Semi-solid Alloy Research Articles

Microstructure evolution and properties of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloy prepared by SIMA

The semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were prepared by strain induced melting activation method (SIMA), and the microstructure evolution, mechanical properties and corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys were investigated. The results indicate that the ideal globular or near-globular microstructures with an average grain size of 29.1 μm and a shape factor of 0.86 can be obtained when the Al80Mg5Li5Zn5Cu5 light weight high entropy alloys with 20% deformation held at 500 °C for 15 min. The coarsening coefficient is 35.8 μm3/s when the temperature is 500 °C, which is lower than the traditional single major element alloys due to the sluggish diffusion effect of high entropy alloys. The compression strength of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is 558.4 MPa, which is 11% higher than that of as-cast state. The corrosion resistance of semi-solid Al80Mg5Li5Zn5Cu5 light weight high entropy alloys is also significantly improved.

Surface wave phenomenon and microstructure evolution mechanism of electromagnetically levitated ternary Ti-Al-Fe alloy

Electromagnetic levitation technique was performed to investigate the surface wave phenomenon and microstructure evolution mechanism of undercooled ternary Ti50Al30Fe20 alloy. Under the condition of high undercooling, the formation process of surface waves on the levitated alloy surface were directly detected by high-speed camera. The cooling gas provided the external perturbation that promoted surface nucleation, providing the suitable site for surface wave generation. On the rotating semisolid alloy surface, the competition between centrifugal force and surface tension caused the surface wrinkling, leading to the formation of surface waves. The residual liquid phase was solidified in the vortex circulation flow, and the vortex-shape pattern was preserved during rapid solidification. With the increases of undercooling, the microstructure evolved from dendrites and interdendritic lamellar eutectics into uniform anomalous eutectics because of the independent nucleation and competitive growth of (βTi) and TiFe phase. The surface wave was formed only at high undercoolings, indicating this phenomenon was related to the fluidity in eutectic growth. In this case, the uniform microstructure was closer to satisfying the continuum medium hypothesis, and the homogeneous medium reduced the energy damage during wave propagation. In addition, the micromechanical properties were remarkably increased as undercooling rose owing to the microstructural morphology and solute trapping effect.

Multi-physics coupled numerical simulation study to optimize process parameters for electromagnetic stirring of semi-solid A356 aluminum alloy under the influence of skin effect

The electromagnetic stirring (EMS) method stands as a widely used technique in creating semi-solid aluminum alloy slurry due to its convenience and precision in parameter control compared to other methods. In this study, a comprehensive model that combines electromagnetics, flow, heat transfer and solidification was formed. By analyzing the influence of input current and frequency on the electromagnetic force, the behavior of various process parameters in velocity field and temperature field under influence of the skin effect is investigated. The aim is to find the optimal process parameters for production of slurry using the low-frequency EMS. The results show that within the investigated range, by adjusting the input current and frequency to 150 A and 15 Hz, higher fluid velocities and appropriate distribution of vortex zones can be observed, while achieving a uniform temperature field, the highest cooling rate and the minimum radial temperature difference. In addition, the sample prepared under the optimal process parameters shows that the melt edge is least affected by the skin effect, which leads to a higher stirring strength and a smaller overall grain size, which is consistent with the theoretical skin effect research found within the simulation section.

Thixomolding Developments

Abstract Thixomolding is a method of molding semi-solid magnesium alloy pellets using equipment and processing methods similar to injection molding. Its commercial growth has been driven by its technical advantages, including enhanced precision, environmental cleanliness, and the ability to produce complex 3D shapes with high yields and minimal waste.

