Dn. Hanlon et Wm. Rainforth, SOME OBSERVATIONS ON CYCLIC DEFORMATION STRUCTURES IN THE HIGH-STRENGTH COMMERCIAL ALUMINUM-ALLOY AA-7150, Metallurgical and materials transactions. A, Physical metallurgy andmaterials science, 29(11), 1998, pp. 2727-2736
Load-controlled fatigue testing of the aluminum alloy AA 7150 has been
conducted using four-point bending with an R ratio of +0.1 over a ran
ge of maximum stress levels from 60 to 120 pet of the 0.2 pet proof st
ress. The alloy, in the form of 12.5-mm rolled plate, was investigated
in underaged (UA), peak-aged (PA), and overaged (OA) conditions, corr
esponding to a change in average precipitate sizes from 5 nm in the UA
condition to 21 nm in the OA condition. Three orientations of the pla
te were investigated. Orientation and aging condition influenced the d
egree of surface topographical development but not fatigue life. Detai
led transmission electron microscopy (TEM) of the fatigued surface ind
icated that deformation in all aging conditions occurred by planar sli
p. Slip was generally restricted to a single slip system within each g
rain, and subgrain boundaries offered little resistance to dislocation
movement facilitating long slip line lengths (measured up to 310 mu m
) between adjacent high-angle grain boundaries. Planar slip observed i
n the OA condition is attributed to shearing of large strengthening pr
ecipitates, which is promoted by long slip line lengths. No evidence o
f surface specific changes in slip character was observed.