Direct Chill Casting Research Articles

Researches on the Macro- and Micro-Structures and Properties of the Vertical Bending Continuous Casted AA6063 Thin Slabs and Their As-Rolled Sheets

A 6063 aluminum alloy thin slab with a cross-section of 260 × 40 mm2 was prepared by a vertical bending continuous casting (VC) process. The effects of homogenization, hot rolling and subsequent heat treatments on the microstructure and properties of the as-cast slabs and as-rolled sheets were investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), field emission electron probe (EPMA), macro- and micro-structure observation and tensile tests. The results show that the as-cast structure of AA 6063 was dominated by fine and uniform equiaxed grains. After homogenization, all Mg2Si phases dissolved back, and the Fe-containing intermetallic phases changed from acicular β-Al5FeSi phase to spherical α-Al8Fe2Si phase. Homogenizing heat treatment before hot rolling can improve the mechanical properties of the alloy. However, in the case of direct rolling without homogenization, the alloy still has good mechanical properties; the strength and plasticity are comparable to that obtained through traditional direct chill (DC) casting, homogenizing and extruding processes, indicating that the VC process has the potential to realize continuous casting and rolling.

Mechanical properties and microstructure of a high-quality Mg-Nd alloy ingot with large size manufactured by direct chill casting

In this work, a high-quality Mg-2.85Nd-0.25Zn-0.5Zr (wt%) alloy ingot with a diameter of 280 mm was successfully fabricated by direct chill casting. There was no obvious composition segregation along the radial direction of the ingot. The large temperature gradient along the radial direction, accurately the higher cooling rate in the surface, gives rise to both grain size and eutectic compounds fraction to gradually decrease from the center to the surface. This results in varying mechanical properties at different positions, such as higher strength and ductility in the surface than in other positions. The peak-aged alloy exhibited a higher strength-ductility synergy, with tensile strength of 282 MPa and elongation of 12.5%, than other Mg-Nd based alloys processed by permanent mold casting and sand casting. Furthermore, it is worth noting that the peak-aged alloy manifested significant strain hardening and high heat resistance, as evidenced by liner strain hardening at temperatures between 100 and 250 °C, which is mostly due to stable solute hardening triggered by the large atomic radius of Nd atoms in the α-Mg matrix. These findings provide references for the application and manufacture of large-scale magnesium alloy ingots. • A high-quality Mg-2.85Nd-0.25Zn-0.5Zr (wt%) alloy ingot with a diameter of 280 mm was successfully fabricated by direct chill casting. • The fraction of eutectic compounds increases and the grain size decreases from the center to the surface. • The alloy exhibited higher strength-ductility synergy than other Mg-Nd based alloys processed by permanent mold casting and sand casting. • The alloy showed abnormal strain hardening at high temperatures, rather than strain softening.

Effect of floating grains on the deformed microstructure of Mn- and Cr-containing Al-Mg-Si-Cu alloys

The effects of floating grains on the deformed microstructure of a Mn- and Cr-containing Al-Mg-Si-Cu alloy were first clarified based on a comparative study of the dispersoid precipitation and recrystallization behavior with and without floating grains. The presence of floating grains in the direct-chill casting billets resulted in inhomogeneous and sparse precipitation of the α-Al(Mn,Cr)Si dispersoids after homogenization. In response, the Zener drag force was significantly reduced and severe localized recrystallization occurred in the specimen containing floating grains after hot working. Whereas, the specimen without floating grains, which had dense and fine dispersoids, still had an ideal recovery microstructure after solution soaking. The innate reason consists in the special microscale features of floating grains, which significantly decreased the nucleation rate of the dispersoids-forming β′ precipitates.

