Three-Point Bending Deformation Behavior of a High Plasticity Mg-2.6Er-0.6Zr Alloy Sheet

doi:10.1007/s40195-025-01843-z

Abstract

Abstract:

Bending is a crucial deformation process in metal sheet forming. In this study, the microstructural evolution of a highly ductile Mg-Er-Zr alloy sheet was examined in various bending regions under different bending strains using electron backscatter diffraction and optical microscopy. The results show that the Mg-Er-Zr extruded sheet has excellent bending properties, with a failure bending strain of 39.3%, bending yield strength, and ultimate bending strength of 75.1 MPa and 250.5 MPa, respectively. The exceptional bending properties of the Mg-Er-Zr extruded sheets are primarily due to their fine grain size and the formation of rare-earth (RE) textures resulting from Er addition. Specifically, the in-grain misorientation axes (IGMA) and the twinning behaviors in various regions of the specimen during bending were thoroughly analyzed. Due to the polarity of the tensile twins and their low activation stress, a significant number of tensile twins are activated in the compression zone to regulate plastic deformation. The addition of Er weakens the basal texture of the sheet and reduces the critical resolved shear stress difference between non-basal slip and basal slip. Consequently, in the tensile zone, the basal and non-basal slips co-operate to coordinate the plastic deformation, effectively impeding crack initiation and propagation, and thereby enhancing the bending toughness of the Mg-Er-Zr sheet.

Key words: Mg alloy sheet, Three-point bending, Deformation mechanism, In-grain misorientation axis (IGMA)

Yuanxiao Dai, Yue Zhang, Mei Wang, Jie Liu, Yaobo Hu, Bin Jiang. Three-Point Bending Deformation Behavior of a High Plasticity Mg-2.6Er-0.6Zr Alloy Sheet[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(7): 1109-1126.

Figures/Tables 21

Fig. 1 a Schematic of sampling and dimensions of the bending specimen, b three-point bending test setup, c schematic of the observation surface of the three-point bending sample

Table 1 Typical slip systems and Taylor axis in magnesium alloys [33]

Slip mode	Miller indices	Number of slip variants	Taylor axis	Number of Taylor axis
Basal <a>	{0001} <11$\bar{2}$0>	3	<1$\bar{1}$00>	3
Prismatic <a>	{10$\bar{1}$0} <1$\bar{2}$10>	3	<0001>	1
Pyramidal <a>	{10$\bar{1}$1} <1$\bar{2}$10>	6	<0$\bar{1}$12>	6
Pyramidal II <c + a>	{11$\bar{2}$2} <11$\bar{2}$3>	6	<$\bar{1}$100>	3

Fig. 2 EBSD results of extruded sheet: a inverse pole figure map, b grain boundary diagram, c grain size distribution histogram, d KAM image, e (0001) pole figure

Fig. 3 Results of three-point bending tests of extruded Mg-Er-Zr alloy: a bending load-displacement curve, b converted bending stress-strain curve

Table 2 Three-point bending properties of extruded Mg-Er-Zr alloy sheet

Ultimate bending depth (mm)	Maximum bending load (N)	Bending yield strength (MPa)	Ultimate bending strength (MPa)	Failure bending strain (%)
6.1	1720.3	75.1 ± 1.5	250.5 ± 2.0	39.3 ± 0.4

Fig. 4 Macroscopic morphology of bending sample

Fig. 5 Metallographic structure in different regions of the extruded sheet with different bending strains: a, b, c CZ, d, e, f NLZ, g, h, i TZ

Fig. 6 Inverse pole figure map, grain boundary diagram, and grain size distribution histogram of the extruded sheet with 7% bending strain: a, b, c CZ, d, e, f NLZ, g, h, i TZ

Fig. 7 Inverse pole figure map, grain boundary diagram, and grain size distribution histogram of the extruded sheet with 21% bending strain: a, b, c CZ, d, e, f NLZ, g, h, i TZ

Fig. 8 Inverse pole figure map, grain boundary diagram, and grain size distribution histogram of the extruded sheet with 35% bending strain: a, b, c CZ, d, e, f NLZ, g, h, i TZ

Fig. 9 KAM image of the extruded sheet in different zones with various bending strains: a, b, c 7%, d, e, f 21%, g, h, i 35%

Fig. 10 (0001) pole figure of the extruded sheet in different zones with various bending strains: a 7%, b 21%, c 35%

Fig. 11 Distribution of SF for the initial sheet across various slip systems: a, b basal slip, c, d prismatic slip, e, f tensile twinning under tensile stress, g, h tensile twinning under compressive stress

Fig. 12 IPF maps and (0001) poles of parent grains (P) and twins (T) of the sheet in the CZ with various bending strains: a 7%, b 21%, c 35%

Fig. 13 Misorientation angle distribution of extruded sheet in the TZ with various bending strains: a 7%, b 21%, c 35%

Fig. 14 Distribution of the orientation difference of some grains of the extruded sheet in the TZ after a 7% bending reduction

Fig. 15 Distribution of the orientation difference of some grains of the extruded sheet in the TZ after 21% bending reduction

Fig. 16 Distribution of the orientation difference of some grains of the extruded sheet in the TZ after 35% bending reduction

Fig. 17 Misorientation angle distribution of extruded sheet in the NLZ with various bending strains: a 7%, b 21%, c 35%

Fig. 18 Distribution of the orientation difference of some grains of the extruded sheet in the NLZ after 35% bending reduction

Fig. 19 Schematic diagram of deformation mechanism in different regions during bending deformation of extruded Mg-Er-Zr alloy sheet

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