La-rich Phase Research Articles

Structure, Magnetic and Magnetocaloric Properties of Attempted P Substitutions in LaFe<sub>11.5</sub>Si<sub>1.5</sub> Giant Magnetocaloric Material

Recent theoretical and experimental studies suggested that P can enter the structure of La(Fe,Si)13 alloys and lead to a significant enhancement of the isothermal entropy change, one of the two main quantities characterizing the magnetocaloric effect. Here, we report a systematic study of P for Si substitutions in La(Fe,Si)13 alloys. Eight LaFe11.5Si1.5-xPx polycrystalline bulk samples with 0 ≤ x ≤ 0.2 were prepared by arc-melting followed by heat treatment. Powder x-ray diffraction and SEM/EDX analyses show that the α-Fe secondary phase progressively increases with the increase in P substitutions and that a La-rich LaP secondary phase appears. We therefore found that P does not actually enter the main La(Fe,Si)13 phase. Magnetization and DSC measurements confirm this interpretation as the Curie temperatures of La(Fe,Si,P)13 alloys are nearly insensitive to P for Si substitutions and the latent heat of the first-order ferromagnetic transition decreases with the increase in nominal P substitutions. Our work put into questions former reports of the literature on P addition in La(Fe,Si)13 and highlights the particularly complex synthesis of these alloys.

Effect of Mn content in the Ti/Zr-based AB2 Laves type alloys on their electrochemical performance

In this work, we studied the impact of Manganese content on the structural and electrochemical properties of the AB2 Laves phase alloys. These multicomponent alloys were composed of 7 individual constituents with a composition Ti0.15Zr0.85La0.03V0.12Mn0.7+xFe0.12Ni1.2 and a variable Manganese content, x = 0.021, 0.035, 0.070. The alloys were prepared using arc melting and rapid solidification techniques. These alloys were characterized by X-ray diffraction and Scanning Electron Microscopy with X-ray Energy Dispersive Spectroscopy allowing to probe the phase-structural composition of the alloys, their microstructures, and elemental distribution among the phase constituents. The rapidly solidified alloys exhibited refined microstructures with a more uniform elemental distribution compared to their as-cast counterparts, the latter containing larger grain sizes and clustered La-rich phases. C15 and C14 Laves type structures contributed to the phase-structural composition of the alloys, with their proportions influenced by the Manganese content and the chosen preparation method. The study revealed a multi-feature relationship between the Manganese content, the phase abundances, and the electrochemical performances, with notable disparities between as-cast and rapidly solidified alloys. The alloy containing 3 wt% Manganese demonstrated the highest discharge capacity and superior activation performance for both preparation methods, suggesting the best choice when optimizing the composition of the anodes for achieving the best battery performance. The highest hydrogen diffusion rate was observed for the alloy containing 10 wt% Manganese which can be related to the catalytic role of Manganese in the processes of hydrogen exchange when present in these alloys.

Microchannel magnetic regenerators with optimized porosity by electrodischarge drilling: Microstructure and refrigeration performance

In this study, electrodischarge drilling is proposed to prepare LaFe11Co0.8Si1.2 magnetic regenerator with circular microchannels. We find that the drilling process leads to the microstructure consisting of the dominant α-Fe phase and sporadic distributed La-rich phase near the channel surface. In contrast, the microstructure away from the channels is not influenced and shows the typical dendritic morphology. Upon annealing, the microchannel blocks show a maximum entropy change of 6.0 J kg−1 K−1 at 0–2 T around room temperature. Further, we evaluated the regeneration performance of our magnetic refrigerators by using a one-dimension active magnetic regeneration numerical model, and a considerable specific cooling power of 11.1–18.3 W kg−1 is obtained. This study suggests electrodischarge drilling as a promising method for fabricating magnetocaloric regenerators with circular microchannels.

