Ultrasonic-Assisted Electrochemical Milling of SLM-Printed Hastelloy X Based on Analysis of Material Passivation Characteristics

Abstract

Hastelloy X (HX) is widely used in the aerospace field for its excellent corrosion resistance and high-temperature mechanical properties that can be fabricated into complex structures directly by the selective laser melting (SLM) technique. However, SLM-printed (SLM-ed) HX with high strength and hardness is challenging to process using conventional manufacturing techniques and may result in machining flaws that don’t fulfill engineering standards. Therefore, an ultrasonic-assisted electrochemical milling (UAECM) method using a tube electrode is proposed to fabricate high aspect ratio structures on SLM-ed HX with high-quality. Firstly, the passivation characteristics of SLM-ed HX before and after solid solution treatment (SST) were investigated using polarization curves and electrochemical impedance spectroscopy (EIS). Secondly, the electrochemical milling process and the electrode gap flow field were simulated. Then, the effect of processing parameters such as ultrasonic amplitude, electrical parameters, and mechanical parameters on the groove width and stability was investigated by the orthogonal and single factor experiments. Finally, the cavity and bump structures were machined by layered milling with an average groove width of 960 ± 15 μm, a groove depth of 4.4 mm, an aspect ratio of 4.5, and surface roughness of 1.524 μm and 1.622 μm, respectively, demonstrating the adaptability and machining accuracy of the UAECM method.