Chemical Surface Treatment and Seawater Aging Effects on AA6082-T6 Adhesive Joints

Abstract

The mechanical strength and durability of the bonds between structural components is a major contributor to the performance of an engineered structure. Due to the potential for weight savings while preserving excellent mechanical characteristics and providing even load distribution without stress concentrations or peak stresses, adhesively bonded joints are being widely adopted in engineering. Therefore, they represent an attractive alternative to other fastening methods, particularly in structural applications where high loads are present. In the current research effort, the effects of a chemical surface treatment and seawater aging on aluminum alloys (AA6082-T6) were investigated. Epoxy resins were chosen as the adhesives for this study because of their excellent mechanical behavior and suitability for various applications. Specifically, two types of epoxy adhesives were evaluated: flexible (Araldite 2015) and rigid (Araldite AV 138/HV 998) adhesives. All specimens were made using single lap joints as defined by ASTM D 1002. To enhance the bond strength between the adhesive and the substrates, three various surface treatments were employed. Specimens were then aged in seawater at room temperature for varying lengths of time. Mechanical testing (tensile tests) was conducted to determine the effects of aging and the type of surface treatment on the mechanical strength and durability of the bonded joints. The results clearly indicate that both the surface treatment and aging duration had significant effects on the performance of bonded joints. Compared to the rigid adhesive, the flexible adhesive exhibited superior tensile strengths and greater resistance to degradation. The surface treatment that provided the best bonding and durability was identified. As expected, tensile strength decreased with increasing aging time due to moisture absorption into the substrate and interfacial degradation. The current research demonstrates the importance of appropriate surface preparation and adhesive choice when designing and implementing adhesive-bonded aluminium alloys for long term use in marine environments.