Effect of basal precipitates on extension twinning and pyramidal slip: A micro-mechanical and electron microscopy study of a Mg–Al binary alloy

The Orowan Stress Measurement of Twinning Dislocations in Magnesium

“…It is worth mentioning that twinning dislocation is not the only shear-driven linedefect that the classic BKS model fails to precisely treat. The Orowan stress of the pyramidal dislocation in Mg alloys [2], and of the LDs in Al-Mg-Si alloys [27], cannot be well predicted by the BKS model either. High-throughput atomistic simulations might help in establishing a connection between the atomic core structure/energy of line-defects and their line tension, and by then, a universal Orowan law for precipitation hardening in crystalline materials can be expected.…”

“…During the past decades, the Orowan stress calculations based on the model developed by Bacon, Kocks and Scattergood (the BKS model) [1] were successful in the scenario of lattice dislocations (LDs) bypassing non-shearable precipitates in metallic alloys. The bowed-out LDs between precipitates before bypassing can be observed by experimental techniques such as transmission electron microscopy (TEM) [2][3][4] and simulation techniques such as molecular dynamics (MD) [5][6][7]. In lightweight, energy-efficient magnesium (Mg) alloys, the BKS model was also applied to calculate the Orowan stress needed by twinning dislocations (TDs), which are shear-driven line-defects and manipulate the behavior of a twin [8,9].…”

“…Unfortunately, the Orowan stress is hard to measure in experiments because the back-stress exists in the strengthening against twins [17,18], and the back-stress cannot be precisely calculated due to the local plastic relaxation [17,19]. Therefore, although the total strengthening against twins can be measured [2,3,20,21], it is not known how much of the strengthening is due to the Orowan stress. Therefore, validating the numerical accuracy of the BKS model for TD needs other approaches than experimental means.…”

“…In 2017, twins in magnesium were approximated by a super dislocation to give an equation calculating the Orowan stress needed for bowing the propagating twinning front between impenetrable particles [22]. This equation was adopted for qualitative analysis in 2020 to support the bias effects on twin growth and twin nucleation by basal precipitate plates in a Mg-Al alloy [2]. In 2018, Robson and Barnett pointed out in a review that an equivalent simple equation to the BKS model predicting the strengthening effect of precipitates against twins would be very useful, but the physical basis for such an equation remains unclear [17].…”

Wear Behavior of the Multiheterostructured AZ91 Mg Alloy Prepared by ECAP and Aging

“…According to the need for lightweight of the structural materials, magnesium (Mg) alloys, as the lightest structural metallic materials, are widely applied in the automobile, aerospace, biomedicine application, and electronics industries [1][2][3][4][5]. Moreover, profiting from all kinds of processing methods, numerous high strength Mg alloys have been produced in the laboratory and even some Mg alloys have been commercialized, such as Mg-Al-Zn (AZ)-typed alloys and Mg-Zn-Zr (ZK)-typed alloys [6][7][8][9]. However, the absolute strength and ductility of Mg alloys at room temperature are still much lower than that of Al alloys, Ti alloys, and steels, which restrict their widespread commercial applications.…”