating step, precipitates as fine (0.1 to 0.3 mu m) dispersoids alpha-Al12Mn3Si and alpha(AlFeMnSi), depending on the local iron content. The presence of the dispersoids increases the alloy's resistance to recrystallization. The remaining manganese along with iron forms coarse (30 to 100 mu m) alpha(AlFeMnSi) phases in the interdendritic channels upon solidification. During rolling, these coarse phases are broken up and the matrix surrounding the phases is highly strained. The highly strained regions around the precipitates are preferential sites for the nucleation and growth of new, strain-free, recrystallized grains. Decreasing the iron content decreases the amount of coarse alpha(AlFeMnSi) constituent phase and increases the recrystallization resistance of the alloy for a given concentration of manganese. For iron-free alloys, coarse alpha-Al12Mn3Si phase forms during solidification. The increased recrystallization resistance is attributed to the lower probability for particle-stimulated recrystallization. Increasing the manganese content beyond what is normally found in 6013 increases the volume fraction of both the dispersoids and the coarse constituent phases. However, the increased volume fraction of the dispersoids in the iron-containing alloys more than compensates for the increase in volume fraction of coarse constituent particles, resulting in an increase in the recrystallization resistance with increased manganese content. In this research, alloys containing varying amounts of manganese and iron with levels of magnesium, silicon, and copper consistent with the nominal composition of 6013 were hot deformed and solution heat treated to produce microstructures ranging from fully recrystallized to unrecrystallized.