Forgeability assessment of Al-6 wt%Mg alloy using biaxial alternate forging

The forgeability of Al-6 wt%Mg alloy extruded rods at room temperature was investigated in this study. A biaxial alternate forging system to allow continuous strain accumulations on the workpiece using octagonal rod shaped dies was designed. According to the die design with octagonal cross-sections, a finite element (FE) model indicated that the strain is mainly concentrated in the core and that the shear bands broadened and developed into a form with an X shape in the cross-section after the multiforging. The strain was distributed consistently along the longitudinal direction throughout the midsection of the workpiece. The effective strain in the core in the workpiece linearly increased with increasing number of forging passes. After the forging experiments using the devised dies, we observed that the Al-6mass%Mg alloy workpieces were substantially deformed with continuous strain accumulation by the multiforging. Cracks formed and began to propagate on the both ends of the workpieces forged with the designed die after five passes. The strain distributions on the cross-sections of the workpieces were in good agreement with that by the FE simulation. Tensile strengths of the forged specimens showed substantial increases depending on the number of forging passes, and a trade-off relationship was observed between the elongation and strength. The microstructures of the forged samples showed the formation and growth of twins and dislocation clusters.