Electrically conductive and corrosion resistant coating on Mg-Li alloys, Part I: chemical conversion coating

Mg-Li alloys are one of the lightest structural materials, but suffer from severe corrosion due to the hyperactivity of Mg and Li. In this work, an electrically conductive and corrosion-resistant chemical conversion coating was fabricated on a duplex Mg-Li alloy LA103Z by two different routes: the first route using a conventional immersion treatment (Im-PCCs); and the second route using a brushing conversion treatment (Br-PCCs). Results demonstrate that chemical composition of conversion coatings remained, but surface morphology was altered. The Im-PCC depicts many lamellar CaHPO4 when the immersion time was longer than 60 s. The Br-PCC shows no lamellas on surface till a treatment time of 120 s. These lamellar crystals are detrimental to the electrical contact resistance (ECR), and the ECR for the Br-PCC was one order of magnitude lower than that for the Im-PCCs. Corrosion resistance for Br-PCCs, however, was slightly lower than Im-PCCs.