EFFECT OF PLASMA-POLYMERIZED PRIMERS ON THE DURABILITY OF ALUMINUM EPOXY ADHESIVE BONDS/

The durability of aluminum/epoxy adhesive joints prepared from substra tes pretreated by plasma etching and then deposition of plasma-polymer ized primers was determined using the wedge crack testing method. Plas ma etching and polymerization were conducted using both direct current (DC) and microwave (2.45 GHz) driven plasma systems. Plasma-polymeriz ed primers were deposited using trimethysilane (TMS) and hexamethyldis iloxane (HMDSO) to form siloxane-like and silica-like films, respectiv ely. Plasma etching with argon and argon/hydrogen plasmas was used as a substrate pretreatment. In some cases etching with an oxygen plasma was used as a post-treatment to give a silica-like surface to siloxane -like films deposited from TMS. Adhesive joints were prepared using tw o different epoxy adhesives, Cytec FM-300 and FM-123-2 Differences in initial adhesion were observed for primer films with chemical differen ces. Siloxane-like primer films were not wetted by the adhesive and re sulted in poor wedge test results. Silica-like primer films were not w etted by the adhesive and resulted in poor wedge test results. Silica- like primer films deposited onto aluminum substrates resulted in wedge specimens with good adhesion and durability. The initial crack was co hesive within the adhesive. However, crack growth occurred at the inte rface between the adhesive and silica-like primer. Durability of the w edge specimens was essentially invariant of the type of microwave plas ma pretreatment for grit-blasted aluminum substrates that were coated with silica-like primers before bonding with FM-123-2.