Analysis of the unstressed lattice spacing, d0, for the determination of the residual stress in a friction stir welded plate of an age-hardenable aluminum alloy - Use of equilibrium conditions and a genetic algorithm

Procedures based on equilibrium conditions (stress and bending moment) have been used to obtain an unstressed lattice spacing, d0, as a crucial requirement for calculating the residual stress (RS) profile across a joint conducted on a 10 mm thick plate of age-hardenable AA2024 alloy by friction stir welding (FSW). Two procedures have been used that take advantage of neutron diffraction measurements. First, equilibrium conditions were imposed on sections parallel to the weld so that a constant d0 value corresponding to the base material region could be calculated analytically. Second, balance conditions were imposed on a section transverse to the weld. Then, using the data and a genetic algorithm, suitable d0 values for the different regions of the weld have been found. For several reasons, the comb method has proved to be inappropriate for RS determination in the case of age-hardenable alloys. However, the equilibrium conditions, together with the genetic algorithm, has been shown to be very suitable for determining RS profiles in FSW joints of these alloys, where inherent microstructural variations of d 0 across the weld are expected. © Published by Elsevier Ltd. All rights reserved.
Support from Projects MAT-05-0527 and MAT-09-09545 from MICINN, and PIE 200960I076 from C.S.I.C., Spain, is gratefully acknowledged. Financial help from the ILL to conduct the neutron diffraction measurements on SALSA, experiments 1-02-6 and 1-02-10, is recognized. Support from Spanish Government Grants TIN 2008-00508 and MEC CONSOLIDER CSD00C-07-20811 and from Spanish MINECO (projects MAT2011-23455 and MAT2011-25991) is also acknowledged by J.I.H. and I.P.O., respectively.