Papers by Keyword: Semi-Solid Casting

Abstract: Resource-efficient manufacturing is a foundation for sustainable and circular manufacturing. Semi-solid processing typically reduces material loss and improves productivity but generally requires a better understanding and control of the solidification of the cast material. Thermal analysis is commonly used in high-pressure die casting (HPDC) processes to determine casting process parameters, such as liquidus and solidus temperatures. However, this method is inadequate for semi-solid casting processes because the eutectic temperature is also a crucial parameter for successful semi-solid casting. This study explores the feasibility of using machine learning and artificial neural networks to predict fundamental values in Al-Si alloy casting. The Thermo-Calc 2022 software Scheil-Gulliver calculation function was used to generate the training and the test datasets, which included features such as melting temperature, alpha aluminium solidification temperature, eutectic temperature, and the solid fraction amounts at eutectic temperature. The results show that both models have a symmetric mean absolute percentage error (SMAPE) of less than 2 % with temperature prediction, with the machine learning model achieving a better accuracy of less than 1 %. A case study comparing practical measurements with prediction results is also discussed, demonstrating the potential of AI methods for predicting semi-solid casting processes.

Abstract: High-pressure die-casting (HPDC) can be a productive process for high-quality cast aluminium alloy components. However, it is also a process prone to generate defects, such as gas porosities and incomplete fillings, resulting in rejections. One way to reduce the reject rate is to employ Semi-Solid Metal processing with HPDC. The most important advantages of Semi-Solid alloys are reduced shrinkage defects, fewer gas porosities, and fewer chances of filling-related problems. To take full advantage of a semi-solid metal slurry, the casting process must be controlled meticulously to reach homogeneous casting quality and high process repeatability. A study has been conducted on cast parts composed of two-dimensional symmetrical cavities. From the mechanical tests, unexpected differences emerged in both tensile strength and fracture elongation, which were confirmed by differences in the microstructure. The paper investigates the reasons for the asymmetry in the proprieties to avoid similar problems in future studies and maximize the effectiveness and repeatability of the high-pressure die-casting process.

Abstract: AZ80 alloy has been widely used to produce high performance Mg casting and wrought parts for high-end applications due to its high mechanical properties and deformation ability. However, at least two important issues still need to be solved in order to further improve its mechanical properties and deformation ability. Firstly, the grain size of α-Mg in AZ80 alloy is relatively large (more than 1000 µm) due to a lack of efficient grain refinement methodologies. Secondly, the size of the eutectic Mg₁₇Al₁₂ phase is also large and the distribution of the eutectic Mg₁₇Al₁₂ phase is continuous, which is very harmful for the mechanical properties, in particular to elongation. In this paper, these two important issues are investigated by adding Mg₃N₂ sub-micron particle into AZ80 alloy and thereby refining the α-Mg and the eutectic Mg₁₇Al₁₂ phase. Firstly, the Mg₃N₂ sub-micron particle was directly added into AZ80 alloy by using mechanically stirring in the semi-solid state, subsequently the melting temperature was increased above the liquidous temperature, and finally the melting was casted in the liquid state. It was found that the grain size of α-Mg can be refined from 883.8 µm to 169.9 µm. More importantly, the eutectic Mg₁₇Al₁₂ phase was also refined and the distribution became discontinuous. It should be noted that directly adding the Mg₃N₂ sub-micron particle into AZ80 alloy leads to a great loss of the Mg₃N₂ sub-micron particle due to the weak wetting behavior between the Mg₃N₂ sub-micron particle and Mg melt. The second methodology through mixing Mg₃N₂ sub-micron particles with AZ91 chips using a twin extruder was also used to prepare AZ91 master alloy with 3wt.% Mg₃N₂ sub-micron particle, which was subsequently added into AZ80 alloy in the liquid state. In this way, a significant grain refinement of α-Mg and a simultaneous refinement of the eutectic Mg₁₇Al₁₂ phase in AZ80 alloy was also achieved. The grain size of α-Mg can be refined from 883.8 µm to 325.9 µm. However, no significant grain refinement by using UST was observed. Instead, the grain size increases from 325.9 µm to 448.6 µm, indicating that the Mg₃N₂ sub-micron particle may lose its grain refinement potency due to possible aggregation and clustering. This paper provides an efficient and simple methodology for the grain refinement of α-Mg and the simultaneous refinement of the eutectic Mg₁₇Al₁₂ phase in AZ80 alloy.

Abstract: Treatment of the slurry is important during RheoMetal^TM casting. In this work, semi-solid slurries were prepared under different stirring intensities, using two types of stirrers: a naked rod (for regular stirring) and a rod with two blades (for intensified stir). Tensile tests were performed, investigating fracture surfaces, as well as metallographic samples. The results show that intensified stir produces castings with finer primary particles and a more homogeneous microstructure. On the other hand, more faceted Fe-rich phases are found along the α-Al grains boundary as well, due to the dissolution of Fe from the stirrers. Moreover, for intensified stir castings, the porosity found on the fracture surfaces are smaller, while more brittle eutectic phases and second (intermetallic) phases, especially Fe-rich phases, are observed. Consequently, the castings with intensified stir show worse ductility. Finally, a quantitative analysis was made regarding ductility, affected both by porosity and the presence of Fe-rich phases.

