The influence of reinforcement morphology on the tensile response of 6061/SiC/25p discontinuously-reinforced aluminum

In order to study the effect of particle morphology on the tensile response of discontinuously-reinforced aluminum (DRA), two P/M 6061/SiC/25p materials were fabricated using established powder blending, compaction and extrusion techniques. One of the materials contained abrasive-grade SiC (F-600) whilst the second material was fabricated using a less angular SiC particulate with a lower aspect ratio, selected to give an overall higher bulk density (HBD) in the as-blended form. Care was taken to ensure that each material contained the same size and volume fraction of SiC particles, and that each material experienced an identical processing route. Mechanical testing was completed at ambient temperature, to measure the effect of particle morphology (F-600 vs. HBD) on both the elastic and plastic tensile response of the DRA. Specimens were tested in as-extruded (F), peak-aged (T6) and over-aged heat treatment (OA) conditions. The DRA produced with the HBD reinforcement consistently showed improved tensile elongation over the DRA containing the F-600 reinforcement, with the most significant effect being observed in the as-extruded (F) condition. The Considère criterion was used to show that different damage mechanisms may be operating in each material. Extensive microstructural and fractographic analyses were also carried out on the as-processed and as-tested specimens, using optical and electron microscopy. The dominant damage and failure mechanisms in each material are discussed in the light of these results.