Corrosion stress relaxation in pure magnesium and die-cast Mg alloys
Keywords:pure magnesium, die-cast Mg alloys, stress relaxation, corrosive solutions, relaxation spectra
The effect of corrosive solutions on stress relaxation behavior of pure Mg and its alloys is studied. Pure magnesium shows a crucial corrosion stress relaxation in 3.5wt.% NaCl even at room temperature in comparison with tests in air. Die-cast Mg alloys AZ91D, AM50 and AS21 at room temperature show a relatively small stress decrease both in air and in different corrosive media. At elevated temperature, all studied die-cast Mg alloys show a strong stress relaxation in a 3.5 % NaCl corrosive solution. In a corrosive environment, the highest sensitivity to stress relaxation was observed both in the alloy with the highest Al content (AZ91D), and in AS21 alloy that contains two intermetallics (Mg17Al12 and Mg2Si). It is shown that the stress relaxation method manifests a high sensitivity to structural homogeneity of alloys, especially in corrosive solutions.According to TEM investigations of pure Mg, an unloaded specimen comprises a few dislocations in the vicinity of such an obstacle as grain boundary. At a constant strain of about 4x10-4, dislocation networks were found with a sharply increasing quantity of dislocations.
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