Conventional Chill Research Articles

Effect of Rapid Quenching on the Solidification Microstructure, Tensile Properties and Fracture of Secondary Hypereutectic Al-18%Si-2%Cu Alloy

In this work, the effect of rapid quenching from the partially liquid and solid condition is studied on the as-cast microstructure, tensile properties and fracture features of a secondary hypereutectic Al-18%Si-2%Cu alloy. For comparison purposes, the same ingots of 50 mm in diameter and 300 mm in height were also fabricated using conventional chill casting. The microstructure of the samples was subjected to detailed characterisation using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses. The tensile properties and fracture were also evaluated. A significant grain refinement of the eutectic constituents (α (Al) + Si), as well as primary silicon and intermetallics accompanying coarse plate and Chinese script with a well-dispersed morphology transition for the intermetallics, was observed in the alloy subjected to the rapid quenching. The connection between primary and eutectic silicon was shown metallographically, confirming the fact that primary silicon served as a nuclei site for eutectic silicon. The microstructure refinement, together with a favourable morphology transition, resulted in greatly enhanced tensile properties and the more ductile fracture behaviour of the studied alloy.

The Effect of Rapid Chilling of Pork Carcasses during the Early Postmortem Period on Fresh Pork Quality

The objective was to investigate the effects of blast chilling on pork quality in cuts from the Longissimus thoracic et lumborum (LM), Psoas major (PM), Semimembranosus (SM; both superficial [SMS] and deep [SMD] portions) and the Triceps brachii (TB). Forty carcasses (10 carcasses per replication) were split and sides were assigned to either blast chill (BC, –32°C for 90 min, followed by spray chill at 2°C for 22.5 h) or conventional chill (CC, spray chilled at 2°C for 24 h) regimens. The LM from BC sides had lower (P < 0.05) temperature at 2 h postmortem (CC 21.8°C, BC 9.7°C), 4 h (CC 13.3°C, 3.8°C BC), 22 h (CC 4.2°C, BC 1.4°C), and 30 h (CC 0.4°C, BC –0.2°C). The LM pH in BC sides was higher at 4 h (CC 6.09, BC 6.34), 22 h (CC 5.81, BC 5.89), and 30 h (CC 5.68, BC 5.74) postmortem. The BC resulted in higher (P < 0.05) 30 h postmortem pH in the SM compared to the CC regime (CC 5.68, BC 5.74). The BC sides had increased (P < 0.05) purge in the PM (CC 0.48%, BC 0.74%) and increased (P < 0.05) cook loss in chops from the LM (CC 22.37%, BC 24.24%). The PM from BC sides were more juicy (CC 7.50, BC 8.30), less chewy (CC 2.80, BC 2.10), and more tender (CC 7.90, BC 8.60). Chops from the LM of BC sides had greater Warner-Bratzler shear force (CC 2.00, BC 2.30). Color was affected in the SM with BC sides showing darker color score (CC 3.00, BC 3.20) and redder Hunter a value (CC 16.35, BC 16.02). Chilling treatment did not affect sarcomere length in the LM. Treatment did not affect postmortem proteolysis in any cut. The response to chilling regimen is different across different muscles which may be caused by location, rate of chilling, and fiber type.

Corrosion behaviour of magnesium AZ31 sheet produced by twin roll casting

In this study, corrosion behaviour of magnesium AZ31 alloy sheets produced by different casting methods was investigated. Magnesium AZ31 sheets of 2 mm in thickness produced by conventional direct chill casting+rolling and AZ31 sheets of 2 mm in thickness and 1500 mm in width produced by twin roll strip casting+rolling were used as samples. For the determination of processing method dependent corrosion behaviour, potentiodynamic electrochemical corrosion and also immersion tests were performed in 0.5M Na2SO4 and 0.01M NaCl solutions. Corrosion damage occurred during the tests was extensively investigated by scanning electron microscopy. Results of the work revealed the clear role of processing method dependent size and distribution of intermetallics on the corrosion behaviour of AZ31 sheets.

