To provide a plate material made of an aluminum alloy having formability to be easily worked into permissible dimensions and further having corrosion resistance, thereby making service life as a heater core, for example, longer.

A plate material made of an aluminum alloy is composed of: a core material including 1.0 to 2.0% Mn, 0.1 to 0.8% Si, 0.001 to 0.5% Fe and 0.001 to 0.1% Cu, and the balance Al with inevitable impurities; and a brazing filler metal including 6.0 to 12.0% Si and 1.0 to 5.0% Zn, and the balance Al with inevitable impurities. The average crystal grain size of the core material after final annealing is controlled to 50 to 400 μm.