THE EFFECT OF TI-COLLOID SURFACE CONDITIONING ON THE PHOSPHATING OF 7075-T6 ALUMINUM-ALLOY

7075-T6 aluminium alloys panels were surface conditioned in a titanium colloid suspension, under a variety of different conditions, and subs equently these samples were immersed in a ZnO + H3PO4 coating mixture, and the phosphate coating layers characterized. Morphologies observed by scanning electron microscopy (SEM) reveal that the coating layer c onsists of two phases, namely an amorphous phase, which is directly bo nded to the substrate, and a crystalline phase, in which larger crysta l grains grow on top of the amorphous base. Chemical compositions of t he coating layers were analysed by X-ray photoelectron spectroscopy (X PS) and by static and imaging secondary ion mass spectroscopy (SIMS). It is found that the details of the surface conditioning affect the fi nal coating, both in terms of morphology and chemical composition. For example, larger amounts of Zn and P are detected in coatings for whic h the initial conditioning is done at 40 degrees C, compared with room temperature; a similar statement can be made for surfaces which are w ater rinsed after the Ti pretreatment, compared with those which are n ot water rinsed prior to the coating treatment.