Semi-solid Processing Research Articles

Numerical Simulation and Experimental Analysis of the Semi-Solid Thixotropic Extrusion Forming Process for Producing the Thin-Wall Wrought Aluminum Alloy Mobile Phone Shells.

Aluminum alloys have been widely used in various engineering applications due to their excellent physical properties such as low density, high strength and good cutting capacity. In this paper, the semi-solid thixotropic extrusion forming process is proposed to produce aluminum alloy 6063 shells for mobile phones. The effects of the operating parameters on the equivalent stress distribution, velocity field, temperature field, and the load of the top mould were investigated through numerical simulations. Optimal parameters were identified from the simulation results. The experiment was then conducted at these optimal parameters. The macromorphology and microstructure results of the mobile phone shells produced from the experiment are presented and discussed. It was found that the optimal process parameters for preparing aluminum alloy 6063 shell by the semi-solid thixotropic extrusion process were a billet temperature of 630 °C, mould temperature of 400 °C, and top mould speed of 10 mm/s. It was found that the mobile phone shells fabricated under the optimal operating conditions were fully filled with a clear outline and a smooth surface. The solid grains in the microstructure were small, uniform and nearly spherical. The average grain size of the microstructure for the product was obtained as 76.92 μm and the average shape factor was found as 0.76.

Semisolid heat treatment processing window of Pb-40% Sn alloy for feedstock in the 3D printing thixo-forming process

The 3D printing thixo-forming process is a method that utilizes semisolid thixotropic feedstock for layer extrusion by controlling feedstock viscosity below the complete melting temperature of metallic alloys to form a 3D structure. The process of producing metallic feedstock has a significant impact on alloy microstructure, which is critical for the material’s printability. This study aims to propose a semisolid heat treatment processing window of Pb-40% Sn alloy for use as feedstock billets for a variety of extruder nozzles (sizes 1–3 mm) during the 3D printing thixo-forming process. Firstly, Pb-40% Sn alloys were cold deformed to reduce the specimens’ diameters. Semisolid treatments for deformed specimens were performed at a variety of semisolid heating temperatures and three separate holding times (2, 5, and 10 min). The microstructure of semisolid feedstock specimens was then investigated. The temperature and time of the semisolid heating processing window of Pb- 40% Sn alloy were optimized to feedstock specimens and thixo-extruding processes with different printed output sizes. Therefore, the proposed semisolid heat treatment processing window was a promising approach to pave the way for the low-cost manufacturing of AM, which yields higher printing rates and improved scalability of printed lines. Additionally, this approach allows for a versatile manufacturing route for producing 3D metal parts with maximum density and intricate geometries as a result of the ability to tailor the microstructure.

Preface

We would like to introduce you to the Proceedings of the 5th PING Junior conference - Modern Trends in Materials Engineering, which took place from 15 to 17 September 2020 in Pilsen, Czech Republic. The conference is regularly organized by the Regional Institute of Technology (RTI, www.rti.zcu.cz) at the University of West Bohemia.This year’s event was focused mainly on master and doctoral students in order to support their research activities and enable them to present the obtained results. Furthermore, selected research projects were presented within the contributions.This year was very demanding for organizing mass events, and our conference was also affected by the coronavirus epidemic. For this reason, it was organized in a combination of fulltime and online participation.A total of 18 contributions were presented at the conferences, which reflected the research projects solved within RTI. Several presentations were devoted to high-strength steels, such as the optimization of their heat treatment, use for hot stamping technology or their corrosion properties. Other contributions were focused on optimizing the heat treatment of stainless steel. Presentations, which were concentrated on heat or cryogenic treatment of maraging steel in the conventional state and after 3D printing, were also presented. Attention was also paid to special technologies such as semi-solid processing. Of these, six were selected for publication in the proceedings of IOP Conference Series.In conclusion, we would like to invite you to the sixth year of the PING conference, which will take place from 7 to 10 September 2021.List of Scientific Committee, Organizing Committee, Program Committee, Contacts, Images are vilaable in this pdf.

On the Use of Conformal Cooling in High-Pressure Die-Casting and Semisolid Casting

Today, tool life in high pressure die casting (HPDC) is of growing interest. A common agreement is that die life is primarily decided by the thermal load and temperature gradients in the die materials. Conformal cooling with the growth of additive manufacturing has raised interest as a means of extending die life. In the current paper, conformal cooling channels’ performance and effect on the thermal cycle in high-pressure die casting and rheocasting are investigated for conventional HPDC and semisolid processing. It was found that conformal cooling aids die temperature reduction, and the use of die spray may be reduced and support the die-life extension. For the die filling, the increased temperature was possibly counterproductive. Instead, it was found that the main focus for conformal cooling should be focused to manage temperature around the in-let bushing and possibly the runner system. Due to the possible higher inlet pressures for semisolid casting, particular benefits could be seen.

