Study on processing galvanized steel/PA6 sandwich composites by hot-pressing: Influence of interface properties and surface treatment on the adhesion strength

Steel/polymer/steel sandwich structures have a high potential in weight reduction at high stiffness values. The aim of this study is to investigate the adhesion properties of galvanized steel/Polyamide 6 sandwich composites, which are produced by hot pressing following a parametric design of experiments plan at varied temperatures, times and pressures. One of the most interesting phenomenon hindering a good adhesion strength was the formation of sub-millimeter sized bubbles during the hot pressing. Possible reasons and methods to avoid these bubbles were investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, ultraviolet photoelectron spectroscopy, metastable induced electron spectroscopy and X-ray diffraction. The proposed solution is to apply a heat treatment on the galvanized sheet prior to pressing, where varied treating regimes were applied. To improve the adhesion quality, mechanical/physical treatments were utilized as well. Furthermore, a compatible adhesive agent was applied in combination with the different surface treatments, where the lap shear strength reached at least 23 MPa, high enough for a delamination-free shaping afterwards.