After Market Paint Repair of Aluminum Closure Panels

The rapid increase over the past few years in the use of aluminum closure panels on vehicles is anticipated to continue well into the next decade. Along with this increased usage comes the need for a greater amount of cosmetic repair of these closures in after market body shops. Although paint repair systems for aluminum have been available for some time, their effectiveness on newer alloys needed to be demonstrated. Some work in the recent literature has also questioned the corrosion and paint performance of aluminum closures after sanding. In this study, extensive surface analysis of AA6111 closure sheet material was carried out in the as-received condition, after phosphating and after sanding, cleaning and pretreating with selected paint repair systems from major automotive paint suppliers to determine the effects of surface residues or contaminants on subsequent corrosion performance. Different sanding media were also evaluated in terms of their effects on sheet surface topography and the potential for embedding grit particulates onto the surface. Both chrome and non-chrome containing pretreatments were examined. Corrosion comparisons were also made for etch primers applied over cleaned metal without any pretreatment and for epoxy primers applied onto pretreated sheet. Apart from the evaluation of corrosion performance of repair primers from different suppliers, selected primers were applied over improperly prepared surfaces and at film thicknesses beyond those recommended to provide insight into the effective operating window for repair procedures. In all cases, comparisons were made with representative OEM phosphated and painted sheet. Corrosion test methods included both filiform and cycling (GM9540P, cycle B) procedures. The study ends with a discussion of the overall effectiveness of repair systems.