Role of phosphorus impurities in decomposition of La2NiO4–La0.5Ce0.5O2-δ oxygen electrode in a solid oxide electrolysis cell

This study explored the decomposition mechanism of a La2NiO4 (LNO) phase in the La2NiO4–La0.5Ce0.5O2-δ (LNO-LDC) oxygen electrode in a solid oxide electrolysis cell (SOEC) after testing at 800 °C. Scanning electron microscopy and scanning transmission electron microscopy examinations of the LNO-LDC oxygen electrode before and after testing were undertaken. Other than phosphorus contamination in the form of P-rich grains and P-rich deposits along all grain boundaries (GBs), LNO and LDC phases were intact without degradation in the as-fabricated electrode. However, mild to aggressive LNO phase decomposition triggered by the phosphorus poisoned GBs was observed after testing at 800 °C for 900 h. The evolution of the LNO phase decomposition was noted beginning with the exsolution of Ni into the surrounding LNO matrix and GBs, forming La-rich and Ni-rich phases correspondingly, in the LNO. This study illustrates a detailed decomposition progress of the LNO phase at the atomic level under an SOEC operation condition, and sheds light on how to ameliorate the fabrication process of SOECs to enhance their performance and durability.

Understanding La2NiO4-La0.5Ce0.5O2 Oxygen Electrode Phase Evolution in a Solid Oxide Electrolysis Cell

This work aims to understand the decomposition mechanism of a La2NiO4 phase in La2NiO4-La0.5Ce0.5O2 (LNO-LDC) oxygen electrodes after testing in a solid oxide electrolysis cell (SOEC) at 800oC. Scanning/transmission electron microscopy (S/TEM) examination of LNO-LDC electrode at atomic level before and after testing was undertaken. Pure LNO and LDC phases as well as a low density of lanthanum phosphate (LPO) grains were detected in the as prepared (untested) oxygen electrode. P enrichment, a potential constituent in some of the synthesis additives, was found as small, nanometer scale, deposits along all grain boundaries which is suggested to poison the LNO phase during SOEC operation. Mild to aggressive decomposition of La2NiO4-La0.5Ce0.5O2 (LNO-LDC) oxygen electrode was observed after SOEC operating at 800 °C at 1.3V for 920 hours. Detailed microstructural and microchemical characterization of the decomposed regions was performed using an aberration (CS) corrected JEM-ARM200CF transmission electron microscope operated at 200 kV. The evolution of the LNO phase decomposition was noted beginning with the expulsion of Ni into the surrounding LNO matrix and grain boundaries, forming La-rich and Ni-rich phases in the LNO correspondingly. An acicular La2O3 phase was always noted initiating at either the LNO/LDC or LNO/LNO interfaces, growing and eventually intersecting one another, especially in aggressively decomposed regions. Initial decomposition exhibited single layers of Ni atoms along (004) plane of LNO, followed by gradual formation of La3Ni2O7, LaNiO3, and fine NiO (several nanometer in size) phases during moderate to aggressive decomposition. In addition, NiO was noted at LDC/LDC grain boundaries ranging from a few to several tens of nanometers thick. This presentation will demonstrate how P contamination may affect the stability of SOEC cells.

Effects of La Addition on Microstructure Evolution and Thermal Stability of Cu-2.35Ni-0.59Si Sheet.

A Cu-2.35Ni-0.69Si alloy with low La content was designed in order to study the role of La addition on microstructure evolution and comprehensive properties. The results indicate that the La element demonstrates a superior ability to combine with Ni and Si elements, via the formation of La-rich primary phases. Owing to existing La-rich primary phases, restricted grain growth was observed, due to the pinning effect during solid solution treatment. It was found that the activation energy of the Ni2Si phase precipitation decreased with the addition of La. Interestingly, the aggregation and distribution of the Ni2Si phase, around the La-rich phase, was observed during the aging process, owing to the attraction of Ni and Si atoms by the La-rich phase during the solid solution. Moreover, the mechanical and conductivity properties of aged alloy sheets suggest that the addition of the La element showed a slight reducing effect on the hardness and electrical conductivity. The decrease in hardness was due to the weakened dispersion and strengthening effect of the Ni2Si phase, while the decrease in electrical conductivity was due to the enhanced scattering of electrons by grain boundaries, caused by grain refinement. More notably, excellent thermal stabilities, including better softening resistance ability and microstructural stability, were detected for the low-La-alloyed Cu-Ni-Si sheet, owing to the delayed recrystallization and restricted grain growth caused by the La-rich phases.

