Recycling silicon carbide-reinforced aluminium metal matrix composites (Al-MMCs) through conventional remelting presents a significant challenge because the process leads to melt quality and promotes the formation of defects that are difficult to reverse. In this study, industrial AlSi9Mg–20

In Gr & uuml;nsandgie ss ereien werden die verwendeten Formsande zur bestm & ouml;glichen Ressourcenschonung so lange wie m & ouml;glich im Kreislauf gef & uuml;hrt und mit Zuschlagstoffen wie z. B. Bentonit und Glanzkohlenstoffbildner sowie weiteren Sandsystemen aufgefrischt. Da das System durch Zulauf w & auml;chst, entsteht der sogenannte & Uuml;berlaufsand, der meist als Altsand deponiert wird. Seit den 1990er Jahren wird an der mechanischen Regenerierung des Altsandes geforscht, bei welcher der enthaltene Formgrundstoff abgeschliffen wird, um als Regenerat wieder in der Kernherstellung eingesetzt zu werden. Der abgeschliffene Regenerierstaub wird derzeit deponiert, wodurch erhebliche Kosten entstehen und Deponieraum verloren geht. Im Artikel wird ein Verfahren zur Regeneration der St & auml;ube mit R & uuml;ckgewinnung der Wertstoffe Bentonit und Glanzkohlenstoffbildner vorgestellt und diskutiert. Die technische L & ouml;sung umfasst die Verwendung eines Abweiseradsichters. In green sand foundries, the sands used for molds are kept in circulation for as long as possible in order to reduce resource consumption. The sands are replenished with additives such as bentonite, carbon black formers, and other sand systems. As the system grows through inflow, the so-called overflow sand is created, which is usually deposited as used sand. Since the 1990s, research has been conducted on the mechanical regeneration of used sand, where the base material for the mold is surface-ground to be reused as a regenerant in core production. The ground-down regeneration dust is deposited which causes substantial costs and deposit space losses. This article presents and discusses a method for regenerating the dusts with the recovery of valuable materials like bentonite and carbon black formers. The technical solution involves the use of a deflector wheel sifter.

In Grünsandgießereien werden die verwendeten Formsande zur bestmöglichen Ressourcenschonung so lange wie möglich im Kreislauf geführt und mit Zuschlagstoffen wie z. B. Bentonit und Glanzkohlenstoffbildner sowie weiteren Sandsystemen aufgefrischt. Da das System durch Zulauf wächst, entsteht der sogenannte Überlaufsand, der meist als Altsand deponiert wird. Seit den 1990er Jahren wird an der mechanischen Regenerierung des Altsandes geforscht, bei welcher der enthaltene Formgrundstoff abgeschliffen wird, um als Regenerat wieder in der Kernherstellung eingesetzt zu werden. Der abgeschliffene Regenerierstaub wird derzeit deponiert, wodurch erhebliche Kosten entstehen und Deponieraum verloren geht. Im Artikel wird ein Verfahren zur Regeneration der Stäube mit Rückgewinnung der Wertstoffe Bentonit und Glanzkohlenstoffbildner vorgestellt und diskutiert. Die technische Lösung umfasst die Verwendung eines Abweiseradsichters.

AbstractCeramic foam filtershavebeen usedin aluminum foundries since 1974 to increase the purity of the melt. In practice, the implementation of the foam ceramic filter in the casting system is in most cases a question of space on the pattern plate. It does not follow any defined rules but is at best guided by design recommendations from the filter manufacturers. To increase the filtration efficiency, the filter position in the casting system is examined. For this, 20 and 30 ppi filters were scanned with computer tomography (CT). The data from the CT were then loaded into the simulation program Flow 3D. With this program, four different filter positions as well as the influence of the filter length and roughness of the filter surface are investigated concerning their filtration effectiveness. The simulation results are subsequently evaluated with casting trials. For this, four different molds for four different filter positions were created. The same alloy (AlSi7) was used for the trials as for the simulation. To study the behavior of particles during the filtration process, impurities were added to the melt using 3 wt.% Al2O3 - Metal Matrix Composite. After the samples were casted, the filters are cut out and the Al2O3 particles in the filter are counted for each filter position. The comparability of the casting trials and the results of the simulation have been examined.

