A new method to prepare MgO and base for further electroless nickel deposition on magnesium substrate

Abstract

The present research uses the safer hydrogen halide to prepare the MgO-MgI2/MgBr2 layers onto AZ91 magnesium alloy in alkaline solution. The water-soluble metal salts (MgI2/MgBr2) were not responsible for the corrosion protection; whereas Mg(OH)2 formed first and then converted to MgO by heat-treatments and this MgO was responsible for the corrosion protection. The electrochemical results showed that the development of MgO mitigated the corrosion process and improved the corrosion resistance. This new treatment was then used as a pre-treatment for further electroless nickel (EN) deposition and it showed the good corrosion current density and better corrosion potential on the magnesium substrate. This new treatment and EN depositions were characterised by XPS and SEM. The electrochemical polarisation and EIS test of these EN depositions were evaluated in 3.5 wt.% NaCl. In addition, pitting behaviour of these EN depositions were evaluated by linear sweep voltammetry test.