Influence of drawing on organic-coating adhesion property in aluminum.

The organic-coating adhesion after drawing was investigated in relation to the pretreatment of aluminum. Chromate phosphate conversion coating showed good organic-coating adhesion after drawing in the case of Cr of about 10mg/m2. Much more Cr, however, resulted in the deterioration of the adhesion property by heat treatment before the organic-coating. Anodizing produced high adhesion strength on the flat plate. However, drawing caused microcracks and the organic-coating delaminated from the side wall of the drawn cup. On the other hand, the organic primer showed good adhesion property even after drawing. The interface of delamination was investigated by SEM and XPS. The deterioration of the adhesion property by drawing was due to the cohesive failure of pretreated films and the change in the surface morphology. These results indicated that the pretreatment for drawing was required to produce high formability as well as high adhesion property.