镁合金板材冷冲压英文文献和中文翻译(2)

菜单

FE simulations were performed on cold drawing using simulation software. The FE model is presented in Fig.2, which is coincident with experimental tool configuration well. Constitutive model of the sheet metal was elastoplastic model, which used ELYSTSCHKOTSAY shell element formulation, and the number of integration points was 5. The mechanical parameters of as-received AZ31 sheets and the sheets underwent RUB process listed in Table 1 were taken as the material model for FE simulation. Punch, die and blank holder binder were defined as a rigid body and the static friction coefficient between them was 0.15.

Fig.2 FE meshes of dies and blank

Table 1 Mechanical parameters of as-received sheets and

sheets underwent RUB process

2.3 Cold stamping of cell phone house

Magnesium alloy sheets with a thickness of 0.6 mm, which were used in these experiments, underwent BUB process. Three sets of stamping dies of cell phone house were used, that was, the blanking die, deep drawing die and piercing die. Three sets of dies, driven by the crank press in turn, completed blanking, deep drawing and piercing process. Fig.3 shows the three specimens of various stamping processes of AZ31B magnesium alloy sheets underwent RUB process.

Fig.3 Stamping processes of cell phone house of magnesium

alloy sheets: (a) Blanking; (b) Deep drawing; (c) Piercing

In the three processes, blanking and piercing were easier to complete, while deep drawing process was hard to complete, due to magnesium alloy sheets with excellent punch-ability and poor drawing formability at room temperature. Different blanking ways were adopted to assess the anisotropy of sheets underwent RUB process, which affected cold deep drawing of magnesium alloy sheets. Fig.4 shows the three kinds of blanking ways of specimens, which were cut along planes coinciding with the angles of 0˚ (RD), 45˚ and 90˚ (TD) to the rolling direction.

Fig.4 Blanking ways along RD, transverse direction (TD) andat angles of 45˚ to RD

3 Results and discussion

3.1 Texture and formability of AZ31B sheet alloys

Fig.5 shows the microstructures of as-received magnesium alloy sheets and the sheets underwent RUB process. It can be seen that organizations of fine equiaxial grains distribute along longitudinal section of as-received sheet. The grains near the surface of the sheet underwent RUB shown in Fig.5(b) grow up slightly, while the grains of the center have not changed significantly. There is a gradient of strain during bending of a sheet, because the magnesium alloy sheets used in these experiments have a given thickness. There is a large amount of deformation near the sheet surface, and the greater energy storage during cold deformation; as a result, the grains during recrystallization are easier to grow up.

Fig.5 Microstructures of as-received sample (a) and sample

underwent RUB process (b)

In order to clarify the effect of RUB process on stamping formability of magnesium alloys, the texture and IE of as-received sheets and the sheets underwent RUB process were investigated in previous experiments[17−18]. Fig.6 shows the {0002} pole figures of as-received magnesium alloy sheet and the sheet underwent RUB process. A typical strong basal texture is observed in the as-received sheet, where the majority of grains are oriented as their {0002} basal planes parallel to the rolling plane of the sheet. Most of grains c-axis of AZ31B magnesium alloy sheets underwent RUB process tend to incline from the ND towards the RD. Texture components of the sheet underwent RUB (Fig.6(b)) become more disperse, and the basal texture is weakened.

Fig.6 {0002} pole figures of as-received sheet and sheet underwent RUB process: (a) as-received sample, Max density=8.66; (b) Sample underwent RUB process, Max density=7.31

Meanwhile, it can also be seen that the texture components of sheet underwent RUB (Fig.6(b)) contain more pole peaks along the RD, which strengthens anisotropy of magnesium alloy sheets. The variation in texture of the specimen underwent RUB process is likely to be responsible for severe shear deformation. Erichsen tests were then performed to study the stretch formability of magnesium alloy sheets. Compared with the as-received sheet, IE of the sheet underwent RUB process increases to 5.90 from 3.53, by 67% at most. Thus, the stretch formability of the specimen underwent RUB process is significantly higher than that of the as-received specimen at room temperature.