APPLICATION POTENTIAL OF RESPONSE SURFACE METHOD ON ELECTRO DISCHARGE MACHINING OF AA6061–CENOSPHERE AMCs PREPARED BY COMPOCASTING METHOD

Cenosphere fly ash particles are incorporated into AA6061 alloys with different concentrations ranging from 0[Formula: see text]wt.% to 10[Formula: see text]wt.% using a modified semi-solid metal processing technique. X-ray diffraction patterns were recorded to analyze the morphology of the aluminum-based metal matrix composites (AMCs). The major diffraction peaks of Al, SiO2, Al2O3 and Fe2O3 are distinctly identified which revealed the presence of cenosphere particles and their integrity within the matrix is preserved. The high-resolution optical micrograph identifies the homogeneous distribution and uniform dispersion of the particles. Machinability of the prepared AMCs was investigated by electro discharge machining (EDM) using response surface methodology (RSM). Face-centered CCD of RSM was considered to design the number of experimental runs required. ANOVA was used to explore the influence of selected process parameters and their interactions on the performance characteristics of the systems by developing a second-order quadratic mathematical model for all the responses. Pulse on-time and pulse current were observed to be the most influencing independent variables of EDM system that affect the selected performance measures during spark erosion process. Finally, desirability function approach was employed to optimize the parameters. The optimal processing condition was identified as follows: pulse current: 6 A, pulse on-time: 1010[Formula: see text][Formula: see text]s, percentage of reinforcement: 2% and flushing pressure: 0.2 MPa. Very small percentages of deviation have been observed while comparing with the experimental results obtained for MRR (8.6%), TWR (10.3%) and SR (2.18%).

Effect of Cooling Slope Process Parameters on Non-dendritic Feedstock Production: A Comprehensive Review

Semi-solid metal processing is the well-known technique used for the production of Al-based alloys components with sound quality and improved properties. To produce and operate successfully, the microstructure of the molten metal at the entry point of the die should consist of a solid, non-dendrite, near-globular primary grains surrounded by a liquid matrix. In the present paper, the authors have made an attempt to present a review on the formation of non-dendrite particles through cooling slope (CS) technique and reported the effect of various process parameters in particular, cooling slope length, degree of superheat of metal, height and diameter of the nozzle, CS plate material, mold material and its temperature, coolant type, coolant temperature and flow rate on the microstructure of the fabricated alloy system.

Microstructural Investigation and High Temperature Mechanical Behavior of AXE622 Cast Mg Alloy

The microstructure and high temperature properties of the AXE622 Mg alloy were investigated after the conventional and semisolid casting processes. The tensile test was conducted at room temperature, and 473 K. Impression creep test was performed at a temperature range of 423–498 K under the stress range of 450–600 MPa. The microstructure of the conventional and semisolid alloys contains α-Mg dendrites, the eutectic phase, secondary phases including (Mg–Al)2Ca, eutectic Mg17Al12, and Al11RE3. During semisolid processing, coarse dendrites of the α-Mg became fine, globular, and Rosetta shape. The average length of the secondary phases in the semisolid alloy decreased from 4.21 to 2 μm and the average grain size of the α-Mg reduced from 113 to 96 μm. Semisolid processing caused a significant improvement in the tensile and creep resistance of the AXE622 Mg alloy. The stress exponent for creep was calculated in the range 5.6–7.7 for the conventional alloy and in the range 10.3–11 for the semisolid alloy. The activation energy for conventional and semisolid alloy was determined as 71.4 kJ/mol and 78.3 kJ/mol, respectively. It was concluded that the dominant creep mechanism in the conventional alloy was the grain boundary diffusion-controlled dislocation climb, while in the semisolid alloy was the power-law breakdown.

