VHCF Properties of A7075-T651 Al Alloy Depending on Shot Peening and Fatigue Testing Methods

Abstract

Fatigue characteristics of A7075-T651 aluminum material were studied with surface treatment of shot peening. The fatigue life was characterized by two fatigue testing methods, ultrasonic fatigue test (UFT, 20 kHz) and the rotary-bending fatigue test (RFT, 53 Hz). The fatigue life improvement was confirmed by rotary bending fatigue tester. However, the surface modification effects were hardly observed by UFT method. The RFT results validate that the fatigue properties of RFT show a fine congruence regardless of the test machine types. The results of hardness, compressive residual stress, fatigue strength, and mechanical properties of specimen were improved by shot peening.

Comparison of SP, SMAT, SMRT, LSP, and UNSM Based on Treatment Effects on the Fatigue Properties of Metals in the HCF and VHCF Regimes

“…In the research by Tian et al [31], SP induced a work-hardened layer of approximately 100 µm in the surface of a 2024-T351 aluminum specimen. Myung et al [29], Trško et al [12], Suh et al [30], and Shiozwa and Lu [10] also observed that material surface microhardness increased after performing SP on SAE 9254 steel, 50CrMo4 steel, 7075-T651 aluminum, and JIS SUJ2 steel specimens, respectively. The research from Gao et al [32] and Li et al [17] showed an increase in microhardness after performing SMAT on TC11 titanium and heattreated AM Ti-6Al-4V titanium specimens.…”

“…Per the uniaxial test results, the level of improvement induced by severe shot peening was instead greater at lower fatigue stress levels. Research from Zhang et al [13] and Suh et al [30] showed that SP improved the bending-load fatigue properties of 35CrMo steel, LZ50 steel, and 7075-T651 aluminum specimens in the HCF and VHCF regimes. Nevertheless, the test results from Tian et al [31] and Suh et al [30] showed that SP had detrimental effects on the axial-load fatigue properties of 2024-T351 and 7075-T651 aluminum specimens in the HCF and VHCF regimes.…”

“…Research from Zhang et al [13] and Suh et al [30] showed that SP improved the bending-load fatigue properties of 35CrMo steel, LZ50 steel, and 7075-T651 aluminum specimens in the HCF and VHCF regimes. Nevertheless, the test results from Tian et al [31] and Suh et al [30] showed that SP had detrimental effects on the axial-load fatigue properties of 2024-T351 and 7075-T651 aluminum specimens in the HCF and VHCF regimes. According to research from Gao et al [5], SMAT had positive effects on the fatigue lives of 7075-T6 aluminum specimens subjected to a uniaxial fatigue load at a stress level of 220 MPa; however, negative effects were observed at a stress level of 180 MPa (reference Table 3 and Figure 7).…”

“…SP can induce a plastic deformation zone in the surface region of metals; however, the standard SP treatment tends to encounter difficulties in inducing the nanograin layer and gradient microstructure due to milder plastic strain. Myung et al [29] observed a 20 µm-thick plastic deformation zone under the surface of SP-treated SAE 9254 steel specimens, and research from Suh et al [30] showed that SP induced a 100 µ m thick plastic deformation zone in the surface region of 7075-T651 aluminum specimens. Neither Myung et al [29] nor Suh et al [30] reported any observation of the nanograin layer and microstructure.…”

“…Myung et al [29] observed a 20 µm-thick plastic deformation zone under the surface of SP-treated SAE 9254 steel specimens, and research from Suh et al [30] showed that SP induced a 100 µ m thick plastic deformation zone in the surface region of 7075-T651 aluminum specimens. Neither Myung et al [29] nor Suh et al [30] reported any observation of the nanograin layer and microstructure. On the other hand, Trško et al [12] observed a 20 µm-thick nanograin layer after the severe shot peening treatment of 50CrMo4 steel specimens.…”