AbstractIron (Fe) provides a non-reactive dissolved impurity in aluminum (Al) alloys, which forms a coarse, plate-shaped intermetallic β-phase during solidification. This β-phase is detrimental to the mechanical and casting properties. Therefore, the reduction of Fe by binding in Fe-containing intermetal-lics (sludge phase) was realized via a two-stage procedure, which consisted of conditioning of the melt by manganese (Mn) and chromium (Cr) with subsequent-ly applied metal melt filtration. For this purpose, the formation characteristics of the Fe-rich intermetallic phases were investigated regarding the temperature, time, and initial chemical composition to separate these intermetallics from the residual melt. To evaluate the different process parameters of Fe removal for a potential implementation in lightweight metal foundries, a process technology on an indus-trial scale was developed in cooperation with an industrial partner. The examina-tion of samples in optical microscopy (OM) using image analysis were conducted to determine the area fractions of Fe-rich intermetallics. In addition, optical emis-sion spectrometer (OES) measurements were performed. Complementary investi-gations were achieved by scanning electron microscopy (SEM), with energy dis-persive spectroscopy (EDS), and electron backscatter diffraction (EBSD) to measure the partial chemical composition and for phase identification. The for-mation characteristics of the Fe-containing phases were investigated using DSC cooling curves and selective sampling in quenching experiments. In the experi-mental trials, a maximum reduction of iron of ≈50% was revealed compared to the unfiltered sample, whereby greater influence on the formation of α-intermetallics was inferred by temperature than by time. Moreover, the elements Mn and Cr were reduced by about 66% and 86% at 620 °C, respectively, thus, the element contents in the filtered samples approached the chemical composition of the standard alloy (EN-AC-AlSi9Cu3(Fe)).

In this study, filtration of aluminum alloy (Al) with different weight fractions of SiC particles (SiCp) was investigated. Therefore, three different filter materials of 20 pores per inch (ppi) ceramic foam filters (CFF) were tested. A special three-chamber furan mold was used for the casting trials to provide uniform filling and flow conditions for the filtration process. Samples from sections of the gating system, as well as from the filter, were analyzed by optical light microscopy to determine the amount, size, and distribution of SiCp. A scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) was used for obtaining the element distribution in the composite. The filtration efficiency increased by decreasing the weight fraction from 20 to 5% of SiCp and reached a significant particle reduction of over 90%. Investigations of CFFs with a weight fraction of 10% have shown a clogging effect and metal flow interruption through the 20 ppi filter. An oxide layer was detected around the respective SiCp in the EDS. Moreover, a strong accumulation effect was observed, indicated by a steadily flattening curve of the density functions after each additional remelting cycle of the same composite material.

The present study investigated existing and potential approaches for hot cracking analysis of cast alloys and showed a promising and very applicable new specimen for high alloyed steels. The reliability of this specimen has been demonstrated by adding niobium to alloy HH (ASTM A297), or alloy 1.4837 (ISO 11973). Niobium shows a very positive impact on hot cracking behavior and can thereby reduce scrap in steel foundries. Amounts above 0.6 wt% niobium can reduce the size and number of hot cracks significantly. The reduction of hot cracking tendency was quantified by the cracking factor CF Nb2 . The positive effect is associated with the reduction in solidification interval length that was measured by thermal analysis and the observed “healing” of cracks in the microsections. Both effects are promoted by niobium. The promotion of the ferritic solidification seems to have no positive impact on the hot cracking behavior.

