The paper concerns the problem of discontinuity in high pressure die castings (HPDC). The compactness of their structure is not perfect, as

it is sometimes believed. The discontinuities present in these castings are the porosity as follow: shrinkage and gas (hydrogen and gas-air

occlusions) origin. The mixed gas and shrinkage nature of porosity makes it difficult to identify and indicate the dominant source. The

selected parameters of metallurgical quality of AlSi9Cu3 alloy before and after refining and the gravity castings samples (as DI - density

index method), were tested and evaluated. This alloy was served to cast the test casting by HPDC method. The penetrating testing (PT) and

metallographic study of both kinds of castings were realized. The application of the NF&S simulation system allowed virtually to indicate

the porosity zones at risk of a particular type in gravity and high-pressure-die-castings. The comparing of these results with the experiment

allowed to conclude about NF&S models validation. The validity of hypotheses concerning the mechanisms of formation and development

of porosity in HPDC casting were also analyzed.