Creep Behavior of Hot Rolled Powder Metallurgy Processed Al-SiCp Composites

Abstract

The structure-property relations and creep behavior of powder metallurgy processed and hot rolled commercially pure Al and its composites with 5, 10, 15 and 20 vol.% SiC particulate reinforcements, have been studied. The results of uninterrupted tests at 623 K under a stress of 21 MPa show the presence of distinct primary, secondary and tertiary stages of creep. Both the creep resistance and Young’s moduli of the composites are deteriorated with increase in particulate volume fraction due to cracking and debonding of SiC particles during rolling. The stress exponents for both Al and Al- SiCp composites, determined using stress jump tests at 623 K, are found to be between 4 and 5, suggesting the predominance of dislocation creep. The creep threshold stress has been found as ≤ 3 MPa, which is attributed to back stress and detachment stress caused by interactions of dislocations with Al2O3 and Fe-rich dispersoids present in both pure Al and Al-SiCp composites. The activation energy estimated from temperature change tests at 11 and 21 MPa is reasonably close to that for grain boundary and lattice self diffusion of Al at low and high stresses, respectively. Pure Al and Al-5 or 10 volume percent SiC particulate composites, has been also evaluated after subjecting to 0, 2 and 8 thermal cycles between 773 and 273 K with rapid quenching.