First-order phase transition La-Fe-Si bulk materials with small hysteresis by laser powder bed fusion: Microstructure and magnetocaloric effect

In this study, laser powder bed fusion method is used to fabricate first-order phase transition LaFe13.9Si1.4 bulk materials. The main finding is that a negligible hysteresis is obtained after annealing. We attribute this primarily to the numerous refined α-Fe residual phase which promotes the paramagnetic/ferromagnetic phase transition by the stray field at the interface. The fine microstructure and amorphous/nanocrystalline La-rich phase in the as-printed sample contribute to the formation of the refined α-Fe phases accompanied by a large α-Fe/La(Fe, Si)13 interface during annealing. More importantly, the first-order phase transition behavior is maintained and the magnetic entropy change for 0-2 T is 13.4 J/kg K. This study demonstrates that laser powder bed fusion is a feasible approach for fabricating high-performance rare-earth-based magnetic materials.

Enhanced mechanical strength in hot-rolled La-Fe-Si/Fe magnetocaloric composites by microstructure manipulation

La-Fe-Si-based alloys possess a giant magnetocaloric effect due to the sharp itinerant-electron metamagnetic transition. However, the relatively poor mechanical strength of these alloys impedes their practical application in the magnetic refrigeration system. In this study, we employed hot rolling to manipulate the microstructure, and thus to improve the mechanical strength of LaFe11.6Si1.4/Fe composites. The microstructure and magnetic phase transition behavior have been systematically investigated by X-ray tomography, high-resolution transmission electron microscope and digital image correlation technique. We found that the bending strength of the hot-rolled LaFe11.6Si1.4/Fe reached up to 176 MPa, which is about 26% higher than the non-rolled one. The refinement of the α-Fe particles plays a key role in hindering crack propagation and enhancing the mechanical strength of the hot-rolled sample. Additionally, the reduction of the La-rich phase and large-size pores is found to be beneficial to the mechanical strength enhancement. The hot-rolled composite shows a sharp metamagnetic transition with a maximum magnetic entropy change of 17 J kg−1 K−1 for 2 T magnetic field change. This study demonstrates that microstructure manipulation based on hot rolling is a feasible approach to improve the mechanical strength of La-Fe-Si materials.

Influence of La addition on Fe-rich intermetallic phases formation and mechanical properties of Al-7Si-4Cu-0.35Mg-0.2Fe alloys prepared by squeeze casting

Brittle β-Al5FeSi (β-Fe) intermetallic phases directly affect the mechanical properties of Al–Si alloys; thus, it is essential to modify these phases. Scanning electron microscope analysis showed that rare earth Lanthanum (La) additions (0, 0.15, 0.30 and 0.50 wt%) had a refining effect on β-Fe phases in Al–7Si–4Cu-0.35Mg-0.2Fe (wt.%) alloys prepared by squeeze casting. The underlying refinement mechanisms of rare earth La on the β-Fe were discussed in terms of experimental observations, nucleation thermodynamics and growth kinetics. For nucleation thermodynamics, La additions could induce the formation of La-rich intermetallic phases Al4Cu2SiLa with orthorhombic structure. Because β-Fe nuclei had a good lattice matching and epitaxial relationship with the Al4Cu2SiLa phases, the Al4Cu2SiLa provided energetically favorable nucleation sites for β-Fe and greatly promoted the nucleation of β-Fe in alloys. Meanwhile, the added La atoms could restrain the diffusion of atoms to the solid/liquid interface front and alter the β-Fe interfacial structure and energy, therefore restricting the β-Fe growth. Furthermore, β-Fe/Al4Cu2SiLa grew into side-by-side and cross-like morphologies, and its growth behaviors were controlled by solute concentration and anisotropy of the solid-liquid interfacial energy in a cooperative eutectic reaction. In addition, different fracture behaviors from brittle fracture to mixed ductile fracture and quasi-cleavage brittle fracture were also illustrated with increasing La addition, and these fracture behaviors were influenced by the characteristics of brittle La-rich and β-Fe intermetallic phases. When the addition of La was increased to 0.3 wt% and 0.5 wt%, it occurred quasi-cleavage brittle fracture, which was caused by the precipitation of coarse plate-like La-rich phases.

