Papers by Keyword: Casting Defect

Abstract: This study investigates the relationship between core gas pressure, solid phase fraction in the sand core, and gas porosity formation in casting processes. The experiments were conducted using EN AC-45500 aluminium alloy, varying casting temperatures and casting diameters. The maximum core gas pressure was measured and correlated closely with the solid phase fraction at the sand core-metal interface. Notably, the study reveals that gas breakthroughs can occur even at core gas pressures lower than the metallostatic pressure. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to analyse the blow-holes imprints and their chemical composition, confirming that the observed porosity originates from core gas. The results underline the importance of the solid phase fraction in controlling gas porosity formation and provide new insights into the mechanisms of blow-holes formation in aluminium alloy casting.

Abstract: Direct chill (DC) casting has been considered as one of the promising casting methods that can be used to produce aluminum alloys billet. The process is conducted by pouring aluminum metal into a water-cooled mold. The billet shell begins to form when molten aluminum contact directly with the mold (this is also known as primary cooling). Afterward, the starting block is pulled downwards at a specified casting speed to achieve desired aluminum billet. The start-up phase during the DC casting process is considered a crucial step since it may determine the formation of defects in the casting products. This research aims to investigate the casting defects on the aluminum alloy that were formed during the start-up process of DC casting. The results show that the billet failed to form following the downward movement of starting block. Meanwhile, the billet tended to stick to the mold wall due to several factors, such as too low a pouring temperature, a less-round mold shape, the poor quality of the hot top and graphite ring, and the water that entered the mold during the casting process. It also noted several markers of the casting defects that occurred during the DC casting process such as liquation or bleeding, cold folding, billet stuck in the mold, butt structure, and rough billet surface.

Abstract: The purpose of this paper is to present the influence of the casting parameters in the process of producing aluminium alloy components of gearbox housing type in automotive industry. The project has as objectives the minimization of the most common casting defects met in casting of gearbox housings through adjusting the parameters of the process. In order to minimize these defects, it was studied the casting speeds in phases I and II, multiplication pressure of phase III and the mould temperature that is influenced by both the cooling channels inside the mould and the spraying process of the mould (lubrication/cooling) that helps regulate the optimum temperature. The experimental results showed that the casting defects such as pores, cast in stages, shrinkage cavities, gas holes and tightness are significantly reduced by periodically controlling and correcting the specific casting parameters.

Abstract: We have developed new type semi-solid injection process for magnesium alloy. This process does not require to use any cover gases and the special magnesium billet such as thixo-billet. In this study, plate specimens were produced by injecting the semi-solid billet with different fraction solid. The microstructure observation, detection of casting defects by an X-ray computed tomography scanner, and tensile test were carried out. With increasing fraction solid, the size and shape of α-Mg solid particles became smaller and more spherical. In the condition of low fraction solid or forming in liquid state, the casting defects were located in the center of the specimen at the thickness direction. Additionally, the volume fraction of the casting defect decreased with increasing fraction solid. Moreover, the casting defects can be reduced by preventing solidifying and clogging of the top of the nozzle. Then, the specimen which has few casting defects could be obtained by injecting the slurry of fraction solid 0.5. However, the tensile strength and yield strength were highest in fraction solid 0.4. It is contemplated that the composition of the solid solution component element in the matrix was increased in fraction solid of 50%, therefore the matrix became brittle.

Abstract: Technology and defect in the low-pressure semi-solid die casting of aluminum wheel hub under different process has been studied. The simulation software ADSTEFAN 2012 is used to analyze the solidification in different die temperature. Stereomicroscope, digital camera and optical microscope (OM) are used to study defect in the casting. The result shows that the low slurry temperature (606°C) will result in higher viscosity, and the low preheated die temperature will increase the cooling rate so that shrinkage is formed in the isolate solidification area. In the technology of casting wheels, the optimum temperature of the slurry is 614°C, preheated temperature of die is 400°C.

Abstract: Fatigue life of a cast Ni-base superalloy IN 713LC under combined cycle loading consisting of a superposition of low- and high-cycle fatigue at 800 °C was experimentally determined. No measurable effect of combined cycle was found for studied loading conditions. High scatter of fatigue life related to the initiation of cracks on casting defects was observed. Size of the largest defect in a specimen was predicted by the largest extreme value distribution method. The predicted size was compared with fractographic observation of defects resulting in final fatigue failure.

Abstract: The fatigue strength of cast Al-Si alloys is strongly sensitive to the presence of casting defects. Extensive rotating bending fatigue testing of cast AlSi7Mg alloy at room temperature and 50 Hz is reported showing that shrinkage pores are the critical casting defect. The porosity of selected fatigue specimens extracted from castings is characterized with metallography using different pore sizing criteria. Data are fitted to EVS distributions and used for critical size prediction. Fatigue fracture surfaces are inspected in the SEM and the critical pores originating the fatigue cracks identified and measured according to criteria used in the metallographic inspection.

Abstract: . In this study, fatigue tests were carried out using a diecast Mg alloy AZ91 to study the distribution of fatigue lives under constant stress amplitudes. During the fatigue process of the diecast Mg alloy, cracks initiated from the casting defect within inside of the specimen, and then propagated prior to final failure of the specimen. Distributions of fatigue lives at the constant stress amplitudes can be represented by the Weibull distributions. The scatter in the distribution of fatigue lives becomes larger at the lower stress amplitude of 80 MPa as compared with those at the higher stress amplitudes. There is a common relationship regardless of the stress amplitudes between the initial maximum stress intensity factors Kimax and fatigue lives Nf. The lower Kimax, the longer Nf becomes. Integrating the fatigue crack propagation law from the initial maximum stress intensity factor Kimax to the fatigue fracture toughness Kfc, the relation Kimax vs. Nf can be successfully evaluated.