Modelling of solidification structure and macro-segregation in an industrial DC cast slab

A cellular automaton (CA)-finite element (FE) model was implemented for multi-scale modelling of micro-segregation, mesoscopic grain structure and macroscopic segregation during direct chill (DC) casting of industrial billets or slabs. The macroscopic transport of mass, momentum, energy and solutes was solved on an FE grid, while the mesoscopic grain structure governed by nucleation, growth kinetics and grain evolution was calculated on a CA grid. The solidification path was determined using a modified micro-segregation model for multi-component aluminium alloys. An Euler representation was used for pre-processing and post-processing, and a Lagrangian representation was used for expanding the calculation domain and for resolving the CAFE model. By simulating a DC casting experiment of the 2024 aluminium alloy, a typical grain structure was reproduced, and the composition map showed a reasonable deviation. This model was applied to an industrial-scale DC cast slab of an Al-3.5Cu-1.5 Mg (wt. %) alloy, and three simulations with different nucleation undercoolings were performed for a grain-unrefined slab, a grain-refined slab and an equilibrium solidified slab, respectively. The slabs tended to solidify at equilibrium with the decreasing nucleation undercooling. The earlier release of latent heat yielded a smaller liquid undercooling region ahead of the solidification front, and a finer grain structure. A typical grain structure with coarse equiaxial grains at the centre and fine columnar grains near the bottom surface as well as sidewall was observed for the grain-unrefined slab. By contrast, the grain structure of the grain-refined slab was fully equiaxial. Furthermore, the grain structure, temperature field, melt flow and macro-segregation were quantitatively investigated.

Effect of temperature field on the porosity and mechanical properties of 2024 aluminum alloy prepared by direct chill casting with melt shearing

Porosity severely deteriorates the mechanical properties of aluminum alloys. Large-sized and aggregated porosity often occurs in the center of Direct-Chill (DC) cast ingot. The variation of the temperature field in the sump affects the formation of porosity. In the present work, high shear technology was introduced into the DC casting process and the rotation speed and position of the high shear device were precisely controlled based on the measured temperature fields of conventional DC casting to realize the control of the temperature field and study its effects on the microstructure and mechanical properties of DC cast ingot. The results showed that when the temperature of the melt near the shear site (TS) was close to the temperature of the melt near the center of ingot and at starting position of the slow cooling zone of conventional DC casting (TG), forced convection can affect the cooling zone which is below the graphite ring in the sump, resulting in uniform microstructure of the ingot. If TS was above the liquidus and close to TG (temperature field II), the microstructure shows rod grains with fine secondary dendrite arms, refined porosity and second phase particles. For the lower TS which is below the liquidus and close to TG, (temperature field III), the mixed microstructure of spherical grains and small equiaxed was formed. And the increase of size and content of porosity can decrease of mechanical properties of the ingot. The concomitant relationship between floating/spherical grains and porosity was also discovered and discussed.

Formation of intermetallic phases in unrefined and refined AA6082 Al alloys investigated by using SEM-based ultramicrotomy tomography

• Microstructure of AA6082 Al alloys was studied using SEM serial ultramicrotomy tomography. • The formation sequence of intermetallic phases is related to the coarsening of α-Al dendrites. • TiB 2 particles act as nuclei for the formation of β, α intermetallics and Mg 2 Si. • The grain refinement processing causes the severe interconnectivity of α-intermetallics. • Melt shearing is better to uniformly distribute and refine intermetallics than grain refiner. The spatial arrangement, distribution and morphology of Fe-bearing intermetallics in AA6082 alloys depends on the manufacturing process of the alloy and thus influences the macroscopic properties. Here, the microstructure of a near industrial scale casting AA6082 Al alloy fabricated by: (a) direct chill casting, (b) Al-5Ti-1B grain refiner addition and (c) intensive melt shearing has been investigated by three-dimensional visualization using SEM-based serial ultramicrotomy tomography. The formation sequence of phases in AA6082 alloys is generally categorized into four stages: formation of α-Al grains, Fe-bearing intermetallics, Mg 2 Si phase, and eutectic rosettes. Results of three-dimensional visualization of the microstructure indicated that TiB 2 particles not only could nucleate Fe-bearing β-intermetallics, but also could provide substrate for the formation of Fe-bearing α-intermetallics and Mg 2 Si. A further deep analysis reveals that the essential condition for the formation of secondary phases such as Fe-bearing intermetallics and Mg 2 Si phase is the build-up of a supersaturated solute front at the α-Al solid-liquid interface irrespective of the specific nucleation site. In addition, the results indicate that grain refinement processing causes the severe interconnectivity of Fe-bearing α-intermetallics. However, the intensive melt shearing is a better manufacturing process because the intermetallics are more evenly distributed and refined than with the addition of the grain refiner, thereby improving the properties of the alloy.