Microstructure control and its observation of rapid solidification Cu–La alloy for the development of fluoride-ion batteries

We report on the microstructure of Cu-La alloys, which is a candidate material for the electrode of fluoride-ion battery, prepared by the rapid solidification method. The Cu-La alloys near eutectic point (24.5at%La) were quenched at different cooling speed to obtain optimized lamellar microstructure. The cross-section of the Cu-24.5at%La alloy exhibited a lamellar microstructure, in which the Cu-rich and La-rich phases were well proportioned. A hexagonal Cu5La phase with a space group P6/mmm was confirmed in the Cu-enriched areas, along with tetragonal Cu4La particles with an I4̅m2 and hexagonal Cu2La with the P6/mmm. Furthermore, different cooling rate during solidification were applied by changing the wheel rotation speed of the device. The higher the rotation speed, the faster the cooling rate, and the finer the microstructure. The width of each layer in the microstructure was approximately 100 nm.

Effect of annealing on microstructure and magnetocaloric properties of plastically deformed La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys

In this study, we have employed a near-net-shape hot forging deformation with ∼67% reduction ratio, and an annealing process at 1223–1423 K to prepare bulk La0.7Ce0.3Fe13.68Mn0.2Si1.4 alloys. The deformed samples are featured by a unique microstructure consisting of layered α-Fe and La-rich phases. These layered phases gradually degrade during the subsequent annealing, and eventually appear as the magnetocaloric phase (the 1:13 phase) matrix embedded mainly with the α-Fe particles. Upon annealing at 1323 K, the deformed sample has the largest 1:13 phase formation rate. Significant magnetic entropy change of 15.6 J/kg K and a relatively small magnetic hysteresis of 30.9 J/kg at 5 T are achieved in the current forged La-Ce-Fe-Mn-Si alloy on an optimal annealing condition, i.e., 1323 K for 24 h. The large magnetic entropy, rapid 1:13 phase formation rate and near-net shape make the hot-forged La-Ce-Fe-Mn-Si alloys promising magnetic refrigerants.

Effect of La addition on Ag-rich phase formation and mechanical properties of Cu-2Ag alloys

A series of novel Cu-2Ag-xLa alloys with reinforced mechanical properties and enhanced electrical conductivities are developed. The effects of La addition on the microstructural features and mechanical properties of as-cast and solution treated Cu-2Ag alloys are systematically investigated. The yielding strength of as-cast Cu-2Ag alloys with 0.02La and 0.07La (wt.%) is considerably reinforced by relative amounts of 55.56% and 30.16%, respectively. The strengthening mechanism for such increased yielding strength is mainly related to the shifting of interfacial relation between matrix and Ag-rich phase from original semi-coherent type to non-coherent type with La doping. Consequently, the interface barrier strength is enhanced by the non-coherent interface, and contributes to the increased yielding strength. Meanwhile, the strengthening effect from La addition closely depends on the exact contents of La element. As La content increases from 0.02 to 0.07 (wt.%), the strengthening effect becomes weaker because of the increased space of Ag-rich phases leading to an 16.33% decrease in yield strength. Additionally, La has dual effects on the dissolution of Ag-rich phases and precipitation of new La-rich phase in the as-cast alloys during solution treatment. Simultaneously, the precipitation of the La-rich phase abnormally enhances the electrical conductivity of the solution La-containing alloys when the solution time exceeds 24 h.

Revisiting high-temperature phase transition and magnetocaloric effect of LaFe11.6Si1.4 alloy

Sufficient understanding on the formation mechanism of the La(Fe,Si)13 phase (1:13 or τ1) in La–Fe–Si alloys would be helpful in optimizing the parameters for high-temperature annealing. In-situ annealing experiments of a centrifugally as-cast LaFe11.6Si1.4 plate were performed by using a differential scanning calorimeter (DSC) in the present study. We confirmed that the τ1 phase is resulted from a peritectic reaction between La-rich liquid phase and α(Fe) solid phase when isothermal annealing at 1423 K. A new finding of a eutectoid decomposition that may occur within the residual La-rich liquid phase upon cooling was revealed. The isothermal transformation kinetics of the τ1 phase in the as-cast plate followed a simplified model of diffusion-controlled continuous network growth. The isothermal entropy change (|ΔSM|) was calculated using the Maxwell equation on M−H data. The maximum |ΔSM| value reached 26.89 J/(kg·K) under 30 kOe in the LaFe11.6Si1.4 sample annealed at 1423 K for 120 min.