Effect of Combined Electromagnetic Fields on the Structure of a HDC Casting 2024 Al Alloy Ingot

2024 Al alloy ingot with diameter of 100 mm is produced by conventional and combined electromagnetic fields (CEMF) horizontal direction chill (HDC) casting processes. The effect of CEMF on the ingot structure is investigated. The results show that the CEMF is effective in changing the inner structure of the 2024 HDC cast ingot. In the conventional HDC ingot, feathery grains mainly distribute over the majority of the area of the ingot, and coarse equiaxed grains mixed with coarse floating grains distribute in a crescent-shaped area near the bottom surface. With the application of the CEMF, the majority of the feathery grains transform to fine equiaxed grains, and the mixture of feathery and fine grains only exist in the area near the upper surface. In addition, the coarse floating grains completely disappeared in the ingot with the application of CEMF.

Effect of DC Casting Processes on Microstructure of AlCu4.5Mn0.8 Alloy

The semi-solid billets of AlCu4.5Mn0.8 alloy were cast respectively by low frequency electromagnetic, low-superheated, and conventional direct chill casting. The effect of casting processes on microstructures was investigated. The results show that due to the effect of the low frequency electromagnetic field, the coarse dentritic microstructure is gradually broken up and turned into the homogeneous, fine rosette-shaped non-dentritic microstructures with the increase of electromagnetic frequency from 10 Hz to 30 Hz. When electromagnetic frequency is 30 Hz, the homogeneous, fine non-dentritic microstructure what is suitable for semi-solid reheating and thixo-forming could be obtained successfully.

Examination of the Microstructure and Properties of Low-Frequency Electromagnetic Casting 6060 Aluminum Alloy Billets and Bars

Abstract This study investigated the advantages of using low-frequency electromagnetic casting (LFEC) process compared to conventional direct chill DC casting of aluminum alloy and considered possible energy savings. The obtained results have indicated that casting in low-frequency electromagnetic field offers a series of advantages regarding the quality of aluminum billet, such as smooth billet surface, uniform grain size on the cross section, finer macrostructure and balanced distribution of intermetallic phases in the alloy. This guarantees their good properties in further processing, i.e. pressing, drawing, anodizing, plasticization etc. If the material is properly prepared for melting and for the technological process of casting and if primary aluminum is used as the basic raw material, the 6xxx-series billets can be extruded with no or minor prior thermal homogenization. This is a significant argument for using low-frequency electromagnetic casting (LFEC) process, which allows for significant savings in energy and labor and simplifies the manufacturing process as well.

Preparing Large Sized Billet of High Strength Aluminum Alloy with the Application of Low Frequency Electromagnetic Field

Grain refinement is quite important for producing 7050 alloy billet especially in large scale. Low frequency electromagnetic casting (LFEC) process was used to make 7050 aluminum alloy Φ500 mm billets and study the effect of electromagnetic field on the microstructure. The sound Φ500 mm billets of 7050 alloys without any grain refiner can be successfully prepared by the LFEC process. The results show that low frequency electromagnetic field has a significant grain refining effect on 7050 alloy and can effectively eliminate feather grain structure. The microstructures of LFEC ingot from the border to the center of the cross section are all equiaxed grains and are finer and more uniform than that of conventional direct chill (DC) cast billets. The LFEC process also shows a strong power to eliminate hot tearing during casting large sized billet of high strength aluminium alloy.

Effect of Physical Fields on Solidification Structures of DC Casting AZ80 Magnesium Alloy Billets

AZ80 magnesium alloy was semi-continuously cast under different physical fields which were conventional direct chill (DC) casting, low frequency electromagnetic casting (LFEC), ultrasonic casting (USC) and electromagnetic-ultrasonic combined casting (ECUC), respectively. The effect of different physical fields on solidification structures of AZ80 alloys was investigated. The results show that compared with the conventional DC casting, structures of AZ80 alloys billets cast with LFEC and USC have been greatly refined. The effective refinement takes place in the edge of billets when LFEC is applied. However, the effective refinement takes place in the center of billets when USC is applied. When combination of low frequency electromagnetic and ultrasonic fields is applied during semi-continuous casting AZ80 magnesium alloy billet, structures of AZ80 alloys are refined significantly in the whole billets everywhere and more uniform.

