| Al 4343(filler)/3003(core)/4343(filler) type of brazing sheet(thickness of 100 ㎛ with each side clad ratio of 10%), which is being widely used in clad fin material for parallel flow type condenser of automobile, was fabricated by casting → hot rolling → cold rolling → intermediate annealing(IA) → final cold rolling(FR), and the relationship between IA/FR condition, microstructure and NOCOLOK brazing characteristics was investigated. When specimen was intermediate annealed at temperatures higher than 330℃, followed by cold rolling with the reduction rate lower than 10%, the core was partially recrystallized during brazing process, including unrecrystallized structure such as sub-grain. In this case, the melted filler infiltrated into the core during brazing through the sub-grain boundary which acts as a preferential penetration path, so the eroded area increased and brazeability decreased. When IA/FR was performed in the condition of 330℃/over 37% or 270℃/over 10%, fine recrystallized grains were formed in the core during the brazing process, which promotes filler penetration through the grain boundary. In this case, brazeability was deteriorated with the increment in eroded area. If IA/FR was carried out in the condition of 420℃/20-45% or 330℃/20-30%, the specimen exhibited superior brazeability with suppressed erosion owing to the formation of coarse recrystallized grains during brazing process. |
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