Slip distribution has been varied in a series of Al–Mg–Si alloys of similar yield strength and grain size, by altering the amounts of manganese-bearing dispersoid and by under- and overaging, which also altered the precipitate-free zones and grain boundary strength. It has been found that fatigue crack propagation thresholds increase with an increase in dispersoid content, as slip is homogenized. However, for a given dispersoid content, under- and overaged alloys have similar crack propagation behaviour. This effect is interpreted in terms of slip distribution and grain boundary strength in the various microstructures.
MST/398
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