Effect of Al content on the critical resolved shear stress for twin nucleation and growth in Mg alloys

Abstract

The effect of Al atoms in solid solution on the critical resolved shear stress for twin nucleation and growth was analyzed by means of the combination of diffusion couples with compression tests in micropillars oriented for twinning. The critical resolved shear stress for twin nucleation was higher than that for twin growth and both increased by the same amount with the Al content. Nevertheless, the increase was small (≈ 10 MPa) for 4 at.%Al but large (up to 60-70 MPa) for 9 at.%Al. These results were in agreement with Labusch-models based on first principles calculations in the dilute regime (< 5 at.%Al) [51]. Comparison with recent data in the literature showed that Al atoms are more effective in increasing the critical resolved shear stresses for twin nucleation and growth than for basal slip [21]. Finally, compression tests in micropillars oriented along [0001] showed the critical shear stress for pyramidal slip increased rapidly with the Al content from 98 MPa in pure Mg to 250 MPa in Mg-9 at.%Al. Thus, the addition of Al increased the plastic anisotropy of Mg alloys.

Deformation mechanisms of Mg-Ca-Zn alloys studied by means of micropillar compression tests

“…Micropillar compression tests were carried out ex situ (Hysitron Triboindenter TI950 system) and in situ (Hysitron PI88 system) within the SEM. It was reported previously that size effects on the flow stress for different deformation modes (basal and pyramidal slip as well as twinning) were minimum in Mg and Mg alloys for micropillars of these dimensions [41,42]. A diamond cylindrical flat punch of 10 µm in diameter was attached to the indenter tip to compress the micropillars.…”

“…These experimental results were carried out in polycrystalline samples and it was difficult to determine the actual values of the CRSS for each slip system and twinning because of the influence of different contributions (texture, grain size, cross-slip) to the overall mechanical response. However, novel micromechanical testing techniques have been recently used to assess the fundamental deformation mechanisms of single crystals of Mg [24,[33][34][35][36][37][38][39][40][41][42], Ti [43,44], Al [45,46], and Ta [47] alloys as well as of intermetallic compounds [48,49]. In particular, micropillar compression tests have been used to measure the CRSS for different slip systems as well as CRSS for twin nucleation and growth in pure Mg [33][34][35][36][37] and different Mg alloys [24,[38][39][40][41][42] at ambient and elevated temperature as a function of the solute or precipitate content.…”

“…However, novel micromechanical testing techniques have been recently used to assess the fundamental deformation mechanisms of single crystals of Mg [24,[33][34][35][36][37][38][39][40][41][42], Ti [43,44], Al [45,46], and Ta [47] alloys as well as of intermetallic compounds [48,49]. In particular, micropillar compression tests have been used to measure the CRSS for different slip systems as well as CRSS for twin nucleation and growth in pure Mg [33][34][35][36][37] and different Mg alloys [24,[38][39][40][41][42] at ambient and elevated temperature as a function of the solute or precipitate content. This methodology is applied in this investigation to elucidate the intrinsic effect of solid solution atoms on the deformation mechanisms of Mg-Ca-Zn alloys.…”

Effect of Pulsed Magnetic Field on the Residual Stress of Rolled Magnium Alloy AZ31 Sheet

“…Therefore, shear stress along RD and TD was calculated as 1.68 MPa and 1.41 MPa, respectively. It was reported that the critical resolved shear stress τ c of the single-crystal magnesium basal slip was about 0.5-0.9 MPa [34][35][36]. It is worth noting that only local plastic deformation occurred, which means that, only grains with large Schmid factor were deformed during PMF treatment.…”

Fracture mechanism and toughness of a rolled magnesium alloy under dynamic loading

“…where, is the specific plastic work due to tensile twinning and V tw = BA tw f avg is the volume of twinned region in the ligament. Here,  tw is the average CRSS for tensile twinning (which is assumed as 40 MPa in the following computation [14,58]) and  tw is the twinning shear which is 0.13 [59]. Also, A tw is the total (in-plane) area of the region adjacent to the uncracked ligament where twinning is observed (semi-circular white region in Fig.10(a),(b), which has a radius of about 6 mm), B is the specimen thickness and f avg is the average twin volume fraction in this region.…”