The formation of iron (Fe)‐containing intermetallics during solidification is challenging due to the influences of cooling rate and chemical composition. Differential scanning calorimetry (DSC) is an accurate analysis method but merely replicates adjustable cooling conditions. Thereby, the solidification range is traversed several times before DSC measurement. For this purpose, thermal analysis cooling curves with double thermocouple are conducted to investigate the formation temperature of Fe‐rich intermetallics in different AlSi casting alloys. In addition, the influence of chemical composition is examined by increasing the initial contents of iron, manganese, and chromium to 0.8 wt% each. The double thermocouple setup allows determining feeding points and solid fractions of the alloy compounds. To evaluate the data sets, the statistical program R is used to improve data processing and smoothing. The signature of Fe‐rich intermetallics in the temperature–time plots corresponds to the detected phases in optical micrographs. In addition, scanning electron microscopy with energy‐dispersive spectroscopy and electron backscattering diffraction are used to measure the local chemical composition and identify the iron‐rich intermetallics. Real‐time evaluation (differential calculation, first derivative, incl. smoothing) for an applicable filtration process can be performed using thermocouples with analog‐to‐digital converter and Python programs with an interactive graphical interface.

The influence of chemical composition and cooling rate is investigated on a secondary die‐casting alloy with the aim of reduction of iron using metal melt filtration in a specially developed laboratory filtration apparatus. Based on the defined thermal conditions of the device, differential scanning calorimetry (DSC) cooling curves are determined to obtain formation temperatures of the primary iron‐containing intermetallic phases (also called sludge phases) for an EN AC‐AlSi9Cu3(Fe) alloy with different contents of Fe, Mn, and Cr. The DSC samples are then analyzed metallographically, and the results are compared with CalPhaD calculations. After that, the temperature of the sludge formation is adjusted using furnace‐operating curves to confirm the presence of the intermetallic phases by sedimentation and filtration trials. The Fe content is reduced by about 50%, as shown by chemical analysis based on remelted materials in optical emission spectroscopy. The elements Mn and Cr decrease by ≈66% and 86% after filtration at 620 °C, respectively.

The present study investigates the influence of melt conditioning and filtration on iron-rich phases in AlSi9Cu3 alloy. This method avoids the formation of brittle β phase (Al4.5FeSi) and reduces the iron content by sedimentation and subsequent filtration. The comparison of this method to conventional casting (reference) with a higher Fe content is performed by means of scanning electron microscopy, tensile tests, ultrasonic fatigue tests, X-ray diffraction and X-ray microtomography. The reference batch revealed a high proportion of β plates, which are responsible for low strength compared to melt conditioned batch under uniaxial tensile stress. The fatigue properties of melt conditioned batch are significantly improved compared to the reference state. X-ray microtomography scans before and after ultrasonic fatigue tests were evaluated by machine learning algorithms (Trainable Weka Segmentation). The superposition of the segmented fatigue crack with the initial, undeformed state was performed for the first time and showed that the fatigue crack path is strongly influenced by the brittle Fe-rich phases.

Low pressure casting is a very well established process for the casting of aluminium alloys. In the field of ferrous materials, however, the process has so far only found a few applications. The crucial reasons for this are the low flexibility and poor economic efficiency of the existing technologies. Since 2016, a new technology has been developed at the Foundry Institute of the TU Bergakademie Freiberg, in which an induction crucible furnace can be used as a melting unit and, in combination with a cover including a casting pipe, as a casting unit. The new technology stands out from existing low-pressure casting technologies for ferrous materials, particularly in terms of its flexibility and cost-effectiveness. The main focus of the activities was the development of a casting pipe as well as the verification of its lifetime, the elaboration and verification of process parameters and sequences as well as the upscaling of the technology for an industrial application. In all considerations, the focus was on both the technical feasibility and the economic efficiency of the process. The result is extensive expertise that can be used in the future to offer a finished product for industrial applications as a plug-and-play solution together with an induction furnace construction company.

