Papers by Keyword: High Pressure Die Casting

Abstract: The demand for structural lightweight in a variety of industries, particularly the automobile industry, has driven the development of heat-free die-cast aluminum alloys with excellent properties. Utilizing lightweight materials, such as Al-Si alloys has several benefits, including higher overall performance in automobiles and other industries, increased heat resistance efficiency, decreased emissions, and reduced weight. The purpose of this study is to modify the microstructure and enhance the mechanical properties of high-pressure die-casting (HPDC) AlSi10MnMg foundry alloy by incorporation of TiB₂ and Sc without any heat treatment. The results showed that the HPDC process significantly refines the grain structure and AlSiMnFe intermetallic compounds, transforming the eutectic morphology from sharp to rounded, and 93% enhancement in elongation at the optimum content (0.018 wt.%) of TiB₂. While the hardness of the alloy was improved by 15.7% with the addition of 0.03wt.% TiB₂. TiB₂ incorporation refines the grain structure and AlSiMnFe phases, while depressing externally solidified crystals (ESCs). The HPDC process refines Al₃Sc phases as well as AlSiMnFe phases while increasing yield strength due to Al₃Sc strengthening effects. After 0.5wt.% Sc addition in 0.018wt.% TiB₂-AlSi10MnMg alloy, the YS, and EL reached the maximum of 196MPa and 9.93% respectively.

Abstract: The Al-Si-Mg family is the preferred group of casting alloys due to their excellent castability, good mechanical properties and corrosion resistance. The ENAC-AlSi7Mg0.3 (A356) alloy has been used for decades to produce structural parts such as automotive wheels or suspension parts. However, this alloy cannot be used for high pressure die casting (HPDC) due to die soldering issues. Casting parameters in rheocasting differs greatly from those in HPDC. The lower injection temperature and lower intensification pressure reduce the reactivity between the mould and the aluminium. This lower interaction allows the injection of permanent mould alloys using HPDC. The objective of this work is to compare current structural alloys with rheocasting. A wide range of alloys in the Al-Si-Mg (-Mn) family were cast using the RheometalTM semi-solid technology in addition to ENAC-AlSi7Mg0.3 (A356) used as a comparison basis. Firstly, it was proven that ENAC-AlSi7Mg0.3 (A356) can successfully be cast using rheocast HPDC. Secondly, the impact of magnesium and manganese were studied. Magnesium has a great impact on strength while manganese can further improve the strength by controlling the iron phase morphology. This work proves that various types of alloys can be cast using rheocast HPDC.

Abstract: In the automotive industry, casting products produced by high pressure die casting are essential. Due to the higher mechanical demands on these castings, the technological requirements of the process are also increasing. Therefore, the control of the microstructure and the development of defects play a major role. High pressure die casting parts made of aluminium usually contain gas porosity due to gas compression during the filling process of the cavity and the intensification during solidification. The use of semi-solid casting thus opens new doors to fulfil promising future demands. In this study, the venting system was adapted to the Rheometal^TM process of aluminium and designed in the form of gaps, thus ensuring better venting. Subsequently, the results obtained were compared with casting process simulations to highlight possible differences.

Abstract: Two casting technologies were introduced to fabricate the Al-7Si-0.6Mg alloy, including high pressure die casting (HPDC) and semi-solid die casting (SSM). The microstructure and mechanical property were studied by optical microscopy (OM), scanning electron microscopy (SEM), X-Ray diffraction (XRD), microhardness and tensile test. The electrical conductivity was also introduced to evaluate the thermal conductivity of the alloys. Results show that the as-cast microstructure of the HPDC alloy and SSM alloy both consists of primary α-Al, eutectic Si and Mg₂Si phase. The primary α-Al phase in HPDC alloy possesses fine equiaxed dendrite structure with an average grain size of 29.4 μm. While the SSM alloy forms abundant coarse and globular structure α-Al phase, and the average grain size reaches 98.9 μm. This is because of the lower cooling rate during slurry preparation promotes the formation of a relative coarse microstructure in the SSM alloy. Furthermore, the increased content of eutectic Mg₂Si phase was also detected in the SSM alloy. Therefore, the average yield strength and ultimate tensile strength decreases from 148 MPa and 275 MPa of the HPDC alloy to 140 MPa and 254 MPa of the SSM alloy, respectively. However, the elongation and electrical conductivity of the SSM alloy both increases from 5.8±1.3% and 20.0±0.1 MS/m of the HPDC alloy to 7.5±1.2% and 20.6±0.1 MS/m, respectively.

Abstract: High Pressure Die Casting (HPDC) is a widely preferred process for the production of non-ferrous metals with low melting temperatures. It is particularly suitable for close-to-finish and high-volume production of relatively complex shaped parts. Aluminum-Silicon-Copper alloys, which are frequently preferred in this method, find themselves in many sectors ranging from automotive to aviation. With the developing technology, the usage of High Pressure Die Casting technology has increased significantly, produced part types and the number of parts produced on an annual basis has reached remarkable amounts with the shortening of cycle times. In this study, a supra-eutectic silicon valued Aluminum-Silicon-Copper alloy was produced by gas-induced semi-solid die casting method using a cold chamber high pressure die casting machine. The study observed that many casting problems, especially shrinkage gaps and gas porosity, were overcome, while the microstructure of the parts on which the gas induced semi-solid die casting method was applied was preserved. In addition, energy saving is achieved by lowering the temperature of the holding pot, and thermal fatigue cracks that will occur in the mold in the long-term depending on the temperature difference will be delayed and the mold life will increase.

