Effects of aging on near-threshold fatigue crack growth of 5083 aluminum alloy

To understand the effects of aging on the near-threshold fatigue crack growth of a 5083 - 0 aluminum alloy, experimental analyses were coducted at 20 deg C, 80 deg C and 130 deg C. The yield strength and the ultimate strength were both unchanged after aging at 80 deg C and 130 deg C for 6000 hours. The 130 deg C aging, however, induced an increase of electrical conductivity, a decrease of impact value and a change of da/dn vs ΔK relations, except for the value of ΔKth itself. The 80 deg C aging did not affect the above properties. Crystallographic facets were found near the ΔKth in samples, but the distribution pattern differed between the virgin and the 130 deg C aged ones. Grain boundary cracking was also observed in the 130 deg C aged ones, bening perpendicular to the main fracture surface. Irrespective of temperature and aging treatment, the cyclic plastic zone size at the crack tip was 13 ∼ 19 μm, comparable to the grain size, at the onset of crystallographic facets, and was 2 ∼ 2.1 μm at the ΔKth. (author)