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The paper aims to evaluate the effect of chemical composition on the Hot Cracking Susceptibility (HCS) using mechanical and non-mechanical hot cracking criteria during solidification. The criteria were SKK as a mechanical criterion. Feurer, Clyne Davis, and Katgerman as non-mechanical criteria. The criteria were implemented at various parameters to evaluate their abilities in the hot cracking susceptibility (HCS) prediction at varied chemical composition. In this study, The Mg content was varied in Al9Zn (1, 1.5, 2, 2.5 %wt.) Mg2Cu alloys and Cu content in Al9Zn2Mg (1, 1.5, 2, 2.5 %wt.) Cu alloys. The validation of the result is also conducted by comparing with the experimental data. Based on Feurer criterion, The hot cracking initiates at lower temperature and at higher critical rate of feeding and shrinkage with Cu content, and the hot cracking initiates at higher temperature with Mg content, and it initiates at higher critical rate of feeding and shrinkage from 1 up to 1.5 of Mg, and the critical rate of feeding and shrinkage remains constant from 1.5 up to 2.5 of Mg. Based on Clyne & Davies, the HCS decreases with Cu content from 1 up to 2 of Cu, and it increases from 2 up to 2.5 of Cu. The HCS decreases with Mg content from 1 up to 2 of Mg, and it remains constant from 2 up to 2.5 of Mg. Based on Katgerman criterion, the HCS decreases with Cu content from 1 up to 1.5 of Cu, it increases from 1.5 up to 2 of Cu, and it decreases from 2 up to 2.5 of Cu. The HCS decreases sequentially with Mg content. Based on SKK criterion, the HCS curves shift to the right with Cu content which means that the hot cracking initiates at lower temperature, and the HCS curves shift to the left with Mg content which means that the hot cracking initiates at higher temperature with Mg content. The Feurer, Clyne & Davies, and some specific range for SKK criteria are in agreement for the effect of Cu content on HCS of alloys, and Katgerman and some specific range for Clyne&, Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Team Joris Dik more...

Over the last 4 decades, remarkable progress has been made in the modelling of casting processes. The development of casting models is well reflected in the proceedings of the 15 Modelling of Casting, Welding and Advanced Solidification Processes (MCWASP) conferences that have been held since 1980. Computer simulations have enabled a better understanding of the physical phenomena involved during solidification. Modelling gives the opportunity to uncouple the physical processes. Furthermore, quantities that are difficult or impossible to measure experimentally can be calculated using computer simulations e.g. flow patterns and recalescence. However, when it comes to accurately predicting casting performance and in particular, the occurrence of defects like cracks, segregation and porosity there is certainly some way to go. In this paper, the current understanding of the main mechanisms of defect formation during shape and DC casting processes will be reviewed and requirements will be discussed to give a direction to making casting models more predictive and quantitative., Team Jilt Sietsma more...

Over the last 4 decades, remarkable progress has been made in the modelling of casting processes. The development of casting models is well reflected in the proceedings of the 15 Modelling of Casting, Welding and Advanced Solidification Processes (MCWASP) conferences that have been held since 1980. Computer simulations have enabled a better understanding of the physical phenomena involved during solidification. Modelling gives the opportunity to uncouple the physical processes. Furthermore, quantities that are difficult or impossible to measure experimentally can be calculated using computer simulations e.g. flow patterns and recalescence. However, when it comes to accurately predicting casting performance and in particular, the occurrence of defects like cracks, segregation and porosity there is certainly some way to go. In this paper, the current understanding of the main mechanisms of defect formation during shape and DC casting processes will be reviewed and requirements will be discussed to give a direction to making casting models more predictive and quantitative., Team Kevin Rossi more...

AA7050 is an aluminum alloy with superior mechanical properties; however, it is prone to hot tearing (HT) during its production via direct-chill casting. This study focuses on extracting constitutive parameters of the alloy thermomechanical behavior in semi-solid state as well as gaining insight in its failure behavior. Tensile tests were performed using an Instron 5944 at solid fractions between 0.85 (550 °C) and 1.0 (465 °C), at deformation rates of 0.2 and 2 mm/min. The results showed that there are three mechanical behavior regimes in this solid fraction range: ductile at 1.0 (T = 465 °C) ≤ fs < 0.97 (T = 473 °C), brittle at 0.97 (T = 473 °C) ≤ fs ≤ 0.9 (T = 485 °C) and then ductile again (at 0.9 (T = 485 °C) < fs ≤ 0.85 (T = 550 °C)). Fracture surface analysis revealed that the fracture mode was mostly intergranular with fracture propagating through solid bridges as well. Semi-solid constitutive parameters were obtained by making a simple thermal model and numerical tensile tests in ALSIM software package and comparing the simulation results with experimental mechanical tests. The extracted constitutive parameters and available information from the literature support the fact that AA7050 is more susceptible to HT than AA5182 and Al-2 wt pct Cu alloys. The obtained parameters can further enhance the predictive capability of computer simulations of direct-chill casting., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Team Jilt Sietsma more...

