Be careful of dissimilar metals.
Some metals, especially those with significant contents of nickel and chromium, are included in the table in both their active and passive conditions. Passivation, (i.e.: surface cleaning and sealing) lowers the metals electrical potential and improves its corrosion behavior. As the series suggests, steel and aluminum are relatively compatible, but if brass and steel contact, the steel will corrode because it is more anodic than the brass. Source: Fastenal Engineering
I don't think overheating can cause the issue, but brazing with brass is the true culprit. Hope this helps.
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