The hybrid corrosion mechanism of titanium in mixed HF-HNO ₃ solution during laser engraving/chemical milling manufacturing

Laser engraving / chemical milling is a hybrid manufacturing technology which is suitable for the fabrication of the key components in aerospace industries. Here, we originally proposed a molecular dynamics model to study the chemical reactions and corrosion mechanism between TA15 titanium alloy and the mixed HF-HNO ₃ solution. Then, experiments on corrosions are carried out to optimise the mixing ratio of the mixed HF-HNO ₃ solution. Results indicate that the corrosion mechanism in chemical milling is governed by HF-induced activation-driven dissolution and HNO ₃ -mediated oxidation-induced passivation. The increase of HF ratio in the mixed solution can lead to higher surface roughness and hydrogen absorption. The increase of HNO ₃ ratio in the mixed solution can lead to lower corrosion rates. A formulation is obtained to reveal the relationship between corrosion rate and concentration of HF and HNO ₃ . By consideration of the corrosion rate, surface roughness and hydrogen embrittlement risk, the optimal mixed ratio is 8% HF concentration and 14% HNO ₃ concentration with corrosion rate of 3.405 g·m ^{− 2} ·s ^{− 1} . The proposed model and the summarised formulation can provide theoretical basis and practical process parameters for chemical milling and surface treatment of TA15 titanium alloy.