There is a need to study the multi-objective optimization technique as the appropriate method to enhance welding qualities under optimal process conditions. The enhanced flow softening in EAT is explained as the comprehensive influences of electrically induced α→β phase transformation, dynamic recovery, dynamic recrystallization, and related enhanced local Joule heating at newly born grain boundaries.
In addition, electric pulse is provided to accelerate the α→β phase transformation by promoting local diffusion, resulting in the increased volume fraction of β phase from 23.02 to 31.42% and the formation of many acicular α phase during the rapid cooling process after EAT at 20 A/mm².
From microstructure observations, dislocation annihilation, formation of dislocation walls, sub-grains, and dynamic recrystallization were found under the EAT process at a temperature lower than the conventional recrystallization temperature range. Moreover, significant flow softening of 14–88 MPa which increases with current density and strain is found in EAT, indicating the existence of electroplasticity. Comparing the results of thermal-assisted tension (TAT) and electrically assisted tension (EAT) at equivalent tensile temperatures, it is found that the flow stress and elongation under EAT are generally lower than the ones under TAT. Near-isothermal electrically assisted tensile tests were performed on Ti–6Al–4V alloy sheet by programmed current–time loading curve and real-time monitoring via infrared thermal imaging. Test specimens made from powder metallurgy (P/M) materials are exempt from this requirement by industry-wide agreement to keep the pressing of the material to a specific projected area and density. The gauge length is the most significant difference between E8 and E8M test specimens. 1.2 The gauge lengths for most round specimens are required to be 4D for E8 and 5D for E8M. Scope* 1.1 These test methods cover the tension testing of metallic materials in any form at room temperature, specifically, the methods of determination of yield strength, yield point elongation, tensile strength, elongation, and reduction of area. This standard has been approved for use by agencies of the Department of Defense. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval. A number in parentheses indicates the year of last reapproval. This standard is issued under the fixed designation E8/E8M the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision.
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