Hot tearing is one of the most severe and irreversible casting defects for many metallic materials. In 2004, Eskin et al. published a review paper in which the development of hot tearing of aluminium alloys was evaluated (Eskin and Suyitno, 2004). Sixteen years have passed and this domain has undergone considerable development. Nevertheless, an updated systematic description of this field has not been presented. Therefore, this article presents the latest research status of the hot tearing during the casting of aluminium alloys. The first part explains the hot tearing phenomenon and its occurrence mechanism. The second part presents a detailed description and analysis of the characterisation methods of the mushy zone mechanical properties and hot tearing susceptibility. The third part presents considerable data pertaining to the mushy zone behaviour, including those of the linear contraction and load behaviour during solidification, semi-solid strength and ductility, and characteristic points related to hot tearing. The fourth part examines the effect of the composition and casting process parameters on the hot tearing susceptibility of aluminium alloys. The fifth part describes the hot tearing simulations and the associated criteria and mechanisms. Finally, recommendations for the further development of hot tearing research are presented., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Team Jilt Sietsma more...

Hot tearing is one of the most severe and irreversible casting defects for many metallic materials. In 2004, Eskin et al. published a review paper in which the development of hot tearing of aluminium alloys was evaluated (Eskin and Suyitno, 2004). Sixteen years have passed and this domain has undergone considerable development. Nevertheless, an updated systematic description of this field has not been presented. Therefore, this article presents the latest research status of the hot tearing during the casting of aluminium alloys. The first part explains the hot tearing phenomenon and its occurrence mechanism. The second part presents a detailed description and analysis of the characterisation methods of the mushy zone mechanical properties and hot tearing susceptibility. The third part presents considerable data pertaining to the mushy zone behaviour, including those of the linear contraction and load behaviour during solidification, semi-solid strength and ductility, and characteristic points related to hot tearing. The fourth part examines the effect of the composition and casting process parameters on the hot tearing susceptibility of aluminium alloys. The fifth part describes the hot tearing simulations and the associated criteria and mechanisms. Finally, recommendations for the further development of hot tearing research are presented., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Team Kevin Rossi more...

AA7050 is an aluminum alloy with superior mechanical properties; however, it is prone to hot tearing (HT) during its production via direct-chill casting. This study focuses on extracting constitutive parameters of the alloy thermomechanical behavior in semi-solid state as well as gaining insight in its failure behavior. Tensile tests were performed using an Instron 5944 at solid fractions between 0.85 (550 °C) and 1.0 (465 °C), at deformation rates of 0.2 and 2 mm/min. The results showed that there are three mechanical behavior regimes in this solid fraction range: ductile at 1.0 (T = 465 °C) ≤ fs < 0.97 (T = 473 °C), brittle at 0.97 (T = 473 °C) ≤ fs ≤ 0.9 (T = 485 °C) and then ductile again (at 0.9 (T = 485 °C) < fs ≤ 0.85 (T = 550 °C)). Fracture surface analysis revealed that the fracture mode was mostly intergranular with fracture propagating through solid bridges as well. Semi-solid constitutive parameters were obtained by making a simple thermal model and numerical tensile tests in ALSIM software package and comparing the simulation results with experimental mechanical tests. The extracted constitutive parameters and available information from the literature support the fact that AA7050 is more susceptible to HT than AA5182 and Al-2 wt pct Cu alloys. The obtained parameters can further enhance the predictive capability of computer simulations of direct-chill casting., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Team Kevin Rossi more...

New 7xxx aluminum alloys with high alloying contents are being designed, which could induce serious hot tearing defects during direct-chill (DC) casting. Among all factors affecting hot tearing of 7xxx alloys, undoubtedly alloying elements play a significant role. In this study, the effect of main alloying elements (Zn, Mg, and Cu) on hot tearing of grain-refined Al-xZn-yMg-zCu alloys was investigated by a dedicated hot tearing rating apparatus simulating the DC-casting process. It was found that the minimum and maximum hot tearing susceptibilities occur for 4 to 6 and 9 wt pct Zn, respectively, indicating the complicated effect of Zn content. The hot tearing resistance of grain-refined Al-9Zn-yMg-zCu alloys is enhanced with increasing Mg content but is deteriorated with increasing Cu content. This can be attributed to the interaction of the thermal stresses, melt feeding, and final eutectics. The observed tendencies of the main alloying elements on hot tearing were also confirmed for four commercial 7xxx alloys. In addition, both the load value at non-equilibrium solidus and the SKK criterion proposed by Suyitno et al. using measured load developments were found to be good indicators in predicting hot tearing susceptibility. This study can provide a beneficial guide in designing 7xxx alloys considering the potential occurrence of hot cracks beforehand., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., (OLD) MSE-1 more...

