The Casting Texture Transformation For Pure Aluminium Modified By Electric Pulse And Its Effect On The Corrosion Resistance

It is an important way to fully improve the potential of material properties by developingand controling texture. For a long time, it has made a series of achievements of texture controlin solid-phase alloys. However, the study of casting texture has lagged far behind, whichgenerated by nuclei preferred orientation growth in almost all metallurgical solidificationstage of solid-phase metal. Therefore, it’s significant to advance the theory and application oftexture control to the stage of metal solidification even the metallurgical melt, which can notonly improve people’s initaitive to engage in control during the whole progress of preparingmaterials, in order to fully tap the potential of materials, but also can enrich and improve thetheory of alloy solidification.In this paper, according to experimental results, a growth mechanism model of aluminumcrystals was established in consideration of the melt environmental factors and coolingconditions. The crystal growth interface has been divided into five regions as melted region,adjustive region, bonding region, defective region and crystal region. It’s found that thegrowth rate of columnar crystals is mainly controlled by the growth speed of the interfacebetween defective region and bonding region, and also that between bonding region andadjustive region.The results show that, EPM (electric pulse modification) could change the solidificationstructure of pure aluminum periodically, and reduce solidification time significantly. Thetexture type and content will be increased to different degree with the reduction ofsupercooling. In general, the influence of EPM on casting texture will be enhanced when thetemperature field decreases. The columnar grain region will be narrowed and the isometricgrain would be enlarged correspondingly by EPM in mushy zone. After EPM with theparameter of300V-3Hz-10s, the distribution of grains is dispersed and the size is less than1mm. EPM in mushy zone can reduce the time of solidification obviously. In addition, it canalso restrain growth of columnar grain. Texture and distribution of crystal change periodicallywith the pulse voltage. Different texture types and volume fraction have no effect oncorrosion potential (Ecorr) of aluminum, but show a significant influence on corrosion currentdensity (Icorr). With the increase of grain size, the corrosion current density will be decreased.The sample after EPM with the parameter of500V-3Hz-10s has the best corrosion resistance,and it keeps almost the same corrosion potential Ecorr=-0.7015V with the original sample.However, the corrosion current density Icorr=0.8133×10-6A·cm-2is only half of the originalsample. This study is bound to facilitate the control of material structure and property fromthe metellagical source.