Effect of Multidirectional Forging on the Microstructures and Mechanical Properties of the Al–Mg–Si Alloy

Abstract

Due to its exceptional machinability, welding prowess, and resistance to corrosion, the lightweight 6061 Al–Mg–Si alloy finds extensive utilization within the realms of aerospace and transportation. Multi-directional forging process is a sever plastic deformation (SPD) process. In this investigation, a pristine 6061 industrial ingot was forged in multiple directions at 530 ℃ via four-upsetting and three-cross-stretching (4U3CS), seven-upsetting and six-cross-stretching (7U6CS), two different forging processes. T6 aging treatment is applied to the forged components after the pre-forging preparation. The investigation delved into the microstructural evolution during the process, alongside the mechanical performance across three orthogonal directions. The research findings underscore that, in comparison to 4U3CS, the cumulative deformation in 7U6CS fosters lattice distortion and defect formation, thereby promoting the dissolution of metastable phases and augmenting the driving force for precipitation during aging. Consequently, the tensile and yield strengths of the specimens increased by approximately 10 MPa across all three directions. Furthermore, 7U6CS retains a greater reservoir of deformation energy, acting as a catalyst for dynamic recrystallization, consequently, this process facilitates the enlargement of recrystallization nucleation regions and improves the degree of recrystallization uniformity. Following hot forging and subsequent T6 aging treatment, the disparity in grain size became more pronounced, diminishing from 418 to 208 μm. Coarse intergranular precipitates emerged as the primary origin of transgranular cracking. Post-T6 aging, the elongation rate of the specimens decreased across all three directions, accompanied by a substantial elevation in tensile and yield strengths. Notably, the mechanical performance of the 7U6CS-T6 specimen reached its zenith in the optimal direction, attaining values of 340 and 315 MPa for tensile strength and yield strength, respectively.

Graphical Abstract