Effects of Texture and Grain Size on the Yield Strength of ZK61 Alloy Rods Processed by Cyclic Extrusion and Compression

Abstract

The ZK61 alloy rods with different grain sizes and crystallographic texture were successfully fabricated by cyclic extrusion and compression (CEC). Their room-temperature tension & compression yield strength displayed a significant dependence on grain size and texture, essentially attributed to {10-12} twinning. The texture variations were characterized by the angle θ between the c-axis of the grain and the extrusion direction (ED) during the process. The contour map of room-temperature yield strength as a function of grain size and the angle θ was obtained. It showed that both the tension yield strength and the compression yield strength of ZK61 alloy were fully consistent with the Hall-Patch relationship at a certain texture, but the change trends of the tension yield strength and the compression yield strength were completely opposite at the same grain size while texture altered. The friction stresses of different deformation modes calculated based on the texture confirmed the tension yield strength of the CECed ZK61 alloy rods, which was determined by both the basal slip and the tension twinning slip during the tension deformation at room temperature, while the compression yield strength was mainly determined by the basal slip during the compression deformation.

Reducing Yield Asymmetry between Tension and Compression by Fabricating ZK60/WE43 Bimetal Composites

“…It is further confirmed that yttrium is one of the most effective elements in reducing yield asymmetry due to texture weakening and precipitation strengthening [19,39,40]. Similarly, the ZK60 alloy also exhibits a reduced yield asymmetry between tension and compression due to the precipitation strengthening and the grain refinement caused by the Zr element [11,32,33]. Up to date, the investigations on the yield tension-compression asymmetry in the magnesium alloys mostly focused on the effect of grain size, pre-deformation, and alloying of single magnesium alloy materials.…”

“…Currently, magnesium alloys are being applied as the structural materials in many important fields such as automotive, aeronautical, and space due to high specific strength and other outstanding properties [1][2][3][4][5][6][7]. However, to further widen the application of wrought magnesium alloy products, one of the key challenges to be solved is yield asymmetry between tension and compression after thermo-mechanical processing [8][9][10][11][12][13][14][15]. That is, for extruded magnesium alloy rods, the yield strength in tension (TYS) is largely different from the yield strength in compression (CYS) in the extrusion direction (ED) [3,8,[11][12][13].…”

“…However, to further widen the application of wrought magnesium alloy products, one of the key challenges to be solved is yield asymmetry between tension and compression after thermo-mechanical processing [8][9][10][11][12][13][14][15]. That is, for extruded magnesium alloy rods, the yield strength in tension (TYS) is largely different from the yield strength in compression (CYS) in the extrusion direction (ED) [3,8,[11][12][13]. The origin of the yield tension-compression asymmetry is explained as follows: the presence of basal fiber texture causes {10-12}<−1011> extension twinning during compression along the extrusion direction, which is activated more easily than the tensile deformation in the highly extruded magnesium products.…”

“…Grain-size reduction, precipitation strengthening, and texture weakening are all proven to be effective in decreasing yield asymmetry between tension and compression [10][11][12]16,19,[25][26][27][28][29][30][31][32][33][34][35][36][37]. For instance, Barnett et al [16] found that the grain size affects yield stress and the sensitivity of twinning to grain size is obviously bigger than that of the slip.…”

“…For instance, Barnett et al [16] found that the grain size affects yield stress and the sensitivity of twinning to grain size is obviously bigger than that of the slip. It was suggested that the yield tension-compression asymmetry for the coarse-grained magnesium alloys is 0.4-0.6, while it can decrease to 0.8-0.9 for fine-grained samples [9,11,12,28,37]. It was noticed that precipitates with a high density such as disk-like β' 2 in the ZK series of Mg alloys can prohibit the propagation of {10-12}<−1011> twinning and harden extension twinning more than prismatic slip, leading to the dramatic suppression of yield asymmetry [10,29,30].…”