Residual Stress Analysis in AA7449 As-Quenched Thick Plates Using Neutrons and Fe Modelling

In the current trend toward thicker aluminium plates, a major concern is the generation of high internal stresses during quenching, which can cause distortions during machining and pose serious safety concerns. Although the material is stretched after quench, substantially reducing residual stresses, they are not fully suppressed. In addition, the cooling rate is not large enough at the core of such thick plates to prevent any precipitation. This has a great impact on the efficiency of ageing. In this work, residual stress distributions in a heat-treatable aluminium alloy AA7449 thick plate in the as-quenched state measured by neutron diffraction are presented. A comparison between single (311) diffraction peak and multiple peaks analysis using Pawley algorithm is shown. The variation of the stress free reference value through the plate thickness is discussed and measured stresses are compared with residual stresses predicted by a thermomechanical finite element model of quenching

Microstructural control and optimization of Haynes 282 manufactured through laser powder bed fusion

The microstructure and properties of alloy Haynes 282 produced through laser powder bed fusion were investigated as a function of the post-deposition heat-treatment. Scanning electron microscopy and X-ray diffraction were utilized to characterize the microstructure, whilst electro-thermal mechanical testing was used to evaluate the tensile and creep properties at 900 °C. In the as-deposited state, the initial microstructure consisted of the γ and γʹ phases along with M6C and M23C6 carbides. These carbides were observed to govern the recrystallization behaviour of the material and resulted in a minimum recrystallization temperature of 1240 °C. Following post-deposition heat-treatments, the microstructures consisted of a monomodal distribution of γʹ with M6C and M23C6 carbides along the grain boundaries. Tertiary γʹ particles were found to form in the vicinity of carbides in samples that employed a γʹ super-solvus step prior to ageing at 788 °C. The tensile properties were found to be similar in all heat-treated states, consistent with the minimal differences observed in the microstructures. In contrast, significant differences in the creep behaviour of the alloy were observed following the different heat-treatments, although no correlation with the microstructures was observed