The investigation of micro formability of superplastic Zn-22Al alloy on room temperature

This thesis aims to determine the deformation behavior and formability of Zn-22Al alloy, which shows superplastic properties at room temperature. For this purpose, two-step equal channel angular extrusion (ECAE) and subsequent heat treatments were performed to obtain different grain sizes in the microstructure. Thus, microstructures with grain sizes ranging from micron to submicron size were obtained. The average grain size was obtained as 200 nm upon ECAE while the grain size of 2,60 µm was achieved after heat treatments carried out 250 ºC for different durations. Upon achieving the desired grain sizes, the deformation behavior of the alloy at room temperature was investigated experimentally and numerically under uni-axial loading (tensile test) and bi-axial loading (Erichsen test) conditions, and also formability of the alloy was studied by micro deep drawing method. The finite element method was used for the numerical analysis, and the analyses were performed with LS-Dyna commercial package. The maximum elongation and limiting dome height (LDH) values decreased with increasing grain size, and it was determined that the samples with submicron size had the highest elongation (400%) and LDH values until failure. The alloy, on the other hand, was subjected to micro-deep drawing experiments and formed successfully with limiting drawing ratios of 1.66, 1.84, 2 and 2.25. Experimental and numerical micro-deep drawing results imply that the superplastic Zn-22Al alloy can be preferred for micro manufacturing.