As-cast Microstructure Research Articles

Effects of Cr-addition on ageing response of an Al–Si–Mg die cast alloy

Chromium (Cr) is rarely added to Al–Si die cast alloys as it has a strong tendency to induce the formation of coarse-sized sludge particles. In the present study, high pressure die-cast samples made of Al-7wt.%Si–Cr–Mg alloys with varied Fe contents (0.11 wt%, 0.26 wt% and 0.32 wt%) were tensile tested under as-cast and T5 heat-treated conditions, in comparison to those made of Al-7wt.% Si–Mn–Mg alloy with a constant Fe content (0.11 wt%). The results demonstrated that under the as-cast condition, the Al–Si–Cr alloys with higher Fe contents can achieve comparable tensile properties as the Al–Si–Mn alloy with strictly controlled Fe level. However, after a T5 heat treatment (205 °C for 60 min), the increment in yield strength is less for the Al–Si–Cr alloys in relative to the Al–Si–Mn alloy, regardless of Fe contents. Scanning electron and scanning transmission electron microscopic characterizations were conducted on the as-cast and heat-treated microstructures, aiming to understand the undermined ageing response caused by Cr addition.

Effects of Annealing Soaking Time on Carbide Precipitates and Mechanical Properties of As-Cast Thin Wall Ductile Iron

Thin Wall Ductile Irons (TWDI) are viable material option in the automotive industry due of their good castability, adequate mechanical properties, wear resistance, good machinability and fatigue properties. However due to size reduction and increased cooling rate, carbide precipitates occur in the as-cast microstructure of TWDIs, impacting negatively on mechanical properties, nodularity and nodule count. Heat treatment processes that reduce or eliminate these carbide phases can be adopted to remedy such defects. In this study, 4 mm TWDI samples cast in green sand moulds, showing carbide precipitation in microstructure were subjected to an Annealing heat treatment by austenizing to 920oC and varying soaking times of 5, 10, 15, 20, 25 and 30 minutes, afterwards they were cooled in the furnace to room temperature. Microstructural analysis and mechanical property tests were carried out in all the samples via Optical microscopy (OM) and Scanning electron microscopy (SEM), hardness and tensile tests. Microstructure of heat-treated samples showed significant reduction of carbide precipitates in comparison with their as cast counterpart. It was observed that the soaking time impacted on carbide precipitation reduction. Hardness values reduced from 291.6 Hv in the as cast sample to 247.8 Hv and 243.5 Hv for samples soaked for 25 and 30 minutes respectively, whereas tensile strength reduced progressively from 596 MPa to 544 MPa for as cast to 30 minutes soaking time respectively. Percent elongation increased from 4.3 % elongation for the as cast sample to 8.7 % elongation in the sample with soaking time of 30 minutes at 920 oC. This study has shown that carbide precipitation can be significantly reduced by adopting the annealing treatment parameters outlined above.

Discontinuous dynamic recrystallization behavior and texture evolution of large-size pure titanium flat ingot via electron beam cold hearth melting during short process direct hot rolling

Large-size pure titanium ingots melted by single electron beam cold hearth melting (EBCHM)) could be rolled into large-width and heavy-weight titanium strip coils using short process without forging. It is crucial to study the large-span refinement mechanism from highly coarse grains, whose sizes are in the order of ∼cm, to micronmeter. In this study, the recrystallization mechanism and texture evolution of pure titanium with a size of 1570 × 200 × > 8000 mm was investigated by multi-pass simulated rolling and experimental rolling. The results indicated the hot deformation can result in marked reduction in grain size of the as-cast grain, from 3 to 5 cm to 17–23 μm. The discontinuous dynamic recrystallization (DDRX) mechanism of a pure titanium ingot during direct multi-pass hot deformation causes the reconstruction of as-cast microstructure and refinement of hot rolling microstructure. Furthermore, DDRX occurred, during hot deformation, and was accompanied with weakening of deformation texture. Raising the initial hot deformation temperature results in a modification of the texture type of the {0001} crystal plane. The strength of the texture experiences a decrease initially and then eventually an increase. This alteration in strength is inversely related to the degree of dynamic recrystallization. Based on the simulated rolling experiment, the results of experimental rolling also found the coarse as-cast grains was broken and reconstructed. It has strength (average yield strength: 334 MPa, ultimate tensile strength: 371 MPa), ductility (total elongation: 30 %). Such a combination of mechanical properties makes the hot rolling plate a potential choice for sheet practical application.

