Effect of Tri-Metallic Microgalvanic Corrosion on Localized Corrosion Based on Numerical Simulation: Geometric Effect of Intermetallic Compounds

This study investigated the corrosion behavior of ADC12 and A365 aluminum alloys for automotive parts in the context of the growing use of aluminum parts in electric vehicles. Only ADC12 exhibited the formation of Al(OH)3 particle layer after corrosion, which was attributed to the microgalvanic effect influenced by the geometry characteristics of its microstructure. Results revealed that ADC12 was prone to forming Al(OH)3 particle layers due to the geometric effects of Si and θ-Al2Cu, which facilitates the isolation of α-Al. The distribution of band-shaped galvanic currents, concentrated in a small α-Al matrix region, was primarily governed by the geometry of Si, creating a preferred structure for α-Al isolation. Additionally, the geometry of θ-Al2Cu contributed to a significant increase in electrochemical kinetics, particularly at the tri-metallic coupled region, further enhancing the susceptibility of the isolation. As a result, the formation of the Al(OH)3 particle layer was attributed to the corrosion of isolated α-Al particles, generated through the synergistic effect of microgalvanic corrosion. Moreover, the corrosion attack progressed along the eutectic Si network, accompanied by θ-Al2Cu. Overall, the corrosion mechanism of ADC12 and A365 alloy was proposed.