Effect of composition and work hardening on solid solution decomposition in twin-roll cast Al-Mn sheets

Fins in automotive heat exchangers are often manufactured from Al-Mn foils. The foils are usually prepared from ingot cast plates. The use of continuous twin-roll casting (TRC) instead of ingot casting substantially reduces energy and work consumption thus resulting in lower foil costs. The paper reports results of a study aimed at understanding the precipitation processes occurring during the annealing of two TRC Al-Mn based alloys differing in manganese and silicon content. The effect of work hardening level introduced by cold rolling prior to annealing was evaluated. Precipitation was studied by resistometric measurements in the course of a stepwise heating from room temperature to 500 deg C. Transmission electron microscopy examinations of specimens quenched from temperatures of expressive changes in resistivity helped to identify the microstructural processes responsible for resistivity changes. The corresponding reflections in mechanical properties were monitored by hardness measurements.