The Effects of Ni Content and Intermediate Annealing Condition on Recrystallization of Al-Fe-Ni-Si Alloy Fin Stocks

Abstract

The effects of Ni content and intermediate annealing conditions on recrystallization behavior during brazing heat treatment of Al–Fe–Ni–Si alloys fin stocks of automotive heat exchangers were studied by means of microstructural analysis. Following brazing heat treatment, coarsening of recrystallized grain structure was observed in both 0.5% Ni and 1.0% Ni fin stocks, which were intermediately annealed in a salt bath. This coarsening was particularly marked in 1.0% Ni fin stocks. The results of the microstructural observations indicated that fine dispersoids were heterogeneously dispersed in 1.0% Ni fin stocks that were annealed at 550°C for 10 s in a salt bath. It was proposed that the preferential recovery and recrystallization during the brazing heat treatment in the low density area of the fine dispersoids contributed to the larger recrystallized gain structure. The coarse recrystallized grains obtained by controlling the salt bath annealing conditions are expected to contribute in improving the properties of Al–Fe–Ni–Si alloy fin stocks of automotive heat exchangers.