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: Recent advances in rheocasting have resulted in significant expansion in the types of products currently in full commercial production. The current paper gives an overview of components in production in Europe and in China produced using the RheoMetal^TM process, that has taken the lead in a strong drive towards new heavy-duty applications made from aluminium alloys. In China, the dominating applications are found in the telecom industry. The trend in Europe is more towards marine and automotive applications commonly in fatigue loaded applications. The reason for the choice of rheocasting for complicated shape thin-walled electronics components with requirements is dominated by process yield and by the ability to improve thermal conductivity. The heavy-duty truck chassis thick walled components target weight reduction through design and to sustain fatigue load normally requiring forged components. Common in all applications are seen in production yield, reduced tool wear and reduction of die soldering.

Abstract: In semi-solid casting, a slurry consisting of primary α-Al crystals and liquid is injected into the die cavity. The solidification in the die-cavity occurs by the growth of the primary α-Al crystals formed during slurry preparation and in the shot sleeve, nucleation and growth of in-cavity solidified crystals and ends with the eutectic reaction. During solidification in the die cavity, the cooling rate near the die wall is higher in comparison to the centre of the casting, particularly for thick-walled castings. The solidification conditions for the slurry α-Al crystals that are closer to the die wall can be very different compared to the slurry α-Al crystals located at the casting centre. This can result in different solute concentration in the interior of the α-Al globules in different regions of the semi-solid casting cross-section and consequently, different response to heat treatament. The RheoMetal™ process was used to produce thick-walled semi-solid castings. Semi-solid castings in the as-cast and T6 conditions were investigated. Indentation tests for hardness measurements in the nano-range were performed in the interior of α-Al globules near the surface and at the casting cross-section centre. The hardness variation across the casting cross-section was evaluated by low-force Vickers hardness. The castings in the as-cast condition showed more uniform properties in the cross-section compared to the T6 condition. Additionally, the results suggest that microsegregation in the interior of α-Al globules is very low in castings in the as-cast and T6 conditions.

Abstract: In the field of material production and application, strength and hardness are the two most common properties of metallic materials. It’s one familiar phenomenon that the hardness of one certain alloy has positive relationship with its strength in conventional dendritic alloys. When it comes to non-dendritic semi-solid alloys, it’s unclear that the relationship is still right or not. In this paper, the molecular mechanics, as well as finite element simulation and experimental verification were combined to study the internal deformation regularity of metallic material and the correlation between the two parameters was illustrated. Firstly, the displacement of solid atom in metallic crystal cell was well described in the view of energy cost. Secondly, the total strain amount under local indenting deformation (resistant boundary) and overall impressing deformation (free boundary) were compared to study the correlation between hardness and compression strength in semi-solid globule grain alloy. Finally, the data collected in semi-solid processed products was applied to be compared against traditional casting and wrought aluminum alloys.

Abstract: The paper introduces a new method to produce large sized Al-B₄C-Al₂O_3np composites, which combines ball milling to prepare Al₂O_3np/Al mixed powder and semi-solid casting to contribute the injection of Al₂O_3np/Al mixed powder into the melt. The deformation performance of Al₂O_3np and micro-Al through ball milling with different Al/Al₂O_3np ratios, different milling time and different balls were studied respectively. It was revealed that micro-Al particles were milled from twisted and crimpled foil pieces to shuttles with Al₂O_3np embedded on it through 4h milling with 10mm balls. And we consider it as the best bonding between Al₂O_3np and micro-Al we could attain. And a plate of 25kg of Al-B₄C-Al₂O_3np composite was fabricated successfully with the injection of the Al₂O_3np/Al mixed powder. Spherical Al₂O_3np of 300nm and needle-like TiB₂ with 200nm in radius and 800nm-4μm in length were found in SEM photographs. Tensile properties of Al-B₄C-Al₂O_3np composites were tested at room temperature and high temperature. It was showed higher mechanical properties than Al-B₄C composites at room temperature and elevated temperature. Particularly, a 40% increase of UTS of Al-15wt.% B₄C-1wt.%Al₂O_3np at 350°C was observed.

Abstract: Grain refining has been studied in the semi-solid-metal (SSM) casting by addition of master alloy Al-5Ti-1B using inclined slope. A356 aluminium alloy was melted at 850 °C and poured at 660 °C on the inclined slope into the steel mould. Grain refiner was added in various percentages of 0.2%, 0.5% and 1.0% in A356 aluminium alloy melt. Microstructure and microhardness were characterized using optical microscope and Vicker’s microhardness tester. The addition of master alloy Al-5Ti-1B not only refined but also increased the globularity of the primary α-Al particles. The higher hardness was achieved with 1% addition of master alloy Al-5Ti-1B.