TRIP-matrix composites unite the outstanding properties of austenitic-martensitic cast steelsMartensitic cast steels with those of ceramics. To manufacture them via infiltration by steel melt, basic investigations are needed. Therefore, the following aspects were studied: the influence of sodium silicate bonded sand moldsSand molds on solidification of high alloyed TRIP-steels, chemical reactions between steel and molding sand and the positive impact of sulfur and phosphorus on the infiltration qualityInfiltration quality. Composite materials made of steel and ceramics, in particular, melt-broken zircon corundum, have comparatively high wear resistance. The wear behavior of the composites is characterized by a ring-block test rig. In order to generate a stable bond between the steel and the ceramic phase, the ceramics were coated with titanium oxide prior to infiltration. During infiltration of the coated ceramicsCoated ceramics, spinel compounds are formed which reduce expansion-related cracks in the boundary layer.

In industrial applications, filter materials are often chosen according to cost as well as their processing and thermomechanical properties, but rarely in terms of their behavior during filtration, which is largely due to there being insufficient information available on the influence of filter materials and surface quality on filtration behavior. In this study, the manufacture of functionalized Al 2 O 3 nanofilters was investigated, along with their filtration performance in short- and long-term filtration trials. In addition, sessile drop tests were performed to measure the contact angle of the nanofunctionalized materials, and yielded an approximately 10 deg (11 pct) higher contact angle for nanocoated materials sintered at 800 °C and 1250 °C than for those sintered at 1600 °C and an approximately 23 deg (23 pct) higher contact angle compared to surfaces without a nanocoating. The filtration mechanism was assessed by means of Porous Disk Filtration Analysis (PoDFA) and Liquid Metal Cleanliness Analyzer (LiMCA) monitoring systems, as well as by analysis of the used and infiltrated filters using Scanning Electron Microscopy and Energy Dispersive X-ray analysis (SEM/EDX) technology. Both short-term and long-term filtration trials showed that the filtration behaviors of the reference and nanocoated filters were comparable. It was therefore determined that nanocoating of such filters with Al 2 O 3 does not provide any improvement with regard to filtration performance.

Melt cleanliness is essential for high quality aluminum production. The main cleanliness criteria are the content of dissolved hydrogen as well as the content of non-metallic inclusions. The latter may impair the castability of the aluminum melt as well as the mechanical properties and the machinability of the aluminum castings. A simple and efficient way to remove non-metallic inclusions is the application of filters during the casting process. The influence of the filter roughness on the filtration is undisputed but experimental proof is still pending. Filters with three different levels of roughness were subjected in filtration trials in a filtration pilot setup at Hydro (Bonn, Germany) allowing determination of the inclusion removal efficiency by the application of two LiMCA devices. In addition to the LiMCA measurements, PoDFA, Alscan measurements and investigations of the casted aluminum were done.

The development of an innovative hybrid lightweight piston for marine engines is intended to help reduce emissions and operating costs. The piston consists of a piston base and a top part. In the manufacture of the piston base a preform is cast and the final geometry is produced by means of subsequent forming (forging). This significantly improves the mechanical properties of the material. As a result of the possible material advantages in the overall process chain, the piston base can be designed as a “lightweight component”. By examining the entire process chain of “primary casting - forging", the amount of used materials is significantly reduced, especially in the “casting” production route, since even minor internal defects can be tolerated after the preform has been cast. For the subsequent forging process, this material pre-distribution thus represents an optimum initial forging shape. The upper part of the piston is made of a layered composite material. Here, the special material is already applied to the blank prior to the forging process by laser or PTA build-up welding. This means that the filler material is also formed together with the base material, which in turn has a positive effect at the mechanical properties. This is followed by a heat treatment, which further improves the high temperature resistance. Due to the higher strength and corrosion resistance of the piston head, the temperature and pressure of the combustion chamber can be increased, enabling the required reduction of emissions and fuel.

This paper focusses on the development of materials for exhaust gas components. The present work will focus on a ferritic SiMo-cast iron to create an economic alternative to the austenitic D5S. Aluminum and silicon are essential for this material development because they increase the transformation temperature. They also improve the durability of the protective oxide layer. Additionally, aluminum improves the high temperature mechanical properties by precipitation of a kappa-phase. The ferritic SiMoAl cast iron shows very good oxidation resistance and also mechanical properties.

