Effect of surfactant contamination on the properties of aluminum/silicone adhesive joints

Adhesives are used to join and seal electronic packaging. In these application, they are often used to bond aluminum components and, during the process of machining aluminum, oils and lubricants are used to facilitate the process. To remove these fluids, detergents such as surfactants are often used. However, if the surfactant itself is not removed completely and remains on the aluminum part, it can affect the bond properties of the joint, leading to abrupt joint failure. In this work, adhesive joint properties as a function of the amount of surfactant at the surface were studied. The joint substrates are Al6082-T6 aluminum, the adhesive a two-part silicone and the surfactant a cocosalkylaminethoxylate. For this, double cantilever beam (DCB) and single lap joints (SLJ) were used. An additional scanning electron microscopy (SEM) analysis was conducted to clarify the results. It was found that the adhesive bond strength continuously decreases with increasing amount of contaminant. Similarly, with increasing amounts of contaminant applied to the surface, the failure mode progressively changed from cohesive to adhesive, which was attributed to the adhesive at the interphase absorbing the contaminant during curing, moving the failure to this region, until the absorption limit of the adhesive is surpassed and the surfactant remains at the interface, leading to interfacial failure. A numerical model was created to simulate the behavior of the experimental joints and obtain the properties of the interphase by applying the inverse method, and a numerical study was done on the sensitivity of the model to variations in cohesive peel properties for the DCB and shear properties for the SLJ.