New 7xxx aluminum alloys with high alloying contents are being designed, which could induce serious hot tearing defects during direct-chill (DC) casting. Among all factors affecting hot tearing of 7xxx alloys, undoubtedly alloying elements play a significant role. In this study, the effect of main alloying elements (Zn, Mg, and Cu) on hot tearing of grain-refined Al-xZn-yMg-zCu alloys was investigated by a dedicated hot tearing rating apparatus simulating the DC-casting process. It was found that the minimum and maximum hot tearing susceptibilities occur for 4 to 6 and 9 wt pct Zn, respectively, indicating the complicated effect of Zn content. The hot tearing resistance of grain-refined Al-9Zn-yMg-zCu alloys is enhanced with increasing Mg content but is deteriorated with increasing Cu content. This can be attributed to the interaction of the thermal stresses, melt feeding, and final eutectics. The observed tendencies of the main alloying elements on hot tearing were also confirmed for four commercial 7xxx alloys. In addition, both the load value at non-equilibrium solidus and the SKK criterion proposed by Suyitno et al. using measured load developments were found to be good indicators in predicting hot tearing susceptibility. This study can provide a beneficial guide in designing 7xxx alloys considering the potential occurrence of hot cracks beforehand., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., (OLD) MSE-1 more...

For almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DC-cast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur., Materials Science & Engineering, Mechanical, Maritime and Materials Engineering more...

Ultrasonic melt treatment (UST) is known to induce grain refining in aluminum alloys. Previous studies have clearly shown that in Al–Zr–Ti alloys, the primary Al3Zr intermetallics were dramatically refined by cavitation-assisted fragmentation, and a good refinement effect was achieved. In this article, Al–Ti, Al–Ti–Zr alloys, and some commercial aluminum alloys are used to analyze the effect of UST on primary intermetallics and grain refinement. The addition of a small amount of Al–3Ti–B master alloy is also studied in order to compare with the addition of Ti and Zr in commercial aluminum alloys. Experimental results show that the ultrasonic grain refining effect is not only related to the size of particles which are refined and/or dispersed by UST, but also related to an undercooling available for activation of these particles in the solidification process. Athermal heterogeneous nucleation theory is considered to explain the effect of size and distribution of substrate particles on the grain structure with different undercoolings. The distribution of primary particle sizes results in the distribution of required undercoolings. Grain refining occurs when the undercooling is large enough to activate the refined primary intermetallics or dispersed inoculants., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

For almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DC-cast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur., Materials Science & Engineering, Mechanical, Maritime and Materials Engineering more...

Ultrasonic melt treatment (UST) is known to induce grain refining in aluminum alloys. Previous studies have clearly shown that in Al–Zr–Ti alloys, the primary Al3Zr intermetallics were dramatically refined by cavitation-assisted fragmentation, and a good refinement effect was achieved. In this article, Al–Ti, Al–Ti–Zr alloys, and some commercial aluminum alloys are used to analyze the effect of UST on primary intermetallics and grain refinement. The addition of a small amount of Al–3Ti–B master alloy is also studied in order to compare with the addition of Ti and Zr in commercial aluminum alloys. Experimental results show that the ultrasonic grain refining effect is not only related to the size of particles which are refined and/or dispersed by UST, but also related to an undercooling available for activation of these particles in the solidification process. Athermal heterogeneous nucleation theory is considered to explain the effect of size and distribution of substrate particles on the grain structure with different undercoolings. The distribution of primary particle sizes results in the distribution of required undercoolings. Grain refining occurs when the undercooling is large enough to activate the refined primary intermetallics or dispersed inoculants., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Materials Science & Engineering, Mechanical, Maritime and Materials Engineering

Direct chill (DC) casting of high strength 7xxx series aluminium alloys is difficult mainly due to solidification cracking (hot cracks) and solid state cracking (cold cracks). Poor thermal properties along with extreme brittleness in the as-cast condition make DC-casting of such alloys a challenging process. Therefore, a criterion that can predict the catastrophic failure and cold cracking of the ingots would be highly beneficial to the aluminium industry. The already established criteria are dealing with the maximum principal stress component in the ingot and the plane strain fracture toughness (KIc) of the alloy under discussion. In this research work such a criterion was applied to a typical 7xxx series alloy which is highly prone to cold cracking. The mechanical properties, constitutive parameters, as well as the KIc values of the alloy were determined experimentally in the genuine as-cast condition and used as input data for the finite element package ALSIM5. Thermomechanical simulations were run for billets of various diameters and the state of residual thermal stresses was determined. Following the contour maps of the critical crack size gained from the model, the casting conditions were optimized to produce a crack-free billet., Materials Science & Engineering, Mechanical, Maritime and Materials Engineering more...