Effects of different processing parameters on the semisolid microstructure of Al6061 produced by a direct thermal method

The effect of different processing parameters consist of pouring temperature and holding time on the semisolid microstructure of Al6061 feedstock billet produced by direct thermal method has been investigated in the present paper. In this experimental works, molten aluminium alloy 6061 was poured into a thin cylindrical copper mould at a constant temperature of 660 °C and held at different holding times of 20 s, 40 s, and 60 s. After it reached the desired holding time, the copper mould was then quenched into room temperature water. The microstructure formation of feedstock billets was characterized after the feedstock billets were taken out from the mould. Results show that, due to the rapid cooling condition of the molten 6061 inside the copper mould, more globular microstructures were obtained. The sample produced with a pouring temperature of 660 °C and holding time of 20 s, globular microstructure were apparent. Simultaneously, the sample with a pouring temperature of 660 °C and a holding time of 20 s produced smaller grain size than the sample with a pouring temperature of 660 °C and a holding time of 40 s and 60 s. Based on the results, the globular microstructures were superior at a shorter holding time, which allowed them to be quenched faster into room temperature water. The results from this experimental works suggest that the DTM feedstock billet globular microstructure formation merely depended on the heat convection of the molten alloy out from the copper mould. The faster heat convection out from the molten alloy which retarded the formation of dendritic microstructure thus transformed it into a globular microstructure for semisolid metal processing.

Isothermal furnace for long-term in situ and real-time X-radiography solidification experiments.

A new x-ray isothermal furnace has been developed, suitable for in situ observations of semi-solid processes including the transition from dendritic to globulitic grain morphology and grain coarsening in metallic samples. A homogeneous, isothermal temperature field is achieved using a novel heater concept. The furnace structure is sandwich-like with heating elements positioned in the beam line and parallel to the sample. Planar heat transfer to the sample enables measurements with low cooling rates and a minimized temperature gradient. Cooling rates from 0.1 to 15K min-1 can be controlled in the temperature range 1170-670K. The furnace setup is integrable in the existing rotatable laboratory x-ray facility (X-RISE) at the German Aerospace Center (DLR). In this setup, an effective pixel size of 3 μm and a field of view of 8mm in diameter can be achieved. Preliminary solidification and semi-solid experiments in the hypo-eutectic alloy systems Al-Ge and Al-Cu, inoculated with Al-5Ti-1B grain refiner, are presented. They indicate a very uniform temperature distribution in the sample.

Adjusting the Si Phase and Forming Nanoprecipitation to Improve the Mechanical Properties of Al–Si–Cu–Mg Alloy by Heat Treatment

To adjust the morphology of the Si phase and improve the mechanical properties of Al–Si–Cu–Mg alloy formed by semisolid squeeze casting, the effects of solution time on microstructure evolution and mechanical properties are systematically studied. Results show that spheroidization occurs in the Si phase, and the content of Cu in the matrix increases simultaneously after solution treatment at 525 °C for 1 h. As solution time increases to 8 h, the content of Cu in the matrix increases from 1.15% to 1.41% and the dislocation density decreases. After an aging treatment at 180 °C for 12 h, the β′, θ′, and Q′ phases precipitate. After heat treatment, the alloy strength value shows a “double peak” phenomenon. After a 1 h solution treatment, the tensile strength of the alloy reaches the first peak, which is mainly ascribed to the large dislocation density induced by the semisolid squeeze casting process. When the solution time is 8 h, the tensile strength of the alloy is 323 MPa and the tensile strength reaches the second peak, which is ascribed to the rounding of the Si phase and the strengthening effects of fine precipitates.

Grey-Fuzzy Logic Based Approach in Multi-Response Optimization of Semi-Solid Forging of A356 Aluminium Alloy

This paper presents an effective approach for the optimization of the semi-solid forging process of A356 Al-alloy based on the orthogonal array with the grey relational analysis and fuzzy logic analysis. Through the grey-fuzzy logic analysis, the optimization of complicated multiple performance characteristics can be converted into the optimization of a single grey-fuzzy reasoning grade. In this semi-solid forging process of A356 Al-alloy, the forging process parameters, namely the forging temperature, percent deformation, and die temperature are optimized with considerations of multiple performance characteristics including the tensile strength and hardness. The experimental results for the optimal setting have shown that the above performance characteristics in the semi-solid forging process of A356 Al-alloy can be improved effectively together through this approach.

Effect on microstructure and corrosion resistance of semi-solid slurry of 7A04 aluminum alloy by electromagnetic stirring

The microstructures and corrosion resistance of electromagnetic stirring (EMS) semi-solid slurry and as-cast 7A04 aluminum alloy were compared in this work. The results show that the primary microstructure of the as-cast 7A04 aluminum alloy is mainly dendritic and columnar dendrite with obvious elements segregation. In contrast, semi-solid processing can effectively form homogeneous and round primary α-Al grains, and significantly reducing element segregation. In addition, the main phases of the two forming methods (as-cast and semi-solid) both involved α-Al, η-MgZn2, θ-Al2Cu. With the decrease of solidification temperature, the semi-solid alloy formed by electromagnetic stirring increases the precipitation of brittle phase S-Al2CuMg. The self-corrosion potential of the semi-solid alloy is greater than that of the as-cast alloy, and the polarization curve has obvious passivation characteristics. Semi-solid processing could improve corrosion resistance of 7A04 aluminum alloy obviously.