Constitutive behavior of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy

The constitutive behavior of engineering materials can predict the change of flow stress with processing parameters, which is of great significance for the selection of processing parameters. In the present work, the constitutive behavior of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy was investigated by using thixotropic compression tests performed at semi-solid temperatures ranging from 500 °C–530 °C with strain rates ranging from 0.01 s−1–1 s−1, and the microstructure evolution was observed. The results indicate that the thixotropic compression deformation process of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy can be divided into three stages: the flow stress increasing stage, the flow stress decreasing stage and the steady-state flowing stage. The peak stress of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy increases with the increase of strain rate. With the increase of deformation temperature, the peak stress decreases obviously. A reasonable constitutive model of the peak stress of semi-solid Al80Mg5Li5Zn5Cu5 light-weight high entropy alloy as a function of strain rate, deformation and liquid fraction was obtained. The average relative error between the calculated and experimental values is 6.35%.

Grain structure evolution during heat treatment of a semisolid Al-Cu alloy studied with lab-based diffraction contrast tomography

3D experimental data of simultaneously high temporal and spatial resolution are key to validating computational models of materials phenomena. In this study, we exploit lab-based X-ray imaging, combining absorption and diffraction contrast tomography, to capture the evolution of grain structure over a series of interrupted heat treatments of a semisolid Al-Cu alloy. The time resolved response measured on the present Al-Cu model system provides insights into the rearrangement, densification and coarsening of powder compacts at late-stage sintering. The initial Al-Cu microstructure containing 1934 grains dropped to 934 grains after ten annealing steps, while the mean grain size increased from 194 µm to 247 µm. The grain maps of all eleven temporal states are made publicly available to the scientific community for further analysis via the Materials Data Facility. Preliminary statistical investigations of the growth of individual grains show a clear tendency for disappearing grains to be among the smaller grains at the beginning of the experiment. In addition, the rotations of individual grains are generally small fluctuations, but when an abruptly large rotation is observed, it is more likely to occur for a smaller grain at the last annealing step(s) before the grain vanishes. The nature of the data also enables interrogating a few grains that display rotation bursts within the context of their entire local environment to reveal the impact of crystallography and grain contacts upon the microstructural evolution.

Rheological Characterization of a Thixotropic Semisolid Slurry by Means of Numerical Simulations of Squeeze-Flow Experiments

We propose a methodology for the rheological characterization of a semisolid metal slurry using experimental squeeze-flow data. The slurry is modeled as a structural thixotropic viscoplastic material, obeying the regularized Herschel–Bulkley constitutive equation. All rheological parameters are assumed to vary with the structure parameter that is governed by first-order kinetics accounting for the material structure breakdown and build-up. The squeeze flow is simulated using finite elements in a Lagrangian framework. The evolution of the sample height has been studied for wide ranges of the Bingham and Reynolds numbers, the power-law exponent as well as the kinetics parameters of the structure parameter. Systematic comparisons have been carried out with available experimental data on a semisolid aluminum alloy (A356), where the sample is compressed from its top side under a specified strain of 80% at a temperature of 582 °C, while the bottom side remains fixed. Excellent agreement with the experimental data could be achieved provided that at the initial instances (up to 0.01 s) of the experiment, the applied load is much higher than the nominal experimental load and that the yield stress and the power-law exponent vary linearly with the structure parameter. The first assumption implies that a different model, such as an elastoviscoplastic one, needs to be employed during the initial stages of the experiment. As for the second one, the evolution of the sample height can be reproduced allowing the yield stress to vary from 0 (no structure) to a maximum nominal value (full structure) and the power-law exponent from 0.2 to 1.4, i.e., from the shear-thinning to the shear-thickening regime. These variations are consistent with the internal microstructure variation pattern known to be exhibited by semisolid slurries.

