Determination of Residual Stress of Aluminum Alloys by X-Rays

Abstract

The distribution of residual lattice strains or lattice spacings and residual stresses in plastically extended aluminum alloys were measured by various characteristic X-rays. Then, the scattering of the distribution of the residual lattice strains vs. sin2ψ were investigated precisely in each stage of plastic strains, and the wave length and lattice plane dependency of the residual stresses were discussed.Hot rolled sheets of Al-1.2 Mn (3003) and Al-4.5 Cu-1.5 Mg-0.6 Mn (2024) alloy were used in this experiment. The shape and dimensions of specimens are shown in Fig. 1. The chemical composition, heat treatment and mechanical properties are indicated in Table 1, 2. To prevent the diffraction lines of these specimens from becoming spotty, the specimen holder8) was equipped with horizontally and vertically oscillating mechanism, by which sufficiently continuous diffraction patterns were obtained (Fig. 2).In order to make sure of the wave length and diffraction plane dependency of the residual stress, the data for several planes by CuKα, CoKα and CrKα radiation were sought and obtained (Fig. 5). On the observation of the distribution of residual lattice strains by sin2ψ method, the direction of the incident X-ray beam to the specimen surface ψ0 is devided at intervals of 5°in the range of 0°∼45°and their diffraction lines on the side of ψ0+η were observed (Fig. 3, 4). The results obtained in this study are summarized as follows.(1) In order to examine the detailed distribution of the lattice strains or lattice spacings, it is necessary to obtain many lattice strains vs. sin2ψ and to observe always only the sharp diffraction lines on the side of ψ0+η precisely.(2) It is confirmed that the distributions of the lattice strains vs. sin2ψ of annealed specimens are nearly linear, but scatter evidently in the early stage of the plastic strain about 2%, and aproach linear relation again with increase of the plastic strain. From these configuration, it is considered that the stress of a second kind9) in terms of Heyn intergranular stress takes place in the residual lattice strain.(3) The residual stresses are independent of the wave length but depend mainly on the lattice planes.