2008 Volume 49 Issue 5 Pages 1157-1161
The effects of the grain size on the fatigue fracture behaviors in extruded AZ31B alloys were investigated. The mean grain sizes are 4.7 μm in F-specimen, 15 μm in M-specimen and 23 μm in C-specimen, respectively. The fatigue tests with R=−1 were carried out with a plane fatigue bending machine, which was originally developed for thin sheet specimen. S-N curves show that the fatigue limit of the F-, the M- and the C-specimens were estimated as 160 MPa, 150 MPa and 150 MPa, respectively. The F-specimen had the highest fatigue limit in the present alloys. On the other hand, the fatigue life in low cycle region of the F-specimen is shorter than those of the M- and C-specimens. Striation-like-patterns were observed on the fracture surfaces in all of the specimens, although the grain sizes were different. Twin was not observed in the F-specimen, but it was near the crack in the C-specimen. Consequently, twinning under the fatigue test depends on the grain size, and it affects the fatigue life of AZ31B alloys.