A high efficiency pre-dissolution electrochemical polishing method for improving surface uniformity in additively manufactured alloys

Electrochemical polishing (ECP) offers significant advantages in reducing surface roughness of complex additively manufactured (AMed) components. However, conventional one-step ECP methods hinder further removal of near-surface defects, such as inherent adhesive powders and step effects, owing to the simultaneous dissolution and smoothing processes. Additionally, the topological conformity between the formed high-resistance oxide layer and the metal matrix limits the polishing effectiveness, producing undesirable surface inconsistency and poor dimensional accuracy. In this study, we introduce a pre-dissolution step prior to the conventional ECP process, namely pre-dissolution ECP. This approach is based on the electrochemical dissolution behavior of adhesive powders and the melt pool (MP) structure to transform the irregular, rough as-built surface into a pre-dissolved MP morphology with a uniform current density distribution, aiming to optimize the subsequent ECP process. By combining in situ X-ray synchrotron radiation observation with comparative quantitative analysis of samples before and after mechanical polishing, precise dissolution parameters were determined to achieve a polished surface with uniformly distributed height differences. For AMed Al alloys with high Si content, when the percentage change rate of dissolved areas of the cross-sectional profile in the pre-dissolution step is 0.060 ± 0.003 %/min, different adhesive powder regions exhibit consistent height differences on the pre-dissolved surface. During the subsequent polishing step, compared to direct ECP (∼5.3 μm), the isotropic etching-based smoothing effect in NaOH solution further reduces surface roughness of the pre-dissolved surface to ∼1.5 μm, and the corresponding standard deviation of height difference is reduced by 80.7 %. Moreover, the use of low voltage and the one-time removal of surface cluster layers ensures improved roundness tolerance (85.7 %) and capillary action (304.4 %) for AMed heat pipes with internal channels (Φ1.4 mm) after polishing. This pre-dissolution strategy mitigates the complexity and randomness of as-built surface features, facilitating better ECP performance. It can also be integrated with advanced ECP technologies, thereby expanding the application potential of AMed structures, including but not limited to internal channels.