Effect of Sc and Zr Microalloying on Grain Structure After Hot Deformation and Brazing in Al–Mn 3xxx Alloys

Al–Mn 3xxx alloysAl-Mn 3xxx alloys are widely used in the fabrication of multi-port extruded (MPE) tubes for aluminumAluminum heat exchangers. The industrial manufacture for those tubes consists of four steps: (1) homogenizationHomogenization, (2) extrusionExtrusion, (3) straightening/sizing, and (4) brazingBrazing. The combination of cold work and brazingBrazing could result in abnormally coarsened grains that have negative impacts on the in-service performance of MPE tubes. A 3xxx alloyAlloys microalloyed with 0.08 wt.% Sc and 0.09 wt.% Zr was assessed with respect to the grain structures after hot deformation and brazingBrazing, and a comparisonComparison was made with the base 3xxx alloyAlloys free of Sc and Zr. The flow stress of the base alloyAlloys during hot compression at 500 °C and 1 s−1 was 48 MPa, while the alloyAlloys with added Sc and Zr showed a higher flow stress of 61.5 MPa. EBSD maps after hot deformation showed that the alloyAlloys with added Sc and Zr exhibited more resistance to dynamic recoveryRecovery and dynamic recrystallizationRecrystallization. After the high-temperatureHigh-temperature simulated brazingSimulated brazing at 605 °C, the base alloyAlloys suffered from abnormal grain growthAbnormal grain growth, whereas the alloyAlloys with added Sc and Zr exhibited an elongated recrystallized microstructureMicrostructure with a finer grain size.