Resolving the mechanism of inclusion-controlled corrosion in advanced high-strength steels with scanning electrochemical probe microscopy.

Advanced high-strength steels (AHSS) enable lightweight automotive design through reduced steel thickness, increasing the need for corrosion-resistant materials. Due to their high alloying element content, localized corrosion in AHSS is often driven by microstructural heterogeneities such as nonmetallic inclusions. In this work, the initiation and propagation of inclusion-induced localized corrosion in AHSS were investigated using a complementary combination of scanning electrochemical microscopy (SECM) and scanning electrochemical cell microscopy (SECCM). Short-term immersion experiments revealed that corrosion initiates preferentially at spinel-type (Al-Mg-O) inclusions and their interfaces with the steel matrix, where micro-crevice formation precedes localized dissolution and eventual inclusion detachment. SECM feedback-mode mapping demonstrated reduced mediator regeneration currents over inclusions relative to the surrounding matrix, consistent with their electrically insulating nature. In contrast, SECCM provided direct, spatially resolved electrochemical measurements under confined electrolyte conditions, revealing enhanced local anodic activity at inclusion-matrix interfaces associated with crevice formation. By combining SECM and SECCM, this study establishes a multiscale electrochemical framework for investigating complex corrosion phenomena. The results show that spinel inclusions promote micro-crevice corrosion, whereas AlN inclusions do not exhibit enhanced reactivity and are not initiation sites for localized corrosion.