Effects of Stirring Time and Cooling Rate on the Rheocast Microstructure and Mechanical Properties of Magnesium Alloy MRI 230D

Abstract Semisolid state processing is a methodology that transforms dendritic as-cast microstructure into globular non-dendritic microstructure with optimized mechanical properties. Rheocasting process involves mechanically stirring metals in a semisolid state and its benefits are associated with processing parameters. In order to evaluate stirring time effects, magnesium alloy MRI 230D (Mg–Al6.45–Ca2.25–Mn0.27–Sr0.25–Sn0.84) was melted and cooled down to semisolid processing temperature (595oC). Moreover, isothermal stirring was executed for 1, 2, 4 and 8 minutes. In each experiment, cylindrical samples with different diameters (6 and 12 mm) were collected to evaluate cooling rates effects. The microstructure was analyzed through optical and electron microscopes. The results showed that in the longest stirring times, the primary α-Mg phase got coarser and the interglobular region became more refined. Although shape factor initially increased, subsequently there was a tendency to stabilize. Regarding cooling conditions, it was found that the interglobular region became more refined at higher cooling rates. Mechanical tests revealed an initial decrease in ultimate tensile strength (UTS) and ductility, but afterwards increased due to a more regular microstructure and superior shape factor. The 8-minutes stirring sample achieved the best results: an increase of 12% in UTS and 16% in ductility.

ПРОБЛЕМЫ РАЗВИТИЯ ЛИТЬЯ ПОД ДАВЛЕНИЕМ ТВЕРДОЖИДКОГО МЕТАЛЛА В РОССИИ

The methods of powder and granular metallurgy are rapidly improving, granulation and spheroidization of solid phase particles is carried out “in–situ” at the stage of alloy preparation, which precedes the casting stage, and on this basis, a new generation of technologies is born and developed. dubbed Thixo – (casting, molding, forming) and PowderInjectionMolding (РIM (МIM, СIM)) technologies. All of the above technologies are united by the term Semi–Solid Processing (SSP), and the mandatory code prefixes Semi–Solid Metal (SSM) and MetalInjectionMolding (MIM) have appeared in the designations of alloys prepared for processing in a solid–liquid state.

Thixoforming of an Al-Si-Zn-Mg Alloy - Thermodynamic Characterization, Microstructural Evolution and Rheological Behavior

Abstract Al-Si-Zn-Mg quaternary alloys represent a potential range of feedstock's for semisolid processing (SSM) that combine the advantages of the thixoforming process with the possibility of heat treatment to improve mechanical performance. In this work, the suitability of the Al-5wt%Si-5wt%Zn-0.5wt%Mg alloy for use in thixoforming was assessed by thermodynamic characterization and by an analysis of its microstructural evolution and rheological behavior. Thermodynamic analysis was performed by numerical simulation and by application of the differentiation method to Differential Scanning Calorimetry (DSC) curves for heating cycles up to 700 °C at 5 and 25 °C/min. Microstructural evolution during partial melting at 594 °C for 0, 30, 60 and 90 s and the corresponding rheological behavior were analyzed. The findings indicate good agreement between the thermodynamic behavior predicted by DSC and Calculation of Phase Diagrams (CALPHAD) and the data obtained from semisolid forging. Although the alloy has a coarse microstructure (GSmax = 200 μm), its rheological behavior is appropriate for thixoforming (σmax = 1.06 MPa and μmax = 1.79x104 Pa.s), indicating that the microstructure only plays a secondary role in determining viscosity when enough liquid (fl = 0.63) is present in the slurry to enhance the flow. The alloy is suitable for use as raw material for semisolid processing.

