High-Cycle Fatigue Properties and Residual Stress Relaxation Mechanism of Micro-Arc Oxidation 6082-T6 Aluminum Alloy
SU Kaixin1, ZHANG Jiwang1(), ZHANG Yanbin2, YAN Tao3, LI Hang1, JI Dongdong1
1.State Key Laboratory of Traction Power, Southwest Jiaotong University, Chengdu 610031, China 2.School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China 3.Bj -baodeli Electrical Equipment Co. , Ltd. , Baoji 721000, China
Cite this article:
SU Kaixin, ZHANG Jiwang, ZHANG Yanbin, YAN Tao, LI Hang, JI Dongdong. High-Cycle Fatigue Properties and Residual Stress Relaxation Mechanism of Micro-Arc Oxidation 6082-T6 Aluminum Alloy. Acta Metall Sin, 2022, 58(3): 334-344.
Recently, the fatigue failure of aluminum alloy components of high-speed railway catenary is becoming increasingly serious, which causes a threat to the normal operation of high-speed trains. In this study, the effect of micro-arc oxidation (MAO) coating on the high-cycle fatigue properties of 6082-T6 aluminum alloy for the catenary cantilever of the high-speed railway was studied. First, the rotating bending fatigue tests of untreated (UP) and MAO specimens of 6082-T6 aluminum alloy were performed. Then, the surface morphology and roughness, cross-section morphology, nanoindentation hardness, and elastic modulus gradient distribution, phase composition of MAO coating, and fatigue fracture morphology of the fatigue samples were studied by a confocal laser microscope, nanoindentation, XRD, and SEM. The experimental results showed that after MAO treatment, a large number of micro-cracks and pores were formed on the surface of the samples, and the morphology of the samples severely deteriorated. The XRD results indicated that the closer the coating surface, the stronger was the diffraction peaks of α-Al2O3 and γ-Al2O3. Besides, there was the higher tensile residual stress at the coating-substrate interface, which led to a significant reduction in fatigue properties. The fatigue strength decreased by 26.7% at 2 × 107 cyc. Finally, the formation and relaxation mechanisms of tensile residual stress under cyclic stress were analyzed using mismatch strain theory, and the effects of the coating on the fatigue properties of the substrate under high and low cyclic stresses were discussed further.
Fig.1 Sample shape and dimensions for mechanical property (a) and fatigue property (b) tests (unit: mm)
Fig.2 Schematic of residual stress measurement
Treatment
Elastic modulus
Yield strength
Ultimate tensile
Elongation
Section shrinkage
GPa
MPa
strength / MPa
%
%
UP
69.4 ± 2.2
317.9 ± 9.4
347.4 ± 7.0
8.2 ± 0.1
34.5 ± 0.3
MAO
67.2 ± 0.2
337.7 ± 0.2
350.9 ± 0.6
8.7 ± 0.6
34.8 ± 0.8
Table 1 Mechanical properties of untreated (UP) and micro-arc oxidation (MAO) 6082-T6 Al alloy
Fig.3 Surface morphologies (a, c) and 3D profiles (b, d) of UP (a, b) and MAO (c, d) samples (Inset in Fig.3c shows a higher magnification for MAO surface morphology)
Treatment
Ra
Rz
Rmax
UP
0.07 ± 0.00
0.60 ± 0.10
0.83 ± 0.28
MAO
2.65 ± 0.05
87.22 ± 9.58
93.69 ± 7.30
Table 2 Surface roughnesses of UP and MAO samples
Fig.4 XRD spectra of the MAO coating surface (a) and interior (b)
Fig.5 Cross section morphologies of UP (a) and MAO (b) samples
Fig.6 Coating hardness and elastic modulus distributions
Fig.7 Stress-fatigue life (S-N) curves of UP and MAO samples
Fig.8 Fracture morphologies of UP and MAO samples
Fig.9 Relaxation of tensile residual stress under different cyclic stresses of MAO samples
Fig.10 Formation (a) and relaxation (b) of tensile residual stress at the MAO coating-substrate interface
Fig.11 The variation trend of fatigue life of MAO sample compared with UP sample under different cyclic stresses (β—percentage of fatigue life change)
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