Influence of injection parameters on the final surface quality of Al-Si-Cu die cast components

In foundry practice the occurrence of solidificationdefects limits the production and the performance of castcomponents. In high-pressure die casting (HPDC) themost common defects are shrinkage or gas porositiesand bifilms.Thin sections, typical of HPDC components, are the mostsusceptible to casting defects, and these microstructuralimperfections can be detrimental to both the mechanicaland aesthetic properties. Even though laminations arenot as harmful as internal defects, die cast componentswith this kind of superficial defects are always rejected bycustomers, thus requiring further machining operations.The aim of this study is to analyse the lamination defectsthat occur on the surface of some Al-Si-Cu cast coversproduced by means of HPDC. In order to evaluate theinfluence of the different injection parameters on the finalquality of the die casting products, melt temperature,plunger speed and upset pressure have been variedwithin a range of suitable values. The obtained castingshave been studied by performing visual inspections andmetallographic analyses by means of optical microscopy(OM), revealing the presence of many bifilms spread overthe entire cross section of some cast parts.The presence of laminations, bifilms and cold shuts hasbeen correlated to the considered processing conditions,proposing a new criterion parameter for the quantificationof surface quality, called Lamination Ratio (LR)