Papers by Keyword: Casting

Abstract: Solution treatments (T4) at 380 °C for 16 h and 500 °C for 8 h were performed for ZK60 magnesium alloys modified with addition of 0.5, 1.5 and 2.5 wt% of mischmetal (combination of rare-earth (RE) elements). The compression behaviour was investigated at room temperature and at 300 °C correlated with the microstructure and differential scanning calorimetry (DSC) data. The as-cast microstructure is formed by a-Mg matrix with globular grains reinforced by a semi continuous network of Mg-Zn, Mg-Zn-RE and Mg-RE intermetallic particles. Solution-treated alloys show lower yield strengths due to partial dissolution of precipitates. Work hardening was not observed for the alloys compressed at 300°C with the compression speed of 10^-3 s^-1, whereas it was observed for the compression speed of 10^-2 s^-1 for the all as-cast, ZK60-1.5RE-T4 at 380 °C and ZK60-1.5RE-T4 at 380 °C.

Abstract: The Mg-Zn-Y alloy with long-period stacking ordered (LPSO) phase is known as attractive for automotive lightening engine components with strength at elevated temperature. On the other hand, it is considered that the thermal conductivity of magnesium alloys is lower than that of commercial aluminum alloys. Low thermal conductivity causes engine performance degradation. However, there is little study on the thermal conductivity of Mg-Zn-Y casting alloys. It is important study when we consider the application of high-temperature parts for engine components. Then we developed the Mg-Zn-Y casting alloys with strength at elevated temperature and good thermal conductivity. Our developed alloys have the fine LPSO phase with a net-like structure for higher strength and the pure magnesium matrix for better thermal conductivity. It is important that there is little or no solute element in the magnesium matrix for thermal conductivity. We accomplished these two good characteristics at the same time by optimizing the amount of zinc and yttrium contained in the Mg-Zn-Y casting alloys. Mg₉₆Zn₂Y₂ die-casting alloy had a good thermal conductivity of over 100 Wm^-1K^-1 at 473 K. This was almost identical to the thermal conductivity of heat-resistant aluminum casting alloys for conventional engine components.

Abstract: AA4045/AA3003 cladding billets with different clad ratios were fabricated by direct chill casting process. The macrostructures, microstructures, compositions distribution and the mechanical properties near the bonding interface were investigated in detail. The results show that the cladding billet with few defects could be obtained by semi-continuous casting process. The metallurgical bonding was formed due to the diffusions of elements. The decreasing of clad ratio changed the microstructure at the interface and reduced the thickness of diffusion layer. The hardness around the interface is higher than that of AA3003 side but lower than that of the other side, indicating that the interface yield strength is also higher than that of AA3003. After extrusion process, the characteristics of the interface remain that of as-cast cladding billet.

Abstract: The design of concrete structures exposed to environmental attack requires serious attention for concrete durability. Early age cracking due to autogenous deformations should be avoided.In this work the study of the structural effects of hydration heat and rheological behaviour of a massive concrete casting is presented. The object of the study is a skyscraper foundation slab. Aim of the work is the numerical simulation of what occurs to the structure during the hardening, in order to avoid unforeseen autogenous cracking and therefore the choice of a tailor-made concrete mixture able to fulfil the performance criteria.Non-linear finite element coupled thermal and mechanical analyses have been performed taking into account: hydration heat generation and dispersion, dimension and sequence of the casting, evolution of concrete mechanical properties in time during the hardening reaction, creep and differential shrinkage.

Abstract: The paper considers the issue of shrinkage stresses of elastic-plastic deformation in the casting ‘Slag bowl’ resulting in a discontinuity and hot crack formation. The stress-strain state of the wall of the as-cast billet during the process of power interaction between the casting and the mould has been analysed according to the existing algorithms. Quantitative indicators of the components of the total stress state in the wall of the casting at the time of hot crack formation were determined. It was found that the bending stress greatly affects the defect, comprising 96 % of the tensile strength of the casting material at the time of destruction. The techniques aimed at reducing hot crack formation in a body of as-cast billet based on the results from the calculations are recommended. In accordance with the proposed recommendations, the changes in the technological parameters in production of a batch of pilot castings showed a decrease in the defect on hot cracks by 73 %.

