Formability and self-repair properties of advanced weldable primers (PrimeForm)

Defect formation and the reactivity of weldable zinc-rich primers induced by it were studied cooperatively. The forming process leads to de-adhesion and microcrack formation between the zinc particles and the surrounding polymeric matrix. The density and size of such defects increase with the degree of forming. Defects can penetrate the composite coating and reach the zinc coating. Microscopic as well as integral and microelectrochemical studies revealed the reactivity and repair properties of such defects. These data were correlated to corrosion studies in open and flange configuration, as well as to the processability and in-life performance. The corrosive reactivity of the defects also increases with the size of the defects. This leads to lower pore resistance values in environments containing chloride. However, during an automotive phosphatation process the kinetics of phosphate crystal formation are increased in the larger cracks and exposed zinc particles will be at least partly recovered prior to an ED-paint deposition. Such a repair process can not occur within flanges. In this case the corrosion protection properties are significantly lowered for high forming degrees. The addition of organosilane adhesion promoters at the zinc particle/binder interface did not lead to a strong reduction in the density and size of cracks. However, for small forming degrees below 5 % a slight improvement was detectable, based on the increased adhesion force at the binder/zinc interface. Organic and inorganic inhibitors and new Zn/alloy particles were incorporated in the composite coating. The leachable organic inhibitors mainly showed an inhibiting effect in the microcracks.