Electrodeposition of chemically and mechanically protective Al-coatings on AZ91D Mg alloy

Electrodeposition of aluminium coatings upon AZ91D in aluminum chloride/1-ethyl-3-methylimidazolium chloride ionic liquid was achieved. Post-plating heat treatment processes compatible with AZ91D solution treatment (420 °C) and aging treatment (200 °C) were explored to improve coatings adhesion and hardness, and to maintain corrosion resistance. 420 °C treatment produced a β-phase (Mg17Al12) enriched two-phase coating; whilst treatment at 200 °C leads to a tri-layer structure, rich in γ-phase (Mg2Al3). The 200 °C treatment was shown to be most effective for corrosion resistance, eradicating water reduction as the principal cathodic reaction and increasing surface hardness.

Research highlights
► Al coatings upon AZ91D were achieved by novel electrodeposition employing IL.
► Advantages: minimum pretreatment, low cost and ability to coat complex shapes.
► Post plating heat treatment to the extent that Mg2Al3 is produced is tolerable.
► Intermetallic layers support water reduction and compromise corrosion resistance.
► Gateway paper to subsequent surface electrodeposition of alloyed layers.