Anodic dissolution behavior of a Zr-based bulk metallic glass and the electrochemical machining of small structures with high geometrical precision and good surface quality

Bulk metallic glasses (BMGs) have excellent mechanical properties, however, it is still challenging to process high-qualtiy BMG structures for their widespread engineering applications. In this work, electrochemical machining (ECM) is adopted to process various small BMG structures with high geometrical precision and surface quality. Firstly, the electrochemical dissolution behavior of a Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ (at.%) BMG in NaNO₃, H₃PO₄, NaCl, and HCl solutions was investigated and discussed. The results shown that obvious corrosion occurred in HCl and NaCl solutions, while mass by-products and pitting corrosion on the workpiece surface in NaCl solution affect the corrosion continuity and surface quality. Therefore, the HCl solution is selected as the electrolyte for the following ECM process. Secondly, the effects of machining parameters on the ECM performance of BMG workpieces were investigated, where the optimal machining performance was achieved with an electrolyte of 0.1 mol/L HCl, a cathode feed rate of 3 μm/s, a machining voltage of 10 V, and a duty cycle of 15%. Finally, a small round hole with a roughness (Ra) of about 0.2 μm, a sidewall taper of less than 2.83°, and a relative error of diameters of 2.1% was obtained. Another square structure (0.899 mm × 0.891 mm) with high geometrical precision and surface quality was also achieved by the optimal parameters, which validates the feasibility to machine small BMG structures using the ECM technique with its optimal parameters.