Study of hot tensile deformation behavior and microstructure characteristics of Zn-22Al microtubes using direct resistance heating-assisted tensile tests

Abstract

To explore the deformation behavior of Zn-22Al alloy microtubes during hot forming processes with rapid heating, direct resistance heating (RH)-assisted tensile tests using microtubes are introduced based on their quick and easy temperature control. Notably, the large temperature difference of the sample during the RH-assisted tensile tests affected the accuracy of the tensile test results. To perform the RH-assisted tensile tests of the microtubes correctly, the specimens were designed with optimized structures of effective and total lengths of 30 and 60 mm, respectively. Better ductility was observed in the microtube drawn at 200 °C owing to the highly activated grain boundary sliding (GBS) caused by its uniform finer grain structure, greater high-angle grain boundary (HAGB) densities in the close-to-fracture area, and intergranular ductile fracture mode. The primary deformation mechanism of the microtube during hot forming was built based on hot tensile behavior, microstructure, and fracture surface analysis. It was also demonstrated that there is an intrinsic relationship between the temperature distribution, change in the microstructure of different parts, and multiple necking phenomena of the microtube formation process.