Development of tubes filled with aluminium foams for lightweight vehicle manufacturing

Abstract

This paper aims to investigate different filling methods of ex situ aluminium foam-filled thin-walled Al alloy tubes to determine the best option for possible applications in automotive industry. The main applied filling methods were joining with heat dilatation, mechanical compression and adhesive bonding. Foam specimens were prepared by shaping and machining operations from an original foam block. The density of the filler foams was 250 kg/m3, 500 kg/m3 and 750 kg/m3 respectively. The foam rods were inserted into empty thin-walled tubes and subjected to quasi-static bending and compression loading conditions. The connection methods between the aluminium foam and the thin-walled tube were examined by microscopy technique. The quality of the assemble was highly influenced by the filling method itself and the surface defects caused by machining operations. The foam-filled tubes, empty tubes and foams were compared in terms of the maximum load carry capacity, specific load capacity, crash energy absorption and specific energy absorption. The obtained results showed that adhesive bonding has the best specific load carrying ability under quasi-static bending loading. Also, it had the lowest average total weight of the specimens. The maximum flexure displacement achieved by the heat dilatation filling method and the minimum was reached by mechanical compression method. Adhesive bonding and mechanical compression showed good energy absorption capabilities against bending loading. The maximum specific energy absorption was produced by density of 750 kg/m3 but the failure of the specimens came earlier than in case of fillers with lower densities. The foams with density of 250 kg/m3 had the lowest specific values but they had the highest displacement values. The machinability is directly proportional with the growing of density. Foams with a density of 500 kg/m3 are very good fillers because they can be machined well, have the best specific load-bearing capacity and less cell displacement under load. The 500 kg/m3 was the best density for ex situ filling with all this in mind. In the case of compression tests, the stress-strain curve of the adhesive bonding filling method exceeded the sum of the stress-strain curve of individual components. The specific energy absorption curve of the adhesive bonding method overtakes the curve of the empty tube at a certain strain.The novelty of this article is the application, investigation and comparison of different filling methods for the production of ex situ foam-filled thin-walled tubes. The experiments were made with very small wall thickness which is even harder to fill with metal foams. The machinability of aluminium foams was also tested in this article. Overall, the goal was to produce foam-filled structures with tools that are widely used in the automotive industry.