Evaluation of detrimental effect on the ductility caused by the inhomogeneous skin and casting defects in a high pressure die cast recycled secondary alloy

The usage of recycled alloys in the high pressure die casting (HPDC) applications for automobiles is gaining rapid interest. Even though the skin microstructure, which is typically induced on the casting surface during the HPDC process, is believed to improve the properties of the HPDC castings, it may not always form continuously throughout on the casting surface, and thereby can influence the mechanical properties. Thus, the current study evaluated and compared the effects of inhomogeneously formed surface skin with that of other defects on the ductility exhibited by the HPDC castings of a recycled secondary AlSi10MnMg(Fe) alloy. The formation of inhomogeneous skin in the current study was attributed to a phenomenon related to the "waves and lakes" type of defects created by the HPDC process. Such skin structure limited the ductility of the HPDC castings, irrespective of the tested strain rates in the current case, by undergoing abrupt fracture due to its poor bonding with the adjoining matrix resulting from the aforementioned inhomogeneity. Even if the investigated AlSi10MnMg (Fe) alloy contained an abundance of porosity, cold flakes and intermetallics, which are usually considered the driving factors behind the fracture of HPDC processed alloys, the effect from the inhomogeneous skin layer dominated all other factors in the current case. The order of detrimental effect on the ductility of HPDC processed AlSi10MnMg(Fe) alloy followed a sequence of inhomogeneous skin, cold flakes and pores, with the inhomogeneity in skin turning out to be the most harmful one.