Study On Technology Of Chrome-free Chemical Conversion Treatment Of Magnesium Alloys

In this study, a technology of chrome-free chemical conversion treatment was introduce-d, which was of simple operation, low treatment temperature and well adhesion.The technical parameters were optimized by orthogonal test; and the experiments were operated on the base of the best scheme .The corrosion resistance ability was tested by the m-ethods of immersing salts water, neutral salt spray and electrochemistry; and the adhesion w-as tested by the national standard of GB1720-79.The results showed that the corrosion resistance of the CFM conversion films which could endure over 96h NSS were better than the films of the polyphosphating, chromate conversion (D0W1) and permanganate conversion, and adhesion was the first grade for three coatings ,such as the iron-red epoxy primer, iron-red acrylic primer and cathodic electrodepositio-n paint.The processes of forming and corrosion resistance of the conversion coatings were investigated by test methods of SEM, XRD and XPS based on the micro- appearance and constitution of the coatings. As a result, the processes of the double-layer films and layer-after-layer c-orrosion are developed. The forming of coatings includes three processes: (a) the beginning of coatings formed; (b) the first step of coatings formed; (c) the second step of coatings formed. The corrosion activates from outer layer and then diffuses into the interior until to the bo-dy.