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

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

“…Table 2 shows that the stress corrosion crack velocities for AM30 (V c = 3.6 × 10 −10 to 9.3 × 10 −10 m/s) are much slower than for AZ91 (V c = 1.6 × 10 −9 to 1.2 × 10 −8 m/s) and AZ31 (V c = 1.2 × 10 −9 to 6.7 × 10 −9 m/s). These results are consistent with the crack velocity measured by Speidel et al [61] for the Mg alloy ZK50A-T5 in distilled water, but much slower than those measured for Mg alloys in other aqueous environments [13,14,36,38,39,49,61] and predicted using our numerical model for DHC (V c ≈ 10 −7 m/s), although this result was based on a speculative diffusion coefficient (D = 10 −9 m 2 /s) since no data exists for Mg alloys at room temperature [15]. The different crack velocities for AZ91, AZ31 and AM30 may be due to a difference in the predominant mechanism for SCC propagation.…”

“…It follows that, at these strain rates, the influence of repassivation at the crack tip is negligible, and the influence of strain rate is related to the mechanism for crack propagation. In contrast with the present work, previous workers [13,14,36,37,12,38,39,49] used strongly passivating solutions containing K 2 CrO 4 . This indicates that the occurrence of maximum SCC susceptibility at intermediate strain rates observed for Mg alloys in strongly passivating solutions is a characteristic of these environments rather than a characteristic of Mg alloys.…”

“…The influence of grain size has been studied only with respect to the propensity for intergranular or transgranular SCC [11,28,34,35]. Grain orientation is likely to have strong influence on TGSCC fracture morphology if the propagation mechanism is crystallographic [11,[36][37]12].…”

Mg and Its Alloys for Biomedical Applications: Exploring Corrosion and Its Interplay with Mechanical Failure

“…Presence of hydrogen is a consequence of the Mg corrosion mechanism in aqueous solutions (see Section 2); according to the cathodic partial reaction, one molecule of hydrogen gas is produced for each atom of Mg dissolved in the human body, but hydrogen is also produced at an anodic potential due to the negative difference effect (NDE, detailed in Section 4). Chakrapani and Pugh [103] suggested that H2 is involved in brittle fracture since it can be related to the formation of brittle hydrides (MgH2) or in decohesion phenomena. Some authors [104] also proposed an adsorption model in order to explain the HE mechanism, where hydrogen is adsorbed from the solution at the crack tip or transported to the cracked region by dislocation motion.…”

Stress Corrosion Cracking Behavior of Fine-Grained AZ61 Magnesium Alloys Processed by Equal-Channel Angular Pressing

“…The fracture surfaces of the as-cast sample that failed in air and in distilled water are shown in Figure 6a,b, respectively. Figure 6a reveals mixed mode with transgranular cleavage and dimpled features, as well as intergranular fracture, mainly initiated by preferential anodic dissolution of the matrix adjacent to β-Mg17Al12 [1], whereas the same sample tested in distilled water showed a predominantly transgranular feature with parallel facets, attributed to hydrogen-assisted embrittlement for the AZ series alloys [5,19,20]. The primary conclusion is that the as-cast AZ61 Mg alloy behaved fairly susceptible to SCC in distilled water.…”