The effects of ageing on the physical and mechanical properties of particulate reinforced aluminium alloys

The changes during aging of the physical, tensile and compressive mechanical properties of 8090 and 2124 reinforced SiC particles is investigated. Dynamic modulus values increase with naturally aged (NA) condition in all materials but decrease on artificial aging only in the metal matrix composites (MMCs). Variations in the degree of dislocation pinning and lattice parameters due to microstructural changes associated with changes in solute/vacancy concentrations, precipitates and internal stresses are thought to be responsible. MMCs exhibit a high damping coefficient in the artificially aged condition. MMCs exhibit strong variation between tensile and compressive mechanical properties under certain aging conditions at low strain values. Tensile elastic limits are greater in as-quenched (AQ) and NA 2124 MMC and in artificially aged (AA) 8090 MMC but are similar to compressive values in AA 2124 MMC and in AQ and NA 8090 MMC. This results from improved strengthening efficiency of Cu solutes and GP(B) zones due to internal stresses in the MMC matrices.