Abstract
In this study, the time-dependent mechanical behavior of the magnesium alloy sheet (AZ31B) was investigated through the creep and stress relaxation tests with respect to the temperature and pre-strain. The microstructure changes during creep and stress relaxation were investigated. As the tensile deformation increased in the material, twinning and dynamic recrystallization occurred, especially after the plastic instability. As a result, AZ31B showed lower resistance to creep and stress relaxation due to dynamic recrystallization. Additionally, time-dependent springback characteristics in the V- and L-bending processes concerning the holding time and different forming conditions were investigated. We analyzed changes of microstructure at each forming temperature and process. The uniaxial tensile creep test was conducted to compare the microstructures in various pre-strain conditions with those at the secondary creep stage. For the bending process, the change of the microstructure after the forming was compared to that with punch holding maintained for 1000 s after forming. Due to recrystallization, with the holding time in the die set of 60 s, the springback angle decreased by nearly 70%. Increased holding time in the die set resulted in a reduced springback angle.
Highlights
When three-point bending was performed using a magnesium alloy sheet at room temperature, the specimen held in a trough after forming showed a tendency to decrease in springback over time
We will present some examples of the time-dependent springback of AZ31B in the V- and L-bending process at various forming temperatures and conditions
The average size of the grain increased with the holding time in the die set at both Materials 2021, 14, 3s8i5d6es. These results show a similar tendency to microstructural changes in stress relaxation according to the forming temperature in the previous section
Summary
Magnesium alloy is an HCP (hexagonal closed packed) structure. It has fewer slip planes at room temperature than BCC (body-centered cubic) or FCC (face-centered cubic) structures [1]. At a forming temperature of 423 to 443 K, the creep behavior of magnesium alloy sheet increases the creep deformation and creep strain rate with increased forming temperature and a higher level of stress [6]. When three-point bending was performed using a magnesium alloy sheet at room temperature, the specimen held in a trough after forming showed a tendency to decrease in springback over time. These results indicate that creep and creep recovery occurred [7]. To model the creep deformation, the stress exponent of creep strain was measured This time-dependent behavior characteristic of magnesium alloys affects the manufacturing process, especially on springback. We will present some examples of the time-dependent springback of AZ31B in the V- and L-bending process at various forming temperatures and conditions
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