Effect of Pulsed Magnetic Field on the Residual Stress of Rolled Magnium Alloy AZ31 Sheet

doi:10.1007/s40195-020-01109-w

Abstract

Abstract:

A novel method of pulsed magnetic field (PMF) treatment was developed to eliminate the residual stress of rolled magnesium alloy AZ31 sheet in this study. The effect of PMF on residual stress of rolled AZ31 sheet was investigated and its mechanism was analyzed. The experimental results revealed that the pulse frequency had a significant impact on residual stress. After 10.0 Hz PMF treatment, the average and maximum reduction rates of residual stress along the rolled direction were 26.6% and 30.3%, respectively. It was found that the dislocation density and parallel dislocation in grains of the rolled sheet increased after it was treated by the pulsed magnetic field. The simulation results showed that the Lorentz force generated by the pulsed magnetic field can lead to basal slip, thereby resulting in local plastic deformation. Besides, the Joule heat produced during the PMF treatment was conducive to the elimination of residual stress.

Key words: Wrought magnesium alloy, Residual stress, Pulsed magnetic field, Rolled AZ31 sheet

Meng Yan, Cong Wang, Tianjiao Luo, Yingju Li, Xiaohui Feng, Qiuyan Huang, Yuansheng Yang. Effect of Pulsed Magnetic Field on the Residual Stress of Rolled Magnium Alloy AZ31 Sheet[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(1): 45-53.

Figures/Tables 12

Fig. 1 Dimension of the specimen and the positions for stress measurementThe apparatus of PMF treatment is illustrated in Fig. 2. The apparatus is composed of a low-voltage pulsed power source, exciting coils, a stainless steel holder, and a cooling water system. The pulsed magnetic field generated by the exciting coils acted on the magnesium alloy AZ31 sheet sample. A cooling system was used to cool the coils and isolate the heat generated in the coils from the sample.

Fig. 2 Schematic illustration of PMF apparatusThe PMF voltage was fixed at 300 V and the treatment time was 60 minutes in the experiment. Besides, the PMF frequency was set at 2.5, 5.0, and 10.0 Hz to investigate the effect of the frequency on residual stress. The sample was placed in the center of the exciting coils for PMF treatment after the initial residual stress was tested.

Fig. 3 Pulse voltage waveform of 10.0 Hz PMF

Fig. 4 Schematic showing the measurement of residual stress by XRD and sampling location for EBSD and TEM

Fig. 5 Effects of PMF frequency on RD and TD residual stress: a 2.5 Hz, b 5.0 Hz, c 10.0 Hz and d average and maximum reduction rate of residual stress

Fig. 6 KAM maps of a untreated and b with 10.0 Hz PMF treatment specimens

Fig. 7 TEM micrograph of dislocation before a and after b 2.5 Hz, c 5.0 Hz, d, e, f 10.0 Hz PMF treatment

Fig. 8 Lorentz force in the rising period PMF treatment

Fig. 9 Schmid factor map and histogram of basal slip a, c loaded along RD and b, d along with TD

Table 1 Residual stress of samples treated with different frequencies Lorentz force

Frequency	Residual stress (MPa)		Reduction rate (%)
Frequency	Before treatment	After treatment	Reduction rate (%)
2.5 Hz	- 50.3 ± 1.7	- 47.0 ± 1.2	6.5
5.0 Hz	- 51.2 ± 2.5	- 44.3 ± 1.4	13.3
10.0 Hz	- 52.5 ± 2.4	- 42.9 ± 1.3	18.1

Fig. 10 a Temperature rise during PMF treatment process and b residual stress elimination caused by Lorentz force and Joule heat

Table 2 Residual stress of samples treated at different temperatures

Temperature	Residual stress (MPa)		Reduction rate (%)
Temperature	Before treatment	After treatment	Reduction rate (%)
47.0 °C	- 50.1 ± 2.2	- 49.5 ± 1.5	1.2
64.5 °C	- 49.5 ± 1.8	- 48.2 ± 1.4	2.6
73.8 °C	- 48.7 ± 2.0	- 46.2 ± 1.2	5.1

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