In view of filtration of Fe‐enriched intermetallics to decrease Fe content in secondary aluminum alloys, the formation of so‐called sludge particles has been investigated depending on dwell time and chemical composition using an AlSi9Cu3 secondary alloy with high Fe content. To evaluate the dwell time dependency, samples are cast into ceramic crucibles and held at 620 °C for varying times. Furthermore, Mn and Cr have been added to the melt in different amounts and the alloys are treated for 6 h at 620 °C. The samples are analyzed using light optical micrographs and image analysis to reveal particle sizes and distribution as well as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD) for phase identification. It is found that the growth of Fe containing sludge particles stagnates after reaching a specific value and is not significantly affected by ultra‐long dwell times. Mn addition has a minor effect on the the particle size distribution preserving large particle sizes, whereas Cr addition leads to a smaller sludge particles. Generally, the sludge consists of the cubic α‐phase. Additionally in the presence of Cr, Fe, and Cr concentration gradients occur in the cubic α–Al–(Fe,Mn,Cr)–Si phase and the Al13Cr4Si4‐phase is contained in the centers of the sludge particles. It is concluded that Mn addition is favored due to larger particle size and higher efficiency to bind Fe in the α‐phase than by Cr or Cr and Mn addition.

The influence of filter surface chemistry on the filtration efficiency of cast aluminum alloys was evaluated for four different filter coating compositions (Al2O3—alumina, MgAl2O4—spinel, 3Al2O3·2SiO2—mullite, and TiO2—rutile). The tests were conducted on a laboratory scale with a filtration pilot plant, which facilitates long-term filtration tests (40 to 76 minutes). This test set-up allows the simultaneous use of two LiMCAs (before and after the filter) for the determination of the efficiency of inclusion removal. The four tested filter surface chemistries exhibited good thermal stability and mechanical robustness after 750 kg of molten aluminum had been cast. All four filter types exhibited a mean filtration efficiency of at least 80 pct. However, differences were also observed. The highest filtration efficiencies were obtained with alumina- and spinel-coated filter surfaces (>90 pct), and the complete removal of the largest inclusions (>90 µm) was observed. The efficiency was slightly lower with mullite- and rutile-coated filter surfaces, in particular for large inclusions. These observations are discussed in relation to the properties of the filters, in particular in terms of, for example, the surface roughness.

Metal–matrix composites (MMCs) are of high interest due to their combination of a ductile matrix with a hard phase for reinforcement. Besides the production via one of the various powder‐metallurgical routes, it is also possible to cast MMCs by infiltrating a porous ceramic structure with liquid melt. In the presented work, the infiltration of a macroporous ceramic through gravity casting is described. The MMC described consists of high‐alloyed metastable austenitic–martensitic CrMnNi‐cast steel and a metastable zirconium dioxide ceramic. Both materials are able to transform martensitic if load is applied. To increase infiltration of the zirconia foam, sulfur has been added to the steel melt. After the casting, the wear behavior during three‐body abrasive wear test of the MMC is examined. The MMC as well as the TRIP steel by itself shows a high improvement in wear resistance, when compared to other wear materials. In order to investigate the increased wear resistance, an XRD‐evaluation is described. The amount of α′‐martensite and ferrite changes from 26 to 97 vol% due to abrasive wear while no transformation of the metastable tetragonal Mg‐PSZ can be observed.

In spite of the formation of a high fraction of deformation-induced α′ martensite, the tensile elongation of a cast high-nitrogen austenitic stainless steel was found to enhance at lower temperatures, a behavior deviating from that exhibited by wrought and homogenized austenitic stainless steels. The observed behavior was explained by the presence of microstructural regions with different stabilities with respect to deformation-induced α′ martensite formation caused by the segregation of alloying elements.