Papers by Keyword: Solidification

Abstract: This article aims to review the recent advances in the laser powder bed fusion process (L-PBF) of H13 tool steel for the dies used in the high pressure die casting (HPDC) applications. The effect of processing variables is briefly reviewed for the evolution of microstructure (phase transformations, as-built microstructure and carbides precipitation), mechanical properties, and defects. The second part of the review is focused on conformal cooling applications to HPDC dies, which is critical for die life and productivity. Achieving better microstructure without defects, understanding the role of processing variables in L-PBF and their interdependencies remains the key challenge for the as-built part, while the benefits of preheating and post-heat treatments are evident. Significant benefits are realized in the applications of die inserts favoring lower die surface temperature, reduced cycle time and lubrication, and thermo-mechanical stresses. In addition, L-PBF also plays a key role in die remanufacturing where significant benefits are achieved in terms of materials savings and improved performance compared to traditional repair technologies. Overall, L-PBF offers a transformative pathway for high-performance HPDC dies; however, most investigations are trial-based. Long-term studies are needed for performance assessment and establishing failure mechanisms in production environments.

Abstract: The effect of time-dependent interfacial heat transfer coefficient () within the shot sleeve and die cavity of high pressure die casting process (HPDC) has been simulated to systematically study the solidification occurring during filling. Two different-profiles have been considered with peak values of 7 kW/m²K and 12 kW/m²K for the shot sleeve, and 18 kW/m²K and 26 kW/m²K for the runner, gate, and die cavity based on the values reported in the literature. In addition, two types of gate designs were considered for plate type castings to analyze their solidification behaviour and filling velocity. Solidification typically occurs along the bottom wall of the shot sleeve, from the mid-region toward the mould-side region along the direction of pouring. At the end of filling, the solid fraction () inside the shot sleeve increases from 10 to 18% with increasing peak value for-profiles. Similarly, the solidification around the gate regions progresses rapidly above 0.4 and reduces the fluid velocity at the gate entry for profile with higher peak values. Despite the lack of consensus on the selection of value (peak value and range), this study highlights the influence profiles and gating design on solidification during filling and discusses its implications on the quality of HPDC parts.

Abstract: The impact of cooling rates on the microstructural evolution of an Al-Sr eutectic alloy was investigated. Two distinct cooling rates, 0.02 and 57.12 °C/s, were employed during the solidification process. To elucidate the characteristics of phase transformations and microstructural evolution during solidification, thermal analyses were conducted on the recorded cooling curves. Both the first and second derivatives of these curves were examined. At the slower cooling rate, the microstructure predominantly consisted of the eutectic Al phase and the eutectic Al-Sr phase, as identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Conversely, at the higher cooling rate of 57.12 °C/s, primary Al phases were observed, indicating a significant departure from equilibrium solidification conditions. Additionally, a substantial quantity of nanosized eutectic Al-Sr particles was detected, resulting in a markedly refined microstructure.

Abstract: Biodegradable magnesium alloy WE43 (Mg-4Y-3RE) has received great attention in orthopaedic applications as it can dissolve completely after bone tissue repair, eliminating the need for a second surgery to remove the WE43 implant. However, the rapid degradation of WE43 implants during bone healing remains a concern. Rapid degradation can deteriorate the mechanical strength and generate a significant amount of hydrogen gas via corrosion in physiological environments, negatively affecting bone healing and the surrounding tissues. To overcome the rapid degradation of medical implants, one commonly used method is surface modification via laser surface melting (LSM) to alter the surface microstructures and improve the corrosion resistance. This paper investigates the possibility of applying LSM technique to refine the surface microstructures of WE43 alloy and compares the microstructures induced by LSM with the extruded alloy without laser treatment. Results show significant grain refinement after LSM with average grain size decreased to 3μm as compared to 5μm before LSM, approximately 40% reduction in grain size. Different types of grain morphology are also identified at different locations in the melt pool due to different temperature gradients and cooling rates. It is observed that the depth of the melt pool increases with increasing laser power and decreasing laser scanning speed due to the higher heat input. It is also observed that grain size decreases with decreasing laser power and increasing laser scanning speed due to increased cooling rate. Results from this study show that LSM, a form of rapid solidification processing, can form a predominantly basal crystallographic texture, homogenise and refine the surface microstructures of WE43, which are beneficial for corrosion resistance.

Abstract: The effects of cooling rates on the microstructure development of an Al-Fe eutectic alloy were studied. Two different cooling rates of 0.03 and 61.00 °C/s were applied to the solidifying alloys. To unfold the characteristics of phase changes and the microstructure evolution taking place during solidification, the recorded cooling curves based on temperature measurements were analyzed by thermal analyses, in which the first and second differences of the cooling curves were derived. The slow cooling resulted in the formation of only the eutectic Al phase and the eutectic Al-Fe phase in the microstructure identified by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). With the cooling rate increasing to 61.00 °C/s, the primary Al phase appeared, as the solidification became strongly non-equilibrium. A large quantity of the nanosized eutectic Al-Fe particles were detected. Overall, the microstructure refined substantially.

