Improvement of high strain rate and room temperature superplasticity in Zn–22Al alloy by two-step equal-channel angular pressing

Effect of chemical composition and grain size on RT superplasticity of Zn-Al alloys processed by ECAP

“…For achieving FG or UFG microstructure and obtain RT and HSR superplasticity in Zn-Al alloys some thermal and thermo-mechanical processes as well as severe plastic deformation (SPD) techniques like equal-channel angular pressing (ECAP) [11,[13][14][15][16][17][18] and friction stir processing (FSP) [12] have been utilized. Previous studies on RT and HSR superplasticity in Zn-Al alloys and the main results achieved are listed in Table 1.…”

“…Yang et al [17] refined the grain size of the Zn-22Al to 800 nm and increased RT elongation to 250 % at 1×10 -2 s -1 by means of 8 passes ECAP performed at 50°C. More recently, Demirtas et al [18] used a two-step ECAP process in which Zn-22Al alloy was subjected to 4 passes ECAP at 350°C followed by 4 passes ECAP at RT. This process brought about more refined microstructure with an average grain size of about 200 nm and resulted in the maximum RT elongation of about 400 % at a relatively high strain rate of 5×10 -2 s -1…”

“…ECAP was applied to Zn-22Al alloy as a two-step process. In the first step, 4 passes ECAP was applied to the alloy at 350°C, and 4 more passes were performed at RT as the second step [18]. Route Bc was used during ECAP processing of both Zn-5Al and Zn-22Al alloys where the billets are rotated by 90° in the same direction around their longitudinal axes in-between passes.…”

“…All these requirements should be fulfilled so that the grain boundary sliding (GBS) can occur easily as the main deformation mechanism in superplastic region [3]. After the first report in 1912 [4], superplasticity-related studies have been one of the main topics among the material scientists and mechanical engineers, and various classes of materials including alloys [5][6][7][8][9][10][11][12][13][14][15][16][17][18], ceramics [19][20][21] and amorphous materials [22,23] have been addressed for this purpose.…”

“…However, it should be noted that it is not possible to achieve RT superplasticity in all UFG or NS materials. RT and HSR superplastic behavior can be achieved in some specific alloys like Sn-Bi [24], Pb-Tl [25], Pb-Sn [26], and Zn-Al [5][6][7][8][9][10][11][12][13][14][15][16][17][18] due to their relatively low melting points. Among them, Zn-Al alloy family is the most suitable one as considering its phase diagram shown in Fig.…”