Materials Science & Engineering, Mechanical, Maritime and Materials Engineering

Materials Science and Engineering, Mechanical, Maritime and Materials Engineering

Materials Science & Engineering, Mechanical, Maritime and Materials Engineering

Non-homogenous cooling rates and solidification conditions during DC-casting of high strength aluminum alloys result in the formation and accumulation of residual thermal stresses with different signs and magnitudes in different locations of the billet. Rapid propagation of microcracks in the presence of thermal stresses can lead to catastrophic failure in the solid state, which is called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine ascast properties. Simulation of residual thermal stresses of an AA7050 alloy during DC-casting by means of ALSIM5 showed that in the steady-state conditions large compressive stresses formed near the surface of the billet in the circumferential direction. Stresses changed sign on moving towards the centre of the billet and became tensile with high magnitudes in radial and transverse directions, which made the alloy prone to hot and cold cracking., Materials Science & Engineering, Mechanical, Maritime and Materials Engineering more...

Materials Science & Engineering, Mechanical, Maritime and Materials Engineering

Direct chill (DC) casting of high strength 7xxx series aluminium alloys is difficult mainly due to solidification cracking (hot cracks) and solid state cracking (cold cracks). Poor thermal properties along with extreme brittleness in the as-cast condition make DC-casting of such alloys a challenging process. Therefore, a criterion that can predict the catastrophic failure and cold cracking of the ingots would be highly beneficial to the aluminium industry. The already established criteria are dealing with the maximum principal stress component in the ingot and the plane strain fracture toughness (KIc) of the alloy under discussion. In this research work such a criterion was applied to a typical 7xxx series alloy which is highly prone to cold cracking. The mechanical properties, constitutive parameters, as well as the KIc values of the alloy were determined experimentally in the genuine as-cast condition and used as input data for the finite element package ALSIM5. Thermomechanical simulations were run for billets of various diameters and the state of residual thermal stresses was determined. Following the contour maps of the critical crack size gained from the model, the casting conditions were optimized to produce a crack-free billet., Materials Science & Engineering, Mechanical, Maritime and Materials Engineering more...

Materials Science & Engineering, Mechanical, Maritime and Materials Engineering

Materials Science and Engineering, Mechanical, Maritime and Materials Engineering

Materials Science & Engineering, Mechanical, Maritime and Materials Engineering

Non-homogenous cooling rates and solidification conditions during DC-casting of high strength aluminum alloys result in the formation and accumulation of residual thermal stresses with different signs and magnitudes in different locations of the billet. Rapid propagation of microcracks in the presence of thermal stresses can lead to catastrophic failure in the solid state, which is called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine ascast properties. Simulation of residual thermal stresses of an AA7050 alloy during DC-casting by means of ALSIM5 showed that in the steady-state conditions large compressive stresses formed near the surface of the billet in the circumferential direction. Stresses changed sign on moving towards the centre of the billet and became tensile with high magnitudes in radial and transverse directions, which made the alloy prone to hot and cold cracking., Materials Science & Engineering, Mechanical, Maritime and Materials Engineering more...

