Tension and fatigue behavior of Al-2124A/SiC-particulate metal matrix composites

The tension and fatigue properties of SupremEX (R) 225XE composites (Al-2124A/25%/SiCp/3 mu m) were determined for extruded samples tested in the longitudinal orientation in the T4 condition. Tension testing was conducted at 0.001/sec on as-machined cylindrical samples tested with high alignment fixtures according to ASTM E-8. The fatigue tests were conducted on polished hourglass fatigue samples with stress ratio R = 0.1 and test frequency of 20 Hz using hydraulic grips on a Model 810 MTS servo-hydraulic testing machine according to ASTM E466-15. A total of 26 samples were tested with stress levels between 448 MPa and 557 MPa. The resulting stress vs. cycles to failure (i.e. S-N) curve was compared to the unreinforced matrix alloy, other unreinforced high strength aerospace aluminum alloys, as well as other conventionally processed MMCs. The SupremEX (R) 225XE MMC exhibited improvements to both the low cycle fatigue (LCF) and high cycle fatigue (HCF) performance compared to these materials. The fatigue strength at 10(7) cycles was 448 MPa, well in excess of those for monolithic aluminum alloys as well as conventionally processed MMCs. Detailed fractography revealed the presence of a unique cone-shaped fracture feature for samples failing in HCF. Calculations based on fracture morphologies suggested catastrophic fatigue fracture occurred as the material reached its critical fracture toughness. Initial modeling of this fatigue performance used a variant of the Universal Slopes Criterion proposed in early work at Case Western Reserve University by S. M. Manson.