Abstract
The plasma electrolytic oxidation (PEO) of pure Al and Al alloys containing 4, 9, 12, or 15 wt.% Si were investigated under pulsed bipolar current and pulsed bipolar voltage modes, respectively. It was determined that the discharge sparks preferentially occurred on the SiO2 relative to the Al2O3 during the initial stage of PEO processing regardless of the power mode. Following 30 min of PEO treatment under the two modes, the thicknesses of the layers decreased, whereas their specific energy consumption increased with increasing Si content in the matrix. The presence of primary Si in the alloy with 15 wt.% Si had a significantly negative effect on the PEO process in the pulsed bipolar current mode: The layer thickness decreased by 45%, and its specific energy consumption increased by 52%, compared with those on pure Al. However, in the pulsed bipolar voltage mode, the layer thickness on the evaluated samples only decreased slightly, and it became much more similar after treatment.
Highlights
Cast Al-Si alloys are commonly used to produce mechanical parts because of their excellent castability, low shrinkage, and high specific strength, among other beneficial features [1,2]
plasma electrolytic oxidation (PEO) has been widely employed for the surface modification of Al, Mg, and Ti alloys because it is an eco-friendly and high-efficiency method [11,12]
Pure Al and Al alloys containing 5, 9, 12, and 15 wt.% Si were treated via PEO for 30 min in pulsed bipolar current and pulsed bipolar voltage power modes
Summary
Cast Al-Si alloys are commonly used to produce mechanical parts because of their excellent castability, low shrinkage, and high specific strength, among other beneficial features [1,2]. The low hardness and poor corrosion and abrasion resistance properties significantly limit the lifetime of Al-Si alloy products [5,6]. Surface technologies, such as anodizing [7], laser remelting [8], plasma electrolytic oxidation (PEO) [9], and cathode plasma electrolytic deposition [10] have been applied to address these issues. PEO has been widely employed for the surface modification of Al, Mg, and Ti alloys because it is an eco-friendly and high-efficiency method [11,12]. A post-PEO sealing process improved the hydrophobicity, impedance, and anti-corrosion performance of the PEO layer on an A356 alloy [30]. The pre- or post-treatments mentioned above render the surface modification process relatively complex, making it undesirable for industrial applications
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