Structure and wear--resistant properties of ceramic layer on LY12 Al alloy by micro--arc oxidation
LY12铝合金微弧氧化陶瓷层的结构和性能

The morphology, content and structure of microarc oxidation ceramic coatings produced on LY12 Al alloy have been investigated. The microhardness, adhesion to the substrate and friction behavior under dry friction and oil lubricating conditions were also measured. It is found the microarc oxidation coatings consist of the loose superficial layer and the inner dense layer. The two layers are composed of $\alpha$--Al$_{2}$O$_{3}$ and $\gamma$--Al$_{2}$O$_{3}$, while the Al--Si--O phase of high content is observed only in loose layer. The $\alpha$--Al$_{2}$O$_{3}$ content in dense layer is distinctly higher than that in loose layer. From the superficial layer to the substrate, the cross--section microhardness first increases and then decreases, reaching a maximum at a distance of 35 $\mu$m from the substrate/coating interface. The adhesion strength of microarc oxidation coatings to Al substrate is high and the critical load increases linearly with increasing the coatings thickness. The microarc oxidation coatings possess excellent antiwear properties, and the friction coefficient under oil lubricating condition is only 1/10 of that under dry friction.