Investigation of Wear Performance of Different Amount SiC Reinforcements A356 Matrix Composite Materials Produced by Semi-Solid Process Method

Bu çalışmada, farklı miktarlarda SiC ilave edilerek yarı katı kalıplama yöntemi ile üretilen Al A356 matrisli kompozit malzemelerin aşınma davranışları incelenmiştir. Al A356 matrise, ağırlıkça 4 farklı oranda (%5, 10, 15 ve 20) SiC ilave edilmiştir. Titreşimli tip değirmende bilyesiz olarak (30 dakika) karıştırılan tozlar, soğuk preslenerek (800 MPa) ham numuneler üretilmiştir. Üretilen ham numuneler 550 °C kalıp sıcaklığı ve 600 °C fırın sıcaklığında 30 dakika ortam atmosferinde bekletilmiş ve 100 MPa basınç ile 1 dakika preslenmiştir. Üretilen numuneler mikroyapı, sertlik ve küresellik oranı ile karakterize edilmiştir. Aşınma testleri standart pin on-disk aşınma test cihazında 0,2 ms-1 kayma hızı, iki farklı yük (30 ve 60 N) ve dört farklı aşınma mesafesi (500, 1000, 1500 ve 2000 m) kullanılarak yapılmıştır. Yapılan çalışmalar sonucunda, kompozit malzeme içerisinde artan SiC miktarı ile sertlik artarken, küresellik oranları ise azalmaktadır. Aşınma testleri sonucunda en yüksek ağırlık kaybı %5 SiC içeren numunelerde elde edilirken, en düşük ağırlık kaybı ise %20 SiC ilave kompozit malzemelerde elde edilmiştir.

Effect of a high magnetic field on the macro- and microstructures of Zn-Mg alloy during semi-solid isothermal annealing process

Zn-Mg alloy was isothermally annealed in the semi-solid range under a high magnetic field (HMF). Results showed that, regardless of the HMF, the specimens exhibit inhomogeneous structures, i.e., primary Zn-rich dendrites and granular (nearly spherical or platelike in three dimensions) particles are distributed in the upper and lower parts, respectively. Applying the HMF and decreasing the annealing temperature significantly contribute to the structural homogeneity, which are ascribed to the induced magnetic viscosity resistance force and the higher viscosity of the interdendritic liquid, respectively. Moreover, the HMF aligns the primary dendrites and platelike particles with their longer axes parallel to the HMF direction B. In addition, the HMF preferentially orients all the granular particles with their c-axis perpendicular to B, regardless of their sizes and shapes. The regular alignment and preferential orientation are related to the magnetocrystalline anisotropy of the primary Zn-rich crystals.

Observations on the compression properties of semisolid Ti–Cu alloys

Ti–Cu alloys are considered viable candidates for thixoforming (semisolid processing) due to their solid–to–liquid transitions and good microstructural properties. In the present study, the deformation behavior of these alloys in the semisolid state has been investigated by performing hot compression tests on Ti–(25, 27, 29)Cu samples isothermally treated at 1035 °C for 300 s. In general, relatively low loads were applied to deform samples with globular microstructure, which decreased with increasing liquid fraction (Cu content). In contrast, dendritic samples required much higher loads; the resulting materials were significantly more heterogeneous and contained large numbers of microstructural defects. At applied compression velocities of 4, 8, and 16 mm s−1, the strain rate had little effect on the response of the globular material; however, longer isothermal heat treatments significantly reduced the compression load due to globularization enhancement. The obtained results suggest potential applicability of Ti–Cu alloys for semisolid processing.

Review on criteria for assessing the processability of semisolid alloys

In recent years, the semisolid processing has received extensive interest because of its noticeable advantages, and a series of criteria have been proposed to assess the processability of semisolid alloys. The aim of this work is to conduct a focused review on the criteria for evaluating the processability of semisolid alloys. It was found that the temperature sensitivity criterion is more commonly adopted, while the time sensitivity criterion has demonstrated a greater adaptability and the enthalpy sensitivity criterion seems to be more reasonable. Despite no general consensus, these criteria actually provide multi-angle evaluation methods for effectively assessing the suitability of semisolid metal (SSM) processing. In the future, the detailed criteria for assessing the semisolid processability of specific alloys need to be further explored, and it is particularly worth extending the evaluation criteria to Mg alloys due to their excellent lightweight effect and potential application, which is expected to attract wide attention of researchers in the semisolid processing field.

A Comparison Between Semisolid Casting Methods for Aluminium Alloys

Semisolid casting of aluminium alloys is growing. For magnesium alloys, Thixomoulding became the dominant process around the world. For aluminium processing, the situation is different as semisolid processing of aluminium is more technically challenging than for magnesium. Today three processes are leading the process implementation, The Gas-Induced Superheated-Slurry (GISS) method, the RheoMetal process and the Swirling Enthalpy Equilibration Device (SEED) process. These processes have all strengths and weaknesses and will fit a particular range of applications. The current paper aims at looking at the strengths and weaknesses of the processes to identify product types and niche applications for each process based on current applications and development directions taken for these processes.