PURPOSE: To obtain an Al alloy for a core material for the fins of a heat exchanger with superior buckling resistance by specifying the amouns of Si and Fe among inevitable impurities contained in pure Al and adding a specified amount of Mn to the pure Al.

CONSTITUTION: The amounts of Si and Fe among inevitable impurities contained in pure Al are restricted to ≤0.15wt% each, and 1.5W2.5wt% Mn is added to the pure Al to prepare an Al alloy. This alloy is used as a core material for the fins of a heat exchanger made of an Al alloy, and it shows superior buckling resistance during the brazing of the fins. When the alloy is used, the weight of the fins can be reduced by about 20%.