Severe Plastic Deformation-induced Microstructure and Mechanical Behavior in 6061 Aluminum Alloy via Biaxial Alternate Forging

This study examines the deformation behavior and microstructural evolution of 6061 aluminum alloy processed through severe plastic deformation (SPD) via biaxial alternate forging. The objective was to evaluate both the alloy's formability limit and mechanical properties. Finite element (FE) analysis was conducted to simulate the biaxial alternate forging process, incorporating the strain-hardening coefficient and the number of forging passes. When the strain-hardening coefficient was set to 0, an average effective strain of approximately 440% was observed in a 4 mm diameter region at the core of the workpiece after eight forging passes. In contrast, with a strain-hardening coefficient of 0.2, the average effective strain under the same conditions decreased to about 300%. The FE analysis of the 6061 aluminum alloy estimated an average effective strain of 326% after eight passes, indicating a level of severe plastic deformation well beyond the elongation capacity of the initial material. Tensile testing revealed that after two passes, the material showed a gradual increase in strength with only a minimal reduction in elongation. Even after accumulating a significant strain of 326% through eight passes, optical microscopy displayed deformed grains and twinning structures, with no signs of recrystallization across all examined forging conditions.