Effect of Si and Fe on the Recrystallization Response of Al-Mn Alloys with Zr Addition

Al-Mn alloys are often used for the production of automotive heat exchanger fins. During brazing at about 600 degrees C, recrystallization and grain coarsening resulting in the reduction of the strength and possible buckling of the fin can occur. In order to obtain a good recrystallization resistance, the alloy should contain a dense and homogeneous distribution of second phase particles. The effect of Si and Fe addition on the recrystallization response of Al-Mn-Zr alloys direct-chill cast in the laboratory conditions and twin-roll cast in the industrial conditions was examined. Microstructure of the alloys was characterized during downstream processing. The particles were analyzed by light metallography, energy dispersive X-ray spectroscopy and by means of electron backscattering diffraction. Computer assisted quantitative particle analysis was carried out on field emission gun scanning electron microscope micrographs. Vickers hardness and electrical conductivity were measured at thicker sheets, while at the final gauge of 65 mu m the 0.2% proof stress was evaluated. The best recrystallization resistance had twin-roll cast alloy containing 0.5 wt% Si and 0.2 wt% Fe.