Effect of Local Pressurization on Microstructure and Mechanical Properties of Aluminum Alloy Flywheel Housing with Complex Shape.

In this work, squeeze casting experiments of flywheel housing components with a large wall thickness difference and a complex shape were carried out with AlSi9Mg aluminum alloy. The defects, microstructures, and mechanical properties under different process parameters were investigated. Furthermore, the local pressurization process was applied to the thick-walled positions to force-feed the cast defects. The mechanical properties and microstructures at these positions were analyzed. The results showed that the surface quality of formed components was good and that local pressurization could effectively reduce the shrinkage cavity and shrinkage porosity in thick walls, but the scope and effect of forced feeding were limited. The optimum process parameters were a pouring temperature of 650 °C, a specific pressure of 48 MPa, a mold temperature of 220 °C, a local pressurization of 800 MPa, and pressure delay times of 15 s (side A) and 17 s (side B). The ultimate tensile strength, yield strength, and elongation of the formed component under validation experiments of the optimum process parameters were 201 MPa, 103 MPa, and 5.1%. Meanwhile, the fine grains of primary α-Al were mainly rosette and equiaxed grains, and the average grain size was about 40 μm. The microstructure of the eutectic silicon was acicular and was prone to segregation under pressure. According to profile morphology, the positions after pressurization were divided into a deformation zone, a direct action zone, and an indirect action zone. The coexistence of as-cast and plastic deformation microstructures was observed. The effect of local pressurization mainly involved a change in the solidification process, plastic deformation, and forced feeding.

Navigating the BCC-B2 refractory alloy space: Stability and thermal processing with Ru-B2 precipitates

Refractory multi-principal element alloys (RMPEAs) could provide next-generation high temperature alloys, but their ductility and high temperature strength need significant improvement. Emulating superalloy γ-γ’ microstructures, RMPEAs combining a ductile BCC matrix with embedded B2 precipitates for strengthening could meet this goal. Two-phase BCC-B2 RMPEAs have recently been demonstrated, but the B2 phase typically exhibits insufficient thermodynamic stability for operating temperatures ≥1300 °C.Using high-throughput CALPHAD predictions, we screen across 3,500 potential BCC-B2 systems. Promising compositions are predicted for alloys combining Ru-based B2s with refractory BCC elements. A total of 20 such compositions were arc-melted to characterize their as-cast and heat-treated microstructures. In these alloys, the RuHf B2 exhibits exceptional stability beyond 1900 °C but cannot be solutionized. By contrast, RuTi does solutionize and reprecipitate between 1300 and 1900 °C, providing a robust thermal processing pathway. RuAl can be solutionized but also tends to form competing intermetallic phases. Altogether, Ru-B2 RMPEAs offer great design flexibility and surpass the stability and thermal processability of previously studied BCC-B2 refractory alloys.

