Investigations on the correlation of surface features and mechanical strength of laser-pretreated Al6082-T6 - epoxy E320 joints

Kurzfassung

In order to reduce fuel consumption and enhance the energy effectivity of future vehicles and aircrafts, further weight reduction through the use of alternative materials and joining techniques is necessary. To be able to join different groups of materials, adhesive bonding plays an important role in present and future development of lightweight construction. The fundamental relationships between physical and chemical properties of joint interfaces and resulting mechanical strength and corrosion resistance are often times still not fully understood and under investigation. Particularly joining defects or damage occurring due to long-term environmental and mechanical load influences pose a major problem limiting the wide-spread use in safety relevant applications as, e.g., structural bonding in aerospace [1]. Since these damages are extremely difficult to detect non-destructively, further research is necessary to understand the mechanisms and avoid damages in first place. Surface pretreatments of metallic bonding partners prior to bonding can significantly increase the mechanical strength and the long-term durability of metal-polymer bonds. Typically, this phenomenon is attributed to cleaning effects (e.g. degreasing) and generating suitable roughness on the metal surface, allowing mechanical interlocking with the polymer matrix [2]. The correlation between surface enlargement and resulting mechanical strength of adhesive joints, both enhancing mechanical interlocking as well as chemical bonding remains difficult to obtain. Therefore, our study focuses on a new approach for investigating the possible correlation between the surface enlargement through laser pretreatment of the metallic surface and the resulting mechanical strength of Al6082-T6-E320 adhesive joints. Scanning electron microscopy (SEM) of joint cross-sections (e.g., after Focused Ion Beam preparation) is used to determine the approximate surface enlargement due to the micro- and nanostructures. For the examination of a possible correlation with the mechanical strength of pretreated joints, results of the SEM analysis are linked with results of performed single lap shear tests.