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| Effect of Pulse Current on Adiabatic Shear Band of 2A10 Aluminum Alloy under High Speed Impact |
| Hu Qiancheng, Li Weihao, Li Chengcheng, Chen Li, Li Xingwen |
| State Key Laboratory of Electrical Insulation and Power Equipment Xi'an Jiaotong University Xi'an 710049 China |
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Abstract During the electromagnetic launch process, the armature and rail are in an extreme multi-physical field environment. Due to rail vibration and uneven forces, the armature and rail generate ultra-high speed impact to form shear. However, melting and ablation caused by current result in the loss of the surface material characterization information. Therefore, it is difficult to carry out the mechanism of extreme multi-physical field on the material, which restricts the application of the material in the environment of ultra-high-speed impact and even electromagnetic launch. In order to address this problem, this paper designs the off-axis long bar with hoop specimen, and investigates the dynamic deformation characterization of 2A10 aluminum alloy under extreme multi-physical field environment, i.e., the current density of 108~109 A/m2 and the strain rate greater than or equal to 104/s. Comparing the distribution of microscopic features under different experiment conditions, and the effect of pulse current under the extreme multi-physical field conditions on dynamic deformation of the material is obtained.
A pulse power supply and an electromagnetic repulsive device are adopted to equivalently simulate the extreme multi-physical field environment of electromagnetic launch. The electromagnetic repulsive device is used to generate a high strain rate in the specimen by generating an instantaneous (390 μs) Lorentz force. While the specimen is deformed at high speed, pulse current is injected at a suitable moment to realize the electro-thermal coupling. After the experiment, the specimens are axially cut, mechanical polished, and chemically etched. The microscopic features of the specimen profile are observed by optical microscope and scanning electron microscope.
The simulation results show that the strain rate is the highest at the diagonal and in the middle, and the strain rate can be up to 2×104/s. Different deformation rates at different locations of the material profile, and the gradual decrease of the strain rate from the diagonal to the middle, may present different microscopic features. The strain distribution and strain rate distribution are basically the same. The shear stresses applied to the two points inside and outside the diagonal region are in opposite directions, thus forming shear in the diagonal region. The shear stress in the diagonal region is 3~4 times larger than that outside the region. Through the calculation of skinning depth, it is known that the pulse current is uniformly distributed in the long bar of the specimen, and the pulse current applied in the experiment satisfies the current density condition.
The critical value of crack repulsion generated on the specimen surface is determined through several experiments, and this value is kept constant as the repulsion value. The experimental results of microscopic characterization of the specimen profile show that the adiabatic shear band can be clearly observed at the diagonal of the specimen profile without current, and cracks are generated at both diagonals, and the experimental observation results correspond to the simulation results. Selecting the appropriate moment to energize the pulse current, and the current densities were 3.68×108 A/m2 and 1.02×109 A/m2, respectively. The experimental results show that: (1) Under the same repulsive condition, the temperature gradient generated by the pulse current at the tip and both sides of the cracks healed the cracks. The crack lengths were reduced by 19.41% and 37.34%, respectively. (2) The pulse current suppressed the rotational dynamic recrystallization through the effects of electron wind and Joule heat, etc. The dynamic recrystallization grains were reduced and it was difficult to form the softening point inside the material, which suppressed the formation of adiabatic shear band. The lengths of adiabatic shear bands were reduced by 18.04% and 29.95%, respectively.
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Received: 25 August 2023
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2024, Vol. 39 
