Abstract. The effect of rapid crystallization on the decomposition of the solid solution of zinc in aluminium has been studied in the 60-160°C temperature range. The maximum relative volume of the rapidly quenched alloy having undergone lamellar decomposition attains 50 per cent at 110-120°C and 10 h quenching, while for the alloy having crystallized in a mould this decomposition attains 100 per cent. The impurities Fe and Si also suppress the lamellar decomposition mechanism. The rapidly crystallized aluminium alloy with 30 wt. per cent Zn and 0.01 t. per cent Fe and Si (altogether) decomposes almost entirely by the discontinuous mechanism.

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