Study of Microscopic Residual Stresses in an Extruded Aluminium Alloy Sample after Thermal Treatment

Abstract: A method is proposed to calculate the microscopic residual stresses in extruded cylindrical samples of non-ageing aluminium alloy 5083 (Al–Mg), arising from quenching in fresh water from 530°C. We start from the premise that the alloy is single-phase and non-isotropic on a microscopic scale; it consists of many grains that exhibit different mechanical response depending on their crystallographic orientation and neighboring grains. Microscopic residual stresses depend on the applied heat treatment, microstructure and mechanical strength of the individual grains. The stresses were calculated from neutron diffraction data. Genetic programming algorithms were used to calculate microscopic residual stresses, considering that each diffraction peak describes the stress distribution of a group of grains having a certain orientation, size and environment. The algorithm assigns a stress value to each grain according to the distribution of the diffraction peaks and the microstructural parameters of these grains.This work was supported by the Madrid Regional Government-FEDER grant Y2018/NMT-4668 (Micro-Stress-MAP-CM) and the project MAT2017-83825-C4-1-R. We would also like to express our gratitude to FLNR-JINP for the beam time allocated on the FSD instrument, and to the HeuristicLab Software developers

Further insights on the stress equilibrium method to investigate macroscopic residual stress fields: Case of aluminum alloys cylinders

The stress equilibrium, SE, method has been shown to be a very powerful, reliable tool for calculating the un-stressed lattice parameter, a, as a critical requirement for the determination of the residual stress, RS, by diffraction techniques. The method can be used in cases where others, such as the powder or comb ones, are limited (e.g., in age-hardenable aluminum alloys components, where a can be affected). Owing to its potential, this method can address complex cases that, however, have not yet been sufficiently exploited. In particular, it makes it possible to delve into the effect of microstructural factors (e.g., texture variations) on the macroscopic residual stress, M-RS. Here, the M-RS obtained after quenching and slow cooling of cylindrical samples of aluminum alloys has been investigated. Data obtained from neutron and synchrotron radiation diffraction in AA5083 and AA2014 alloy samples (of different size), respectively, have been used. Specifically, the development of a texture gradient, a very common consequence derived from conventional manufacturing processes of components, has been taken into account. The known fact that a parabolic profile of the M-RS is obtained in cylindrical samples is used to generalize the SE method to determine a and to strengthen its quality and reliability.The authors thank Consejería de Educación e Investigación from Comunidad Autónoma de Madrid, CAM, Madrid, Spain, for the grant of Micro-Stress-MAP project, ref., Y2018/NMT-4668, and the Spanish Ministerio de Economía y Competitividad, MINECO, for the project of ref. MAT2017-R83825-C4–1-R, to which this work is linked. The FLNP of the JINR (Dubna, Russia) is acknowledged for the beam-time allocation for the experiments on FSD instrument. Support from BESSY, Berlin, for the SR experiment (proposal nº 2008-80215) on EDDI instrument is also acknowledge. Special mention also deserves the technical body of the National Center for Metallurgical Research, CENIM, for the preparation of the samples

The Application of Scanning Contact Potentiometry Method and Diffraction of Thermal Neutrons at Physico-Mechanical Tests of Materials

The results of physical and mechanical tests on the tensile strength of austenitic steel 12X18H10T, in the stress range from 100 MPa to the maximum value of 700 MPa, at which the sample was destroyed, are presented. Structural changes were registered synchronously by two methods: the method of scanning contact potentiometry and the method of diffraction of thermal neutrons. At loads above 650 MPa, the α-martensite phase was found in the austenite matrix, as well as the appearance of diffraction peaks characteristic of a cubic martensitic BCC lattice was observed in neutron spectra. On the potentiograms, this process corresponds to the appearance of local regions in which high values of electric potential gradients were observed. This is the case of discovery of the fatigue nucleus cracks in the tensile testing of steel ЭИ847 by the method of scanning contact potentiometry