Age hardening in 3xxx series brazing sheet core alloys

摘要

The effect of age hardening after brazing was demonstrated to occur at typical operating temperatures of aluminum radiators and charge air coolers. The age hardening effect is dependent on the magnesium content of the core alloy from no hardening without magnesium to a doubling of the yield strength for 0.5% Mg core alloys. The phenomenon is caused by diffusion of silicon into the core alloy during brazing, retention of silicon and magnesium in solution during cooling from the braze cycle and then age hardening by precipitation of Mg_2Si during subsequent vehicle operation or post braze aging treatment.The age hardening effect is also dependent on the composite thickness and whether it is clad on one or both sides. No significant over aging occurs up to 2500 hours for typical radiator operating temperatures. The fatigue life as measured by S-N curves is also not affected by the age hardening phenomenon.