Electro-pulse modification and reheating process for production of thixotropic microstructure in AlSi7Mg alloy

Electro-pulse modification (EPM) was used to change the dendritic structure of AlSi7Mg alloy to globular one. The effects of the modified temperature, electro-pulse frequency and time on the solidified structure were examined. The results show that these parameters play an important role in the solidified microstructures. That is to say, under the same modified temperature, the solidified microstructure will be improved greatly with the increase of electro-pulse frequency and time, but when they exceed to limit values, the solidified microstructure will become worse, resulting from the decrease of the ratio of nucleation. The experimental results indicate that the suitable modified temperature of AlSi7Mg alloy is 720 °C, and the appropriate electro-pulse frequency and time are 5 Hz and 40 s, respectively. Then the microstructures produced by suitable EPM process were reheated at temperatures between liquidus and solidus, the primary-Al grains ripen further and become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.