Effects of Si phase refinement on the plasma electrolytic oxidation of eutectic Al-Si alloy
Abstract The plasma electrolytic oxidation (PEO) process of high-silicon aluminum alloys is hard to be started and the properties of the PEO coating is also not satisfactory, which is caused by the existence of coarse eutectic or primary silicon (Si) phase in the substrate. In this study, the Si phase in the eutectic Al-Si alloy was firstly controlled to a much smaller size by 0.1 wt % strontium (Sr) modification treatment. Subsequently, PEO was carried out on the Sr-modified Al-Si alloy. It was shown that as the eutectic Si phase in the substrate getting much smaller and more homogeneous, PEO was much easier to be started. The PEO coating was thicker and more uniform at the initial discharge stage compared with that on the un-modified eutectic Al-Si alloy. The influence of Si refinement was less pronounced after certain time of spark discharge oxidation. After 30 min treatment, the PEO coating was composed of γ-Al 2 O 3 , α-Al 2 O 3 , mullite and some amorphous phase. The PEO coating on Sr-modified Al-Si alloy showed a more compacted structure and better anticorrosion property compared with that on the un-modified eutectic Al-Si alloy.