Fractographic Analysis of the Low Energy Fracture of an Aluminum Alloy

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Abstract
The brittle fracture of many high-strength alloys occurs by dimpled rupture. It is recognized that, as in ductile materials, voids which nucleate at non-metallic particles, grow and coalesce during deformation leading to final rupture. The density and distribution of impurity particles, therefore, may affect strongly the toughness of high-strength alloys without contributing significantly to their strength. To understand better this problem the fracture process of a high-strength aluminum alloy (2014-T6) was studied. Two types of large impurity particles (3 to 10 μm in diameter), where voids were nucleated, have been identified by microprobe analysis. Voids were nucleated at these inclusions by fracture of the inclusions, and this happened at rather low strains. From the examination of the fracture surface of plane strain fracture specimens, by replicas and directly with the scanning electron microscope, it was concluded that the joining of the large voids initiated at the large inclusions occurred through the matrix by a mechanism of void sheet formation. The void sheet formation seems to be developed through the formation of voids at small particles (0.1 to 0.2 μm in diameter) distributed uniformly in the matrix. These particles should be regarded as a dispersion which strengthens the matrix.

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