Special Issue Paper
(Received 26 November 2013; accepted 27 February 2014)
Published Online: 2014
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This investigation characterises the fracture toughness of the very high strength Aluminium alloy 7449. This Al-Zn-Mg-Cu alloy is heat treatable and relies on rapid quenching from the solution heat treatment temperature to promote subsequent artificial aging. While the influence of quench paths on strength is well understood and can be predicted using techniques like quench factor analysis, the influence of quench rate on fracture toughness is more challenging. The rate of quenching can influence the fracture toughness through complex precipitation reactions occurring during cooling. The precipitate locations dictate the magnitude of the detrimental effect on the fracture toughness. In this investigation, the fracture toughness of 7449 in two product forms was measured using compact tension specimens cut from forged blocks and rolled plate. These plane strain (KIC) results were also augmented with Charpy impact tests. Various quench conditions were investigated, including water at three different temperatures and poly oxyethylene glycol (PAG) in two concentrations. The influence of standard and novel aging procedures including retrogression and reaging was also determined. The combinations of strength and toughness have been related to the prevailing microstructural condition. Fracture toughness magnitudes were found to vary most significantly with rapidity of cooling from the solution treatment temperature, with the subsequent aging treatments having a much smaller effect.
Robinson, J. S.
Department of Mechanical, Aeronautical and Biomedical Engineering, and Materials Surface Science Institute, Univ. of Limerick, Limerick,
Department of Civil Engineering and Materials Science Univ. of Limerick, Limerick,
Stock #: MPC20130094