Semi-solid Metal Research Articles

The Effect of Cooling Rate on Solidification Characteristics and Grain Structure of Al-9Si Cast Alloy

A thermal analysis study is essential before the semisolid metal processing of a particular alloy. The surrounding environment, especially the cooling rate is also an important factor. This study investigated the influence of different cooling rates on the solidification characteristics and microstructure evolution of the Al-9Si cast alloy. Four cooling mediums were designed, and their cooling rates are 0.16 ℃/s, 1.0 ℃/s, 1.3 ℃/s, and 1.9 ℃/s, respectively. The results show that the primary dendrite size of the Al-9Si alloy was reduced from 162.61 μm to 86.86 μm as the cooling rate increased from 0.16 ℃/s to 1.9 ℃/s. Significant grain refinement was observed, however, the external cooling has a negligible impact on solid fraction. The optimal temperature range of the Al-9Si cast alloy for the semisolid metal processing at a solid fraction of 0.5 to 0.7 is between 554 ℃ and 563 ℃. With these thermal profiles provided, the relationship between the solid fraction and the solidification time could be expressed using the polynomial equation, which is also useful for point prediction in the subsequent semisolid metal processing.

Editorial of the 2nd issue of Engineering Manufacturing Letters

This is the second issue of the Engineering Manufacturing Letters (EML). The journal is published by the University of Porto and invites submissions from a diverse array of industries, including transportation (automotive, rail, aeronautical, and marine), packaging, electronics, sports, and more. Additionally, academic institutions and research institutions are encouraged to contribute their research findings in this field. Accepted topics encompass additive manufacturing, vacuum-assisted high-pressure die casting, semi-solid metal casting, compressive and tensile forming processes, micro and nano machining, nanocomposite manufacturing, adhesive bonding, laser cutting and joining, and related areas. Specific subtopics include process modelling and optimization, design for manufacturing strategies, development of novel manufacturing technologies and equipment, comparative case studies, cost-benefit analyses, ecological considerations, and destructive and non-destructive testing of manufactured components. Technological advances in manufacturing often outpace traditional scientific publication methods. To bridge this gap, our journal focuses on concise reports and letters highlighting innovative manufacturing processes. The journal is open access, but no fees will be charged to the authors until the journal is indexed in the major databases. This journal is associated to the international conference on Engineering Manufacture that takes place every even years in May at the Faculty of Engineering of the University of Porto (www.fe.up.pt/em2024). The editorial board of this journal includes experienced researchers from all disciplines of engineering manufacture. The papers presented in this first issue are varied. They include papers on health monitoring (Vilela et al.), mechanical characterization (Oliveira et al.) and short papers, two papers on metal forming (Peixoto et al., and Winiarski et al.) and additive manufacturing (Nogueira et al., and Sardinha et al.) which is one very dynamic field at the moment. We extend our sincere thanks to the authors for their gently participation in this second issue. The submitted papers offer valuable insights into the recent advancements in engineering technological processes. These contributions serve as a good foundation for what promises to be a dynamic forum of the last developments in engineering manufacturing.

Identifying the Working Conditions of Semisolid Metal Slagging Operations Under Strong Light Based on Gabor Feature and Multichannel PGAN

Identifying the Working Conditions of Semisolid Metal Slagging Operations Under Strong Light Based on Gabor Feature and Multichannel PGAN

Impacts of T6 heat treatment on the microstructural, mechanical, and corrosion properties of thixoformed AA7075 alloy produced by cooling slope casting

Abstract Research into semi-solid metal forming techniques has been ongoing for an extended period with the aim of producing near-net shape products from aluminum alloys. The primary focus has traditionally been on casting alloys seeking to offer an alternative to the other processes such as high pressure die casting. Over the past twenty years, wrought aluminum alloys have also been explored for thixoforming operations as an alternative to traditional plastic deformation techniques. This research investigated the impacts of T6 heat treatment on the microstructural, mechanical, and corrosion properties of AA7075 alloy samples produced through cooling slope casting and subsequent thixoforming with different reheating durations. The selected alloy was chosen due to its widespread use in various industries, attributed to its excellent strength-to-density ratio achieved after T6 heat treatment. Building on optimized cooling slope casting parameters from a prior study, the standard solution treatment procedure following thixoforming with extended reheating times was found to be inadequate. Hardness and tensile tests revealed that specimens reheated for 120 min exhibited significantly reduced response to T6 treatment. Despite achieving the targeted hardness value of 154 HB with samples reheated for 20 min prior to thixoforming and T6 heat treatment, especially the elongation at break values were unsatisfactory. Potentiodynamic polarization tests indicated that corrosion primarily involved grain dissolution, with longer reheating times decreasing corrosion resistance due to increased amount of secondary phases and grain isolation. These findings highlight that while AA7075 alloy can be processed into semi-solid formable materials via cooling slope casting, issues such as hot tearing, micro-shrinkage, and physical defects post-thixoforming hinder the achievement of desired tensile properties.

