**4. Conclusions**

In this paper, three groups of creep age forming experiments of 7075 aluminum alloy under different prebending radii were carried out, and the effects of three prebending radii (500 mm, 1000 mm, and 1500 mm) on the mechanical properties, HCF performance and microstructure of 7075 aluminum alloy after forming were studied. The following conclusions were drawn:

(1) Under the condition of 443 K + 10 h, with the increase of the prebending radius, the hardness, strength, and elongation increased. When the prebending radius was 1500 mm, the maximum value was 187 HV, σ<sup>b</sup> = 568.98 MPa, σ0.2 = 466.51 MPa, δ = 6.12%.

(2) The conditional fatigue limit increases with the increase of the prebending radius. When the prebending radius was 1500 mm, the maximum value was 188.91 MPa.

(3) With the increase of prebending radius, the size and density of precipitated phase become smaller and larger, and the width of PFZ also becomes narrower. In this experiment, when the preloading radius was 500 mm, the width of the PFZ was the largest (100 nm), while when the preloading radius was 1500 mm, the width of the PFZ was the smallest (50 nm).

**Author Contributions:** D.Y. and Y.L. conceived and designed the experiment; D.Y., J.M. and F.Z. performed the experiments; D.Y., J.M., and F.Z. analyzed the data; Z.F. and Y.L. contributed reagents, materials, and analysis tools; D.Y. wrote and edited the paper; all authors were involved in discussion for the paper.

**Funding:** This research was funded by the Project Supported by Scientific Research Fund of Hunan Provincial Education Department, grant number 17C0638; National Natural Science Foundation of China, grant number 11702091 and the Natural Science Foundation of Hunan Province of China, grant number 2018JJ3140; Science and Technology Foundation of Changsha, grant number k1705052.

**Conflicts of Interest:** The authors declare no conflict of interest.
