An Evaluation of Quality Parameters for High Pressure Die Castings

Abstract

Several techniques for examining casting “quality” as it relates to high pressure diecast alloy A380 have been evaluated in the as-cast condition. The roles of three simple parameters were considered: a) metal velocity at the gate, b) the effect of increased Cu or Zn content, and c) the effect of rotary degassing on a recycled melt. It was shown that tensile failure in high pressure die casting (HPDC) specimens is influenced by complex defect clusters and the interaction of a variety of casting defects. The two major defect cluster types identified in the current work were comprised of a dispersed foam-like shrinkage defect, and/or large oxide films present on the fracture surfaces. The removal of hydrogen had little effect on average tensile properties which was a surprising result, but rotary degassing did appear to remove a portion of the oxides present in the melt, thereby improving casting quality. It is shown that of the different analyses conducted, all could differentiate a degree of casting quality, but some techniques (i.e., Weibull statistics combined with flow curve derivations based on the Ludwik-Holloman equation) are particularly useful. It is proposed that complex strain localization and failure occurs in HPDC specimens, which results in a proportionately large fraction of defects appearing on the fracture surface.