Ageing of Adhesively Bonded Stainless Steel Joints under Thermo-oxidative, Hydro-thermal and Industrial Standard Conditions

Comparing ageing of adhesively bonded stainless steel joints under thermo-oxidative, hydrothermal and industrial standard conditions Adhering is coming up as an alternative technology to welding, not only in vehicle construction, respectively. A main task in this relation is the estimation of long-time resistance of adhesive joints under various conditions. Therefore, stainless steel adhesive joints were aged under different temperatures and moisture influences to get fast-motion results of the resistance. Special ageing standards were applied by companies, tailored to the prospective application. Generally, the testing criteria are mechanical parameters. A further question is the effect of deformation auxiliaries like oils on strength and ageing of the adhesive joints. The presented results comparing the effects of ageing under thermo-oxidative, hydrothermal and industrial standard (VDA-saltspray-test, VW P1200 test) conditions on stainless steel (1.4301, 1.4376) joints, bonded with three commercial epoxy-based hot curing adhesives. Steel samples with two oil-based and one surfactant-based surface treatment and degreased samples were adhered. Besides the mechanical properties the focus was set on the ageing-effected changes of the chemical structure of the adhesives. Therefore, fracture surfaces of unaged and aged lap-shear test samples were investigated by µ-ATR-FTIR-spectroscopy. It is possible to take location-resolved spectra by this method with a resolution of 100 µm. In combination with different ageing periods the results providing a correlation between the progression of ageing in time and location. It was proven that ageing by industrial standards lead to remarkable changes of the polymer structure (VW P1200 test) or of the substrate surface nearby the adhesive (VDA saltspray test). The relatively low glass transition temperatures may contribute to the observed ageing phenomenas in a large scale. Chemical mechanisms are proposed for ageing reactions. The investigated deformation auxiliaries did not influencing the mechanical and chemical properties of the adhesive before and after ageing. They are resorbed by the epoxy during joining.