Hot Deformation Behavior and Post-brazing Grain Structure of Dilute Al–(Sc–Zr) Alloys for Brazed Heat Exchangers

An abnormally coarsened grain structure after brazingBrazing can negatively affect the in-service performance of a brazed heat exchanger. One of the numerous beneficial effects from the Sc addition to aluminumAluminum is its retardation effect on recrystallizationRecrystallization and grain growth. In this work, dilute Al–0.07Sc and Al–0.07Sc–0.09Zr alloysAlloys were assessed with respect to the hot deformation and the post-brazingBrazing grain structure and compared with the base 1xxx alloyAlloys. The flow curves of the hot compression testsCompression tests showed that the Al–Sc–Zr alloysAlloys exhibited higher flow stresses compared to the base alloyAlloys. The microstructureMicrostructure of the deformed samples in all three investigated alloysAlloys exhibited a recovered microstructureMicrostructure, but both Sc-containing alloysAlloys showed an improvement in the resistance to dynamic recoveryRecovery. EBSD maps after a high temperature simulated brazingSimulated brazing showed that the microstructureMicrostructure of the base alloyAlloys suffered from abnormal grain growthAbnormal grain growth. Severe grain coarseningGrain coarsening was still observed in the recrystallized microstructureMicrostructure of Al–0.07Sc alloyAlloys after brazingBrazing. The combined addition of Sc and Zr in Al–0.07Sc–0.09Zr alloyAlloys suppressed the abnormal grain growthAbnormal grain growth, showing an improved control on the brazed microstructureMicrostructure. After post-braze agingAging at 350 °C for 4 h, the hardnessHardness of both Sc-containing alloysAlloys increased by 90–122% relative to the base alloyAlloys hardnessHardness.