Coarsening within the mushy zone during continuous directional solidification experiments was studied on an Al-30 wt pct Cu alloy. High brilliance synchrotron X-radiation microscopy allowed images to be taken in-situ during solidification. Transient conditions were present during directional solidification. Under these conditions, solute-rich settling liquid flow affects the dendritic array and thus coarsening. Coarsening was studied by following the secondary dendrite arm spacing (SDAS) of a developing dendrite at different local solidification times according to the mush depth and instant interface velocity. Solute enrichment and liquid flow cause deceleration and acceleration of the solidification front, which in turn influences both the mush depth and local growth and coarsening due to variations in solutal gradients and thus local undercooling. In addition, spacing between neighboring dendrites (i.e., primary dendrite arm spacing), which determines permeability within the mushy zone, affects the development of high-order branches., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Thermally induced strains and stresses developed during direct-chill (DC) semicontinuous casting of high strength aluminum alloys can result in formation of micro-cracks in different locations of the billet. Rapid propagation of such micro-cracks in tensile thermal stress fields can lead to catastrophic failure of ingots in the solid state called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine as-cast properties. Application of fracture mechanics, on the other hand, can help to derive the critical crack length leading to failure. In the present research work, the state of residual thermal stresses was determined in an AA7050 billet during DC casting by means of ALSIM5. Simulation results showed that in the steady-state conditions, large compressive stresses form near the surface of the billet in the circumferential direction, whereas in the center, the stresses are tensile in all directions. Magnitudes of von Mises effective stresses, the largest component of principal stresses and the fracture mechanics concepts, were then applied to investigate the crack susceptibility of the billet., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Shrinkage, imposed strain rate, and (lack of) feeding are considered the main factors that determine cavity formation or the formation of hot tears. A hot-tearing model is proposed that will combine a macroscopic description of the casting process and a microscopic model. The micromodel predicts whether porosity will form or a hot tear will develop. Results for an Al-4.5 pct Cu alloy are presented as a function of the constant strain rate and cooling rate. Also, incorporation of the model in a finite element method (FEM) simulation of the direct-chill (DC) casting process is reported. The model shows features well known from literature such as increasing hot-tearing sensitivity with increasing deformation rate, cooling rate, and grain size. Similar trends are found for the porosity formation as well. The model also predicts a beneficial effect of applying a ramping procedure during the start-up phase, which is an improvement in comparison with earlier findings obtained with alternative models. In principle, the model does not contain adjustable parameters, but several parameters are not well known. A full quantitative validation not only requires detailed casting trials but also independent determination of some thermophysical parameters of the semisolid mush., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Coarsening within the mushy zone during continuous directional solidification experiments was studied on an Al-30 wt pct Cu alloy. High brilliance synchrotron X-radiation microscopy allowed images to be taken in-situ during solidification. Transient conditions were present during directional solidification. Under these conditions, solute-rich settling liquid flow affects the dendritic array and thus coarsening. Coarsening was studied by following the secondary dendrite arm spacing (SDAS) of a developing dendrite at different local solidification times according to the mush depth and instant interface velocity. Solute enrichment and liquid flow cause deceleration and acceleration of the solidification front, which in turn influences both the mush depth and local growth and coarsening due to variations in solutal gradients and thus local undercooling. In addition, spacing between neighboring dendrites (i.e., primary dendrite arm spacing), which determines permeability within the mushy zone, affects the development of high-order branches., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Thermally induced strains and stresses developed during direct-chill (DC) semicontinuous casting of high strength aluminum alloys can result in formation of micro-cracks in different locations of the billet. Rapid propagation of such micro-cracks in tensile thermal stress fields can lead to catastrophic failure of ingots in the solid state called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine as-cast properties. Application of fracture mechanics, on the other hand, can help to derive the critical crack length leading to failure. In the present research work, the state of residual thermal stresses was determined in an AA7050 billet during DC casting by means of ALSIM5. Simulation results showed that in the steady-state conditions, large compressive stresses form near the surface of the billet in the circumferential direction, whereas in the center, the stresses are tensile in all directions. Magnitudes of von Mises effective stresses, the largest component of principal stresses and the fracture mechanics concepts, were then applied to investigate the crack susceptibility of the billet., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Shrinkage, imposed strain rate, and (lack of) feeding are considered the main factors that determine cavity formation or the formation of hot tears. A hot-tearing model is proposed that will combine a macroscopic description of the casting process and a microscopic model. The micromodel predicts whether porosity will form or a hot tear will develop. Results for an Al-4.5 pct Cu alloy are presented as a function of the constant strain rate and cooling rate. Also, incorporation of the model in a finite element method (FEM) simulation of the direct-chill (DC) casting process is reported. The model shows features well known from literature such as increasing hot-tearing sensitivity with increasing deformation rate, cooling rate, and grain size. Similar trends are found for the porosity formation as well. The model also predicts a beneficial effect of applying a ramping procedure during the start-up phase, which is an improvement in comparison with earlier findings obtained with alternative models. In principle, the model does not contain adjustable parameters, but several parameters are not well known. A full quantitative validation not only requires detailed casting trials but also independent determination of some thermophysical parameters of the semisolid mush., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

