The transgranular SCC of a Mg-Al alloy: Crystallographic, fractographic and acoustic-emission studies


A study has been made of the propagation of transgranular stress-corrosion cracks in a Mg−7.5 wt pct Al alloy tested at room temperature in an aqueous NaCl-K2CrO4 solution; the studies were carried out on single cracks which initiated and propagated within single grains in coarse-grained bend specimens. The resulting fracture surfaces were flat, and two-surface analysis established their orientation to be {ie1155-01}. Specimens fractured at liquid-nitrogen temperature cleaved on {ie1155-02}, indicating that the {ie1155-03} are not the normal cleavage planes in this material. The stress-corrosion fracture surfaces were cleavage-like in appearance, containing shallow steps which were matching and interlocking on opposite faces. Discrete acoustic signals were emitted during crack propagation, and these are considered to result from discontinuous crack advance. It is concluded that stress-corrosion cracking in this system occurs by discontinuous cleavage on {ie1155-04} planes.

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Formerly a Research Assistant in the Department of Metallurgy and Mining Engineering, University of Illinois, Urbana, Ill. 61801.

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Chakrapani, D.G., Pugh, E.N. The transgranular SCC of a Mg-Al alloy: Crystallographic, fractographic and acoustic-emission studies. Metall Mater Trans A 6, 1155–1163 (1975).

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  • Fracture Surface
  • Metallurgical Transaction
  • Tension Face
  • Cleavage Step
  • Bend Specimen