Post-welding high temperature aging and localized corrosion in welding zones of A286 RSW joints

Abstract

Small-scale single and double loop electrochemical potentiokinetic reactivation (EPR and DLEPR) with an electrochemical minicell were used to study the effect of post-welding high temperature aging treatment (there were six different aging treatments performed at the same aging temperature of 840°C for six different aging times of 0.5 h, 1, 25, 50, 100 and 200 h) on localized corrosion of small-sized welding zones of A286 resistance spot welding (RSW) joints, where welding parameters were welding time (0.36 s), welding current (6 kA) and electrode force (2300 N). Results obtained from EPR and DLEPR and from scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) mapping showed that: (i) the maximum localised corrosion is reached at the aging time from which η phase, whose precipitation gives rise to Cr-depleted zones, is observable (0.5 h for base metal (BM) and 10 h for fusion zone (FZ)); (ii) segregation that occurs in FZ causes the zones adjacent to interdendritic regions to become Cr-depleted zones; (iii) Widmanstätten precipitation mode emergence leads to higher levels of localized corrosion; (iv) grain growth occurs in heat affected zone (HAZ) with respect to BM and, thus, localized corrosion is different in both zones.