Compression properties of three-layered functionally graded ADC12 aluminum foam fabricated by friction stir welding

Al foam is expected to be used as automotive components because of its light weight as well as its good energy absorption properties. When Al foam is applied to automotive components with complicated shapes, it is desirable to optimally distribute the low-plateau-stress and high-plateau-stress regions in a single Al foam, such as functionally graded (FG) Al foam, to realize components with superior and efficient energy absorption properties. In this study, two types of closed-cell FG Al foam, one composed of larger-smaller-larger three layers with different porosity and pore size to indicate lower-higher-lower plateau stress, and the other composed of smaller-larger-smaller three layers with different porosity and pore size to indicate higher-lower-higher plateau stress, were fabricated by varying the amount of blowing agent added. It was shown that the large-porosity and large-pore-size layers first deformed and, thereafter, the layers with small porosity and pore size deformed, regardless of the location of the large-porosity and large-pore-size layers in the compression test specimens. It was also shown that the first (lower) and second (higher) plateau regions appeared independently, which corresponds to the pore structures of each layer. Therefore, it was demonstrated that the plateau stress of Al foam can be controlled by varying the pore structures.