Abstract
The mechanism behind shearing of β11 precipitates in Al-Mg-Si alloys during deformation is investigated by applying advanced transmission electron microscopy (TEM) techniques and frozen phonon multislice TEM image simulations on a selection of shearing configurations. In particular, the results indicate that the needle-like precipitates are sheared several times in single matrix Burgers vector steps. The multislice image simulations suggest that shearing events are most likely achieved in single Burgers vector steps, and there are some experimental evidence that the shearing planes are the matrix glide planes.
Highlights
During plastic deformation of precipitate strengthened alloys, dislocations either bypass or shear precipitates, depending on the precipitate phase, size, and shape [1]
In order to predict the strength of such alloys, it is important to understand the physical mechanisms of each process for various alloy systems and their precipitate phases
high resolution TEM (HRTEM) images were acquired on a Gatan 2k UltraScan CCD, while scanning precession electron diffraction (SPED) data with a frame rate of 25 Hz was acquired by an external Allied StingRay CCD and the NanoMEGAS DigiSTAR system
Summary
During plastic deformation of precipitate strengthened alloys, dislocations either bypass or shear precipitates, depending on the precipitate phase, size, and shape [1]. The β precipitates are the main strengthening phase in the Al-Mg-Si alloy system (AA6xxx) and have composition Mg5Si4Al2 [2] They appear as long needles oriented along the matrix 100 and usually with a monoclinic unit cell with aβ = 15.16 Å, bβ = 4.05 Å, cβ = 6.74 Å, and β = 105.3◦ with (001) (010)β , [310] [001]β , and 2 ̄30 [100]β [2,3,4]. [110] and 11 ̄0 will produce interface steps and internal planar defects of different surface areas This illustrates the complexity of how these precipitates are sheared, as a glide of one particular Burgers vector through a precipitate will be different from other. Burgers vectors and produces different defects in the precipitate crystal structure. The experimental and theoretical results indicate that β precipitates are sheared in single Burgers vector steps distributed along the needles. The results form a basis for future works to better understand how this precipitate phase strengthens the industrially important AA6xxx alloys
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