The commonly used hyperbolic sine constitutive equation for metal forming at elevated temperatures, with no strain incorporated, is in principle applicable only to deformation in the steady state. However, the actual deformation processes applied to magnesium alloys are mostly in the non-steady state. In the present research, the results of hot uniaxial compression tests of three wrought magnesium alloys covering wide ranges of temperatures and strain rates were used for a strain-dependent constitutive analysis. A strain-dependent constitutive relationship for these alloys was established. It appeared that the apparent activation energy for deformation decreased with increasing the alloying content in these alloys. The constitutive parameters obtained were used to predict flow stresses at given strains and the results were in good agreement with experimental measurements., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

An existing constitutive model for creep, developed by Dorn and Harmathy, is modified in order to be used for fire-exposed aluminum alloys. Two alloys, 5083-O/H111 and 6060-T66, are selected for the development of this constitutive model because of their different behavior at elevated temperature and their frequent application in structures for which fire design is relevant. The material parameters in the model are calibrated with the experimental results of creep tests, carried out with constant load and temperature in time. The model is validated with so-called transient state tests, with a constant load in time (stresses ranging from 20 to 150 N/mm2) and with an increasing temperature (with heating rates ranging from 1.6 °C/min to 11 °C/min and critical temperatures ranging from 170 °C to 380 °C). These tests are considered as representative for fire-exposed, insulated aluminum members. The existing constitutive model of Dorn and Harmathy provides good agreement with the transient state tests carried out for the 5xxx series alloy, but appeared to be not suited for the 6xxx series alloy. This is attributed to the early development of tertiary creep in case of 6xxx series alloys. The existing model was modified to incorporate this first stage of tertiary creep, to arrive at a good agreement between the tests and the modified model for 6xxx series alloys., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

An existing constitutive model for creep, developed by Dorn and Harmathy, is modified in order to be used for fire-exposed aluminum alloys. Two alloys, 5083-O/H111 and 6060-T66, are selected for the development of this constitutive model because of their different behavior at elevated temperature and their frequent application in structures for which fire design is relevant. The material parameters in the model are calibrated with the experimental results of creep tests, carried out with constant load and temperature in time. The model is validated with so-called transient state tests, with a constant load in time (stresses ranging from 20 to 150 N/mm2) and with an increasing temperature (with heating rates ranging from 1.6 °C/min to 11 °C/min and critical temperatures ranging from 170 °C to 380 °C). These tests are considered as representative for fire-exposed, insulated aluminum members. The existing constitutive model of Dorn and Harmathy provides good agreement with the transient state tests carried out for the 5xxx series alloy, but appeared to be not suited for the 6xxx series alloy. This is attributed to the early development of tertiary creep in case of 6xxx series alloys. The existing model was modified to incorporate this first stage of tertiary creep, to arrive at a good agreement between the tests and the modified model for 6xxx series alloys. more...

The purification of gaseous and liquid media by means of a cyclone concept is well known and has been successfully applied in different industries. While the impurities removal from molten metal has been an important issue for many years, to the best of our knowledge, the application of a cyclone concept has rarely been considered for molten metal applications. The presence of impurities in cast products is detrimental to their quality. In this article, computer simulations are used to evaluate the possibilities of cyclone application in molten aluminum processing by determining the following: the fluid flow for flow velocities of 0.01, 0.1, and 1 m/s; the particle behavior for discrete particle sizes in the range of 20 to 100 ?m; and the collection efficiency of the cyclone. The geometrical features are discussed. The results show that the cyclone concept can be effectively used as an alternative method to remove the impurities from a stream of molten aluminum in a wide range of flow regimes., Department of Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

An existing constitutive model for creep, developed by Dorn and Harmathy, is modified in order to be used for fire-exposed aluminum alloys. Two alloys, 5083-O/H111 and 6060-T66, are selected for the development of this constitutive model because of their different behavior at elevated temperature and their frequent application in structures for which fire design is relevant. The material parameters in the model are calibrated with the experimental results of creep tests, carried out with constant load and temperature in time. The model is validated with so-called transient state tests, with a constant load in time (stresses ranging from 20 to 150 N/mm2) and with an increasing temperature (with heating rates ranging from 1.6 °C/min to 11 °C/min and critical temperatures ranging from 170 °C to 380 °C). These tests are considered as representative for fire-exposed, insulated aluminum members. The existing constitutive model of Dorn and Harmathy provides good agreement with the transient state tests carried out for the 5xxx series alloy, but appeared to be not suited for the 6xxx series alloy. This is attributed to the early development of tertiary creep in case of 6xxx series alloys. The existing model was modified to incorporate this first stage of tertiary creep, to arrive at a good agreement between the tests and the modified model for 6xxx series alloys. more...

