Study on the residual stress relaxation in 7050 aluminum alloy by new uphill quenching processes using neutron diffraction

This study innovatively applies induction heating technology to the uphill quenching process to achieve residual stress relaxation. The full-thickness residual stress distribution is quantitatively characterized in quenching (S), conventional uphill quenching (SCH), and induction heating uphill quenching at 100 °C (SCIH1) and 200 °C (SCIH2) samples. Neutron diffraction and finite element simulation are used to evaluate residual stress, supplemented by microhardness testing and microstructural analysis. The results indicate that the stress relief effect is determined by both the maximum temperature difference (ΔT) between the surface and core and the evolution of the microstructure. Traditional uphill quenching based on boiling water can achieve a maximum ΔT of 162 °C, and a large amount of fine phase precipitates in the grains. This reduces the residual stress of the SCH sample by about 30%, with the maximum stress on the surface and core reduced by 29% and 33%, respectively. However, the new SCIH2 process demonstrates even more remarkable results, with maximum stress reductions of approximately 36% on the surface and 68% in the core. This is attributed to the use of rapid induction heating to 200 °C, which can increase the maximum ΔT to 213 °C. Simultaneously, the high temperature accelerates dynamic recovery, reducing the dislocation density. It also transforms fine semi-coherent precipitates into coarse non-coherent phases, which eliminates local stress concentration. Furthermore, rapid heating to 200 °C by induction heating can result in higher microhardness compared to the S sample.