No abstract

The plane-strain initiation fracture toughness (K JICi ) and plane-stress crack growth resistance of two Al-Cu-Mg-Ag alloy sheets are characterized as a function of temperature by a J-integral method. For AA2519 ϩ Mg ϩ Ag, K JICi decreases from 32.5 MPa at 25 ЊC to 28.5 MPa at 175 ЊC, ͌ ͌ m m while K JICi for a lower Cu variant increases from 34.2 MPa at 25 ЊC to 36.0 MPa at 150 ЊC. ͌ ͌m m Crack-tip damage in AA2519 ϩ Mg ϩ Ag evolves by nucleation and growth of voids from large undissolved Al 2 Cu particles, but fracture resistance is controlled by void sheeting coalescence associated with dispersoids. Quantitative fractography, three-dimensional (3-D) reconstruction of fracture surfaces, and metallographic crack profiles indicate that void sheeting is retarded as temperature increases from 25 ЊC to 150 ЊC, consistent with a rising fracture resistance. Primary microvoids nucleate from smaller constituent particles in the low Cu alloy, and fracture strain increases. A straincontrolled micromechanical model accurately predicts K JICi as a function of temperature, but includes a critical distance parameter (l*) that is not definable a priori. Nearly constant initiation toughness for AA2519 ϩ Mg ϩ Ag is due to rising fracture strain with temperature, which balances the effects of decreasing flow strength, work hardening, and elastic modulus on the crack-tip strain distribution. Ambient temperature toughnesses of the low Cu variant are comparable to those of AA2519 ϩ Mg ϩ Ag, despite increased fracture strain, because of reduced constituent spacing and l*.

No abstract

No abstract

No abstract