Characterisation of aluminium alloys by X-ray diffraction line profile analysi

From a research and development perspective Alcan Inc. maintains a global leadership position in aluminium can stock by understanding the relationships between processing microstructure and properties. TEM analysis is of little use in examining the associated microstructures from its most important products. In contrast X-ray Diffraction Line Profile Analysis (LPA) has shown that information about the microstructure of heavily cold worked materials may be reliably obtained.;Al-2.5%Mg, Al-4%Cu and Al-0.2%Cu-1.2%Mg based alloys were processed to provide microstructures modified by 'deformation only', 'precipitation only' and 'precipitation and deformation' respectively. The processing routes from these alloys were optimised for reproducibility of X-ray diffraction results. This involved stages of alloy development that included 0.4% iron additions and sophisticated thermomechanical processing routes.;A systematic approach to LPA was made and X-ray diffraction mounting techniques, profile fitting and Kai stripping were optimised to obtain robust and reproducible results using a conventional X-ray diffractometer.;A number of LPA techniques were investigated and reliable measurements of crystallite size and (square) root mean squared sfrains (r.m.s.s.) were obtained by applying the Warren-Averbach LPA technique. By adapting and developing models the results from LPA were used to estimate dislocation densities and precipitation effects. To help in interpreting the LPA results, TEM was used as a complementary technique.;The major conclusions of the project were: (i) Routine methods for LPA using as rolled sheet may be implemented at Alcan Inc.'s Banbury Laboratories. This would allow for the determination of crystallite size, r.m.s.s., dislocation densities and coherent precipitate effects. (ii) In cold worked structures the crystallite size was related to the spacing of dislocations, while in a recovered material it was related to the subgrain size. At high levels of cold work, dislocation rearrangement occurred to lower the energy in the lattice that reduced the trend of decreasing crystallite size with cold work. The crystallite size in Al-Cu alloys was related to the spacing of parallel precipitates. (iii) LPA may be used to distinguish between cold worked and recovered structures in an Al-Mg alloy. This was possible because cold worked and recovered structures have different dislocation arrangements that lead to variations in the shape of diffraction peaks. (iv) An estimation of Vickers Hardness Number and yield strength may be calculated directly from LPA in conjunction with a model and calibration curve. (v) S' (Al2CuMg) did not contribute to X-ray Line Broadening. Therefore LPA may be performed on S' containing materials to investigate effects caused by other sources of broadening. (vi) The project has had a positive financial impact on Alcan's research and development activities. The project also contributes towards the incorporations technological competitive advantage.