Effects of the Low Frequency Electromagnetic Field on the Centerline Macrosegregation of 7075 Aluminum Ingots

The effects of the low frequency electromagnetic field on the macrosegregation of the 7075 aluminum ingots were investigated. The 7075 aluminum ingots with the diameter of 200 mm were prepared by the conventional direct chill casting and the low frequency electromagnetic field casting (LFEC) processes, respectively. The temperature during casting at steady state was measured, and the mushy region was observed from the temperature contour. The concentrations of the alloying elements were measured by the spectrograph. It was found that the transition region was broadened, but the mushy zone became narrower with presence of the low frequency electromagnetic field. The centerline macrosegregation of the ingots was alleviated by the low frequency electromagnetic casting process.

Direct Chill Casting of Φ500mm ZK60 Magnesium Alloy Billets under Low Frequency Electromagnetic Field

Effects of low frequency electromagnetic field on surface quality, microstructure and hot-tearing tendency of direct chill casting of Φ500mm ZK60 magnesium alloy billets were investigated. The results show that with the application of the low frequency electromagnetic field, the surface quality of Φ500mm ZK60 magnesium alloy billets has been markedly improved, and the depth of cold fold is decreased. In the conventional direct chill casting, the microstructures of the billet, especially at the center, are coarse. The distribution of the grain size is non-uniform throughout the billet. From the edge to the center, the microstructure gradually changes from fine to coarse in all billets. However, under the low frequency electromagnetic casting, the microstructures of the billet is significantly refined, the distribution of the grains size is relatively uniform from the billets edge to the billets center. And it also shows that the hot-tearing tendency of direct chill casting Φ500mm ZK60 magnesium alloy billets under low frequency electromagnetic field is significantly reduced.

Experimental investigation of microsegregation in low frequency electromagnetic casting 7075 aluminum alloy

Abstract7075 aluminum alloy ingots were prepared by the process of low frequency electromagnetic casting (low frequency electromagnetic casting = LFEC) and conventional direct chill (direct chill = DC) casting, respectively. The effects of low frequency electromagnetic field on microsegregation were investigated from eutectic analysis and electro probe microanalysis (EPMA). It was found that the amount of the eutectic, which was composed of α‐Al (aluminum phase), T phase and MgZn2 was decreased markedly. In contrast, the solute concentration profiles which depend on solid fraction were increased to a certain extent with the presence of low frequency electromagnetic field. The effective distribution coefficient ke was calculated, and the values of ke for solutes in the LFEC sample were bigger than those in the DC sample. The LFEC process alleviated the microsegregation in 7075 aluminum alloy.

Grain refinement of DC cast AZ91D Mg alloy by intensive melt shearing

Melt conditioning by advanced shear technology (MCAST) is a new process for microstructural refinement of both cast and wrought magnesium alloys. Melt conditioned direct chill (MCDC) casting combines the MCAST process with conventional direct chill (DC) casting. In the present work, melt conditioning has been combined with permanent mould casting to simulate the production of DC cast AZ91D billets and slabs. The results show that the MCDC process can achieve significantly finer grain size and more uniform microstructure than conventional DC process for both billets and slabs. Grain refinement in the MCDC process is due to the fine and well dispersed oxide particles produced after processing in the MCAST unit.

Experimental Investigation of Microsegregation in Low Frequency Electromagnetic Casting of Al-4.5%Cu Binary Alloy

Al-4.5%Cu ingots were prepared by a process of low frequency electromagnetic casting (LFEC) and conventional direct chill (DC) casting, respectively. The effects of low frequency electromagnetic field on the microsegregation were investigated from eutectic analysis and electro probe microanalysis (EPMA). It was found that the amount of the nonequilibrium eutectic and the dimension of the nonequilibrium eutectic were decreasing markedly. In contrast, the solute content in the α-Al phase increased to a certain extent in the presence of the low frequency electromagnetic field, and it increased with the incerasing electromagnetic.

