Microstructure Evolution, Mechanical Properties And Mechanism Analysis Of AZ31 Magnesium Alloy By Electroplastic Rolling

When electrical pulses are applied to metals undergoing deformation, the deformation resistance reduces dramatically and plasticity increases significantly at the same time. This influence of the electric current pulses on the plastic flow is called the electroplastic effect or EPE. Traditional manufacturing processes rely on the use of heat to reduce the forces associated with fabricated parts. Relative to the negative implications associated with hot working, EP manufacturing is an efficient energy conserving means. However, the lackness of theoretical and experimental researches gives rise to the limited application of EP manufacturing processes. On account of the hcp structure and inactiveness of the non-basal slip systems, it is difficult to process magnesium alloys at room temperature or low temperature (< 200°C). Magnesium alloy sheets are usually fabricated by hot or warm rolling. During this process, a multiple-pass operation incorporating small rolling reduction, intermediate annealing, and maintaining rolls at 150~200°C is employed to suppress edge cracks and fracture of the alloys and to maintain the workability. The complex process and high energy consumption lead to a high production cost, thereby hampering commercial applications of magnesium alloys. Here, a new fabricating process, electroplastic manufacturing processing for magnesium alloy sheets is one of the most effective ways to simplify the manufacturing processes while enhancing the properties of the final products.The objectives of the research work described in this thesis are: (1) to analyze the mechanism of the microstructural evolution in cold rolled AZ31 magnesium alloy during electropulsing treatment by texture analysis. The mechanism of the microstuctural evolution during electropulsing is discussed from the point of view of grain boundary motion. Subsequently, we simulate the Joule heating effect by rapid thermal annealing and investigate the microstructural evolution; (2) to investigate the microstructure and texture development during electroplastic rolling. Single large pass draught rolling by electroplastic rolling is conducted on AZ31 magnesium alloy sheets below 200°C without heating rolls. The synergistic thermal and athermal effects during EPR are responsible for the low temperature dynamic recrystallization within twins and shear bands; (3) to explore the microstructure and texture evolution in EPR AZ31 magnesium alloy sheets during EPT and correlate with the mechanical properties. Excellent mechanical properties of thin magnesium alloys sheets can be obtained by employing the EPT-EPR processings of high rolling speed, large rolling reduction and the rolling temperature of 200°C.