Структурно-фазові характеристики та механічні властивості TWIP-сталі Fe-24Mn-11Al-1,4C

TWIP steels belong to a number of modern innovative structural materials that combine a high level of mechanical characteristics and low density, which brings their specific strength closer to the level of titanium alloys. Such steels usually do not contain deficient components and they are suitable for wide commercial industrial production. The most high-strength alloys include around 20-30 % Mn (wt.), around 10 % (wt.) Al and 1% (wt.) C. Such chemical composition brings them closer to the three-phase region, in which austenite, ferrite and k-carbides can simultaneously exist. According to this, it is possible to change mechanical characteristics of such alloys in a wide range only by heat treatment. Although in practice the best results are shown by a combination of deformation and heat treatment. The Manuscript presents a study of changes in the structural and phase characteristics and mechanical properties of the Fe-24Mn-11Al-1,4C alloy, prepared by electroslag melting, in its initial state, after deformation and annealing, and after deformation with subsequent hardening and aging. A fractographic analysis of the studied samples destruction places was also carried out. It is shown that the original sample obtained by electroslag remelting has the highest plasticity and the lowest strength, which is explained by combination of largest alloying of austenite and as-cast microstructure. The deformed and annealed sample is characterized by a pronounced fine-grained structure in which carbides are separated along the grain boundaries. Such a sample exhibits a strength greater than 1.1 GPa and the lowest ductility of 4.26 %. The deformed sample after quenching and aging has a similar structure, but the carbide inclusions are much finer, and the alloying rate of austenite is higher than the previous one. Such a sample shows the highest strength of more than 1.2 GPa and plasticity of 8.6 %. Keywords: TWIP-steels, casting, deformation and heat treatment, structural and phase characteristics, fractography, mechanical properties.

Application of novel constrained friction processing method to produce fine grained biomedical Mg-Zn-Ca alloy

In order to obtain Mg alloys with fine microstructures and high mechanical performances, a novel friction-based processing method, name as “constrained friction processing (CFP)”, was investigated. Via CFP, defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced. Compared to the previous as-cast microstructure, the grain size was reduced from more than 1 mm to around 4 µm within 3 s by a single process cycle. The compressive yield strength was increased by 350% while the ultimate compressive strength by 53%. According to the established material flow behaviors by “tracer material”, the plastic material was transported by shear deformation. From the base material to the rod, the material experienced three stages, i.e. deformation by the tool, upward flow with additional tilt, followed by upward transportation. The microstructural evolution was revealed by “stop-action” technique. The microstructural development at regions adjacent to the rod is mainly controlled by twinning, dynamic recrystallization (DRX) as well as particle stimulated nucleation, while that within the rod is related to DRX combined with grain growth.

Effect of as-cast microstructure on precipitation behavior and thermal conductivity of T5-treated Al[sbnd]7Si[sbnd]0.35Mg alloy

This study examines the precipitation evolution during T5 heat treatment (casting and direct aging) of an Al7Si0.35Mg alloy component with varying thicknesses. We employ a step mold casting technique to develop an Al7Si0.35Mg alloy component with cavity thickness ranging from 4 to 40 mm. Our experimental investigations unveil varying solidification times (from 5.0 to 152.2 s) and cooling rates (ranging from 2 to 50 K/s) due to the step mold casting. The thermal conductivity of component sections increase from 174.1 to 178.9 W/mK as the cooling rate surged to 50 K/s. Microstructure analysis of 50 K/s alloy reveals a large number density of coarse Mg-Si-rich pre-precipitates near dendritic cell boundaries, alongside fine GPII and β″ pre-precipitates within the cell interior. The pre-precipitation behavior in 50 K/s alloy is attributed to the retention in the mold until thick sections fully solidify, leading to low solute supersaturation and higher conductivity. Contrarily, 2 K/s alloy exhibits the formation of fine dot-like β″ and a few coarse Mg-Si-rich pre-precipitates along the cell boundaries. This alloy demonstrates superior age-hardening behavior and its low thermal conductivity increases during aging. This increment is associated with a small lattice misfit between precipitates and matrix in the as-cast state, inducing significant lattice distortion which lowers the thermal conductivity. Upon peak aging, these distortions are replaced by dislocations at the precipitate-matrix interface due to large lattice misfits. Finally, we offer an insight into how the solidification microstructure affects T5 treatment considering hardness and conductivity synergy.

