Processing of in-situ aluminium foam-filled stainless steel tube with foam-tube bonding for enhanced crashworthiness

This work aims to achieve superior mechanical properties in in-situ aluminium foam-filled stainless steel 316L tubes by promoting good bonding between the foam and the tube. Towards this end, the stainless steel tubes (inner surface) were electroplated with copper before in-situ foam-filling. Detailed microstructural studies were conducted at the foam/tube interface. In-situ foam-filled tube specimens were subjected to uniaxial compression and three-point bend testing. The axial compression and bending performance of the in-situ foam-filled tubes were compared with ex-situ foam-filled tubes and in-situ foam-filled tubes produced without copper coating. The deformed samples were sectioned and analysed to understand the deformation modes. The results show that copper coating is very effective in promoting good bonding between the foam and the tube during in-situ foaming, leading to considerable improvement in the mechanical performance of the foam-filled tubes. Ex-situ-heat processed (ex-situ-HP) foam-filled tubes (FFTs) and in-situ-uncoated (in-situ-UC) FFTs were found to display approximately 34 % and 46 % increase in specific energy absorption (SEA) as compared to empty-HP tubes. Electroplating of the inner surface of the steel tube with copper before in-situ foam-filling was found to promote good metallurgical bonding between the foam and the steel tube. Because of the enhanced foam-tube bonding, the in-situ-copper coated (in-situ-CC) FFTs were found to display ~61 % and 10 % higher SEA as compared to the empty-HP and in-situ-UC FFTs, respectively. The deformation mechanisms in foam-filled tubes are discussed in detail.