Experimental Investigation on Formability of AZ31B Magnesium Alloy V-Bending Under Pulse Current

doi:10.1007/s40195-018-0734-4

Abstract

Abstract:

In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy during electropulse-assisted (EPA) V-bending was investigated. The experimental results showed that pulse current can effectively reduce the springback and the bending force compared to the experiments without current. The frequency has a more significant influence on bending force and springback than electric current density. Electroplastic (EP) effect begins to work when pulse current parameters reach a threshold value. To explore the mechanism of EPA V-bending, the microstructure evolution and fracture surface of the bending specimen were studied. It was found that pulse current can promote the occurrence of dynamic recrystallization (DRX) of magnesium alloy compared to traditional hot forming process. The fracture mode of AZ31B under EPA V-bending evolves from brittle fracture to ductile fracture with increasing pulse current parameters. Based on the discussion of athermal and thermal effects of EP effect, the mechanism of pulse current to promote DRX is studied and athermal effect is proved to exist.

Key words: AZ31B alloy, Pulse current, Electroplastic (EP) effect, Springback, Dynamic recrystallization

Xing-Rong Chu, Lei Wang, Shu-Xia Lin, Zhen-Ming Yue, Jun Gao. Experimental Investigation on Formability of AZ31B Magnesium Alloy V-Bending Under Pulse Current[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(12): 1249-1257.

Figures/Tables 14

Table 1 Chemical composition of AZ31B sheet (wt%)

Al	Zn	Mn	Si	Ca	Cu	Mg
2.5-3.5	0.6-1.4	0.2-1.0	0.08	0.04	0.01	Bal.

Fig. 1 Microstructure of original AZ31B sheet

Fig. 2 Experiment setup and its schematic diagram: a experiment setup, b setup schematic diagram

Fig. 3 Pulse current waveform in the experiment

Table 2 Experimental results under different forming conditions

Sample	Voltage (V)	Frequency (Hz)	J_r (A/mm²)	J_p (A/mm²)	Measured forming angle (°)
Sample	Voltage (V)	Frequency (Hz)	J_r (A/mm²)	J_p (A/mm²)	Group I	Group II
0	-	-	-	-	107.1	Fracture (A)
1	50	200	6.5	83.3	104.4	Fracture (B)
2	70	200	8.94	100	98.6	Fracture (C)
3	70	350	11.83	100	89.8	Fracture (D)
4	80	350	13.02	110	87.8	78.9° (E)
5	70	450	13.42	100	83	78.8° (F)
6	90	350	15.56	116	81.0	77.8° (G)

Fig. 4 Measured specimens temperature curves under different electrical parameters

Fig. 5 Specimens after EPA V-bending (Group I)

Fig. 6 V-bending (Group II): a different electropulse parameters, b without current and Jr?=?13.02 A/mm2

Fig. 7 Force-displacement curves under different current parameters: a Group I, b Group II

Fig. 8 Influences of RMS current density on bending force and springback angle

Fig. 9 Fracture position and fracture force under different RMS current densities

Fig. 10 Temperature a and bending force b evolution under traditional hot and EPA bending

Fig. 11 Microstructure images under different forming conditions: (0) after bending without current; (1) 50 V, 200 Hz; (3) 70 V, 350 Hz; (4) 80 V, 350 Hz; (6) 90 V, 350 Hz. EX, IN represent extrados and intrados of specimen, respectively

Fig. 12 Fracture morphology of specimens in Group II: a without current, b RMS current density of 11.83 A/mm2

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