Comparison of the fatigue behaviour of an Al-Zn-Mg-Cu alloy (7010) in the form of squeeze and chill castings and rolled plate

The relationship between the fatigue properties and grain size of the commercial 7010 alloy composition in squeeze-cast form has been established and the properties compared to those of rolled plate and gravity-cast 7010 material. The fatigue strength of the squeeze-cast material was found to lie between those of the gravity-cast and the plate material. A decrease in the grain size of the squeeze-cast material considerably improved its fatigue strength. However, the reverse was found to be the case for the fatigue crack propagation resistance. At ΔK values below ∼ 11 MPa m-1/2, fatigue cracks in plate material grew at a lower rate than in the squeeze-cast material and vice versa at higher ΔK values. The effects of some of the microstructural differences on the fatigue behaviours of the squeeze-cast, gravity-cast and plate material are discussed.