Prediction method of crack sensitivity during DC casting of Al–Mn and Al–Mg series aluminum alloys

Since it has been difficult to predict a crack sensitivity depending on alloy composition during aluminum DC casting, a new prediction method based on a relation between calculated solid fraction and temperature was developed concerning Al–Mn and Al–Mg series aluminum alloys. In order to understand that the surface crack is located at ingot surface, two cracking modes were considered. They were due to “difference in strain between water chilling surface and mushy surface (crack mode Z)” and “difference in strain rate between surface and just inner surface (crack mode Y)”. It's common knowledge that the material is cracked at high solid fraction region since melt cannot go into a crack gap and ductility is very low. Therefore we assumed the high solid fraction region was from 0.75 to 0.95 (Region II) and set up two indexes which are calculated from temperature difference (ΔTII) and difference in a temperature drop per unit solid fraction (ΔRII/ΔTII) within the Region II. By using the both indexes, which were called “Brittle temperature range” and “Parameter of the strain rate difference” respectively, the crack sensitivities through DC casting experiments were suitably represented.