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.

AlSi9Cu3(Fe) aluminum alloy fatigue test specimens were produced by high pressure die casting (HPDC) and vacuum‐assisted die casting (VPDC) techniques. Non‐destructive material tests (NDT) have been performed on cast specimens by computed tomography (CT). Uniaxial fatigue tests with two stress ratios of R = −1 and R = 0.1 have been performed in the high cycle fatigue (HCF) regime, and the CT results were reassigned after the fatigue test in order to identify the origin of the failure. The aim of this paper is to establish a relationship between the CT result and fatigue failure of die cast specimens. The location and the size of the casting defect determine the specimen fatigue life. It has also been found that the fatigue life is determined not only by the size of the defect but also by its location with respect to the position of the highly stressed area. The results can be used to judge the applicability of cast parts after non‐destructive testing.

AlSi 9 Cu 3 (Fe) aluminum alloy specimens were produced by conventional high-pressure die casting (HPDC) and vacuum-assisted high-pressure die casting (VPDC) processes under atmospheric and 3 different absolute pressures of 170 mbar, 90 mbar, and 70 mbar. The influence of absolute pressure in the die cavity on the porosity and mechanical properties of the die castings were investigated and compared with the traditional casting method. The life data analysis was applied to deal with the variation in mechanical properties of the die cast flat tensile specimens. The porosity of castings was assessed on the basis of X-ray observation and density measurements performed by Archimedes method. The fracture surfaces were examined by scanning electron microscopy (SEM), and the chemical composition was measured by energy dispersive X-ray analysis (EDX). The investigations proved that the volume of gas porosity and the pore sizes in the castings can be significantly reduced by using vacuum assistance during the die casting process. Based on the data presented in the study, the porosity reduced from 1.10% at an atmospheric level to 0.47% at 70 mbar, which corresponds to 57% reduction. The boundary condition of the present investigation is the porosity content higher than 0.40% and lower than 1.10%. As a result, the density and the mechanical properties, particularly the tensile strength (10%) and elongation (50%) were significantly improved. The specimens contained smaller pores under lower pressure. Meanwhile, the shape of pores is found to be also an important factor, affecting the mechanical properties. In general, higher vacuum degree contributes to the reduction the porosity, which would be the basis to improve the mechanical properties of die cast parts.

Highlights Fatigue life was affected by the measure of the casting defects and the characteristics of the casting defects. The Kitagawa–Takahashi approach is proved to be a correct indirect method to determine the threshold stress intensity value. The Murakami parameter was used to consider the differences of defect shape and defect size.

High pressure die casting (HPDC) is a widely used casting technology for product that is made of light metal such as aluminum alloy. During die casting process the molten metal is injected into a mold at high speed and solidify under high pressure. The amount of porosity in the cast part is an important question. Lots of technologies have been developed to minimize porosities, for example, vacuum-assisted high pressure die casting process (VPDC). In this paper, AlSi9Cu3(Fe) aluminum alloy castings were produced by conventional HPDC with atmospheric venting and VPDC process under three different absolute cavity air pressures of 170 mbar, 90 mbar and 70 mbar at the cavity. The influence of absolute cavity air pressure on the porosity and on the mechanical properties of the castings were investigated and compared with conventional HPDC casting method. The results of the present study proved that the amount of porosity and the pore sizes in the castings can be significantly reduced from 1.10% at an atmospheric level to 0.47% at 70 mbar. This corresponds to 57% reduction. As a result, the mechanical properties are improved significantly, particularly, the tensile strength from 271.6 MPa to 299.8 MPa, which corresponds to 10% increment and the elongation from 1.66% to 2.49%, which shows 50% increment. At lower absolute cavity air pressure the entrapped gases become the final gas porosities in the die castings and shows solidification shrinkage form inspected with scanning electron microscopy. In general, lower cavity air pressure contributes to reduce the pores, which improve the mechanical properties of die casting.