High Strength Aluminum Brazing Sheets for Condenser Fins of Automotive Heat Exchangers

Abstract

Aluminum brazing sheets for automotive heat exchangers are extensively used and their mechanical properties are mainly related to the microstructure of core alloys. In this study, strip-cast 3000-series aluminum alloys having high strengths are used as core alloys for aluminum clad sheets. The high strength 4343/3003M/4343 clad sheets are fabricated by the roll bonding process and further cold-rolled down to the thickness of 0.08 mm. Intermediate annealing (IA) is conducted during cold rolling at 270~350°C with 20~40% of final reduction in thickness. Tensile test is performed with the clad sheets before and after brazing heat treatment and sag resistance is evaluated measuring the deflection of sheet under the brazing condition. Ultimate tensile strength (UTS) of the as-rolled clad sheets increases in proportion to the final reduction in thickness up to 228MPa (IA 270°C, 40% reduction) and decreases with increasing intermediate annealing temperature. Post brazing UTS remains in the range from 167 to 185MPa although decreases by brazing heat treatment.