It's not really "work hardening" and a lot more intense than anodizing, micro arc oxidation is also known as plasma electrolytic oxidation. It is an electrochemical surface treatment process for generating oxide coating on metals. Similar to anodizing, it employs higher potentials (voltage) so that discharges (dielectric breakdown of the naturally occurring oxide on metal) occur and the resulting plasma modifies the structure of the oxide layer. This process can be used to grow thick oxide coatings (end or hundreds of micrometers, largely crystalline, i.e. structural) on metals such as aluminum, magnesium, and titanium. The oxide coating provides a continuous hard barrier protecting against wear, corrosion, or heat as well as electrical insulation.
The coating is a chemical conversion of the substrate metal into the oxide, and grows both inwards and outwards from the original metal surface. Because it is a conversion coating, rather than a deposited coating (such as coating formed by plasma spraying), it has excellent adhesion to the metal the oxide grew from. High levels of silicon in an alloy that needs to be coating can reduce the quality of the coating.
Processes include melting, melt-flow, re-solidfication, sintering and densification of the growing oxide.
-- From Wikipedia.