Optimization of rolling temperature for ZK61 alloy sheets via microstructure uniformity analysis

Property improvements in fine–grained Mg–Zn–Zr alloy sheets produced by temperature–step–down multi–pass rolling

“…Microstructure characteristics Fig. 1 displays the microstructures of ZK61 Mg alloy sheets following rolling at decreasing temperature from 400 C to~240 C. The average grain size d and the relative diameter range Rd (calculated by Rd ¼ d max =d [11], where d max means the maximum grain size observed) shown in Fig. 2 are used to characterize the microstructure and its homogeneity.…”

“…The dimensions of ingots prepared for temperatureestepedown multiepass rolling are machined to size: 150 mm width  26e28 mm thick  200 mm length. Preliminary rolling experiments were carried out to maximize thickness reduction (taking plate yield and efficiency into consideration for normal production) and to optimize recrystallization temperature for thin (thickness less than 4 mm) Mg alloy sheets [7,11,20]. The optimum values obtained for a single pass are~40% in thickness reduction, and~240 C in rolling temperature.…”

“…Metallographic observations in the RDeTD plane (RD: rolling direction, TD: transverse direction) were performed on OLYMPUS GX71 optical microscopy (OM), and the mean linear intercept method [11,20] (d ¼ 1:74L, L is the linear intercept) was used to measure grain size and to quantify the microstructural homogeneity. TECNAI transmission electron microscopy (TEM) equipped with energy dispersive spectroscopic (EDS) system was used to image microscopic features and identify precipitates.…”

“…Referring to the researches in Refs. [11,12], recrystallized grain size after DRX largely depends on the ZenereHollomon parameter ZðZ ¼ _ εexpðQ =RTÞÞ, where_ ε is the strain rate, T is the deformation temperature, Q is the activation energy and R the gas constant). This means that fineegrained Mg alloy sheets with improved properties may be realized by carefully controlling rolling temperature.…”

“…Thus, the aim of the present work is to explore the fabrication feasibility of higheperformance wrought Mg alloy sheets processed via a carefully designed temperatureestepedown multiepass rolling. The material chosen was a commercial ZK61 alloy, which has received widespread attention owing to its excellent plasticity [11,18,19]. Meanwhile, the microstructure evolution as well as its influence on the associated mechanical properties was examined in detail.…”