A Review of Viscosity Measurement Techniques for Semi-Solid Metal Fluids in Thixoforming Processes

This paper critically reviews two viscometry techniques: capillary viscometers and parallel plate compression (PPC) viscometers, which are used in the viscosity measurement of semi-solid metal (SSM) fluids for thixo routes. Capillary and PPC viscometers have emerged as valuable viscometers in the study of thixo routes of SSM, with insights into their unique flow behavior being explored. Thixoprocessing of SSM is particularly suitable for specific alloys, especially those with specific solidification properties such as eutectics. It is a method of thixoforming that uses a material's non-dendritic microstructure. The thixo method's viscosity measurement is challenging, requiring sample preparation, sophisticated equipment, precise temperature, and pressure control. Previous studies have lacked sufficient information on measurement methods, viscometers, and limitations to measuring viscosity for the thixo route of SSM. Hence, this study thoroughly examines the principles, advantages, limitations, and application areas of viscometry methods. Several factors influencing viscosity measurements, such as temperature, shear rate, and sample preparation, are discussed in detail. A comparative analysis is conducted to evaluate the performance and accuracy of capillary viscometers and parallel plate compression viscometers. This review will provide a comprehensive understanding of SSM's viscometry techniques and assist researchers and practitioners in selecting the most appropriate method for their specific applications in semi-solid metal processing and characterization.

Interfacial bonding mechanism of graphene nanoplatelets reinforced AZ91D magnesium alloy prepared by semi-solid injection molding

The incompatibility between the strength and thermal conductivity of magnesium alloys limits their application in heat dissipation components. Magnesium matrix composites were obtained by adding reinforcements into the AZ91D alloy to achieve synergistic enhancement of mechanical and thermal conductivity to promote the application of magnesium alloy. Graphene nanoplatelets (GNPs) reinforced magnesium matrix composites were successfully prepared by semi-solid injection molding. The high viscosity of the semi-solid metal slurry contributes to the homogeneous dispersion of GNPs in the magnesium matrix. A GNPs/MgO/Mg heterostructure with high interfacial bonding strength was found at the interface of GNPs and α-Mg matrix. The semi-solid casting method improves the mechanical properties of the composites by grain refinement and simultaneously reduces the thermal conductivity. The addition of GNPs can balance the mechanical and thermal conductivity enhancement, and the most balanced properties of the composites are obtained when the content of GNPs is 0.3 wt%, with a tensile strength of 243.1 MPa, Vickers hardness of 93.7 HV, and thermal conductivity of 74.8 W/(m·K). Therefore, the semi-solid forming method is considered a promising processing method, and GNPs is considered an ideal reinforcement material to improve the performance of the magnesium matrix.

Morphology-controlled metal–organic frameworks as molecular traps for enhanced ion dynamics in practical semi-solid lithium metal batteries

Controlling electrostatic interactions between charged molecules is crucial to enabling advanced batteries with reliable lithium (Li)-ion conductors. To address this issue, herein, we present a class of morphology-controlled metal–organic frameworks (MOFs) that serve as Li+ boosting molecular traps for fast Li+ conduction. A rod-like MOF is incorporated into semi-interpenetrating polymer networks to construct Li+ boosting fluidic nanochannels, which enable fast Li+ transport (σ = 1.5 mS cm−1, tLi+ = 0.76) through the ionic pathway. Molecular dynamics simulations further elucidate the Li+ transport mechanism in these MOF-based molecular traps. This unusual Li+ conduction behavior of MOF-based semi-solid electrolytes suppresses the anion-triggered ion concentration gradient and facilitates the electrochemical reaction kinetics at the electrodes, ultimately improving the rate performance and cycling retention of Li-metal cells (consisting of LiNi0.7Co0.2Mn0.1O2 cathodes and Li-metal anodes). Notably, a scalable pouch-type semi-solid Li-metal cell provides stable cycling performance for realistic batteries, exceeding those of previously reported Li batteries including porous crystalline frameworks.

