Characterisation of stress corrosion cracking (SCC) of Mg-Al alloys

Stress corrosion cracking (SCC) of the Mg-Al alloys AZ91, AZ31 and AM30 in distilled water has been characterised using constant extension rate tests (CERTs) and linearly increasing stress tests (LISTs). AZ91 consists of an alpha-matrix with extensive beta-particles, whereas AZ31 and AM30 consist only of an alpha-matrix with an Al-concentration similar to that in AZ91. The presence of beta-particles in AZ91 was associated with: (i) a lower threshold stress, sigma(SCC), for AZ91 (55-75 MPa) relative to AZ31 (105-170 MPa) and AM30 (130-140 MPa); and (ii) a different SCC initiation mechanism for AZ91 relative to AZ31 and AM30. The SCC velocity, V-c, for AM30 (3.6 x 10(-10) to 9.3 x 10(-10) m/s) was lower than that for AZ91 (1.6 x 10(-9) to 1.2 x 10(-8) m/s) and AZ31 (1.2 x 10(-9) to 6.7 x 10(-9) m/s). This was attributed to the influence of Zn and second phase particles, which are more concentrated in AZ31, on the diffusivity of H in the alpha-matrix. (C) 2007 Elsevier B.V. All rights reserved.