Abstract: During the process of the aluminum ingot manufacturing obtaining of a fine-grained structure has a huge significance for effectiveness of the further rolling process. The reduction of the grain size leads to an increased plasticity and higher grades of deformability. Today the multiple methods of improving the casting process are being developed varying from mechanical to physical or chemical methods, and their choice depends on different factors. However, the effect on the size of grains of the multi-factor impact was not described in literature. This paper investigates methods of casting including piston pressing with simultaneous exposure to the weak pulsed currents from electromagnetic field during crystallization of melted metal for the first time. The fine-grained uniform over the cross-section structure was achieved in the AD0 alloy ingots.

Abstract: This paper presents a critical analysis of molding technology a steel castings (340-550W steel grade), of the Toothed framework type. This casting is used to manufacture an reducer on 125kW (is a subset of the reducer). In the industrial practice, for the casting by Toothed framework type, cast of steel is used a molding mixture based on chromite-sand, with clayed binders. This type of material is used in the conditions where the quartz sand is not appropriate. However, the critical analysis of the molding-casting technology of the piece analyzed reveals the emergence of the defect called Chromite type crust or Elephant skin. The paper present some solutions to prevent the formation of this type of defect, so that the percentaje of waste casting registered decreased from 4,5% to 3%, which lead to the important economies of the company.

Abstract: The cooling curve and its derivatives display patterns that can be used to predict the characteristics of a cast iron. The effects of melting, superheating and holding in an acid lined coreless induction furnace were explored, as they affect the role of preconditioning and / or inoculation to restore solidification with low eutectic undercooling. Increased chill (iron carbides amount) in the experimental irons correlates well with certain thermal analysis parameters, such as the degree of eutectic undercooling. Preconditioning of the molten base iron before tapping led to improved solidification parameters in both untreated and inoculated irons as measured by the most significant thermal analysis cooling curve events. A double treatment incorporating preconditioning with inoculation improved the thermal analysis parameters, and consequently, the quality of the cast iron. If standard Ca-FeSi alloys do not have sufficient inoculation potential, the addition of the inoculant enhancing alloy (S, O and oxy-sulphides forming elements) will greatly enhance inoculation, well illustrated by changes to the thermal analysis parameters. A newly defined Inoculation Specific Factor [inoculation effect / inoculant consumption which led to that beneficial effect ratio] of different alloys is illustrated by thermal analysis, with good correlation with microstructural characteristics.

Abstract: A new approach for the analysis of high pressure die casting geometries concerning form filling is introduced. It enables the reduction of simulation cycles needed in the product development process, as they are highly time and cost intensive. Therefore, we developed an analysis tool, which uses shortest paths from each part of the geometry to the chosen ingate surfaces. This way, and by evaluating the information given by basic filling simulations, we can evaluate the usability of a given geometry for a high pressure die casting process and are able to suggest useful strategies to place ingates and to design a filling system.

Abstract: The problem presented in the paper concerns physical properties of porous multi-component mould material, into which a liquid metal is poured. The aim of the study was to determine the distribution of moisture in an intensively heated porous sand mould. In the past, several measuring methods have been developed, consisting in water evaporation out of a test sample (at a given time moment , the selected position coordinates of a sample), to determine the accumulated amount of water in the sample, which is a percentage of moisture content. The study described in the paper includes experiments of heating a green sand sample. Moisture distribution in a moisture transfer zone of the sample (temperature of the molding sand is approx. 100°C) was determined. In order to determine the moisture distribution, an original method was used. This method allows interfere in various layers of material of predetermined thickness, parallel to the surface of the mould in contact with a heat source. The classical measurement method (gravimetric method) was used for determining the moisture content of each layer.