Tribological properties of Mg(OH)2 coating on magnesium alloys by anodic treatment

Abstract

Magnesium is given anodic oxidation coatings to improve corrosion and wear resistance and for decorative purposes and so on. Representative anodic treatments for magnesium, H.A.E. and Dow17 have useful corrosion resistance to the atmosphere, wear resistance and heat resistance. But these treatments require high voltage with break down when coatings are formed. On the other hand, it is known that magnesium hydroxide coatings can be formed at low voltage 0.3 V to 3 V in 1 M NaOH solutions by alternating electrolysis. Magnesium hydroxide has the same lamella structure as the representative solid lubricants graphite and molybdenum disulfide. This paper describes the friction characteristics of magnesium hydroxide coatings by periodic reverse electrolysis in NaOH solution on pure magnesium 3N (99.9%), magnesium alloy AZ31 and magnesium alloy AZ91D. Magnesium hydroxide coatings on magnesium by anodic treatment provide superior friction characteristics and specific wear resistance than untreated magnesium.