Inducing low-temperature melting of TiNiCuNb eutectic alloy for manufacturing strong C/C-SiC composite joints

This work designed a novel TiNiCuNb eutectic alloy for manufacturing C/C-SiC composite joints. By introducing Ti into the semi-solid TiNiCuNb alloy, low-temperature melting of this eutectic alloy was induced. Ti/TiNiCuNb/Ti composite interlayers were utilized to join C/C-SiC composite lower than the melting temperature of TiNiCuNb alloy. Effects of joining temperature on the microstructure evolution and mechanical property of joints were investigated. The melting range of this TiNiCuNb alloy was 944 °C to 1064 °C. During the initial melting of the TiNiCuNb alloy, a thin liquid layer formed on the alloy's surface, which provided a path for the rapid diffusion of elements. Without pressure, Ti could be easily introduced into the TiNiCuNb alloy, which induced the complete melting of this alloy at 950 °C. Based on this, we successfully brazed C/C-SiC composite using Ti/TiNiCuNb/Ti interlayers. It not only hindered the formation of brittle compounds in the joints, but also weakened the overreaction between filler and C/C-SiC composite. Due to the high solubility of Si in liquid filler, the joint microstructure was controlled by the interaction between filler and SiC at different temperatures. At 1010 °C for 10 min, the maximum shear strength of 28.5 MPa was obtained. This work contributed to preparing and repairing the C/C-SiC composite.

Relationship between solidification path, microstructure evolution and solidification cracking behavior of Mg-Al-Ca alloy during TIG welding

The high-strength and creep-resistant Mg-Al-Ca-Mn alloys have broad application prospects. However, solidification cracking occurs in these alloys in certain conditions and the origin is still unclear. This work investigated the relationship between the solidification path, microstructure evolution and solidification cracking behavior of the Mg-xAl-2Ca-Mn alloys during tungsten inert gas (TIG) welding. Results show that when the fusion zone's Ca/Al mass ratio ranges from 0.4 to 1.64, solidification cracking occurs at a Ca/Al mass ratio of ∼0.7. As the Ca/Al mass ratio approaches this value, the grain size increases, and the Laves phases are reduced gradually. The early formed Laves phases play an important role in promoting dendrite segmentation, refining grain size and enhancing grain boundaries. When a solidification path delays the formation of Laves phases, the Laves phases will be reduced accompanied by grain coarsening. In such a solidifying microstructure, intergranular cavitation is easy to occur, and the resistance of the semi-solid alloy to crack propagation is severely reduced.

To improve robustness of mechanical properties of semi-solid cast A356 alloy using taguchi design method

To improve robustness of mechanical properties of semi-solid cast A356 alloy using taguchi design method

Study on Preparation Process and Performance Properties of High-Solid-Fraction Semi-Solid A380 Alloy

Study on Preparation Process and Performance Properties of High-Solid-Fraction Semi-Solid A380 Alloy

Effect of flow characteristics in the inner gate on the microstructure of a semi-solid processed hypereutectic Al–Si alloy

ABSTRACTThis study aims to prepare hypereutectic Al–Si alloy cylindrical samples with hard inner surfaces by changing the depth of inner gates in squeeze casting molds. The characteristic parameters (volume fraction and equivalent diameter) of the hard phases (primary Si and Fe-rich phases) and the hardness of the samples were observed. When the depth of the inner gate is 5 mm, there is a radial gradient in the characteristic parameters of the hard phases in the members resulting in surface strengthening of the structural member. However, when the depth of the inner gate is 9 mm, there is no radial gradient. The mechanisms of achieving surface strengthening in hypereutectic Al–Si alloy cylindrical samples by changing the rheological characteristics of semi-solid Al–Si alloy slurries were revealed.

The Microstructural Refinement of the A356 Alloy Using Semi-Solid and Severe Plastic-Deformation Processing

Improving the engineering properties of A356 alloy is an appealing option for the automotive industry. This study aimed at refining and redistributing Si particles and the eutectic phase by applying T6 heat treatment to a semi-solid A356 alloy, followed by severe plastic deformation (SPD). Using a cooling-slope technique, the as-cast and rheocast samples were subjected to heat treatment prior to being processed using equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) at room temperature. The results show that the brittle Si particles were effectively fragmented and redistributed in the homogenous microstructure. The grain size reduced from 170 μm to 23 μm in the as-cast sample after combining heat treatment and the cooling-slope. This was followed by the ECAP sample after six passes through route A (where the sample is not rotated between each pass), while it reduced to 160 nm after five turns of the HPT process in a heat-treated cooling-slope sample. The hardness of the heat-treated cooling-slope casting samples increased with the ECAP process; there was an increase from 61 HV to 134 HV for the as-cast alloy after six passes through route A. The hardness of the heat-treated cooling-slope sample improved with the HPT process to 211 HV after five turns.

