Gas porosity

Gas porosity consists of nearly circular pores with smooth inner surfaces, evenly distributed over large cross-sections. It's different from rough-walled pores caused by void formation. This defect is common in metal alloys with wide solidification intervals, especially those with poor fluidity such as aluminium, magnesium and copper alloys and cast steel. To minimise porosity, the hydrogen and nitrogen contents must be minimised, and the carbon/oxygen reaction prevented by a sufficiently strong deoxidation practice. Cast iron parts, on the other hand, are more prone to gas blowing due to differences in metallurgy. 

Small voids of varying depth and size are typical of die castings, regardless of the material used. Porosity may not be visible and is often characterised by smooth walls and rounded shapes. 

Back