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5A06 Sheet metal parts vacuum annealing

A product part is manufactured by sheet metal stamping process, and the material used is 5A06 sheet. Cracking often occurs over a period of time, and the stamping rate is low. In order to improve the forming rate of 5A06 sheet, this paper analyzes the reasons for stamping cracking, studies the effect of vacuum annealing temperature on the microstructure and properties of 5A06 sheet, and provides a reference for the formulation of vacuum annealing process in stamping process.

1.Sheet metal forming process:

The specific sheet metal process of this part is: 5A06-H14 sheet → cut into round wool → vacuum annealing → air cooling → primary drawing → vacuum annealing → air cooling → secondary drawing.

2.Influencing factors of sheet stamping performance

Sheet metal forming is generally referred to as stamping. It is a processing method for a sheet with a small thickness, using a special mold to plastically deform the metal without damaging it, thereby obtaining parts or blanks of the required shape and size. The drawing coefficient when deformation and rupture occurs is m=d/D, and mmin is called the ultimate drawing coefficient (D and d are the diameters of the blanks before and after drawing respectively). rupture occurs, which is called plastic rupture. Table 1 lists the ultimate drawing coefficients of some aluminum alloys.

The drawing coefficient m represents the degree of deep drawing deformation of the material. The smaller m is, the greater the deformation degree is. For too small parts, multiple deep drawing methods must be adopted, and the drawing coefficient mn of each time should be greater than the limit drawing coefficient mmin. At present, according to the stamping process of the head, in order to ensure the smooth progress of stamping, stamping is carried out in two times, and the drawing coefficients m1 and m2 of the first stamping and the second stamping are both greater than 0.75. The current state of the material is not fully annealed, and the drawing coefficient is large, so each drawing coefficient of the process specification is larger than the limit drawing coefficient in Table 1. The stamping process is mainly affected by the deep drawing coefficient of the material, and the deep drawing coefficient is affected by the state of the material. Therefore, under the current process specification, the stamping parts have many cracking failures, which are mainly related to the state of the material, that is, the structure of the material. , yield ratio and plasticity.

3.Microstructure and properties of stamping parts in different forming states

The yield strength of punch-cracked parts is 260MPa and the elongation is 15.3%. 1%。 The highest yield strength in stamped parts was 212MPa, and the lowest elongation was 19.1%. Compared with the properties of stamping and cracking materials, the elongation of stamped parts is 25% to 57% higher, and the yield strength is 18% to 40% lower. After the sheet was vacuum annealed at 2509C x 2h before stamping, the mechanical properties of the stamped parts were lower than those of the original H14 sheet, the yield strength was reduced, and the plasticity was increased. After the sheet was vacuum annealed, the yield ratio decreased. The yield ratio of stamped parts is between 0.43 and 0.56, which is lower than that of stamped and cracked parts.

4.Microstructure and properties of sheets at different vacuum annealing temperatures

In order to determine the effect of vacuum annealing temperature on the microstructure and properties of the material, the microstructure and properties of the material treated at different temperatures were studied. With the increase of the original vacuum annealing temperature, the rate of change of the yield ratio decreases. Compared with vacuum annealing at 280℃, the yield-strength ratio did not change much. There is basically no difference in the transverse and longitudinal yield-strength ratios in each state.

When the vacuum annealing temperature increases, the material structure changes obviously. When vacuum annealed at 260°C, the material is still fibrous, and the grain boundaries of recrystallized grains are not observed. When the vacuum annealing temperature rises to above 280 °C, the recrystallization is sufficient and the grain boundaries are obvious.

5.Analysis and discussion

(1) The reason for the cracking of stamping parts

The raw material of the parts is rust-proof aluminum 5A06, which is a 2.8~2.9mm thick cold-rolled plate, and the work hardening state is

Y2 state. The stamping process is carried out in two times, the drawing coefficient of the second time is higher than that of the first time, and the forming rate is high in the previous stamping process, indicating that the stamping process specification is reasonable.

Through the research on stamping-formed parts and stamping-cracked parts, it is found that the highest yield strength of the stamped-formed parts tested is 212MPa, which is significantly lower than the yield strength of stamping-cracked parts of 260MPa, and the yield-to-strength ratio of the formed parts is 0.43~0.57, low The yield-strength ratio of the cracked part is 0.67. The transverse and longitudinal elongation of stamping-formed parts are all above 19%, while the highest elongation of the tested stamping-cracked parts does not exceed 15.3%.

From the above results and analysis, it can be seen that under the condition of unchanged stamping equipment and process specifications, the main reason for material cracking is that the yield strength of the cracked part material is relatively high and the elongation is low, so the limit of the cracked part material is The drawing coefficient is larger, and the drawing coefficient is smaller than the current limit drawing coefficient of the material.

(2) Effect of vacuum annealing temperature on microstructure and properties

The research on the effect of different vacuum annealing temperatures on the microstructure and properties of 5A06 shows that the material structure changes during the vacuum annealing process, the internal deformation energy of the material decreases, the degree of work hardening decreases, and the material gradually softens. With the increase of vacuum annealing temperature, the yield strength of the material decreases, the elongation increases, and it gradually transitions from the recovery stage to the recrystallization stage, the texture changes, and the material anisotropy decreases. Compared with the original sheet, when vacuum annealed at 260 °C, the optical microstructure does not change significantly, all of which are typical fibrous structures. It shows that only recovery has occurred at present, and the dislocations inside the material have moved and gradually disappeared, and no recrystallization has occurred. When the vacuum annealing temperature is increased to 270 °C, some grain boundaries can be observed in the structure, indicating that the material has begun to recrystallize at this time, but the recrystallization is not sufficient. When the vacuum annealing temperature is increased to 280 °C, the grain boundaries are obvious, the recrystallization is relatively sufficient, and the change of the microstructure of the material leads to the change of the material properties, which gradually decreases with the strength. Continue to increase the vacuum annealing temperature, the strength does not change much, and the elongation has been increasing with the increase of the vacuum annealing temperature.

6.Conclusion

(1) Compared with the material of stamping and cracking parts, the material of stamping parts has high plasticity, low yield-strength ratio, and recrystallization occurs in the drawing process. The ultimate deep drawing coefficient of the cracked material is large, and the cooperation between the yield ratio and the plasticity cannot reach the forming conditions under the existing process specification.

(2) The yield ratio and elongation of the material are the main factors affecting the drawing coefficient and the stamping deformation ability, and these two factors are mainly affected by the vacuum annealing temperature of the material.

(3) The vacuum annealing temperature has a great influence on the microstructure and properties of the 5A06 cold-rolled sheet. When the vacuum annealing temperature reached 280℃, the yield strength decreased to 162MPa, the yield strength ratio decreased to 0.47, and the elongation increased to 23.4%. The vacuum annealing above 280C can meet the requirements of the stamping process for the stamping performance of the material.

Selection of vacuum annealing furnace equipment: The RVA series vacuum annealing furnace produced by SIMUWU is a high-quality product for the vacuum annealing process of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum annealing process.