The thickness of defect bands in high-pressure die castings

Defect bands following the casting contour are often observed in high-pressure die cast (HPDC) components. In this article, suitable methods for measuring the thickness (w) and grain size in the bands (d(sb)) in HPDCs have been developed. The w/d(sb) relationship of defect bands has been investigated in HPDC specimens from a range of alloys, casting geometries and band locations within castings. Samples include aluminum alloy, AlSi4MgMn and AlMg5Si2Mn, tensile test bars cast by cold-chamber (cc) HPDC and a magnesium alloy, AM50, hot-chamber (hc) HPDC steering-wheel component. The band thicknesses were measured to be in the range 7-18 mean grains wide. This is substantial evidence that defect bands form due to strain localization in partially solidified alloys during cc and hc HPDC. Additionally, within this range, the w/d(sb) ratio decreases with increasing distance from the casting center in a cross-section containing multiple bands. (C) 2009 Elsevier Inc. All rights reserved.