The Effect of Pre-strain and Subsequent Electrically Assisted Annealing on the Mechanical Behaviors of Two Different Aluminum Alloys

The effects of pre-strain and subsequent electrically assisted annealing on the mechanical behaviors of two different (Al–Mg and Al–Si–Mg) aluminum alloys during electrically assisted dual stage forming are experimentally investigated. First, a specimen is deformed to a specific pre-strain by uniaxial tension and then automatically unloaded. After that, the pre-strained specimen is subjected to electrically assisted annealing by electric current with a fixed subsecond duration. Finally, the specimen is reloaded until fracture. Experimental results show that application of electric current with a subsecond duration induces electrically assisted annealing to both pre-strained aluminum alloys. The electric current also increases total achievable elongation until fracture during electrically assisted dual stage forming for both aluminum alloys. However, analysis of the stress–strain behavior during reloading and microstructural observations suggest that the quantitative effects of electric current on the post-electrically assisted annealing mechanical behavior and resultant microstructure are strongly dependent on the type of aluminum alloy. With the electric current density of 140 A/mm2, a full recrystallization followed by grain growth occurs in the pre-strained Al–Mg alloy specimens. For the pre-strained Al–Mg–Si alloy specimens, the electric current density of 140 A/mm2 induces both annealing and solid solutioning. Together, our findings indicate that while electrically assisted annealing is effective at improving the productivity of dual stage forming of an aluminum alloy, the composition of the aluminum alloy should be carefully considered in the design of forming process utilizing the concept of electrically assisted annealing since the beneficial effect was limited for the precipitation hardening 6061-T6 aluminum alloy.