Microstructural and mechanical characterization of two aluminium based in situ composite foams

Abstract

In situ composites are multiphase materials where the reinforcing phase is synthesized within the matrix during composite fabrication. The present paper deals with the processing, microstructural and mechanical characterization of Al–7Si–0.3Mg–10TiB₂ and Al–4Cu–10TiB₂ foams. Composite foams with very low relative density (ρ_r = 0.17–0.37) and foams containing uniform cell sizes were successfully processed. Since the TiB₂ particle sizes are less than 2 μm and have a good wetting behaviour, TiB₂ can be very good foam stabilizers. Microstructural characterization of the cell walls showed significant grain refinement since TiB₂ is a grain refiner. Elemental mapping clearly showed TiB₂ particles at inter dendritic boundaries. Compression testing of the processed foams showed some interesting features. Stress–strain curve showed a lot of serrations which indicated brittle fracture of the cell walls and edges. Hence, it is observed that a balance should be attained between the grain refinement of α-Al grains and the amount of TiB₂ particles to obtain desirable mechanical properties. Energy absorbed by the processed foams was calculated and they were observed to be close to that of the commercially available ALPORAS foams.