Behavior of Ultrafine-Grained Zn-1%Mg-0.1%Ca Alloy under Cyclic Loading

Abstract

The paper studies the microstructure and mechanical characteristics, in particular, fatigue strength, of the Zn-1%Mg-0.1%Ca alloy subjected to high-pressure torsion (HPT) at room temperature. The study shows that a mixed microstructure is formed in the alloy after HPT, which consists of α-Zn grains 700–900 nm in size, nanograins of a magnesium-rich phase 50–100 nm in size, and finely dispersed particles ~30–50 nm in size. The formation of such a structure leads to an increase in the yield stress of the alloy by ~2.5 times and in the ultimate tensile strength by ~2.7 times with a simultaneous significant growth in ductility (approximately by 13 times). An increase in the static strength is also accompanied by an increase in the fatigue strength by 1.7 times. However, the increase in fatigue strength is less pronounced compared to the increase in static strength. The fatigue strength increases by almost 70% above that of the initial alloy (from 65 MPa to 110 MPa, respectively). Upon reaching 2.8 × 10⁶ loading cycles by the repeated tension scheme, fracture of the specimen is accompanied by the formation of microcracks directed perpendicular to the fatigue crack front and located near the final fracture zone.