Casting and comprehensive analysis of nitinol-based self-healing metal matrix composite of A356 alloy prepared via clamp technique

The present research explores the development and casting of a self-healing metal matrix composite using A356 alloy reinforced with Nitinol wire through the Clamp technique. The matrix provided a high-strength base, while Nitinol wire acted as a shape memory alloy reinforcement. The clamp technique ensured proper integration and alignment between the matrix and the reinforcement. Semi-solid metal processing enhances the mechanical properties of the base alloy and the wire integration as reinforcement. Mechanical properties of the composite including tensile strength and impact resistance were evaluated. The self-healing capability of the composite was evident through its significant recovery i.e. 61.53% of the deformed surface after thermal loading cycles. Additionally, the self-healing behavior of the composite was examined through cyclic thermal loading. This could provide valuable insight into the design and fabrication of self-healing metal matrix composite.

General Semi-Solid Freeze Casting for Uniform Large-Scale Isotropic Porous Scaffolds: An Application for Extensive Oral Mucosal Reconstruction.

Ice-templated porous biomaterials possess transformative potential in regenerative medicine; yet, scaling up ice-templating processes for broader applications-owing to inconsistent pore formation-remains challenging. This study reports an innovative semi-solid freeze-casting technique that draws inspiration from semi-solid metal processing (SSMP) combined with ice cream-production routines. This versatile approach allows for the large-scale assembly of various materials, from polymers to inorganic particles, into isotropic 3D scaffolds featuring uniformly equiaxed pores throughout the centimeter scale. Through (cryo-)electron microscopy, X-ray tomography, and finite element modeling, the structural evolution of ice grains/pores is elucidated, demonstrating how the method increases the initial ice nucleus density by pre-fabricating a semi-frozen slurry, which facilitates a transition from columnar to equiaxed grain structures. For a practical demonstration, as-prepared scaffolds are integrated into a bilayer tissue patch using biodegradable waterborne polyurethane (WPU) for large-scale oral mucosal reconstruction in minipigs. Systematic analyses, including histology and RNA sequencing, prove that the patch modulates the healing process toward near-scarless mucosal remodeling via innate and adaptive immunomodulation and activation of pro-healing genes converging on matrix synthesis and epithelialization. This study not only advances the field of ice-templating fabrication but sets a promising precedent for scaffold-based large-scaletissue regeneration.

Reduction of Surface Cracking for Al-4.6%Mg Strips Cast Surface Using an Unequal-Diameter Twin-Roll Caster by Back-Dam Plate with Lip

Cracks occur on the surface of Al-Mg strips cast using a high-speed twin-roll caster. Surface cracking of the as-cast strip decreases with decreasing roll load. However, the difficulty of roll casting increases as the roll load is decreased because the strip becomes brittle and is easily broken because the strip is not completely solidified. In the present study, an unequal-diameter twin-roll caster, which is capable of high-speed casting, was used with a lip attached to a back-dam plate in an attempt to decrease surface cracking without deceasing the roll load. The thickness of the solidified layer was found to decrease as the length of the solidified region decreased. The thickness of the solidified layer at the center of the width direction of a strip on the lower roll decreased by shortening the solidification length by a lip attached to a back dam-plate. The solidified layer at the edges was thicker than that inside the cast strip. The thickness of semisolid metal inside the cast strip increased more than that at the edges of the roll bite. The roll load at the width of the lip decreased. The effect of the lip length on surface cracks was investigated.

Regression model based properties prediction of A356 aluminum alloy rheocast using cooling slope technique

The current research work involves experimental research of the Al-alloy rheocasting with enhanced microstructural and mechanical characteristics after using the Semi-Solid Metal (SSM) processing method, which is the cooling slope method. The studies here were carried out online with Central Composite Design (CCD) in order to create a non-linear regression model to represent the fabrication of A356 casting considering the Cooling Slope (CS) Technique. During the rheocasting, the angle as well as the length of the slope, along with nozzle height were taken as the input process parameters, whereas the microhardness, grain size, and sphericity of the sample were treated as the responses. The variation of such responses across the cross-section of the casting was measured at three different locations such as the center, mean, and outer radii. The non-linear regression techniques applied to the A356 sample were manufactured under two circumstances, such as ‘with’ and ‘without’ isothermal treatment. The regression models thus developed were validated by incorporating Analysis of the Variance (ANOVA). Further, the correctness of the regression representations was verified through ten experimental test samples. The percentage deviation of experimental outcomes from the model-predicted outputs was minimal. The developed mathematical models were representative of the physical process with reasonably good accuracy.

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.

Synthesis of a crosslinked ether-based polymer for high-performance semi-solid lithium metal batteries via in situ integration

The synergistic effect of the crosslinking molecular design of poly(1,3-dioxolane) and the HOMO–LUMO screening of high voltage resistant fluorinated solvents realizes high-performance lithium metal batteries.

