Influence of surface pretreatment and electrocoating parameters on the adhesion of cathodic electrocoat to the Al alloy surfaces

Adhesion of cathodic electrocoat films to the aluminum alloys 2024-T3 bare and Alclad 2024-T3 with different pretreatments and with different cathodic electrocoat process parameters was investigated. The pretreatments studied were acetone wipe and alkaline cleaning. The cathodic electrocoat process parameters studied include variation of cathodic electrocoating voltage and time. Adhesion performance was evaluated by measuring the delamination tim e and percent delamination of the electrocoat from the alloy surface by pla cing the small specimen of the sample in the N-methyl pyrrolidinone (NMP) s olution at 60 degrees C until the film lifts off or for 2 h whichever comes first. NMP times for electrodeposited film delamination from alkaline clea ned surfaces were found to be higher than the acetone wiped and or those of as-supplied metal surfaces. There was not much effect of acetone cleaning of these alloy surfaces on the adhesion performance of the cathodic electro coat. The voltage-current (of cathodic electrocoating process) relationship s for alkaline cleaned surfaces were also found to be significantly differe nt from the other two types of surfaces. The NMP times of cathodic electroc oat delamination at lower cathodic electrocoating voltage and lower electro coating times were higher than those at higher cathodic electrocoating volt age and electrocoating times for alkaline cleaned 2024 bare surfaces. Elect rocoat thickness developed on the surfaces during the electrodeposition pro cess increased with increasing electrodeposition voltage and time as antici pated. (C) 1998 Elsevier Science S.A. All rights reserved.