Numerical simulation of DC casting of large-size rare earth magnesium alloy ingot under low-frequency electromagnetic field

For studying the changes of macro-physical field in the casting process of large-scale rare earth magnesium alloy, through the numerical simulation method, a two-dimensional axisymmetric multi-physical field coupling model was established by using the multi-physical simulation software COMSOL Multiphysics. The changes of temperature field, flow field, Lorentz force, and liquid fraction of large-size rare earth magnesium alloy with diameter of 750 mm under different electromagnetic parameters (magnetic field frequency and current intensity) in steady state of direct-chill (DC) casting were studied. The results reveal that using a magnetic field can reduce the temperature gradient and greatly accelerate the melt flow, the depth of the sump is reduced by about 50 mm. As the current intensity rises, the flow rate in the melt becomes accelerated, the sump depth becomes shallower, while the melt area with a liquid fraction of 0.5 to 0.63 increases. The Lorentz force rises as the magnetic field frequency increases, but the skin depth of the magnetic field decreases from 64.9 to 36.4 mm.

Microstructure, Precipitates Behavior, and Mechanical Properties of Age-Hardened Al-Mg-Si Alloy Sheet Fabricated by Twin-Roll Casting.

Twin-roll casting (TRC), as a near-net-shape technology, is employed to fabricate age-hardened Al-Mg-Si alloy. Compared with conventional direct chill (DC) casting, the TRC method is much more economical and efficient. In this work, the microstructure, precipitates behavior, and mechanical properties of age-hardened Al-Mg-Si alloy sheet fabricated by TRC were investigated by hardness measurements and tensile tests, metallographic microscopy, field emission gun scanning electron microscope, electron backscatter diffraction, transmission electron microscopy, and differential scanning calorimetry analyses. It was found that the size of recrystallized grains for DC casting alloy with finely dispersed particles was larger than that of TRC alloy with coarse particles. Typical CubeND texture accompanied by P texture formed after solution treatment made the value of r reach ~0.7 in the TRC alloy due to the PSN effect caused by the segregation of particles. More GP zones resulted in the strength of TRC alloy being higher than that of DC casting alloy after T8X treatment. With the time of paint-bake hardening extended to 8 h, few segregation particles remained in the TRC alloy. This decreased the concentration of supersaturated atoms. The hardness of the TRC alloy with the lower density of the β″ strengthening phase was lower compared to the DC casting alloy.

Effect of aging treatment on the microstructure, fracture toughness and fracture behavior of the extruded Mg-7Gd-2Y–1Zn-0.5Zr alloy