The commonly used hyperbolic sine constitutive equation for metal forming at elevated temperatures, with no strain incorporated, is in principle applicable only to deformation in the steady state. However, the actual deformation processes applied to magnesium alloys are mostly in the non-steady state. In the present research, the results of hot uniaxial compression tests of three wrought magnesium alloys covering wide ranges of temperatures and strain rates were used for a strain-dependent constitutive analysis. A strain-dependent constitutive relationship for these alloys was established. It appeared that the apparent activation energy for deformation decreased with increasing the alloying content in these alloys. The constitutive parameters obtained were used to predict flow stresses at given strains and the results were in good agreement with experimental measurements., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

The purification of gaseous and liquid media by means of a cyclone concept is well known and has been successfully applied in different industries. While the impurities removal from molten metal has been an important issue for many years, to the best of our knowledge, the application of a cyclone concept has rarely been considered for molten metal applications. The presence of impurities in cast products is detrimental to their quality. In this article, computer simulations are used to evaluate the possibilities of cyclone application in molten aluminum processing by determining the following: the fluid flow for flow velocities of 0.01, 0.1, and 1 m/s; the particle behavior for discrete particle sizes in the range of 20 to 100 ?m; and the collection efficiency of the cyclone. The geometrical features are discussed. The results show that the cyclone concept can be effectively used as an alternative method to remove the impurities from a stream of molten aluminum in a wide range of flow regimes., Department of Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

An existing constitutive model for creep, developed by Dorn and Harmathy, is modified in order to be used for fire-exposed aluminum alloys. Two alloys, 5083-O/H111 and 6060-T66, are selected for the development of this constitutive model because of their different behavior at elevated temperature and their frequent application in structures for which fire design is relevant. The material parameters in the model are calibrated with the experimental results of creep tests, carried out with constant load and temperature in time. The model is validated with so-called transient state tests, with a constant load in time (stresses ranging from 20 to 150 N/mm2) and with an increasing temperature (with heating rates ranging from 1.6 °C/min to 11 °C/min and critical temperatures ranging from 170 °C to 380 °C). These tests are considered as representative for fire-exposed, insulated aluminum members. The existing constitutive model of Dorn and Harmathy provides good agreement with the transient state tests carried out for the 5xxx series alloy, but appeared to be not suited for the 6xxx series alloy. This is attributed to the early development of tertiary creep in case of 6xxx series alloys. The existing model was modified to incorporate this first stage of tertiary creep, to arrive at a good agreement between the tests and the modified model for 6xxx series alloys., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Reactive mixtures based on nano aluminium and nano- or micron size molybdenum trioxide have been pressed. These energetic mixtures have been tested in the Ballistic Impact Chamber and as an energetic projectile impacting a steel plate. Al/ MoO3-based reactive mixtures can be initiated by a controlled mechanical stimulus. The sensitivity depends on deformation velocity, pressing density, addition of fluorine containing binder and particle size. Nanometric mixtures of Al and MoO3 have a shorter time to reaction compared to the corresponding mixtures with micron size MoO3. The sensitivity decreases with increase in porosity. No influence of fuel/oxidizer ratio has been found in the experiments. An extensive deformation is needed before the start of reaction is observed. An analytical evaluation of shear rate cannot be applied as a detailed numerical simulation of the deformation process in PBXN-109 shows. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA. more...

Hot tearing remains a major problem of casting technology despite decades-long efforts to develop working hot tearing criteria and to implement those into casting process computer simulation. Existing models allow one to calculate the stress-strain and temperature situation in a casting (ingot, billet) and to compare those with the chosen hot tearing criterion. In most successful cases, the simulation shows the relative probability of hot tearing and the sensitivity of this probability to such process parameters as casting speed, casting dimensions, and casting recipe. None of the existing criteria, however, can give the answer on whether the hot crack will appear or not and what will be the extent of hot cracking (position, length, shape). This article outlines the requirements for a modern hot tearing model and a criterion based on this model as well as the future development of hot tearing research in terms of mechanisms of hot crack nucleation and propagation. It is suggested that the new model and criterion should take into account different mechanisms of hot tearing that are operational at different stages of solidification and be based on fracture mechanics, i.e., include the mechanisms of nucleation and propagation of a crack., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Direct-chill (DC) cast billets 192 mm in diameter of an Al-Cu-Mg alloy were examined in detail with the aim to reveal the effects of grain refining (GR) and casting speed on structure, “floating” grains, and centerline macrosegregation. Experimental results show that grain size and dendrite arm spacing (DAS) tend to coarsen toward the billet center with a local refinement DAS in the center. In GR billets, grain size does not change much with the cooling rate, casting speed, and grain refiner amount. Coarse-DAS (floating) grains are observed around the billet axis regardless of GR and the amount of Ti, though their amount is significantly higher in GR billets. Macrosegregation profiles show a negligible influence of GR, while the effect of casting speed is large. The concept of solute-depleted floating grains contributing to the centerline macrosegregation is substantiated by microsegregation measurements, which show that, independent of GR, coarse dendrite branches have a depleted concentration plateau in contrast to the fine dendrite arms., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Hot tearing remains a major problem of casting technology despite decades-long efforts to develop working hot tearing criteria and to implement those into casting process computer simulation. Existing models allow one to calculate the stress-strain and temperature situation in a casting (ingot, billet) and to compare those with the chosen hot tearing criterion. In most successful cases, the simulation shows the relative probability of hot tearing and the sensitivity of this probability to such process parameters as casting speed, casting dimensions, and casting recipe. None of the existing criteria, however, can give the answer on whether the hot crack will appear or not and what will be the extent of hot cracking (position, length, shape). This article outlines the requirements for a modern hot tearing model and a criterion based on this model as well as the future development of hot tearing research in terms of mechanisms of hot crack nucleation and propagation. It is suggested that the new model and criterion should take into account different mechanisms of hot tearing that are operational at different stages of solidification and be based on fracture mechanics, i.e., include the mechanisms of nucleation and propagation of a crack., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

