Grain refinement mechanism in 6082 Al alloy fabricated by cryo-multiaxial forging

Abstract

In the present investigation, grain refinement mechanism in 6082 Al alloy fabricated by multi-axial forging at liquid nitrogen temperature (MCF) was proposed. The hardness and tensile properties were correlated to the microstructural characteristics of the processed alloy. The samples were subjected to open die MCF up to the 2 cycle (true strain = 1.26), 4 cycle (true strain = 2.52), and 6 cycle (true strain = 3.78), respectively. With the increased number of induced forging cycles, strength of the processed samples was significantly increased. The number density of dynamic recrystallized (DRXed) grains has significantly increased as the number of induced MCF cycles increases. The micro-texture analysis suggested the presence of the strong recrystallization (Rotated Cube ({001} <110>)) and strong deformation (Goss ({110}<001>) & Cu ({112}<111>)) texture components, after inducing the total true strain of 3.78. The supressed and broadened differential scanning calorimetry (DSC) exothermic peaks of β″&β′-phases of the MCF up to 6 cycles have revealed the high dislocation density in the processed samples. The MCF up to 6 cycles, followed by isochronal annealing treatment of Al alloy exhibit the highest strength in all investigated conditions. It was occurred due to the grain boundary strengthening owing to the development of nano-size sub-grains, as well as formation of needle shape β″-phases, which imparted the greater pinning effect during the interaction with the dislocations and grain boundaries.