Protective polysiloxane films on MgLi alloy by PECVD: Optimized oxygen flow rate to obtain highly anti-corrosion properties

Abstract

The high corrosivity of MgLi alloy limits its wide application in maritime, aerospace, electronic device, etc. Therefore, there is an urgent need for an efficient coating to effectively protect it. In this study, hexamethyldisiloxane (HMDSO) was utilized as a precursor to deposit polysiloxane films on MgLi alloy using Plasma Enhanced Chemical Vapor Deposition (PECVD) technology, aimed at improving surface properties and enhancing corrosion resistance. By adjusting the O₂ flow rate, a series of films with different properties were prepared, and their structures were transitioned from organic (SiO_xC_yH_z) to inorganic (SiO_x). The test results showed that different O₂ flow rates led to different deposition rates, the film thickness initially increased and then decreased. With the increase in O₂ flow rate, the content of O element in the film gradually increases, the molecular chain extension of the film increases the crosslinking degree, which changes the mechanical properties and wettability. Electrochemical tests showed that the corrosion current density of the coated MgLi alloy is decreased by 5 orders of magnitude compared to the bare MgLi alloy. Additionally, in the voltage corrosion test at 10 V, the film showed good endurance against current breakdown, and the film surface was not damaged after 2 min of test.