Synergistic influence of La and Zr on microstructure and mechanical performance of an Al-Si-Mg alloy at casting state

The evolution of microstructure and mechanical properties of Al-7Si-0.4Mg alloys doped with La/Zr/La+Zr was investigated by experimental characterization and thermodynamic calculation. The combination of growth restriction effect by La-rich intermetallics and inoculation effect by peritectic Zr-rich cores led to the most dramatic grain refining. Furthermore, eutectic silicon was observed to be refined from avg. 9.8 µm in length within original alloy to avg. 5.8, 8.7, and 6.4 µm under the effect of La/Zr/La+Zr additions, respectively. The length reduction in eutectic silicon was attributed to the shrunk growth space caused by grain refinement and the presence of La-rich phases, as well as the impeded effect of several microns La-rich phases distribute directly on the growth front of Si phase. The strength and ductility were both elevated in the alloys at the casting state alloyed with La, Zr, or La+Zr. Particularly, the simultaneous introduction of La+Zr led to the optimal combination properties with a yield strength of 103 ± 3.4 Mpa, an ultimate tensile strength of 189.2 ± 4.6 Mpa, and fracture elongation of 6.1 ± 0.8%. The enhancement of yield strength was related to the strengthening from grain refining and dispersed precipitates. The improved ultimate tensile strength was ascribed to the higher and more stable strain-hardening rate, resulting from the combined influence of refined microstructures (e.g. grain and eutectic Si), as well as the emergence of La-rich and/or Zr-rich intermetallics. The elevation of fracture elongation was intimately correlated with the refining in eutectic silicon, which relieved the nucleation and development of crack along the interface between silicon and Al matrix.

Optimization of microstructure and magnetocaloric effect by heat treatment process in LaFe11.7Si1.3 microwire

A large magnetocaloric effect and significantly shortened annealing process were obtained simultaneously in melt-extracted LaFe11.7Si1.3 microwires. Large amounts of La(Fe,Si)13 phases were formed within 5 min when annealed at 1353 K via a rapid peritectic reaction, because the nanoscale dendrites and a small amount of nanoscale La(Fe,Si)13 phases discovered inside grains could provide a lot of nucleation sites. Thereby, the main phase in LaFe11.7Si1.3 microwire after annealed at 1353 K for 5 min was La(Fe,Si)13 phase, although a small quantity of α-Fe and La-rich phases still remained in the microstructure. The annealed LaFe11.7Si1.3 microwires exhibited a first-order magnetic transition behavior and a large maximum magnetic entropy change of 7.7 J/kg K under a magnetic field of 1.4 T with negligible magnetic hysteresis. However, the strength of the first-order transition became weakened with the extension of annealing time. Finally, the working temperature range of LaFe11.7Si1.3 microwires was elevated to room temperature by hydrogenation, which expanded the application of LaFe11.7Si1.3 microwires in active magnetic regenerator.

Effect of La Addition on Solidification Behavior and Phase Composition of Cast Al-Mg-Si Alloy

The current study focusses on the phase composition, solidification path, and microstructure evaluation of gravity cast Al-4Mg-0.5Si-xLa aluminum alloy, where x = 0, 0.1, 0.25, 0.5, 0.75, and 1 wt.% La. A computational CalPhaD approach implemented in Thermo-Calc software and scanning electron microscopy technique equipped with electron microprobe analysis (EMPA) was employed to assess its above-mentioned characteristics. The thermodynamic analysis showed that the equilibrium solidification path of La-containing Al-Mg-Si alloys consists of only binary phases LaSi2 and Mg2Si precipitation along with α-Al from the liquid and further solid-state transformation of this mixture into α-Al + Al11La3 + Mg2Si + Al3Mg2 composition. Scheil–Gulliver simulation showed a similar solidification pathway but was accompanied by an increase in the solidification range (from ~55 °C to 210 °C). Furthermore, microstructural observations were congruent with the calculated fraction of phases at 560 °C and related to α-Al + LaSi2 + Mg2Si three-phase region in terms of formation of La-rich phase having both eliminating effect on the eutectic Mg2Si phase. Quantitative EMPA analysis and elemental mapping revealed that the La-rich phase included Al, La, and Si and may be described as Al2LaSi2 phase. This phase shows a visible modifying effect on the eutectic Mg2Si phase, likely due to absorbing on the liquid/solid interface.