Effect of γ forming element additions on the homogenization behavior and formation of hierarchical microstructures in Ni-based superalloys

Here, we study the homogenization behavior and microstructure of seven Ni-Al-Ti alloys with quaternary additions of γ forming elements 4Cr, 4Co, 4Ru, 4Mo, 4Hf, 4 W and 2Re. To design a homogenization treatment, the as-cast microstructure is analyzed revealing the diffusion distances x between dendrite cores and interdendritic regions. The temperatures for homogenization are determined using differential scanning calorimetry (DSC) and Thermo-Calc simulations, to be between 1150 and 1275 °C. The time to achieve homogenization is modelled based on the residual segregation index δ utilizing diffusion distance, homogenization temperature and diffusion data. Electron probe micro analyzer (EPMA) measurements show that our predictions match for the 4Cr, 4Co, 4Ru, 4 W and 2Re alloys while the 4Hf alloy shows insufficient homogenization. Transmission electron microscopy (TEM) reveals a two-phase γ/γ’ microstructure after 750 °C / 24 h, whereby the 4Co and 4Ru alloys form hierarchical microstructures. We observe γ plates in the 4Co alloy and γ spheres in the 4Ru alloy. Ru in the 4Ru alloy is involved in stabilizing the morphology of γ spheres. We provide a straightforward method for the design of homogenization treatments of Ni-based superalloys and demonstrate an alloy design pathway for tailoring the phase stability of hierarchical microstructures.

Comprehensive Analysis of Microstructure and Hot Deformation Behavior of Al-Cu-Y-Mg-Cr-Zr-Ti-Fe-Si Alloy

Low sensitivity to hot cracking is very important not only for casting but also for ingots of wrought alloys. Doping of Al-Cu-(Mg) alloys by eutectic forming elements provides an increasing resistance to hot cracking susceptibility, but it also leads to a decrease in plasticity. The quasi-binary alloys based on an Al-Cu-REM system with an atomic ratio of Cu/REM = 4 have a high solidus temperature, narrow solidification range and fine microstructure. The detailed investigation of microstructure, precipitation and hot deformation behavior, and mechanical properties of novel Al-Cu-Y-Mg-Cr-Zr-Ti-Fe-Si alloy was performed in this study. The fine Al8Cu4Y, needle-shaped Al11Cu2Y2Si2, compact primary (Al,Ti)84Cu6.4Y4.3Cr5.3 and Q (Al8Cu2Mg8Si6) phases were identified in the as-cast microstructure. Near-spherical coarse Al3(Zr,Y) and fine Al45Cr7 precipitates with a size of 60 nm and 10 nm were formed after 3 h of solution treatment at 580 °C. S′(Al2CuMg) precipitates with an average diameter of 140 nm, thickness of 6 nm and calculated volume fraction of 0.033 strengthened 36 HV during aging at 210 °C for 3 h. Three-dimensional hot processing maps demonstrated an excellent and stable deformation behavior at 440–540 °C and strain rates of 0.01–10 s−1. The rolled sheets had a good combination of yield strength (313 MPa) and plasticity (10.8%) in the recrystallized at 580 °C, with water quenched and aged at 210 °C for a 3 h state. The main calculated effect in the yield strength was contributed by Al45Cr7 precipitates.

Crystallization kinetics and mechanical property of yttrium-modified Zr-Cu-Ag-Al bulk metallic glasses

The bulk metallic glasses of two different compositions i.e. Zr44Cu40Al8Ag8 and Zr44Cu40Al8Ag7Y1 were prepared by copper mold casting technique in this study. As-cast microstructure both BMG’s found to completely amorphous as depicted by X-ray diffraction and transmission electron microscopy. The differential scanning calorimetry (DSC) results reveal that Y-addition leads to an increase in the nucleation rate at the initial stages of crystallization but imposes resistance to the growth of the crystalline phases at later stages. Furthermore, the Y-addition results in better creep resistance for Zr44Cu40Al8Ag7Y1 glassy alloy at room temperature.

