The Effect of Precipitates on Twinning in Magnesium AlloysFriday (10.11.2017) 09:55 - 10:15 Part of:
Precipitates are known to provide obstacles to the growth of twins in magnesium. This effect, if exploited, can be used to reduce mechanical anisotropy and asymmetry, which are currently obstacles to the wider use of wrought magnesium alloys. It has been demonstrated that precipitate shape and habit play a critical role in determining the strengthening effect, but the detailed mechanism by which twins and precipitates interact is still unclear.
In this paper, the interaction of twins and precipitates has been studied in Mg—Al (AZ80) using high resolution scanning electron microscopy and electron backscattered diffraction. A strongly textured rolled plate has been loaded in a direction to activate c-axis tension twinning. By comparing material before aging with peak aged and heavily overaged material, the influence of precipitates on the twinning behaviour has been determined. Consistent with previous studies, it is shown that the precipitate containing microstructures lead to the formation of a larger number of smaller twins, with only a small change in the overall twin volume fraction. It is shown that in the overaged material, the twins grow in a way to minimize their interaction with the precipitates, and their width is effectively pinned by precipitate bands. These observations help to explain the measured effect on both the yield strength and work hardening response.
The implications of these results for the design of precipitation strengthened wrought magnesium alloys with reduced asymmetry are discussed.
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