Dc Current And Pulse Current Experimental Study Of The Organizational Impact Of Za27 Alloy Solidification

Controllable Solidification process is the key way to improve the properties of materials and to R&D the advanced materials at the present. Compared with effects of other physics field (e.g. oscillation field, high pressure field, ultra sonic field), electrical field and magnetic field has its own specific characteristics when it is imposed on the metal or alloy solidification process. The electro-magnetic field makes the phase transformation to be changed. By influencing the moving behavior of the atoms and ions in the melt, the macro properties and the microstructure are closely concerned with the moving behaviors of the atoms and ions in the melt. So, on the base of thermal energy field (e.g. temperature field) during Solidification process, cold energy field (e.g. electrical field, magnetic field) is imposed simultaneously, the materials will appear new properties under the action of the composite fields.In this article, a specific power source, which can generate the rectangular wave pulse electrical current, and a device of solidification experiment been matched for the power source was developed. By the apparatus, the action of pulse electric current and direct electric current on ZA27 alloy solidification structure was researched. The results are as follows.The direct electric and pulse current has well effect of modification and inoculation on the metal solidification structure. To some extent, the grain size of ZA27 alloy was reduced with the increase of the direct electric current density, and the component was homogenized. That's mainly because the electric current promoted the effect of electrical migration and the convergence of the electric current in the melt, which resulted in the joule heat effect and fusing the arm of dendrite.Effects of the pulse parameters on the material solidification structure were also analyzed. It is suggested that the pulse wave pattern, pulse current amplitude, pulse frequency and pulse duration are not only related with the energy magnitude which the environment acted on the solidification system, but also concerned with the inertia responding frequency of the melt.The mechanism for pulse current reduced the grain size and resulted in the non-dendrite formation is that the pulse current changed the thermodynamic potential of the nucleation and diffusion activation energy, forcing the melt been in the oscillating state, and then reduced the grain size. At the same time, because of the interaction between pulse current and the induced magnetic field, the effect of MHD and the oscillating state was caused, thus considerable disturbance was induced in the melt, which could result in the dispersion of elements in the alloy, homogenizing the temperature field, increasing the general super cooling, dispersing the nucleation nucleus, restraining the dendrite growth, promoting the non-dendrite formation and reducing the grain size.The influence of different pulse frequency and pulse duration on the solidification structure of ZA27 alloy showed that, when the pulse amplitude is 30A, pulse frequency is 300Hz, and pulse duration is 100us, the pulse current can notably reduce the grain size and result in non-dendrite formation.The experiment result showed that, as the research to be developed in depth, byimposing the electric field, magnetic field and the composite field consisted of electric field and other physics field, the effective control on solidification process and structure could be implemented, and it could be developed to an advanced technology for thesolidification control.