Joining C/C–SiC composite and Ti60 alloy using a semi-solid TiNiCuNb filler

This paper developed an innovative pressure-free contact reaction brazing technique that facilitated joining ceramics at low temperatures. Using this method, a semi-solid TiNiCuNb filler was employed to join C/C–SiC composite and Ti60 alloy. By facilitating elements’ diffusion through the partial liquid of semi-solid TiNiCuNb alloy, Ti could be introduced into this alloy without pressure, and the complete melting was achieved above 950 °C. Based on this, Ti60 alloy was joined to C/C–SiC composite below its β-transus temperature. Significant reaction differences between C/C and SiC with filler were found, mainly due to the different solubility and diffusion characteristics of C and Si in liquid filler. SiC exhibited higher sensitivity to temperature changes and was more prone to overreaction to induce defects. At 1010 °C, the maximum shear strength of 22.5 MPa was obtained due to the moderate reaction of both C/C and SiC with filler. This work contributed to manufacturing lightweight brake systems.

Numerical simulations of thixotropic semi-solid aluminium alloys in open-rotor and rotor–stator mixers

Numerical simulations of thixotropic semi-solid aluminium alloys in open-rotor and rotor–stator mixers

Differential scanning calorimetry of aluminium EN AB-42000 alloy rheocasting semi-solid in different stage heating rates

Differential scanning calorimetry (DSC) is used to identify the thermal histories of samples to analyse and diagnose production and quality concerns connected to industrial rheocasting semi-solid alloy, that had undergone different tempers of aluminium alloy EN AB-42000 alloy. In this study, the solidus temperatures of several alloy samples are investigated using thermodynamic calculations and DSC observations in this work. The balance of important characteristics, including pseudo-eutectic, thermal sensitivity, heat flow, and enthalpies behaviour, of Al alloys has been investigated using experimental data from DSC and solid fractions. In addition, the choice of heating rates is critical as high rates can blur the two peaks in the mushy zone, while low rates lead to slower measurements. Using smaller sample weights and slower rates is preferable to obtain more accurate results. Analysing the shape of the fs curve, exact composition, and a reference composition without contaminants is essential for understanding complex behaviours, including pseudo-eutectic phenomena. The thermal sensitivity of compositions also plays a crucial role in the analysis. Despite heat flow decreasing with decreased sample weight, the measurement limit can still be exceeded at high heating or cooling rates (20 °C/min) during the eutectic reaction. The eutectic reaction exhibits higher peaks with enthalpies ranging from 360 to 430 mJ/g. However, drawing conclusions regarding trends in heating versus cooling or comparing low-mass and higher-mass samples can be challenging. The non-equilibrium transformation of the eutectic occurs within a more confined temperature range. Increasing rates lead to overlapping reactions, resulting in complex thermal behaviour.

Effects of Heating Rates on Microstructural Evolution of Hot Extruded 7075 Aluminum Alloy in the Semi-Solid State and Thixotropic Deformation Behavior.

The non-dendritic microstructure plays a crucial role in determining the rheological properties of semi-solid alloys, which are of the utmost importance for the successful industrial application of the thixoforging process. To further understand the impact of the reheating process on the evolution of microstructure and thixotropic deformation behavior in the semi-solid state, a hot extruded and T6 treated 7075 aluminum alloy was reheated to the selected temperature ranges using varying heating rates. Subsequently, thixo-compression tests were performed. The study found that during reheating and isothermal holding, the elongated microstructure of the as-supplied alloy can transform into equiaxed or spherical grains. The presence of recrystallized grains was found to be closely linked to the penetration of the liquid phase into the recrystallized grain boundaries. Furthermore, it was observed that higher heating rates resulted in smaller grain sizes. The thixotropic flow behavior of the alloy with various microstructures was analyzed using the true stress-strain curves obtained by thixo-compression experiments, which exhibited three stages: a rapid increase in true stress to a peak value, followed by a decrease in true stress and a steady stress until the end of compression. The stress fluctuated with strain during the formation of the slurry at a strain rate of 10 s-1, indicating the significant role of strain rate in material flow during semisolid formation.

