Effect of structural state upon fatigue fracture in MA12 magnesium alloy in air and in vacuo

Abstract

1. The structural state of MA12 magnesium alloy has a considerable effect upon its life in cyclic deformation: toughening of the alloy by thermal aging and a reduction in grain size lead to an increase in life and in the crack generation stage compared with those for the coarse-grained alloy in the annealed state. 2. Fatigue crack generation and growth along the grain boundaries irrespective of grain size is characteristic of the annealed state in the alloy. Cyclic deformation of the alloy in the aged state leads to softening, crack generation in stable slip bands, and intragranular crack growth. 3. In a vacuum the fatigue life of MA12 alloy increases in all the structural states, by virtue of increases in the length of the crack generation and propagation stages. The effect of vacuum upon life and the duration of the crack generation stage is more apparent in the intragranular situation than in the intergranular situation. 4. The number of slip bands on the surface and the number of grains to which slip extends are greater when the alloy is deformed in a vacuum than in air. This is particularly apparent in the aged state.