Influence of Vacuum Support on the Fatigue Life of AlSi9Cu3(Fe) Aluminum Alloy Die Castings

Abstract

High-pressure die casting (HPDC) is a near-net-shape process that produces high quality castings with narrow dimensional tolerances. The HPDC castings are being increasingly used due to good flexibility and high productivity, especially for the automotive industry. Depending on the location of the cast components, there are ever more complex geometries and increasing strength requirements that can be achieved by the application of vacuum-assisted die casting (VPDC). The most specific features of the HPDC process are the rapid mold filling, high cooling rate and intensification pressure. As a consequence of these highlighted features, the process generally leads to the formation of casting defects, such as gas porosity, shrinkage, and entrapped oxide films. However, the VPDC casting process is capable to significantly reduce the amount of these casting defects. The aim of this work is to compare the HPDC and VPDC castings’ high-cycle fatigue behavior and to describe how the casting defects affect the fatigue failure. Before the fatigue tests, the samples were investigated with non-destructive (NDT) materials testing methods such as hydrostatic weighing, x-ray, and computer tomography (CT) to characterize the gas pore and shrinkage pore populations of the material. The AlSi9Cu3(Fe) aluminum alloy castings have been subjected to constant amplitude load by uniaxial fatigue tests in the high-cycle fatigue region with a stress asymmetry ratios of R = −1 and R = 0.1. The resulting fracture surfaces are analyzed through light optical microscopy (LOM) and scanning electron microscopy (SEM). VPDC increased the number of cycles to fracture and decreased the scatter at the given load levels compared to conventional HPDC casting. Moreover, VPDC significantly decreased the porosity size and volume, and the occurrence of oxide flakes is also decreased, resulting in the improvement in the number of cycle to failure.