Abstract: Porosity is one of the main defects that limits the performance of castings. Porosity in aluminum castings can originate from several sources, including the volumetric shrinkage occurring during solidification, the precipitation of dissolved hydrogen, and entrapment of gasses such as air, boiling water, vaporized lubricants, etc. Traditional methods of identifying and measuring porosity in castings include 2D x-rays, sectioning and polishing, and Archimedes density measurements, but none of these provide a satisfactory quantitative estimate of the size, total volume and distribution of the pores. X-ray CT scanning is a relatively new method that generates not only a 3-dimensional view of the size and distribution of the pores, but can also provide quantitative information of the volume, surface area, size, shape and position of each pore within a casting. Micro-CT scanning is a specialized sub-category of CT scanning, which provides excellent resolution of fine porosity (a resolution limit of 4 microns in one of the case-stores presented in this paper), but it should be noted that the resolution limit in CT scanning techniques is related to sample size. This paper describes results from micro-CT scanning studies of two high pressure die castings and a semi-solid casting, and provides quantitative data on the total porosity content, and the porosity distribution. The paper will also demonstrate the capabilities of the micro-CT scanning process to provide a quantitative comparison of the porosity content in these different types of aluminum castings.

Abstract: Sustainable development is increasing in importance with restrictions on emission and carbon footprint. Similarly, both energy and resources efficiency are required, and at the same time, cost-efficiency is required. The current paper is focusing on carbon footprint, energy usage and material use efficiency of semisolid metal casting. A detailed analysis is made on the RheoMetal process, which is benchmarked to conventional HPDC casting. The analysis includes the gating system and the importance of the use of primary or secondary material. It furthermore includes a discussion of process yield and benefits based on process capability.

Abstract: Semi-solid processing works on the principal of a solidification temperature interval of a substance. The substance is heated to a temperature within this interval so that there exists a related solid-liquid fraction ratio. The substance with this phase structure is then shaped by a forging or casting process. It has been stated before that it is impossible to semi-solid process and cast pure metals or eutectic alloys due to their thermodynamic temperature invariance, meaning that there is no temperature interval. It was demonstrated recently that it is possible to semi-solid casting high purity aluminium (Curle UA, Möller H, Wilkins JD. Scripta Materialia 64 (2011) 479-482) and the Al-Si binary eutectic (Curle UA, Möller H, Wilkins JD. Materials Letters 65 (2011) 1469-1472). The working principal is that there exists a time interval during thermal arrest during which solidification takes place with a solid-liquid fraction ratio until all the liquid is consumed upon cooling. The aim with this work is to demonstrate that pure magnesium can also be rheo-high pressure die cast (R-HPDC) with the system developed at the CSIR in South Africa. Magnesium is notoriously difficult to cast due to the thermal properties of magnesium. The metal was poured into a cup, processed for about 6 seconds after which it was HPDC into a plate. The microstructure of the casting consists of a structure that was solid and a structure that was liquid during thermal arrest at the time of casting.

Abstract: From the point of view of its design solution, the shape, the dimensions and the position of an gate have the biggest impact on the final quality of castings. The gate is where the stream of hot-melt flowing into the mould cavity is modulated, and where the speed of this stream changes, which eventually determines the loading mode of the mould cavity affecting the homogeneity of any casting, and thus its mechanical properties as well. The length of the gate for a specific type of casting is determined constantly according to the projection methodology for connecting the gate to the casting. The gate height is determined by its area to length ratio. In practice, several methods are used to determine the gate area. The presented paper deals with an assessment of particular methods of designing the gate area for a specific type of a lightweight casting on the basis of silumin produced, using die casting technology. Since the length of the gate is constant, based on particular methods for determining the area, the gate height is the variable parameter. The performed experiments focus on an assessment of permanent deformation of parts cast at certain gate heights, determined analytically according to particular calculation methods. Permanent deformation serves as an indicator of the most suitable method for the gate area calculation. At the same time, the paper specifies patterns required for the calculation of gate dimensional characteristics, since the available scientific literature only provides indicative values depending on the nature of any given casting or an alloy.

Abstract: The quality of thin wall castings produced by metal die-casting depends on the coherence and consistency of various aspects influencing the process of casting cycle. The qualitative properties of castings should already be considered in the design phase of construction of the gating system. The simulation software is an effective facility for the initial revealing of defects of the design phase. The assessment of casting cycle by the means of simulation predicts an incidence of defects of the casting core in the design phase and therefore reduces both the incidence of defects in the production and the costs while the production efficiency is increased. The article deals with the assessment of the design of the gating system for a particular casting type. The filling of mould cavity, casting solidification and time course of temperature changes occurring in the selected locations of gating system were defined as parameters indicating the assumptions of design accuracy. Simulation tests were carried out in the NovaFlow&Solid program. The tests resulted in a conclusion evaluating and describing the adequacy of structural design of the gating system.