A commercial scale Mg-7Gd-2Y–1Zn-0.5Zr alloy extrusion rod with synergetic high yield strength of 350 MPa and fracture toughness KIC of 22.4 MPa m1/2 was fabricated by direct-chill casting, hot extrusion and subsequent aging treatment at 200 °C for 108 h. The microstructures and mechanical properties of the as-extruded and peak-aged alloys were investigated, and the fracture toughness and fracture mechanisms before and after aging treatment were also analyzed. The results showed that the as-extruded alloy consisted of long period stacking ordered (LPSO) phase and bimodal matrix microstructure composed of fine dynamic recrystallized (DRXed) grains and coarse deformed grains. Microstructural analysis near fracture surfaces indicted that twinning was activated in the coarse deformed grains during fracture toughness test, which may be conducive to the improvement of the fracture toughness of the alloys. The lamellar-shaped LPSO phases enhanced the fracture toughness since the formation of secondary cracks parallel to the lamellar LPSO can cause significant energy dissipation and deflection of main crack. The micro-cracks were initiated and propagated in the bulk LPSO phases, which may deteriorate the fracture toughness. Large amount of nano β' phase precipitated in the T5 peak-aged alloy significantly improved the strength of the alloy. Fractography analysis indicated that fracture mechanism changed from ductile fracture of the as-extruded alloy to quasi-cleavage fracture of the peak-aged alloy. The precipitation of β' would suppress twin growth and induce the microcracks initiated at the DRXed grain boundaries and in the deformed grains, which led to slight decrease of KIC.

Hot-top direct chill casting assisted by a twin-cooling field: Improving the ingot quality of a large-size 2024 Al alloy

Microstructure inhomogeneity and negative segregation have long been challenges for large-size alloy ingots, directly affecting the downstream processing and final performance of products. Here, we used 2024 aluminum alloy as a model alloy to propose a technique, named double-cooling field casting, i.e., one 2024 Al alloy rod (Φ20 mm) at room temperature was introduced into the melt along the central axis of the hot-top with the protection of a thermal-insulation tube during the direct chill (DC) casting process of a Φ300 mm 2024 Al alloy ingot. The results show that the introduction of the same alloy solid insert has a remarkable influence on refining grains in the center region of the ingot, reducing negative centerline segregation and decreasing the depth of the center part of the sump. With the application of the 2024 Al insert, the mean size of equiaxed grains at the center part of the ingot decreased from 1204 ± 132 μm to 721 ± 69 μm. The relative deviation of the Cu and Mg main solutes reduced from -0.062 and -0.054 to -0.03 and -0.024, respectively, and the sump depth decreased from 280 mm to 242 mm. Moreover, the shape of the solidification front was changed from ‘V’-shaped to ‘W’-shaped. The ingot quality was thus improved, mainly arising from the dissolution of the cold 2024 Al insert at a proper position of the hot-top counteracting some latent heat of solidification of the ingot, dissipating the heat of the central part of the hot-top by conducting the 2024 Al insert to the outside, and providing extra-nuclei from the unmolten α-Al particles of the insert.

Grain Size and Macrosegregation Control of Large-Sized AA2219 Billets by Internal Electromagnetic Stirring in DC Casting

This work focuses on the effect of internal electromagnetic stirring (IEMS) on grain size and macrosegregation in direct-chill (DC) casting of an AA2219 billet with a diameter of 880 mm. The IEMS process has been applied to provide forced convection within the solidifying melt to achieve an efficient reduction of mean grain size and alleviate the formation of macrosegregation. Two casting electromagnetic parameters (the stirring electric current and frequency) of the IEMS process were applied to assess the uniformity of the microstructure and macrosegregation of the billet. The experimental results show that finer and more uniform grains in the billet prepared by the IEMS process than those of traditional DC casting have been observed. The IEMS process has a great influence on the improvement of the macrosegregation, but the greater electromagnetic field would result in worse macrosegregation in the center of the billet.

Effect of EMS Process on the Primary Si Refinement, Tensile and Fatigue Properties of Hyper-eutectic Al-15wt.%Si Alloy

