Corrosion Resistance of AZ91 Mg-Alloy Modified with La/Ce Conversion Coatings for Sports Equipment

The surfaces of AZ91 Mg-alloy,an advance sports equipment material,were modified with La/Ce conversion coatings grown via chemical route and densified in(NH₄)₃PO₄ solution.The influence of the La/Ce-coating and densification conditions on the tribological behavior of AZ91-alloy was investigated with X-ray diffraction,scanning electron microscopy,electrochemical station and orthogonal test.The results show that the La/Ce-coatings and densification conditions all had a major impact.For example,a descending order of corrosion resistance exists:densified La/Ce-coatings>La/Ce-coatings>AZ91-alloy;and another descending order of impact factor can be listed:densification-temperature>densification-time>(NH₄)₃PO₄-concentration.The optimized conditions included:a temperature of 45℃,a time of 3 min and a concentration of 6%.Moreover,phosphate densification significantly improved the compactness via decreasing the size/density of pores/cracks,and further enhanced the corrosion resistance because CePO₄/Mg₃(PO₄)₂/LaPO₄ phases formed,possibly in pores and voids of La/Ce conversion coatings.