Potentiodynamic Polarization Aspects of the As-cast and Sprayed Al-Si, Al-Sn and Al-Sn-Si Alloys in a Sodium Chloride Solution

The present study compares the corrosion behavior of Al-Sn, Al-Si and Al-Sn-Si alloys processed by spray forming with that of the conventional chill cast ones in aqueous 0.1 N NaCl solution. Spray forming resulted in finer microstructural features with uniform distribution of second-phase particles. The spray formed Al-Si samples showed improved corrosion resistance as compared to the chill cast ones. The Sn containing alloys showed inferior corrosion resistance in the neutral electrolyte. The addition of 12.5 wt.% Si to Al-Sn alloys improves the corrosion resistance.

On The Formation of Extruded Surface Segregation Layer in Aluminum Direct Chill Casting Process

The aim of this research work was to develop a mathematical model to study the formation of extruded surface segregation phenomenon during the early stages of solidification in an aluminum direct chill casting process. The mathematical analyses contain a one dimensional mathematical model of heat flow, solidification, interdendritic strain and macrosegregation. Some typical cases in conventional direct chill casting processes related to increase surface segregation and fluctuation in macrosegregation with distance from the ingot surface were simulated. Good agreement was found by previous measurements and simulated results. Model results were discussed to explain the effects of different thermal solidification factors and interdendritic strain on the extruded surface segregation layer phenomenon. The results show that this phenomenon is sensitive to alloy composition and forms in the gap between the ingot surface and mould wall. Also, the model results point out that this phenomenon appears as a direct effect of the extrusion mechanism of interdendritic solute liquid associated with the interdendritic strain distribution in the coherent region in the mushy zone.

Evaluation of fresh-cut apple slices enriched with probiotic bacteria

Abstract The aim of this study was to apply a probiotic microorganism ( Lactobacillus rhamnosus GG; LGG) to fresh-cut apple wedges (cultivar Braeburn ) and measure entrapment and stability of the microorganism. Instrumental eating quality parameters (Colour Lab, texture, soluble solids, titratable acidity and pH) and sensory acceptability were also monitored to investigate if application of the probiotic significantly influenced eating quality. Apple samples were cut into skin-on wedges and were dipped in an edible buffer solution containing approximately 10 10 cfu/ml of LGG. LGG were enumerated on each test day (0, 2, 4, 6, 8 and 10) on whole wedges, on wedges flushed with a buffer solution (2% tri-sodium citrate), and on the flush-off liquid itself. All three samples sets contained ca. 10 8 cfu/g over the test period, which is sufficient for a probiotic effect, and is comparable to counts of probiotic bacteria in commercially available dairy products. This included the sample set of wedges which had been flushed with buffer solution indicating good adherence of the bacteria over the test period. Physicochemical properties of the apple wedges containing LGG compared to the control remained stable over the 10 day period. Cryo scanning electron microscopy and confocal scanning laser microscopy demonstrated good adherence of LGG to the surface of apple wedges. Industrial relevance Probiotic dairy foods, e.g. yoghurts, are well recognised by most consumers and command a significant market share. However, many people are allergic or intolerant to dairy products and an alternative option is desirable. Minimally processed freshly prepared fruits are a popular item and are perceived as healthy by consumers. They are therefore an ideal vehicle for incorporation of other functional components such as probiotics. Therefore, a probiotic bacterium was applied to fresh-cut apple wedges. This will provide an alternative probiotic food choice for consumers and could be particularly appealing to children. The process for making this product is relatively simple and the product would retail from the conventional chill counters of supermarket stores. It is likely that its price would be competitive with existing probiotic dairy products.