This study investigated the effect of the electromagnetic stirring (EMS) process on the microstructure and mechanical properties of hyper-eutectic Al-15 wt.%Si alloy. The tensile and high-cycle fatigue properties of the EMS Al-15wt.%Si alloy were examined and compared with conventional direct chill (DC) cast alloy. The initial microstructure of the as-cast DC alloy showed a coarse primary Si of 70 µm, in contrast to the size (40 µm) of the as-cast EMS alloy. The DC extruded alloy exhibited a massive primary Si size of 40~55 µm. In contrast, the EMS extruded alloy had a spherical primary Si with 30~40 µm sizes. The average grain sizes were measured to be 8.8 µm (EMS extruded alloy) and 11.4 µm (DC extruded alloy), respectively. The EMS process was confirmed to contribute to the refinement of the grain size and the primary Si size of the hyper-eutectic Al-Si alloy. The yield strengths at room temperature were measured to be 388.0 MPa (EMS extruded alloy) and 375.0 MPa (DC extruded alloy), and the tensile strengths were 426.0 MPa (EMS extruded alloy) and 412.4MPa (DC extruded alloy), respectively. The elongations of both alloys were similar at room temperature. The fatigue limit of the EMS extruded alloy (130 MPa) was higher than that of the DC extruded alloy (120 MPa). The EMS extruded alloy exhibited superior fatigue resistance compared to the DC extruded alloy, regardless of the cyclic stress condition. This study also discussed the potential value of the EMS process as a method for improving the properties of hyper-eutectic Al-Si alloy, as well as the deformation and fracture mechanisms of the EMS Al-15wt.%Si alloy.

Processing map of 2219 Al alloy prepared by internal electromagnetic stirring direct chill casting

Hot compression tests are carried out for the 2219 Al alloys, which are prepared by conventional direct chill casting and internal electromagnetic stirring direct chill casting respectively. The processing maps are constructed and the as-deformed microstructures are observed to investigate the effects of internal electromagnetic stirring on the hot deformation of 2219 Al alloy. The results show that the internal electromagnetic stirring expends of stability domain, especially increasing the corresponding range of strain temperature. The suitable deformation parameters of internal electromagnetic stirring direct chill casting 2219 Al alloy includes a relatively lower strain temperature and a relatively higher strain rate. The internal electromagnetic stirring promotes the formation of more homogeneous as-deformed microstructures and more dynamic recrystallization grains.

Impact of thermal exposure on the microstructure and mechanical properties of a twin-roll cast Al-Mn-Fe-Si strip

Al-Mn-Fe-Si strips were fabricated via both the twin-roll casting (TRC) and the more conventional route, direct-chill casting (DC). The two types of strips prepared were subjected to thermal exposure at a series of temperatures. Uniaxial tensile tests after the thermal exposure showed that while the DC strip presented a ∼74% decrease in the yield strength and ∼35% decrease in the ultimate tensile strength (UTS) after being exposed to 350 °C for 12 h, the TRC strip, in contrast, maintained its strength at temperatures up to ∼460 °C for the same duration. Systematic microstructure characterization revealed that the different thermal stability in the strength of the two types of strips arised from their distinct evolution in grain morphology and second phase particles during the thermal exposure. The calculation based on Cahn-Lücke-Stüwe (CLS) model suggested that due to the highly supersaturated solute atoms, at the beginning of the thermal exposure, the TRC strip experienced a strong solute drag which reduced the grain boundary migrating velocity to a value that is orders of magnitude smaller than that in the DC strip. With the progress of the thermal exposure, the solute atoms precipitated out, forming densely distributed second phase particles. For one thing, these particles stabilized the grain structure by inducing Zener pinning pressure which could be ten times higher than that in the DC strip, depending on the temperature. For another, they acted as dislocation obstacles and compensated for the strength loss owing to decreasing solution hardening. Both effects contributed to the TRC strip's fairly stable strength regarding thermal exposure below 460 °C. The present work could guide the direct application of the TRC strips in the industry. The results should also be helpful for the development of a fundamental framework for designing advanced TRC Al strips with improved mechanical properties at elevated temperatures.

