Microstructure and mechanical properties of ZK61 magnesium alloy thin-walled cylindrical component processed by two-step forging

Abstract

Magnesium alloy thin-walled cylindrical components with the advantages of high specific stiffness and strength present broad prospect for the lightweight of aerospace components. However, poor formability resulting from the hexagonal close-packed crystal structure in magnesium alloy puts forwards a great challenge for thin-walled cylindrical components fabrication, especially for extreme structure with the thickness-changing web and the high thin-wall. In this research, an ZK61 magnesium alloy thin-walled cylindrical component was successfully fabricated by two-step forging, i.e., the pre-forging and final-forging is mainly used for wed and thin-wall formation, respectively. Microstructure and mechanical properties at the core, middle and margin of the web and the thin-wall of the pre-forged and final-forged components are studied in detail. Due to the large strain-effectiveness and metal flow along the radial direction (RD), the grains of the web are all elongated along RD for the pre-forged component, where an increasingly elongated trend is found from the core to the margin of the wed. A relatively low recrystallized degree occurs during pre-forging, and the web at different positions are all with prismatic and pyramid textures. During final-forging, the microstructures of the web and the thin-wall are almost equiaxed due to the remarkable occurrence of dynamic recrystallization. Similarity, except for few basal texture of the thin-wall, only prismatic and pyramid textures are found for the final-forged component. Compared with the initial billet, an obviously improved mechanical isotropy is achieved during pre-forging, which is well-maintained during final-forging.