PURPOSE: To obtain a cold rolled sheet of alloy without periodic fluctuation of thickness due to the difference of thickness of oxidized film by the temp. difference inside a coil when annealing by specifying the composition of Al-alloy ingot contg. Mg, cleaning liquid and cleaning time for this.

CONSTITUTION: After Al-alloy ingot contg. Mg ≥0.3% is performed with soaking treatment, this ingot is cleaned with the lye of ≥pH10 or acid solution of ≤pH3 for 1-500 sec after performing hot rolling and succesive annealing and, after that, cold rolling is executed. The reason for confining the Mg content ≥0.3% is that the oxidized film on the surface is difficult to grow when Mg content is under 0.3% and thickness fluctuation is not generated. The removing effect of the oxidized film with the lye under pH10 or acid liquid over pH3 is small and they are not suitable and sufficient removing effect is hopeless when cleaning time is under 1sec and the surface of sheet is excessively etched when this time is over 500sec.