Adhesive bond durability with conversion coatings

Abstract

The effect of processing time during conversion coating of 2024-T3 clad aluminum alloy on adhesive bond strength and durability was investigated. Iridite 14-2, both by immersion (leached and non-leached) and brush application methods, and alodine 1500 processes were studied. Bond durability and strength were determined on both primed and unprimed surfaces by performing wedge and T-peel tests, respectively. The morphology and thickness of the conversion coatings prepared by varying the processing time were studied by scanning transmission electron microscopy (STEM). The chemical composition of the surfaces was determined by electron spectroscopy for chemical analysis (ESCA). It was found that wedge test crack extensions for brush iridite 14-2 (both primed and unprimed) and primed leached iridite 14-2 surfaces were comparable to those of FPL-prepared surfaces when recommended application times were observed. Unfavorable crack extensions for primed iridite 14-2, alodine 1500 (both primed and unprimed) and unprimed leached iridite 14-2 surfaces dictate that those surface preparation methods should not be used where adhesive bond durability is desired. All crack extension behavior observed can be explained by radiations in surface roughness. Surface roughness seems to be critical in achieving durable adhesive bonds.