Application of four-dimensional impedance analysis to elucidating corrosion mechanisms in additively manufactured metals and alloys

This review describes a four-dimensional (4D) impedance analysis approach for analyzing the oxide film formation process that accompanies the dissolution of metals and alloys. In this analysis, the measured impedance was plotted on a three-dimensional (3D) complex impedance plot composed of real, imaginary, and time axes. Since the impedance plots of the same frequency in each spectrum are smoothly connected using a spline under tension function, the instantaneous impedance can be determined at an arbitrary time on the 3D complex impedance plot. In this review, the application of 4D impedance analysis to an additively manufactured aluminum alloy produced by a laser powder bed fusion process is introduced as a representative additive manufacturing technology. Additionally, the corrosion resistance mechanisms are discussed based on the impedance variation, which is attributed to dissolution and oxide film formation to generate a unique alloy structure.