Plasma polymer surfaces, chromated

Adhesion of the cathodic E-coat to the plasma polymer surfaces is an important parameter in the corrosion protection of A1 alloys. In general, the adhesion performance of E-coat applied to plasma polymers was found to be far superior to that of the control panels. A-Methylpyrrolidinone (NMP) paint delamination was not observed after 120 min for E-coat on plasma polymer surfaces as compared to a maximal time for complete delamination of 5 min for E-coat on chromate conversion coating [2B] CC/E panels. The adhesion performance of cathodic E-coat on the plasma polymer surfaces could not be differentiated by the conventional tape test (ASTM D3359-93B), since E-coat on all of the combinations... 

CHROMATED AND NONCHROMATED SPRAY PAINTS ON PLASMA POLYMER SURFACES... 

A nonchromated, water-borne primer applied to [2B] alloy samples, with the appropriate surface preparation and plasma deposition of an ultrathin plasma polymer, was also compared to controls prepared by depositing a chromated primer on chromate conversion-coated A1 substrate. The same comparison was also performed for IVD Al-coated 2024-T6 substrates (pure aluminum is deposited by ion vapor deposition process on aluminum alloy 2024-T6). In the latter case, the primer could not be removed from the IVD Al-coated panels that were treated with the plasma polymer prior to spray primer application. It is interpreted that the water-borne spray paint penetrates into the column structure of the top surface of the IVD Al-coated substrates when the surface energy was modified by the application of a plasma polymer. This effect could be viewed as interactive coating with a porous surface. 

Figure 31.14 shows the Rp values of [2A] with three different chemical pretreatments and with a TMS plasma polymer on each of the three pretreated surfaces, as well as on the control [2A]CC surfaces (chromate conversion-coated 2A). It can be seen that the Rp values of [2A] were decreased to some extent by pretreatment of alkaline cleaning and were drastically reduced by alkaline cleaning plus deoxidization. As observed in the XPS results, the accumulation of Cu elements and removal of oxide layer on [2A] surfaces were presumed responsible for the reduction in corrosion resistance of these chemically pretreated [2A] panels. 

Deoxidized surfaces of [7B] with a plasma polymer coating ([7B] (Dox)/T) showed higher polarization resistance than the chemically deoxidized surfaces without a plasma polymer. This indicates that the added corrosion resistance offered by plasma polymer films is much higher than that of the barrier-type oxides, formed after chemical cleaning, alone. As compared to the chromate conversion-coated surfaces ([7B] CQ, the deoxidized and plasma polymer-coated ([7B] (Dox)/T) surfaces showed higher Rp values, suggesting that these surfaces have higher corrosion resistance. 

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