Abstract: The solidification mechanism of ductile iron is a bit complex due to the precipitation of graphite and silicon. These elements change the solidification pattern of cast iron. Density of these elements is less than iron leads to occupying more volume consequently increase the overall metal volume. There are two aspects on this increase in metal volume. One is, reducing this volume increase to reduce the creation of porosities at the earlier stage of solidification and second is, using this volume increase to remove porosity at the later stage of solidification. Proper understanding of this graphite expansion in cast iron solidification will bring insights on reducing or removing of the risers. The current study focus on correlating the net contraction and austenitic liquidus point with shrinkage. The average contraction found through this study is 1.36 % which is more than the net expansion of 0.25 % (without riser) reported in literature.

Abstract: Soil contamination by heavy metals significantly damages the environment, human health, plants, and animals, which has become a burning issue recently. The presence of contaminated soils due to industrials and mining activities is a major concern in today’s heavily industrialized world. With the rapid development of society, more and more soils are polluted by heavy metals, which leads to a change in soil engineering properties. Several types of technology have long been in use to remedy the heavy metal-contaminated soil. Among them, solidification and stabilization have been widely adopted. In engineering practice, engineers usually use additives to solidify and stabilize (s/s) heavy metal-contaminated soils. Solidification and Stabilization is an economic and effective technology in the remediation of contaminated soil by heavy metals, as well as sludge and sediment. The main purpose of the study was to investigate the effect of (nanomaterial materials) on the remediation of contaminated soil by the (S/S) technique. The soil was polluted with (2000 mg/kg and 1000 mg/kg) of Lead and Cadmium respectively by using Lead and Cadmium nitrates. The Pb and Cd- impacted soil was remediation using rich silicon materials of (nano-silica ) as an alternative cementitious material, and replaced with contaminated soil at (3, 5, and 7%) respectively with (5% and 10%) Lime. Nanosilica was prepared from plant extracts. The binder performance was analyzed by using unconfined compressive strength ( UCS) on the solidified soil at three curing times which were 7, 14, and 28 days. TCLP was also applied to investigate the treatment degree of solidified soil for the specimens within 28 days. The result of (UCS) indicated development in strength with curing day for all binders and proved that all mix ratios exceed the minimum Criteria of landfill disposal which is 340 kPa (0.34 N/mm2). It also showed increases in strength with using nano-silica with a lime binder. The result of the leaching test for the stabilized soil after 28 days of curing, showed a reduction in lead and cadmium leaching rate for all binders, below the EPA lead leachability limit of 5 mg/l and cadmium 1 mg/l. The results showed that the sample SH2N5L10 after 28 days is the best percentage for decreasing the leaching rate of lead and cadmium, as it reached (1.4 mg /l and 0.012 mg/l) respectively with the highest compressive strength of 4852 Kpa.

Abstract: To understand the nano phase formation, cooling experiments of a hypereutectic Zn-Al alloy containing 6 wt% of Al are carried out under two different cooling rates of 0.04 and 10.00 °C/s. The applied cooling rates significantly influence the phase change behavior of the investigated alloy. The liquidus temperature (T_N) for the nucleation of the primary phase decreases from 390.3 to 382.9 °C, and the undercooling increases from 0.7 to 8.1 °C, as the cooling rate rises from 0.04 to 10 °C/s. The eutectic and eutectoid temperatures decrease from 381.5, 277.7 to 375.6 and 267.6 °C, respectively, when the cooling rate increases from 0.04 to 10.00 °C/s. The SEM and EDS analyses reveal that the solidified alloy contains the primary γ-ZnAl phase, the eutectic β-Zn phase, and the eutectoid α-Al and eutectoid β-Zn phases. The fast phase change and transformation caused by rapid cooling results in the formation of nano eutectoid phases and fine microstructure.

Abstract: The aim of this work was to evaluate the possibility to solidify radioactive expanded clay balls or radioactive sludge originating from the decommissioning of NPP V1 in Jaslovské Bohunice (Slovak Republic) into the geopolymer matrices. The radioactive wastes (RAW) in the proportion of 0 wt.%, 20 wt.%, 25 wt.%, and 30 wt.% were solidified using a geopolymer mixture GEOCEM (producer GEOFIX Ltd., Slovak Republic). The value of compressive strength linearly decreased with increasing addition of RAW from the value of 16.1 MPa to 12.4 MPa for radioactive expanded clay balls solidified and from the value of 16.1 MPa to 10.6 MPa in the case of radioactive sludge. Leaching test carried out according to ANSI/ANS 16.1.1986 showed that the calculated value of leachability index L_i at the highest proportion (30 wt.%) of radioactive expanded clay balls or radioactive sludge reached the value L_i = 10.3 or L_i = 9.7, respectively.

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.