The effects of grain size and heat treatment on the deformation heterogeneities and fatigue behaviors of GW83K magnesium alloys

This work investigates the strain-controlled fatigue performance of the cast GW83K (Mg-9.33Gd-2.61Y-0.34Zr) magnesium alloys with different grain sizes (82 mu n and 163 mu m) and thermal conditions (T4 and T6). It is found that distinguishing damage patterns (serried and uniform persistent slip bands of the T4 alloy; Sparse and concentrated persistent slip bands of the T6 alloy) significantly affect both the level and distribution of strain localization within and among the grains, which lead to different crack initiation behaviors. Compared with the T6 alloys, the strain localizations in the T4 alloys are more effectively alleviated and dispersed and thus the crack initiation life accounts for a much larger part in the total fatigue life. Additionally, the strain localizations are mostly accommodated in individual grains by grain boundaries (GBs) in the T4 alloys, while tend to pass through GBs extending into grain interiors and stretching across several grains in a long range in the T6 alloys. Therefore, the crack initiation life of the T6 alloys is not as sensitive to the grain size as the T4 alloys. Grain refinement can significantly improve the crack initiation life and thus the total fatigue life of the GW83K-T4 alloys but has limited contribution to that of the GW83K-T6 alloys.