The Microstructure, Solidification Path, and Microhardness of As-Cast Ni-Al-Cr-Os Alloys in a Ni-Rich Region.

In this study, nine as-cast Ni-Al-Cr-Os alloys were prepared, and their constituent phases and microstructure were examined using X-ray diffraction and electron probe microanalysis techniques. The solidification paths of all the alloys in a Ni-rich corner were revealed based on a detailed analysis of the as-cast microstructure. The liquidus cube of the quaternary Ni-Al-Cr-Os system in a Ni-rich corner was established accordingly. A eutectic-type invariant reaction on the liquidus surface was explicitly identified, and its reaction can be expressed as L → α + β + γ. No quaternary invariant reaction was found in the alloys following the addition of Os. The Ni-Al-Cr-Os alloy points were then vertically mapped onto the Ni-Al-Cr liquid phase projection to better observe the effect of Os addition on the solidification path of the Ni-Al-Cr system. It was found that the addition of a small amount of Os has no significant effect on the solidification path of the Ni-Al-Cr system. Furthermore, the microhardness of each alloy, which was determined to be in the range of 207 HV to 565 HV, was found to be closely related to the phase constitution and phase fraction of the alloy.

Critical role of initial multi-phase microstructure on the phase transformations during hydrogenation in Fe–Mo alloy system

Given Fe is a low-cost earth-abundant element, there is a need to develop novel Fe-based metal hydrides. The conventional Fe-based hydrides consist of at least one metal with high hydrogen affinity. To synthesize novel low-affinity Fe-based hydrides, the high-pressure and high-temperature method is currently being used. The microstructure is known to influence the de-/hydrogenation processes in metal hydrides. However, in the context of low-affinity Fe-based hydrides, the role of the initial multi-phase microstructure is unknown, which is the objective of the current work. We investigate three as-cast Fe–Mo binary alloys: Fe0.33Mo0.67, Fe0.5Mo0.5, and Fe0.67Mo0.33. Firstly, we first explain in detail the formation mechanisms of the non-equilibrium initial as-cast microstructures caused by the sluggish diffusion of Mo. Subsequently, we present the phase transformations and microstructure evolution during the hydrogenation, depressurization, and aging of Fe–Mo alloys. We demonstrate that each phase in the initial microstructure act as an independent phase during hydrogenation.

Using different strategies to improve properties of the biodegradable Mg–4Li–4Zn alloy

Recently, novel super light Mg–Li based alloys have attracted wide attention for potential use as biodegradable implants. However, like most of the biodegradable Mg alloys, Mg–Li alloys suffer from high degradation rate and poor mechanical properties, but the degradation is much faster and thus critical in these alloys. Different strategies have been introduced and used to address these weaknesses, including alloying, heat treatment and severe plastic deformation. However, efficiency of these methods have not been yet evaluated and compared with each other. In this investigation, the effects of alloying (0.5 and 1.0 wt% Ca addition), homogenization heat treatment and multidirectional forging process on the microstructure, biodegradation behavior, and mechanical properties of the as-cast Mg–4Li–4Zn base alloy are evaluated and compared. The obtained results indicate that Ca addition is beneficial to improving both mechanical strength and corrosion resistance of the as-cast base alloy. In addition to microstructural refinement, the addition of Ca resulted in formation of Ca- and Zn-rich precipitates, with a network-like structure, which was found to be beneficial to inhibiting the corrosion progress. Although homogenization treatment led to a slight decrease in mechanical strength, it considerably improved the corrosion resistance, through partial dissolution of precipitates and more uniformity of the as-cast microstructure. Finally, it was found that the multi-directionally forged alloy demonstrated improved mechanical and corrosion properties in comparison with the as-cast alloy, which stemmed mainly from the more uniform distribution of fine secondary phases, as well as the reduced average grain size.

