The PEO treatment for ZL101 aluminum alloy in sodium silicate solution was carried out

and the formation

constituent and structure of the PEO coatings were investigated. The coating can be created on the primary α phase and eutectic phase respectively in initial stage of PEO

and the absence of plasma discharge in the Si phase can be observed. SiO2 phase in the coatings is formed by high temperature oxidization of Si from the plasma discharge adjacent to α phase. The coating on the primary α phase is composed of major Al2O3 and minor SiO2 phase while SiO2 phase content is much more than Al2O3 content in the coatings on the eutectic phase. PEO coating of ZL101 aluminum alloy is composed of γ-Al2O3

α-Al2O3

SiO2 and mullite （3 Al2O3·2SiO2）

in which with the extend of PEO treating time

the α-Al2O3 phase is raised due to the transformation of γ-Al2O3 into α-Al2O3.