• RFSSW of dissimilar 2B06/7B04 Al alloys produces distinct microstructural zones with grain size order HAZ > TMAZ > SZ.
• Larger secondary-phase particles are present in TMAZ and HAZ, with HAZ particle size increasing at higher rotational speeds.
• Corrosion susceptibility follows HAZ > TMAZ > SZ > BM, and increases with higher rotational speeds.
• Post-corrosion mechanical degradation is mainly due to crevice corrosion at joint overlaps, not microstructural changes.