Improvement of strength and ductility synergy in a room-temperature stretch-formable Mg-Al-Mn alloy sheet by twin-roll casting and low-temperature annealing

• Twin-roll casting leads to the formation of uniform and fine grain structures. • The microstructure feature is effective to improve strengths-ductility synergy. • In-plane isotropic tensile property and good RT formability have been obtained. Strength and ductility synergy in an Mg-3mass%Al-Mn (AM30) alloy sheet was successfully improved via twin-roll casting and annealing at low-temperature. An AM30 alloy sheet produced by twin-roll casting, homogenization, hot-rolling, and subsequent annealing at 170 °C for 64 h exhibits a good 0.2% proof stress of 170 MPa and a large elongation to failure of 33.1% along the rolling direction. The sheet also shows in-plane isotropic tensile properties, and the 0.2% proof stress and elongation to failure along the transverse direction are 176 MPa and 35.5%, respectively. Though the sheet produced by direct-chill casting also shows moderate strengths if the annealing condition is same, the direct-chill casting leads to the deteriorated elongation to failure of 23.9% and 30.0% for the rolling and transverse directions, respectively. As well as such excellent tensile properties, a high room-temperature stretch formability with an Index Erichsen value of 8.3 mm could be obtained in the twin-roll cast sheet annealed at 170 °C for 64 h. The annealing at a higher temperature further improves the stretch formability; however, this results in the decrease of the tensile properties. Microstructure characterization reveals that the excellent combination of strengths, ductility, and stretch formability in the twin-roll cast sheet annealed at the low-temperature annealing is mainly attributed to the uniform recrystallized microstructure, fine grain size, and circular distribution of (0001) poles away from the normal direction of the sheet.

Numerical study on transient melt oscillation and solidification characteristic during magnesium alloy direct chill casting under out-of-phase pulsed magnetic field

Understanding the complex physical fields during electromagnetic DC casting remains limited through experiments as these physical quantities are hard to measure in a molten melt. Numerical simulation is a desirable way to make clear the physical field involved when investigating the parameters of DC casting. The present work used a two-dimensional multi-field coupling model based on the finite element method and investigated the influences of out-of-phase pulsed magnetic field (PMF) on the transient fluid flow and heat transfer process during the direct chill (DC) casting of an AZ80 magnesium alloy billet with a diameter of 500 mm. Effects of pulsed parameters (current intensity, frequency, duty cycle and phase difference) on transient Lorentz force, melt oscillation behavior, temperature field and solidification characteristic were investigated systematically. Results show that in order to realize desirable metallurgical transport behaviors, including the forceful stirring and vibration with a certain intensity and depth, uniform temperature distribution, and faster cooling rate, the pulsed parameters should be set within a reasonable range, that is, the current intensity is 250 A, the frequency is 10 Hz, the duty cycle is 20% and the phase difference is between 36° and 72°

The effect of melt flow induced by RMF on the meso- and micro-structure of unidirectionally solidified Al–7wt.% Si alloy Benchmark experiment under magnetic stirring

This work deals with the effect of melt flow on the solidified structure by RMF. The microstructure of the first non-stirred part of the Al-7Si alloy is columnar. After switching on stirring first a transient zone was formed with eutectic “cupola”. After the first transient zone, the “Christmas Tree Like” microstructure was formed. During the solidification of stirred part, a “tulip-like” interface evolves. During the last two decades, many algorithms were developed to simulate the solidification process for different casting methods like ingots, continuous casting of steel and the direct chill cast of aluminum. Experiments performed under exactly known conditions and with the detailed knowledge of meso- and micro-structures are required for validating these simulations. The aim of this paper is to give a data set to validate these simulations. Unidirectional solidification experiments were performed by using a rotating magnetic field (RMF) to study the effect of melt flow on the solidified micro- and meso-structure of the Al–7wt.% Si binary alloy. The first and the third 1/3 parts of samples were solidified without magnetic stirring, and the second (middle) 1/3 part was solidified by using magnetic stirring. The magnetic induction was 10 mT, the temperature gradient was ∼7 K/mm, and the sample movement velocity was 0.1 mm/s. On the longitudinal section of the sample, the columnar/equiaxed transition (CET), the equiaxed/columnar transition (ECT), the secondary dendrite arm spacing (SDAS), and the macrosegregation (concentration distribution and the amount of eutectic) were investigated. The primary dendrite arm spacing (PDAS) and the grain structure were studied on the cross-section after color etching. The effect of melt flow induced by RMF on the meso- and microstructure of unidirectionally solidified Al–7wt.% Si alloy Benchmark experiment under magnetic stirring .

