Mechanical analysis and microstructural characterisation of metal foams

Abstract

The mechanical behaviour of closed cell Al alloy foams has been studied. Specimens of Al foams made both by powder metallurgy and casting processes have been tested in compression, under static and dynamic conditions, for a wide range of density values. Experimental results revealed that, depending on the alloy chemical composition and the microstructure, ductile and brittle deformation occur. The formation of deformation bands has been observed. Scaling relationships correlating the mechanical properties of Al foams to their relative density have been derived. However, inhomogeneous density distribution as well as imperfections in the microstructure cause a different behaviour from that of ideal foams. Previous models developed to predict the mechanical performance of foams are dependent on the apparent density, the properties of the solid material from which the cell face are made, and the cell geometry. Therefore, X-ray microfocus computed tomography is used for the internal investigation and quality control of Al foams. This method provides a qualitative characterisation of the cell structure and enables the description of the deformation mechanisms within the foam at different strain values. Using a commercial image analysis software 2D quantitative measurements such as cell size, cell shape, cell size distribution, and cell orientation have been performed. A new image analysis algorithm has been developed for 2D and 3D quantitative measurement.