Destabilization Treatment and Its Influence on Microstructure and Matrix Hardness of High-Cr Cast Iron

AbstractHigh-chromium cast irons are an essential class of wear-resistant materials commonly used for wear-resistant applications in the mining and steel industries. There is ongoing debate on the secondary carbide types and their formation sequences during heat treatment. This work examines the microstructural evolution during destabilization treatment of a hypoeutectic high-chromium cast iron containing 2.2 wt pct C and 16.5 wt pct Cr. Starting from an inhomogeneous as-cast microstructure consisting of ~ 28 pct M7C3 eutectic carbide and a mixed matrix of martensite and retained austenite, destabilization treatments resulted in the establishment of near homogeneous structure with a near equilibrium level of carbon concentration in the matrix, which fully transformed to martensite upon cooling. Homogeneously distributed M23C6 secondary carbides with a square-shaped morphology and 100 to 500 nm in size precipitated during heating up to the destabilization temperature. For higher destabilization temperatures (1000 °C), M7C3 secondary carbides formed together with M23C6 and were identifiable by a distinctly different morphology (elongated). It was found that the carbon content of the matrix, a function of the destabilization temperature and subsequent eutectic carbide dissolution, controls the martensite start temperature and has a dominating influence on bulk-hardness.

Effect of Mischmetal Addition on Microstructure and Mechanical Properties of As-Cast and As-Rolled Mg–Sn–Ca Alloys

The microstructures and mechanical properties of Mg–3Sn–0.1Ca–xMM (mischmetal, x = 0.3, 0.6, and 0.9 wt.%) alloys were investigated. Optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) were used to characterize the microstructures and phase constitutions of the cast and rolled alloys. Room temperature tensile tests were conducted to obtain the mechanical properties and macro-textures to evaluate the texture weakening effect results of the MM. The results show that an abundance of second phase formed, confirmed as the (Ca,MM)MgSn phase, and the volume fraction increased with the increasing MM addition. The tensile yield strength of the as-cast alloys increased with the MM addition, but the elongation decreased. All of the rolled Mg–3Sn–0.1Ca–xMM alloys showed a strong basal texture, and only slightly decreased in intensity after annealing treatment due to the particle-stimulated nucleation of recrystallization. The as-annealed Mg–3Sn–0.1Ca–0.6MM alloys exhibited the highest tensile strengths of 266.5 ± 3.3 MPa and 136.1 ± 3.7 MPa, which are mainly ascribed to grain refinement strengthening, Orowan strengthening and texture strengthening.

Microstructural characterization of U-20Pu-10Zr-4Sb and U-20Pu-10Zr-4Sb-4Ln

Antimony is being investigated as a potential additive to metallic fuel to control fuel-cladding chemical interactions (FCCI). The most detrimental elements involved in FCCI are fission product lanthanides, leading to brittle intermetallics and low melting eutectic phases. Previous investigations of Sb as an additive focused on U-10Zr, in wt. %, as the fuel. The current investigation expands that to include Pu in the fuel. Two alloys, U-20Pu-10Zr-4Sb and U-20Pu-10Zr-4Sb-4Ln (wt. %, Ln=53Nd-25Ce-16Pr-6La) have been investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to characterize the fuel as-cast microstructure and the microstructure after introduction of lanthanides. Sb reacts with Zr initially, forming Zr2Sb and Zr5Sb3, with as much as 20 at. % interstitial Pu present. In the presence of lanthanides, Sb forms Ln4Sb3 with the lanthanides, containing ∼14 at. % Pu. The Pu is substitutional for the lanthanides in the crystal lattice.

