An Evaluation of Quality Parameters for High Pressure Die castings

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.