Electrochemical polishing of additively manufactured titanium alloys: a mechanism-to-parameter framework for process...

Additive manufacturing (AM) has expanded the use of titanium and its alloys in aerospace, biomedical, marine, and automotive components, but the rapid melting-solidification cycles inherent to AM leave characteristic surface defects-balling, partially melted particles, scan-track ridges, and near-surface porosity-that make post-process finishing essential. Electrochemical polishing (ECP) is a leading candidate because material is removed by anodic dissolution, allowing treatment of geometrically complex surfaces inaccessible to mechanical methods. The literature available to newcomers remains divided: classical electropolishing theory addresses idealized surfaces prior to AM, while recent AM reviews focus empirically on electrolytes and roughness outcomes rather than current-distribution and mass-transport physics. Consequently, researchers often reproduce published conditions as empirical recipes, relying on trial-and-error optimization. This review is therefore organized not as a chronological survey but as a mechanism-to-parameter design framework for engineers adopting ECP for Ti and Ti-6Al-4V. It (i) relates classical current-distribution theory (primary, secondary, and tertiary distributions; the Wagner number (Wa)) and salt-film and acceptor-based mass-transport mechanisms to macro- and micro-smoothing of AM Ti surfaces and to the diffusion-limited plateau of the J-V curve that defines the practical process window; (ii) decomposes electrolytes into functional units-solvent, supporting electrolyte, acid, and additive-so that composition becomes a set of design rules rather than a list of recipes; (iii) consolidates acid-based, organic, ionic-liquid, and deep-eutectic systems, and AM and wrought substrates, into a unified condition database; and (iv) positions finite-element (COMSOL and others) prediction of fields, current-density distributions, and material removal as a means of narrowing the experimental search space. Viewed through this framework, the diversity of reported ECP conditions converges on one objective: forming and sustaining a stable, mass-transport-controlled interfacial layer. Viscosity, additive chemistry, agitation, temperature, and waveform are not independent variables but alternative routes to controlling the diffusion layer, and specimen geometry sets how much geometry-driven current concentration can contribute to leveling. Framed this way, condition selection becomes a reasoned choice of where to sit within the process window rather than searching across a catalogue of recipes-the basis on which ECP can be transferred from coupon-level demonstrations to component-scale Ti parts.