Direct-chill (DC) cast billets 192 mm in diameter of an Al-Cu-Mg alloy were examined in detail with the aim to reveal the effects of grain refining (GR) and casting speed on structure, “floating” grains, and centerline macrosegregation. Experimental results show that grain size and dendrite arm spacing (DAS) tend to coarsen toward the billet center with a local refinement DAS in the center. In GR billets, grain size does not change much with the cooling rate, casting speed, and grain refiner amount. Coarse-DAS (floating) grains are observed around the billet axis regardless of GR and the amount of Ti, though their amount is significantly higher in GR billets. Macrosegregation profiles show a negligible influence of GR, while the effect of casting speed is large. The concept of solute-depleted floating grains contributing to the centerline macrosegregation is substantiated by microsegregation measurements, which show that, independent of GR, coarse dendrite branches have a depleted concentration plateau in contrast to the fine dendrite arms., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...

The invention relates to a method of recovering a metal from a mixture comprising more than one metal. According to the invention, the methods comprises the steps of (a) melting the mixture to produce a melt; (b) passing the melt over a cooled surface, causing the metal to be recovered to crystallise out on the cooled surface and a desired metal-depleted melt is discharged from the cooled surface, Mechanical, Maritime and Materials Engineering more...

The invention relates to a method of recovering a metal from a mixture comprising more than one metal. According to the invention, the methods comprises the steps of (a) melting the mixture to produce a melt; (b) passing the melt over a cooled surface, causing the metal to be recovered to crystallise out on the cooled surface and a desired metal-depleted melt is discharged from the cooled surface, Mechanical, Maritime and Materials Engineering more...

Method for reactively joining materials in solid form, such as intermetallic compounds and technical ceramics, wherein: a) a mixed powder is provided in solid form between the materials to be joined; b) at least the powder mixture is locally heated, causing exothermic reactions to take place, whereby the heat is released at the contact surfaces of the materials to be joined, where it causes a local melting; and c) subsequently cools down. At least one of the materials to be joined has a melting point coinciding with the melting point of the lowest-melting component in the powder mixture; and the exothermic process is initiated at a temperature before the melting point of one of the materials to be joined is reached, Mechanical, Maritime and Materials Engineering more...

Method for reactively joining materials in solid form, such as intermetallic compounds and technical ceramics, wherein: a) a mixed powder is provided in solid form between the materials to be joined; b) at least the powder mixture is locally heated, causing exothermic reactions to take place, whereby the heat is released at the contact surfaces of the materials to be joined, where it causes a local melting; and c) subsequently cools down. At least one of the materials to be joined has a melting point coinciding with the melting point of the lowest-melting component in the powder mixture; and the exothermic process is initiated at a temperature before the melting point of one of the materials to be joined is reached, Mechanical, Maritime and Materials Engineering more...

The invention relates to a method of preparing an Al-Ti-B grain refiner for cast aluminium-comprising products. According to the invention the preparation is realized by mixing powders selected from the group comprising aluminium, titanium, boron, and alloys and intermetallic compounds thereof, compressing, heating in an inert environment until an exothermic reaction is initiated and cooling. It has been shown that when the grain refiner thus prepared is applied, the quality of cast products remains substantially constant even during lengthy casting processes. The invention also relates to a method of casting aluminium products., Materials Science and Engineering, Mechanical, Maritime and Materials Engineering more...