Workability improvement on Al alloy inhomogeneous blanks by cryogenic forming

ABSTRACT

A novel cryogenic forming method is proposed to improve the workability of Al-Cu-Mn alloy friction stir-welded (FSW) blanks in this paper. Experiments were conducted to study the formability, deformation processing, and microstructure evolution of FSW blanks at liquid nitrogen temperatures. The cryogenic tensile properties of the joints showed that the plastic efficiency increased from 70.6% to 91.1%. The longitudinal weld fracture strain increased, and the ultimate tensile strength difference between the weld and base material decreased by 77.5% at −196°C. The cryogenic limiting dome height of the FSW blank increased from 25.4 mm at room temperature to 36.3 mm. The strain inhomogeneity of the bulged part decreased at −196°C. The FSW blank exhibited synergistic enhanced formability and deformation uniformity because of the improved plasticity of the weld zone and the smaller strength differences of the base material zone and weld zone at −196°C. The easy multiple slips in the nugget zone decreased the localized slips and increased the plasticity during cryogenic deformation. The decreased strength differences at cryogenic temperature were attributed to the significant dislocation strengthening of the coarse-grained base material.

KEYWORDS:

• FSW
• aluminium
• cryogenic
• workability
• formability
• deformation
• plastic
• hardening
• strength
• dome
• slips
• dislocations

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the National Natural Science Foundation of China [51875125]; National Key Research and Development Program of China [2019YFA0708801]