Solidification time effects on surface and subsurface aluminum casting defects

The effects of aluminum casting solidification time on the intensity and distribution of surface and subsurface defects were reported nine samples of Al castings were used with different solidification time ranged from 5 to 30 minutes. Two nondestructive testing were used to study surface and subsurface defects, the penetrant testing and the ultrasonic testing. It was found that as the solidification time was
increasing for the Al casting samples, the surface defects were not significantly decreased in number but they were getting smaller in size. Longer solidification time means the sample external surfaces got solidified before the sample was removed from the casting mould. While taking the sample out of the mould before getting completely solidified
results in rapid shrinkage of surfaces and defects formed. On the other hand as the solidification time was increasing as the subsurface defects were getting less in number and they become closer to the surface of the sample. Longer solidification time gaves the sample the chance to build its microstructure with less voids and defects, and longer solidification time permits for the internal gases to escape and not forming internal voids.