Modelling of fracture toughness in high strength 7xxx aluminium alloys

Kamp, N., Sinclair, I. and Starink, M.J. (2002) Modelling of fracture toughness in high strength 7xxx aluminium alloys. Gregson, P.J. and Harris, S. (eds.) In Aluminium Alloys 2002: Their Physical and Mechanical Properties. Trans Tech Publications Ltd. pp. 1335-1340 .

Abstract

The relationship between plane strain fracture toughness, KIc, tensile properties and the microstructure of two high strength 7xxx alloys has been examined. Two formulations of the 7449 composition were examined, specifically, one containing Zr as the dispersoid forming element, whilst the other contained Mn. Fractography revealed coarse voiding at intermetallics, fine tensile voiding at dispersoids and a combined intergranular/transgranular shear fracture mode. In the Zr containing alloy in particular, the observed increase in toughness with overageing is accompanied by a change in fracture mode from predominantly intergranular/transgranular shear failure to coarse voiding. A new fracture toughness model has been derived based on the microstructurally dependent work hardening factor, KA, introduced in Ashby’s theory of work hardening. This model predicts a linear relationship between KIc and KA^0.85/?ys^0.35 which is shown to be consistent with the experimental data.

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