Effect of low-frequency electromagnetic field on the as-casting microstructures and mechanical properties of HDC 2024 aluminum alloy

The influences of the low frequency electromagnetic field on the horizontal direct chill casting process were investigated experimentally. Ingots of 2024 aluminum alloy with a cross size of 40 mm×200 mm were produced by the conventional horizontal chill casting process and low frequency electromagnetic horizontal chill casting process respectively. The as-cast structures and the mechanical property of the ingots were examined. The results showed that the low frequency electromagnetic field could substantially refine the microstructures and pronouncedly reduce the macrosegregation in the horizontal direct chill casting process. Moreover, the surface quality of the ingot was prominently improved by the low frequency electromagnetic field. The fracture strength and elongation percentage of the ingot was increased with the low frequency electromagnetic field.

Effects of rapid chilling of carcasses and time of deboning on weight loss and technological quality of pork semimembranosus muscle

The effect of rapid air chilling of carcasses in the first 3 h of chilling at −31 °C (then at 2–4 °C, till 24 h post-mortem) and the possibility of earlier deboning (8 h post-mortem) after rapid air chilling, compared to conventional air chilling (at 2–4 °C, till 24 h post-mortem) on weight loss and technological quality (pH value, tenderness, drip loss, cooking loss and colour - L ∗ a ∗ b ∗ values) of pork M. semimembranosus was investigated. Under the rapid chilling conditions, weight loss was 0.8% at 8 h post-mortem and increased to 1.4% at 24 h post-mortem when weight loss was 2.0% under conventional chilling. Carcasses that were rapid chilled had significantly lower ( P < 0.001) internal temperature in the deep leg at 4 (25.7 °C), 6 (13.0 °C), 8 (6.2 °C) and 24 h (3.8 °C) post-mortem compared to conventional chill treatment (32.7, 24.2, 19.1 and 5.1 °C, respectively). Rapid chilling reduced significantly ( P < 0.05) the rate of pH value decline at 8 h (6.02) post-mortem in M. semimembranosus compared to conventional chill treatment (5.88). Compared to conventional chilling, in M. semimembranosus deboned in different time post- mortem, rapid chilling had a positive significant effect on drip loss ( P < 0.05, muscles deboned 8 h post- mortem), cooking loss ( P < 0.001) and incidence of pale colour ( L ∗ value). Rapid chilling i.e. rapid chilling and earlier deboning had neither positive nor negative significant effects ( P > 0.05) on other investigated technological quality parameters of M. semimembranosus (tenderness, a ∗ value and b ∗ value) compared to conventional chilling.

Mathematical modelling of air evacuation in die casting process via CASTvac and other venting devices

Air venting in the die casting process has been an issue since its inception. A mathematical model that predicts the venting efficiency via different devices, including a new technology known as CASTvac, is presented. This model offers an advantage over other models reported in the literature in that it includes air leakage through die parting faces and the rates of volume compression due to a rapid change of plunger speed. The model has been verified and has predicted that (a) a majority of air is removed during the first stage of injection, in the case of atmospheric venting either using a conventional chill vent or CASTvac; (b) the duration of vacuum application is critical for a simple vacuum system due to die leakage; and (c) CASTvac used as a vent can achieve nearly the same evacuation efficiency as the best simple vacuum system.

Study on the sump and temperature field during low frequency electromagnetic casting a superhigh strength Al–Zn–Mg–Cu alloy

Abstract The effects of low frequency electromagnetic field on the sump depth and temperature field of a molten aluminum alloy (Al–Zn–Mg–Cu) were investigated by temperature measurement method. The results showed that during low frequency electromagnetic casting (LFEC) process the temperature field of the whole melt in the hot top is very uniform, and about 6 °C lower than liquidus temperature, which is very helpful to obtain uniform and fine microstructures. It was considered that LFEC process is like a kind of liquidus or near liquidus semi-continuous casting. It was also found that the sump depth during LFEC process is shallower than that of conventional direct chill (DC) casting process.