Effect of the sampling method on the results of melt quality assessment of aluminum alloys with computed tomography

Liquid metal quality is one of the key factors which determine the soundness of cast parts. This is the reason why the assessment of the melt quality is of critical importance prior to casting. The most common and most deleterious defects of liquid aluminum alloys are the so-called bifilms whose quantity can be characterized by the computed tomographic porosity analysis of reduced pressure test pieces. During the sampling of these specimens, however, generally pouring is involved, which is known to damage melt quality and introduce bifilms into the liquid metal. For this reason, a new sampling method was tested and compared with conventional pouring. It was found, that by using the new sampling method, the pore volume fraction of the test pieces can be lowered, however, regarding the pore number density, no clear difference could be observed. The results also suggest that fluxes have a remarkable effect on the structure of double oxide films, and in this way, on the susceptibility to pore formation.