Microstructure evolution and its influence on the thermal expansion of La(Fe0.79Al0.21)13 alloy prepared by arc-melting

NaZn13-type La(Fe1−xAlx)13 alloys show tunable thermal expansion. However, whether the arc-melted alloys contain secondary phase, which can obviously influence the thermal expansion, is still unclear. Facing to this question, we take arc-melted La(Fe0.79Al0.21)13 as an example and investigate its microstructure evolution. The as-cast ingot consists of NaZn13, α-Fe and amorphous La-rich phases. Their size and distribution are different at different positions, indicating the existence of microstructure segregation. During annealing,NaZn13 phase grows up through a reaction between α-Fe and amorphous La-rich phases, but a single-phase sample still can’t be obtained even after 15-days-annealing. Nonuniformly distributed α-Fe phase, which is a result of microstructure segregation, exists in the NaZn13 main phase. Our measurements on different parts of the annealed sample indicate that the thermal expansion is highly related with the local concentration of α-Fe phase.

Researches on corrosion behavior and magnetocaloric effect of the LaFe11.7-xCoxAl1.3 alloys

Researches have been made on microstructures, magnetic properties and corrosion behavior of the LaFe11.7-xCoxAl1.3 (x = 0.78, 0.92) alloys. The results show that increment of Co content from x = 0.78 to x = 0.92 promoted formation of the 1:13 phase with Tc tuned to higher temperature range and magnetocaloric effect improved. The annealed LaFe11.7-xCoxAl1.3(x = 0.78,0.92) alloys suffered galvanic corrosion in distilled water. Corrosion occurred first in the La-rich phase and then in the 1:13 phase, causing Tc shift to higher temperatures and deteriorating magnetocaloric effect. The x = 0.78 alloy suffered more severe corrosion than the x = 0.92 alloy after 12-day immersion in distilled water. The stability of performance of the x = 0.92 alloy in distilled water was superior to that of the x = 0.78 alloy, which made the x = 0.92 alloy a good candidate for magnetic refrigeration at ambient temperature.

Multi-Refinement Effect of Rare Earth Lanthanum on α-Al and Eutectic Si Phase in Hypoeutectic Al-7Si Alloy

The effect of La addition on primary α-Al and the eutectic Si phase of Al-7Si alloy is investigated systematically in this work. The results indicate that La addition causes a multi-refining efficiency on the microstructure of Al-7Si alloy, including refinement of α-Al grains and secondary dendrite arm spacing as well as eutectic Si particles. The grain size, secondary dendrite arm spacing and area of eutectic Si particles are decreased by 26.8%, 7.7% and 26.7%, respectively, with the addition of 0.1 wt.% La. It is also found that La-rich phases of Al2Si2La form and distribute in the vicinity of the eutectic Si phase. The crystal structure and lattice parameter of Al2Si2La phase are determined to be hexagonal (a = b = 0.405 nm, c = 6.944 nm) based on the TEM analysis results. The multi-refinement effects are mainly attributed to the increased constitutional undercooling caused by the low solubility of La in Al alloy and the growth-restricting factor caused by the Al2Si2La phase.

Effect of Cooling Rates on the Microstructure and Mechanical Property of La Modified Al7SiMg Alloys Processed by Gravity Die Casting and Semi-Solid Die Casting

Rare earth (RE) additions are capable of refining the α-Al phase as well as modifying the eutectic Si particles of alloys. The cooling rate in casting process should be carefully concerned when the Al-Si alloys are refined and modified by adding RE elements. In this study, the effect of cooling rates on the microstructure and mechanical properties of La modified Al-7.0Si-0.3Mg alloys was studied in gravity die casting and semi-solid die casting. It is found that in La modified Al-7.0Si-0.3Mg alloys, with increasing the cooling rate from 0.2 to 9 K/s in gravity die casting, the α-Al grains are greatly refined and the Si particles are modified to branching morphology, which evidently increases the UTS and elongation of alloys. In addition, when increasing the cooling rate from 30 to 130 K/s in semi-solid die casting, the α-Al grains are refined from 140 to 47 μm, and the Si particles are modified to fibrous morphology, which increases the UTS from 190 to 230 MPa and elongation from 10% to 11%. However, the 0.4 wt.% La addition results to La-rich phases formed in microstructure, which impairs the mechanical properties of Al-7.0Si-0.3Mg alloys in semi-solid die casting.