Abstract
The fast fracture of high-strength aluminium alloys appears to be closely involved with the fracture or cavitation of dispersoid particles, in the size range 0·1–0·5 μm, which are present in high volume fraction and which contribute to grain refinement. In the present study, two high-strength A1–Zn–Mg–Cu (7000 series) alloys have been examined: one treated with Zr (7010) and one treated with Cr (7475). It was found that the crack paths in these alloys were of a ‘zig-zag’ nature due to a ‘fast shear’ fracture process, in which the critical step appears to be the decohesion of dispersoids within narrow shear bands. A model has been used to relate the toughness of the alloys to the basic tensile properties of yield stress and strain-hardening exponent, and to dispersoid parameters such as size, shape, distribution and dispersoid/matrix interfacial strength. The model has also been employed to try to explain the difference between the effects of dispersoids on toughness in the Zr-treated alloys and the Cr-treated alloys.
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