Semi-Solid Metal Slag Thickness Distribution Identification Based on Statistical Temporal Fusion of Multisource Image for Robotic Operation

Semi-Solid Metal Slag Thickness Distribution Identification Based on Statistical Temporal Fusion of Multisource Image for Robotic Operation

Microstructure, segregation and mechanical properties of A356 alloy components fabricated by rheo-HPDC combined with the swirled enthalpy equilibration device (SEED) process

The challenges commonly associated with conventional high pressure die casting (HPDC) have led to increased interest in semi-solid metal (SSM) forming processes. In the present study, semi-solid slurries of A356 alloy prepared by the Swirled Enthalpy Equilibration Device (SEED) process were used for manufacturing components with complex shape by using a high pressure die casting machine. The segregation phenomenon and the effect of heat treatment on the microstructure evolution and mechanical properties were investigated. The results showed that the alloy consists of primary spherical α-Al grains, secondary solidified α-Al grains, eutectic Si, iron-rich intermetallic phases and low porosities. The microstructural investigations revealed that the eutectic Si particles underwent fragmentation, spheroidization and coarsening with increasing solution temperature. Furthermore, the solution treatment results in the dissolution of the π-Al8FeMg3Si6 phase and the growth of the β-Al5FeSi phase. The hardening peaks at 170 °C could be obtained with ageing for 5 h. Due to both solution and precipitation strengthenings, the yield strength, ultimate tensile strength and hardness of A356 alloy after heat treatment increase significantly compared to those in the as-rheocast state: they reach 266 MPa, 343 MPa and 110 HV0.2, respectively. The analysis of fracture surfaces of rheo-HPDC samples in both the as-rheocast and the heat-treated states revealed a mixed mechanism of dimples and quasi-cleavage. The microstructure inside the part was found to be quasi-homogeneous while the segregation phenomenon in different zones of the part is affected by die geometry during the filling process. The results imply that the SEED-HPDC process has the potential to be industrialized by implementing appropriate heat treatments for producing complex components with good mechanical properties.

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.

Mechanical and Microstructural Investigations on a Symmetric Mould Processed with Semi-Solid Aluminum RheoMetal<sup>TM</sup>: Analysis of the As-Cast Proprieties

High-pressure die-casting (HPDC) can be a productive process for high-quality cast aluminium alloy components. However, it is also a process prone to generate defects, such as gas porosities and incomplete fillings, resulting in rejections. One way to reduce the reject rate is to employ Semi-Solid Metal processing with HPDC. The most important advantages of Semi-Solid alloys are reduced shrinkage defects, fewer gas porosities, and fewer chances of filling-related problems. To take full advantage of a semi-solid metal slurry, the casting process must be controlled meticulously to reach homogeneous casting quality and high process repeatability. A study has been conducted on cast parts composed of two-dimensional symmetrical cavities. From the mechanical tests, unexpected differences emerged in both tensile strength and fracture elongation, which were confirmed by differences in the microstructure. The paper investigates the reasons for the asymmetry in the proprieties to avoid similar problems in future studies and maximize the effectiveness and repeatability of the high-pressure die-casting process.

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.

Fatigue Properties of Thixoformed Al-6wt%Si-2.5wt%Cu

One of the main functions of semisolid metal alloy forming processes, notably rheocasting and thixoforming, is the manufacture of parts, casings and frames for mechanical assemblies and systems. These parts not only must have the required minimum mechanical properties in terms of yield strength and elongation, but also must be able to withstand cyclic tensile and compressive forces. However, there is little fatigue strength data for the materials used for these parts. The present work seeks to fill this gap by determining the fatigue limit at 107 cycles of Al-6.0wt%Si-2.5wt%Cu alloy, or simply Al6Si2.5Cu, thixoformed in a pneumatic press at 585 °C (the temperature corresponding to 40 % solid fraction) with isothermal treatment times of 30 and 60 seconds. The parts were also subjected to T6 heat treatment, for which they were solution heat treated at a temperature of 520 °C for 4 hours followed by aging at 180 °C for 10 hours. For all the conditions tested, the microstructures were characterized to determine the grain size, appearance and shape of the silicon particles, in addition to the residual porosity. For the best conditions observed, 30 s holding time and T6 heat treatment, the grain size varied between 100 µm and 130 µm; the shape factor was around 0.60, indicating an excellent degree of roundness; and there was low residual porosity of around 0.3 %, resulting in a yield strength of up to 240 MPa with 4.5 % elongation. The average fatigue strength was estimated by the staircase method and was between 95 MPa and 98 MPa for 107 cycles.

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.