Numerical and Experimental Study on the Direct Chill Casting of Large-Scale AA2219 Billets via Annular Coupled Electromagnetic Field.

The internal coupled electromagnetic melt treatment (ICEMT) method is firstly proposed to produce high-quality and large-sized aluminum alloy billets. A three-dimensional model was established to describe the ICEMT process of direct chill casting (DC casting). The effect of ICEMT on the fluid flow patterns and temperature field in the DC casting of ϕ880 mm AA2219 billets is numerically analyzed. Moreover, the mechanisms of the ICEMT process on grain refinement and macrosegregation were discussed. The calculated results indicate that the electromagnetic field appears to be coupled circinate at the cross section of the melt, the fluid flow becomes unstable accompanied by the bias flow, and the temperature profiles are significantly more uniform. An experimental verification was conducted and the results prove that compared with traditional direct chill casting, the microstructures of the AA2219 large-scale billet under the ICEMT process are uniform and fine.

Effects of Intercooling Intensity on Temperature Field and Microstructure of Large-Scale 2219 Al Alloy Billet Prepared by Internal Electromagnetic Stirring Casting.

Internal electromagnetic stirring is an advanced melt treatment method, which can be used in direct chill casting to prepare large-scale Al alloy billets. Intercooling intensity is a primary parameter of internal electromagnetic stirring; its effects on temperature fields and microstructures have been investigated via numerical simulations and industrial experiments, respectively. The simulated results show an increase in the intercooling affected area and a decrease in sump depth with an increase in the intercooling heat transfer coefficient. The heat transfer coefficient should not exceed 500 W/(m2 °C) because the solid fraction of the intercooling end bottom may exceed 50%. The experiment’s results demonstrate that the average grain sizes in the edge, 1/2 radius, and center are 151 ± 13 μm, 159 ± 14 μm, and 149 ± 16 μm, respectively, under a liquid nitrogen flow rate of 160 L/min, which is much finer than that of 80 L/min and more homogeneous than that of 240 L/min. Furthermore, an experimental liquid nitrogen flow rate of 80 L/min, 160 L/min, and 240 L/min approximately correspond to the simulated heat transfer coefficient of 200 W/(m2 °C), 300 W/(m2 °C), and 400 W/(m2 °C), respectively.

Al-Mn Intermetallics in High Pressure Die Cast AZ91 and Direct Chill Cast AZ80

Manganese-bearing intermetallic compounds (IMCs) are important for ensuring adequate corrosion performance of magnesium-aluminium alloys and can be deleterious to mechanical performance if they are large and/or form clusters. Here, we explore the formation of Al-Mn IMCs in Mg-9Al-0.7Zn-0.2Mn produced by two industrial casting processes, high-pressure die casting (HPDC) and direct chill (DC) casting. As Al8Mn5 starts forming above the α-Mg liquidus temperature in this alloy, we consider its formation during melt handling as well as during casting and heat treatment. In HPDC, we focus on sludge formation in the holding pot, partial solidification of IMCs in the shot chamber, and Al-Mn IMC solidification in the die cavity. In DC casting, we focus on interactions between Al-Mn IMCs and oxide films in the launder system, Al-Mn IMC solidification in the billet, and the partial transformation of Al8Mn5 into Al11Mn4 during solution heat treatment. The results show that minimising pre-solidification in the shot sleeve of HPDC and controlling pouring and filtration in DC casting are important for ensuring small Al-Mn intermetallic particles in these casting processes.