Roduction and characterization of steel sandwich structures with aluminum foam core [Realizzazione e caratterizzazione di strutture sandwich di acciaio con core in schiuma di Al]

The present work describes the results carried out in the manufacture of sandwich panels with stainless steel (SS) AISI 316 skins and an aluminium alloy AISI 10 foam core. Sandwich structures with a core of AI or AI alloys are often realized by ex-situ bonding, i.e. adhesive are employed for joining foam to external sheets. This method is easy to apply, however it entails a strength reduction when temperature increases, which results in serious problems during recycling and high costs. Another approach is the in-situ bonding, which involves the preliminary joining of the skins to the foam precursor to make the composite structure. This composite, once submitted to the foaming heat treatment, achieves the final Foam Sandwich by metallurgical bonding. In this study, a new method to obtain in-situ bonding between the Stainless Steel (SS) skins sheets and the aluminium foam core is described. The first part of this work has focused on the production of sandwich of small size: 20 × 20 mm. The production of the sandwich was done in two steps. The first step is the manufacture of the composite precursor, by both hot and cold pressing. The Composite precursor was made, using two sheets of (SS) for the skins and a foamable precursor of AISI 10 placed in middle. Great importance in the manufacture of such a composite lies in surface finishing, consisting in the middle removal of the surface oxide layer by mechanical and chemical treatments. As shown in Fig. 2 (a-b) as a function of the procedure of preparation, bad or good preliminary bonding have been obtained. During the second step, the composite precursor was then foamed in the oven at 640 °C. In this step the pore walls at the interface make a metallurgical joint with the steel surface, as shown by the concentration profile of the chemical elements at the interface (Fig. 4, Fig. 5).