Thermomechanical characterization and conventional rolling of a novel β-solidifying γ-TiAl alloy with excellent comprehensive properties

The development of the β-solidifying γ-TiAl alloys with good oxidation resistance and thermal deformation ability has always been crucial for the practical application. However, increasing the content of the antioxidant elements, such as Nb, Al, etc., tends to be detrimental to the deformability of the alloys. In this work, a novel Nb, Mn containing β-solidifying TiAl alloy with the nominal composition of Ti-43Al-1.5Mn-3Nb-0.2C-0.2Si-0.1B (at. %) (named as NbMn-TiAl) is invented, which goes through the single β phase as well as the α phase during solidification, resulting in the final as-cast microstructure of nearly full lamellar structure (NFL). Subsequently, the isothermal compression tests were performed within a temperature range of 1100 °C–1300 °C and a strain rate range of 0.001 s−1-10 s−1, the hot processing maps and constitutive equation were established. Moreover, the deformation mechanisms were clarified, including the bending/kinking of the α2/γ lamellar colonies, the dynamic recrystallization (DRX) of γ phase and α phase at different temperatures. Rolled bars with a diameter of 12 mm were then directly fabricated from the ingot by conventional hot rolling process. The as-rolled bars exhibited excellent oxidation resistance and mechanical properties that outperform many available TiAl alloys manufactured using various methods.

Research Progress on Cu-15Ni-8Sn Alloys: The Effect of Microalloying and Heat Treatment on Microstructure and Properties.

Cu-15Ni-8Sn alloy is the best choice to replace beryllium bronze alloy. This alloy has unparalleled application value in aerospace, ocean engineering, electronic information, equipment manufacturing, and other fields. However, the application of Cu-15Ni-8Sn alloy is challenged and limited because of a series of problems in its preparation and processing, such as easy segregation, difficult deformation, and discontinuous precipitation. It is an effective way to improve the comprehensive properties of Cu-15Ni-8Sn alloy using alloying design and process optimization to control the as-cast, deformed, and heat-treated microstructures. At present, it is a hot spot for scholars to study. In this paper, the grade generation, system evolution, and preparation technology development of Cu-15Ni-8Sn alloy are comprehensively reviewed. The phase transformation sequence of the Cu-15Ni-8Sn alloy is discussed. The influence of the type, amount, and existing form of alloying elements on the strength of Cu-15Ni-8Sn alloy and its mechanism are systematically summarized. Furthermore, the latest research progress on the effects of solid solution, cold deformation, and aging on the phase structure transformation and mechanical properties of Cu-15Ni-8Sn alloy is summarized. Finally, the future development trend of the Cu-15Ni-8Sn alloy is projected. The research results of this paper can provide a reference for the control of the microstructure and properties of high-performance Cu-15Ni-8Sn alloys used in key fields, as well as the optimization of the preparation process and alloy composition.

A Study on Microstructure and Properties of Aluminum Alloy Bracket Produced by a New Semi-Solid Rheo-Diecasting Process

The performance of bracket component is low with uneven micro-structure, internal porosity and shrinkage defects produced by traditional liquid die casting process which cannot be strengthened by T6 heat treatment. In this paper, the aluminum alloy bracket with high-performance and light weight was prepared by a novel semi-solid slurry preparation technique that included chilling rod stirring and funnel-shaped cylinder device, which rapidly reducing the liquid temperature to near liquidus and realizing explosive nucleation. The effects of pouring temperature and CRS process on the microstructure and mechanical property of bracket were studied by optical microscopy (OM) equipped with polarizing mode and bench failure test. The results show that the as-cast microstructure mainly consists of near-spherical α-Al. And the semi-solid micro-structure was affected by these two critical parameters, the pouring temperature and CRS process. Without the condition of stirring, the micro-structure is typical dendritic with a certain proportion of fine spherical crystals, which was mainly generated during the filling of die casting process. And with the addition of the chilling rod, the finer and more uniform spherical semi-solid micro-structure was obtained with the lower pouring temperature. Based on the above semi-solid process and flow controlling through the mould design and vertical die casting process optimization, the high-performance bracket component without shrinkage can be prepared. Additionally, compared with the liquid die casting process, the internal quality and bench testing force of bracket prepared by CRS vertical die casting process are significantly improved.