PSI - Issue 66

Miu Hayashi et al. / Procedia Structural Integrity 66 (2024) 161–166 Author name / Structural Integrity Procedia 00 (2025) 000–000

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2

fatigue strength, which typically results from rotating bending or plane bending 1-5 . There are few reports on the fatigue properties of anodised aluminium alloys under axial load 6 . Moreover, the fatigue fracture mechanism of anodised Al alloys has not yet been elucidated. Therefore, to investigate the effect of the anodising treatment on the fatigue properties and to clarify the fatigue fracture mechanism, specimens with anodised films of different thicknesses were prepared, and fatigue tests were conducted.

2. Specimen and experimental method 2.1 Specimen

The material used in this study was A6061 alloy (extrusion material). The chemical composition and mechanical properties of the A6061 alloy are listed in Tables 1 and 2, respectively. The s olution heat and ageing treatments were performed using a round bar. The round bar was then machined into a specimen shape (Fig. 1), and the R section of each specimen was mirror-polished using emery paper (#120, #320, #400, #600, #800, #1000, #1200, #1500, and #2000) and a diamond spray (0.25 μ m). Hereafter, we refer to this as Virgin . Moreover, to investigate the effect of film thickness of anodising treatment on fatigue strength, anodised films of 7 and 20 μ m, which are commonly used in anodised products, were formed. These specimens were referred to as An-7 and An-20 .

Table 1. Chemical composition of A6061 [mass%]. Si Fe Cu

Mn

Mg

Cr

Zn

Ti

Al

0.67

0.18

0.35

0.02

0.98

0.08

0.01

0.02

Bal.

Table 2. Mechanical properties of A6061. 0.2 % proof stress [MPa]

Tensile strength [MPa]

Elongation [%]

Hardness [HV]

280

320

22

105

2.2 Experimental method Static tensile and fatigue tests were performed using a hydraulic servo pulser EHF-ED10T-20L manufactured by Shimadzu Corporation. Both types of static tensile tests were conducted at room temperature in air at a load speed of 2 MPa/s. The fatigue tests were conducted at a frequency of f = 20 Hz, a stress ratio of R = -1, and a maximum number of fatigue cycles of N = 1×10 7 cycles. All the fracture surfaces were observed using a scanning electron microscope (SEM; TM4000, Hitachi Corporation).

3. Experimental results 3.1 Static tensile test result

Fig. 2 shows the results of static tensile tests of Virgin , An-7 , and An-20 . The vertical and horizontal axes represent the applied stresses and strains, respectively. Virgin , An-7 , and An-20 have tensile strengths of σ B = 380, 368, and