Corrosion creep and fatigue behavior of magnesium alloys

Key words magnesium alloys, corrosion creep, corrosion fatigue, buffer solution, NaCl, Na2S04. 

2 Historical review of environmentally enhanced creep and fatigue of metals 

Adsorption of one or more reactants on surfaces is only one of the steps of the reaction at the metal/hquid interface. Therefore, creeping metals surrounded by electrolytes undergo electrochemical and mechanical interactions (corrosion attack, stress corrosion cracking, etc.) and show a pronounced difference in plastic flow compared with that in a neutral medium. For example, the multifold increase in the creep rate of zinc crystal after the removal of oxide film by hydrochloric acid during a creep test [8] or cadmium single crystal at the replacement of water by sulfuric acid [9] can be explained not only by adsorption phenomena but also by electrochemical and mechanochemical interactions of liquid with stressed solid. 

The effect of electrolytes on the creep of metals at a constant load was discovered by Andrade and Randall using the apparatus presented in Fig. 9.1(a) [10,11]. They observed an immediate increase in the secondary creep rate of a cadmium single-crystal wire from about 0.01 h to 0.02-0.04 h  

How do films formed on the surface of metal as a reaction product between stressed solid and a surrounding liquid influence creep and creep-rupture of metals There is no evidence to support the suggestion of surface cracks healing-up by an oxide film. If the relation of the film thickness to the specimen diameter is relatively large (thin wires) compared with common samples, load capacity of the film is a valid hypothesis. For example, a decrease in TY S of single cadmium crystal covered by thick oxide film from 25% to zero was found with an increase in the sample diameter from 0.3 to 2.8 mm [6]. 

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