Fatigue Crack Initiation Behavior and Notch Sensitivity of AZ92A Magnesium Alloy.

Abstract

Plane bending fatigue tests were carried out for sand cast magnesium alloy AZ 92 A-T 6 in air at room temperature, in order to investigate fatigue crack initiation behavior and notch sensitivity. Successive observations on the surface have shown that the fatigue crack initiates along the slip bands in an α grain and starts to grow into the neighboring grain or lamellar precipitate phase. The notch sensitivity was higher than that in pure titanium that has hcp crystal structure. However, no non-propagating crack exists for a sharp notch (ρ=0.1 mm). Fractography using SEM has shown that the crack in which the micro pores in the vicinity of the surface became an origin, propagated and often led to final failure in the region of life Nf≥5× 105. In this case, the initial stress intensity factor; ΔKI ini was from 0.52 to 0.73 MPa ·√m, when the micro pore was considered to be a crack.