Comparison of residual stress determination using different crystal planes by short-wavelength X-ray diffraction in a friction-stir-welded aluminum alloy plate

A friction-stir-welded (FSW) AA7050-T7451 pre-stretched plate was investigated nondestructively using the short-wavelength X-ray diffraction method to study the distribution of internal residual stress. During the investigation, anomalous deviation of the diffraction peak with crystal plane Al (111) was observed causing large testing errors. The relationship between texture of the material and the anomalous deviation peaks of (111), (200) and (311) and the method to eliminate their effect on residual stress determination were investigated. In addition, the comparison of the average d (0) method and the in situ d (0) method was performed using the three crystal planes to solve the problem caused by gradient in weld structure. Results showed that the anomalous deviations of different crystal planes were different from each other in the directions deflected from the maximum pole density direction. The method of residual stress determination performed in the directions of maximum pole density proved to be helpful to reduce the effect of anomalous deviations. The values and profiles of the residual stress tested by this method using (111), (200) and (311) were identical. The results suggest that in situ d (0) method could be used to eliminate the influence of the difference in lattice spacing among different areas of the FSW plate. The errors of residual stress determination decreased with the increase in the diffracting plane crystal indices.