THE EFFECT OF COOLING RATE FROM THE MELT ON THE RECRYSTALLIZATION BEHAVIOR OF ALUMINUM-ALLOY-6013

In most commercial operations, the plant metallurgist likely has littl e control over the solidification rate of the process. However, solidi fication rate is affected by the dimensions of the ingot, and product form (plate ingot vs extrusion billet, for example) determines the dim ensions of the ingot to be cast. Consequently, understanding the effec ts of solidification rate might be useful in explaining differences in microstructure that are often observed in various product forms cast from equivalent compositions. To provide this microstructural informat ion, the effect of cooling rate from the melt on the microstructural c hanges in hot-rolled and solution heat treated (SHT) aluminum alloy 60 13 was investigated. The range of cooling rates in this investigation is comparable to what might be observed through the thickness of a pla te ingot. Over the cooling rate range investigated (0.5 to 5 K/s), rec rystallization behavior of the alloy appears to be primarily affected by the size and number density of the coarse alpha(AlFeMnSi) constitue nt particles, which act as sites for particle stimulated nucleation (P SN) of recrystallized grains. At intermediate cooling rates (1.5 K/s), the resistance to recrystallization is at a minimum. As the cooling r ate increases beyond 1.5 K/s, the number of particles available for PS N decreases; thus, there is a decrease in the fraction of recrystalliz ed grains after heat treating. On the other hand, as the cooling rate is decreased from 1.5 K/s, the size of the constituents increases; how ever, their number decreases, once again leading to a decrease in the fraction of recrystallized grains observed after heat treatment.