Patent ID: 7998288

Claim:
A method of producing a heat exchanger use high strength aluminum alloy fin material containing Si: 0.8 to 1.4 wt %, Fe: 0.15 to 0.7 wt %, Mn: 1.5 to 3.0 wt %, and Zn: 0.5 to 2.5 wt %, limiting the Mg as an impurity to 0.05 wt % or less, and having a balance of ordinary impurities and Al in chemical composition, having a metal structure before brazing of a fibrous crystal grain structure, a tensile strength before brazing of not more than 240 MPa, a tensile strength after brazing of not less than 150 MPa, and a recrystallized grain size after brazing of 1800 μm or more, comprising casting a melt having the chemical composition above so as to continuously cast and coil into a roll a thin slab having a thickness of 5 to 10 mm by a twin-belt casting machine, cold rolling the slab to a sheet thickness of 1.0 to 6.0 mm, treating the sheet by primary intermediate annealing at 200 to 350° C., further cold rolling the sheet to a sheet thickness 0.05 to 0.4 mm, treating the sheet by secondary intermediate annealing performed by a batch annealing furnace with a holding temperature of 360 to 450° C., and cold rolling the sheet by a final cold rolling rate of 10% to less than 50% to a final sheet thickness 40 to 200 μm.