Pulsed Electric Current V-Bending Springback of AZ31B Magnesium Alloy Sheets
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OVER the past few decades, the requirement of weight reduction for vehicles in the automotive industry has led to increased usage of lightweight alloys. In particular, magnesium (Mg) alloys have helped reduce a significant amount of weight owing to their low density while maintaining the high strength of structural parts. However, basal-textured Mg alloy sheets, such as AZ31B, exhibit inferior formability at low temperatures because of the limited number of active slip systems.[1] A warm forming technology has been applied[2] to improve the formability of Mg alloy sheets in the temperature range of 423 K523 K (150 °C250 °C).[3]
JINWOO LEE, HYUK JONG BONG, and DAEYONG KIM are with the Materials Deformation Department, Korea Institute of Materials Science, Changwon, 51508, Republic of Korea. Contact email: [email protected] YOUNG-SEON LEE is with the Materials Processing Innovation Research Division, Korea Institute of Materials Science, Changwon, 51508, Republic of Korea. MYOUNG-GYU LEE is with the Department of Materials Science and Engineering & RIAM, Seoul National University, Seoul, 08826, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted December 14, 2018. Article published online April 9, 2019 2720—VOLUME 50A, JUNE 2019
However, several drawbacks in the warm forming process have been reported, including increased manufacturing cost, reduced strength due to heat effect during forming,[4] and requirement of special lubricants to reduce the friction between the tool and the sheet.[5] As an alternative to the conventional warm forming process, an electrically assisted forming technology has been developed by applying a continuous current[6,7] or a pulsed current.[8–11] The effects of electric current on the deformation of metallic materials have been investigated from different perspectives. For instance, the application of electric current helped reduce the reaction (punch) force during forming (by decreasing the flow stress of the materials),[12] improve the ductility,[13] accelerate aging and recrystallization,[14] and reduce the springback by eliminating the residual stress.[15] The combined effect of electric current on the deformation of metals is known as the electroplastic effect. The mechanism of this effect has not been fully understood.[16] Some studies have decoupled the thermal and athermal effect (electroplastic effect) of the electric current, which influences the deformation of metals.[17] The numerical modeling of an electrically assisted tension test showed that Joule heating of Al5052 alloy accounted for 60 pct of the electrical effect on the plastic deformation.[18]
METALLURGICAL AND MATERIALS TRANSACTIONS A
Electrically assisted tension tests with an air-cooling system at room temperature showed largely the same flow stress curve as that for a specimen without applying electric current.[19] Coupled thermo-mechanical-electrical finite element simulations of Mg alloy sheets under pulsed electric current were conducted, and the stress–strain responses were compared with experim
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