LONG-TERM DURABILITY IN WATER OF ALUMINUM-ALLOY ADHESIVE JOINTS BONDED WITH EPOXY ADHESIVES

This paper begins with a review of some of the previous literature on the topic of durability of adhesive bonds to aluminium alloys. A numbe r of papers published during the period 1977 to 1991 are discussed. Th e paper then details the current test programme using the wedge test t o ASTM D-3762 and the adhesives and surface preparations chosen. A num ber of cold-setting epoxies were tested and a smaller number of hot-se tting epoxy film adhesives. All testing was done on 2024-T3 clad alumi nium alloy; specimens were immersed in distilled water at room tempera ture and readings of crack length taken at intervals. Readings were ta ken frequently for the first month and then at longer intervals. Fract ure energy values were calculated after each set of readings. In the l ast 3 years of the programme readings were taken at intervals of 2 or 3 months. After 5.5 years of total Immersion the specimens were handed over to AEA Harwell for further testing and surface analysis of failu res by scanning electron microscopy. Four surface preparation methods were compared. These were: (1) tank-type chromic acid anodise; (2) por table chromic acid anodise (Selectrons); (3) Deoxidine 202, a phosphor ic acid paste etch; and (4) abrasion with 100 grit glass paper. From t he literature a number of factors affecting durability are listed.A nu mber of conclusions are drawn from the test programme and a further se t from subsequent work on these specimens at AEA Harwell. Some relate to observations on electron microscope photographs of the surfaces of specimens after joint failure. Others show that, for a given type of s urface preparation and a given type of adhesive chemistry, the durabil ity of adhesive bonds depends on the permeability of the adhesive towa rds water. (C) 1997 Elsevier Science Ltd.