Change in Hardness Statistics during Isothermal Annealing of Cold-Rolled Aluminum
1050 aluminum sheet was cold-rolled by 50% with mineral oil. Hardness was measured on longitudinal section through the thickness of the rolled sheet. The overall hardness statistics of the as-rolled sheet followed the normal (Gaussian) distribution. Though the sheet was rolled under good lubrication, considerable redundant shear deformation was introduced beneath the surfaces by friction. The layers beneath the surfaces showed higher hardness than the center. The hardness subset statistics in one layer in the thickness also followed normal distribution. Isothermal changes in Vickers hardness statistics and in tensile properties during annealing at 548K were investigated. Beneath the surfaces, the recrystallization initiated and completed earlier than the center. The fully recrystallized sheet also shows the normal distribution of hardness, however the standard deviation is much smaller than that before annealing. The layers beneath the surfaces show lower hardness than the center after recrystallization. The partially recrystallized sheet shows bi-modal distribution of hardness. The partially recrysrallized sheet shows slightly better tensile-elongation balance than both the as-rolled sheet and the sheet-fully recrystallized.
T. Chandra, N. Wanderka, W. Reimers , M. Ionescu
T. Yukimoto et al., "Change in Hardness Statistics during Isothermal Annealing of Cold-Rolled Aluminum", Materials Science Forum, Vols. 638-642, pp. 469-474, 2010