Mechanical properties and microstructure evolution of aluminum alloy tubes with normal gradient grains under biaxial stress

Grain size gradient materials are a type of new structural material with the advantages both coarse and fine grains. To study effect normal grain on mechanical properties microstructure aluminum alloy tubes during hydroforming, distribution outer inner grains was obtained using spinning annealing methods, biaxial stress determined hydraulic bulging experiments. Gradient thicknesses 300, 475, 575 μm were through at different temperatures; tensile strengths 79, 89, 109 MPa; maximum expansion rates 18%, 17%, 10%; work-hardening indices 0.19, 0.20, 0.17, respectively, under stress. With an increase in refined area, density low-angular boundaries (LAGBs) increased chance stitching dislocation process intragranular deformation, causing strength. However, thickness weakened compatible deformation due to reduction number large grains, leading decrease plasticity. The quantitative relationship between strength/ductility can be applied guide production tubular parts aerospace automotive industries.