Surface characterization of AISI 304L stainless steel subjected to various prebonding treatments. Correlation with adhesion measurements

Abstract

AbstractIn order to promote strong and durable steel/epoxy adhesive joints, various stainless steel surface treatments are investigated. The adherend surface characterization is achieved by both spectroscopic (low energy electron‐induced x‐ray spectrometry (LEEIXS), AES, XPS) and microscopic (SEM) techniques. The strength of the steel/epoxy bonds is evaluated, after bonded sample ageing under hydrothermal conditions (70°C, 95% r.h.), by means of a mechanical three‐point flexure test, sensitive to the interfacial properties of the bonded systems.The stainless steel surface treatments used in this study include conventional ones, such as solvent degreasing, acid etching, and phosphating and more original ones such as anodizing in sulphuric‐chromic or nitric acid electrolytes. These two last treatments lead to the formation of a ‘thick’ (in the range 10 to 90 nm) surface layer, highly chromium (as Cr(III))‐enriched, as determined by LEEIXS and XPS.The anodized stainless steel/epoxy systems exhibit performances which largely outclass those allowed by conventional steel prebonding treatments. These performances are very dependent upon the electrochemical conditions (current density, treatment duration, electrolyte temperature and composition) chosen for the anodizing process.