Microstructure, Texture and Mechanical Properties of Mg-6Sn Alloy Processed by Differential Speed Rolling

Abstract

The effect of shear deformation introduced by differential speed rolling (DSR) on the microstructure, texture and mechanical properties of Mg-6Sn alloy was investigated. Mg-6Sn sheets were obtained by DSR at speed ratio between upper and lower rolls of R = 1, 1.25, 2 and 3 (R = 1 refers to symmetric rolling). The microstructural and textural changes were investigated by electron backscattered diffraction (EBSD) and XRD, while the mechanical performance was evaluated based on tensile tests and calculated Lankford parameters. DSR resulted in the pronounced grain refinement of Mg-6Sn sheets and spreading of basal texture as compared to conventionally rolled one. The average grain size and basal texture intensity gradually decreased with increasing speed ratio. The basal poles splitting to transverse direction (TD) or rolling direction (RD) was observed for all Mg-6Sn sheets. For the as-rolled sheets, YS and UTS increased with increasing speed ratio, but a significant anisotropy of strength and ductility between RD and TD has been observed. After annealing at 300 °C, Mg-6Sn sheets became more homogeneous, and the elongation to failure was increased with higher speed ratios. Moreover, the annealed Mg-6Sn sheets were characterized by a very low normal anisotropy (0.91–1.16), which is normally not achieved for the most common Mg-Al-Zn alloys.

Comparison of Microstructure, Texture, and Mechanical Properties of TZ61 and AZ61 Mg Alloys Processed by Differential Speed Rolling

“…A higher speed asymmetry (R > 2) results also in a significant grain refinement, which allows for further increase of formability [23,26]. Similar findings have been found in our previous work [27] dedicated to Mg-6Sn (wt.%) alloy processed at different speed ratios (ranging from 1 to 3). Up to now, Mg-Sn-Zn alloys processed by DSR method have been studied only by Verma et al [28].…”

“…TZ61 and AZ61 alloys were subjected to conventional symmetric rolling with equal speed of rolls (R = 1) as well as asymmetric rolling at a speed ratio of R = 3 (the ratio between upper and lower rolls) with the constant velocity of the upper roll maintained at 4 m/min. As shown in our previous work [27], such a relatively high speed ratio causes a significant grain refinement, texture weakening, and improvement of mechanical properties of Mg-Sn alloys. Finally, TZ61 and AZ61 sheets were investigated in the as-rolled state and after further annealing at 300 • C for 1 h.…”

“…The results for the as-rolled TZ61 and AZ61 sheets showed that the average values of YS and UTS were enhanced by DSR processing at the expense of the reduced uniform elongation and strain hardening exponent. It should be stated that all sheets exhibited a significant anisotropy of strength and plasticity (i.e., higher YS and UTS with lowered elongation were noted at 0 • as compared to 90 • ) and the estimated n values for TZ61 and AZ61 sheets were close to those obtained for the common AZ31 (n = 0.09-0.16 [23]) or Mg-6Sn (n = 0.10-0.12 [27]) alloys processed by DSR. The enhanced strength of asymmetrically rolled sheets was a result of their higher grain refinement and dislocation density (represented by higher 3-5 • LAGBs fraction in Figure 2).…”

“…Both AZ61 sheets exhibited a strong single-peak basal texture, which is common for Mg-Al-Zn alloys [1,2,4]. The basal texture spreading has been observed so far mainly for Mg-RE [49], Mg-Zn [50], or Mg-Li [51] alloys, but our latest study [27] as well as Verma et al [52] have shown that it is possible to obtain basal texture splitting in the Mg-Sn-based alloys as well. The reason of the RD and TD spreading seems to be the activation of pyramidal <c + a> and prismatic <a> slip, respectively [51,53].…”

Effect of Cold Rolling and Annealing on the Microstructure and Texture of Erbium Metal

“…Most rare earth metals have hexagonal close-packed (HCP) structure and fewer slip systems; therefore, the plastic deformation is very difficult because the rolling deformation process can easily cause stress concentration and lead to cracking [10,11]. There is a lot of research involving magnesium [12][13][14] and magnesium alloy [15,16], and titanium [17,18] and titanium alloy [19][20][21], but there are few studies on the deformation of rare earth metal. Huang P. [22] studied the effects of annealing temperatures on the hardness and microstructure of high-purity metal scandium metal after hot forging, and obtained the optimum annealing process of 725 • C × 0.5 h. Wang S. [23] studied the effect of annealing temperature on the microstructure of high-purity Er target under 80% deformation after hot rolling and obtained the optimum annealing process of 570 • C × 1 h. However, hot deformation process can easily lead to target oxidation, serious loss of raw materials, and worse surface quality.…”