Microstructural Evolution Of Aluminium Alloy Under Mechanical And Electromagnetic Deformation With High Velocity

In recent years, the requirements of lightweight structure makes that the lightweightmaterials (represented as aluminum alloys) have been widely used in the manufacturingfield. With the rapid development of the forming technology, the formability and serviceperformance of aluminum alloy have been pushed to higher requirements. Literatures haveshown that high-speed deformation can improve the formability of aluminum alloyseffectively. Electromagnetic forming is a new high-speed deformation technique, whichcan shape metal workpiece through electromagnetic force without mechanical contact,playing a significant role in improving the formability of aluminum forming. However,how does the microstructure evolute for aluminum alloys during electromagnetic forming,what are the differences of these microstructural evolutions of aluminum alloys underelectromagnetic forming, by comparsion with that obtained under conventionalmechanical high-speed forming. All these questions are remaining unanswered. In thepresent work, the microstructural evolutions of aluminum alloy under both mechanicaland electromagnetic deformations with high speed are investigated systematically, in orderto reveal the difference in microstructural evolutions and the corresponding mechanismunder above loadings with high speed.Aluminum alloys used in automobile and aerospace were selected as subject in thisstudy. Firstly, the dynamic compression of AA7055aluminum alloy under high strain ratewas carried out by a split Hopkinson pressure bar, and compared with that obtained underquasi-static mechanical loading by using a universal mechanical testing machine. Themicrostructural evolutions are characteristicd by transmission electron microscopy (TEM),the results showed different features of dislocation cells under above dynamic--quasi-staticcompressions. In addition, the high strain rate compression also induced the formation ofadiabatic shear bands in which the recrystallizations are observed. The microstructuralevolutions under dynamic--quasi-static compression are rationalized in terms of thedislocation cell model combined with the dislocation kinetics.Besides, in order to reveal the difference in microstructural evolutions of aluminumalloy under both mechanical and electromagnetic deformations with high speed, a series of experiments for5052aluminum alloy under mechanical--electromagnetic deformationswere carried out by an electromagnetic forming machine with a driving piece. The straindistribution and forming limit are measured based on ASAME Lite Version4.1strainanalysis software. The microstructural evolutions are characteristicd by electron backscattering diffraction (EBSD) and TEM. Results indicated similar strain distribution andorientation distribution in both electromagnetic and mechanical deformations. However,the dislocation configurations were significantly different, namely, wavy slip (denoted bydislocation cells and carpets structure) and planar slip (denoted by parallel dislocationconfigurations) are observed in deformed samples after electromagnetic and mechanicaldeformations, respectively. Furthermore, the distributions of eddy current and temperatureare simulated by ANSYS software. The dislocation nucleation and slip are also modeledcombined with different stress state under electromagnetic and mechanical deformationsin order to reveal the mechanism of slip mode difference.