Impact of Processing Conditions on the Fluidity and Consistency of GISS-Processed Semi-Solid Aluminum Alloys

GISS (Gas Induced Superheated Slurry) is one of the more popular processes for the production of commercial semi-solid castings. For the successful production of high-quality castings, it is necessary to understand the impact of processing parameters on the flow behavior of the semi-solid metal. This paper describes the results of laboratory studies to examine the effects of processing conditions on the development of semi-solid feed material during GISS processing for two aluminum casting alloys, ADC12 and A356. Two series of tests were performed. The first involved a simple pouring test along an inclined section of a v-channel, to determine if differences in flow behavior could be identified. The second series of trials examined the effect of processing temperature and time on the consistency and flow behavior of the aluminum alloys. Ladles of molten aluminum alloy were treated using the GISS process at different temperatures for between zero and 10 seconds. After the treatment, the alloy was allowed to further cool in the ladle into the semi-solid temperature range, at which time the flow behavior of was compared. Consistency more suited to semi-solid casting was obtained when the GISS treatment temperature was lower and treatment time longer.

Rheological Behaviour of Secondary AlSi7Mg Alloy for Semi-Solid Processing

Semisolid castings are usually produced using primary Al alloys to ensure significant mechanical performances. However, the need to increase the use of secondary alloys is becoming more and more urgent to reduce the carbon footprint of the manufacturing process. In fact, it is well known that the production of primary alloys is far more demanding in terms of energy and emissions than the recycling route. To extend the use of secondary alloys to semisolid processing, it is necessary to thoroughly understand their properties and how they can influence a material with peculiar properties as the semisolid one. Besides microstructural and mechanical features, the rheological behaviour also plays a major role when dealing with processing metals in the semisolid state. Therefore, in the present study, a rheological characterization of secondary AlSi7Mg commercial alloy was carried out and compared to that of the conventional primary alloy. In details, a different content of Fe, Cu and Mn was considered, as these impurities easily form primary intermetallic particles, which can remain dispersed in the liquid matrix of the semisolid metal. The aim of this work is to understand if this can affect the rheological properties of the considered semisolid alloy. Flow curves and yield stresses were obtained from the experimental results to compare the behaviour of the different alloys.

Numerical Simulations of the Squeeze Flow of Thixotropic Semisolid Slurries

We propose a methodology for the rheological characterization of semisolid metal slurries using experimental squeeze flow data. The material is modelled as a structural thixotropic viscoplastic material, obeying the regularized Herschel-Bulkley constitutive equation. The yield stress and the power-law exponent are assumed to vary with the structural parameter that is governed by a first-order kinetics. The squeeze flow is simulated using finite elements in a Lagrangian framework. The evolution of the sample height has been studied for all the ranges of the Bingham and Reynolds numbers, the power-law exponent as well as the kinetics parameters of the structural parameter. Systematic comparisons have been carried out with experimental data on a semisolid aluminium alloy (A356) sample, compressed from its topside at a temperature of 582 °C under a specified load, which eventually becomes constant. Excellent agreement with the experimental data could be achieved provided that at the initial instances (up to 0.01s) of the experiment the applied load is much higher than the nominal experimental load and that the yield stress and the power-law exponent vary linearly with the structural parameter. The first requirement implies that a different model should be employed during the initial stages of the experiment. As for the second one, the evolution of the sample height can be reproduced allowing the yield stress to vary from 0 (no structure) to a maximum nominal value (full structure) and the power-law exponent from 0.2 to 1.4.