Semi-solid Processing Research Articles

Thixoforming of Aluminum A201- Expectations and Fulfilment

Thixoforming as a Semi-Solid Metal Processing (SSM) route is a near net shape forming of metals in the semi-solid state, i.e. within the freezing or melting range between the fully solid and fully liquid states. Aluminum A201 is a copper containing casting alloy with additional small quantities of magnesium, silicon and silver. Although this alloy is difficult to cast, it has a particularly high response to age-hardening and therefore offers mechanical properties close to the wrought 2014 alloy. Alloy development experiments carried out at the University of Sheffield on A201 alloy have shown that feedstock of this alloy can be produced having uniform non-dendritic microstructures amenable to thixoforming, exhibits thixotropic properties under these conditions, can be shaped into complex near net-shape parts and develops impressive mechanical properties after appropriate heat treatment. A201 aluminum alloy billets when thixoformed in the semi-solid state and heat treated with a T7 followed by T6 treatment before being mechanically tested, have exhibited properties approaching those of wrought 2000 series aluminum alloys. Here follows a review of work done to date on shaping the A201 aluminum alloy in the semi-solid state, describing the hopes, expectations and fulfilment of researchers in the field.

Behavior of Threaded Cylinder tool in the Friction Stir Welding of Al-SiC composite

Abstract Friction stir welding, a novel semi-solid state welding process, has been constantly evolving technology since 1991. In this work friction stir welding was carried out on aluminium metal matrix composites reinforced with SiC. The influence of tool profile and material on the strength of weldment was studied. Threaded cylinder tool made of materials such as OHNS, HCHCr, and H13 with varying D/d ratios were used. The friction stir welded specimens were subjected to mechanical and metallurgical characterization. Threaded cylinder profiled tool made of H13 steel with a D/d ratio of 2 yielded weld joints of highest strength.

Study on Thixoforming Process of 15%SiCp/2A14 Composite for Production of Track Shoe

Semi-solid thixoforming process was applied to produce track shoe of 15%SiCp/2A14 composites. The thixoforming process optimization was simulated by using Deform 3D software. The effects of forging pressure, slug size and reheating temperature on formability of track shoe were investigated. The results showed that a track shoe with better integrity was prepared by optimizing the process, and its microstructure and mechanical properties could meet requirements.

Microstructure and mechanical properties of Mg–Zn–RE–Zr alloy after thixoforming

Magnesium is particularly challenging material, when formed from liquid phase because of high flammability risk. An alternative process for casting, which eliminates above mentioned disadvantage, is thixoforming, which involves a lower temperature of process and operation in the partially solidified state. Influence of semi-solid metal processing on EZ33A magnesium alloy (Mg–Zn–RE–Zr) microstructure and mechanical properties was studied. Ingot microstructure revealed globular grains with coarse eutectic mixture consisting of Mg7Zn3RE, T-phase – RE(Mg,Zn)11 and α(Mg). Heterogeneous nucleation of magnesium solid solution allowed obtaining structure appropriate for thixoforming. Using differential scanning calorimetry, temperature of process was determined to be 622°C, which corresponded to about 30% of the liquid phase. Thixo-cast microstructure consisted of α(Mg) globular grains with a size of 76±1.1 surrounded by fine eutectic mixture in a volume of 35%. T6 heat treatment (solution at 500°C for 6h and ageing at 190°C for 33h) caused increase of grain size to 92μm and the precipitation of two kinds of phases within the α(Mg): β′1 and β′2 responsible for the increase of yield strength to 135MPa, compression strength to 383MPa and hardness to 73HV5.

The Status of Magnesium Injection Molding in China

Thixomolding, or magnesium injection molding as it is more generally known, is an established semi-solid casting process for producing thin-walled near net shape components from magnesium alloys. Magnesium injection molding produces components using a machine similar to a plastic injection molder, where magnesium-alloy chips are feed into the back end, and a rotating screw feeds the chips forward as they are heated to the semi-solid temperature range. The semi-solid alloy collects in a nozzle at the front of the screw, where it is then injected into a re-usable steel die. This paper will initially describe the commercial status of magnesium injection molding in China, and will review several types of components being produced commercially. Comparisons to conventional hot chamber magnesium die casting will be made, and a new magnesium injection molding machine design that incorporates an intensifier will be introduced. In addition, new technology trends utilizing the magnesium injection molding process will be described. One such application involves the magnesium injection molding of Mg-Li alloys. Lithium has the lowest density of all metals, and so the addition of lithium further reduces the density of the magnesium.

Damaging of Ultrasonic Horn for Semisolid Feedstock Production

Ultrasound treatment is one of the known method to obtain the globular microstructure for semisolid processing of aluminum alloys. Notwithstanding the numerous advantages, the main industrial limit of this method is the low service life of the horn due to the combined hot corrosion and erosion phenomena. Various approaches are reported in literature to overcome this problem, but a real satisfactory option does not seem to be available yet. In this paper, the behavior of a H11 tool steel sonotrode coated with a thin layer of TiAlCN is investigated and compared with the performance of an uncoated steel one. The lifetime of the horn was evaluated in terms of effectiveness in semisolid feedstock material preparation. For this purpose, the microstructure of semisolid cast samples obtained after different working times was analyses by optical and scanning electron microscopy. Moreover, melt contaminations due to the probe dissolution were also evaluated. The applied coating exhibited a significant resistance to separate hot corrosion in liquid Al alloy and cavitation erosion phenomena in water. However, the combined effect of the two damaging mechanisms during ultrasound treatment of the molten alloy leaded to coating removal and to a horn consumption comparable to that of bare steel.

SIMA Processing of Cu34wt.%Zn2wt.%Pb Brass Alloy

Effects of SIMA processing on size and shape of primary solid particles of Cu34wt.%Zn2wt.%Pb brass alloy was investigated. The optimal temperature for semisolid processing of the alloy was found to be around 890 °C using Thermo-calc simulation software. Liquid fraction sensitivity of the alloy around this temperature is 0.012. The results indicated the formation of non-dendritic microstructure even after 1 min holding of 10% cold worked sample at 890 °C. Sphericity of the primary solid particles increased by increasing the cold working ratio and holding time. The smallest size (103 μm) and highest shape factor (0.84) of the primary solid particles were achieved at 30% cold working ratio and 5 min holding time.

Microstructural Development of Aluminum A201 Alloy Semi-Solid Processing Feedstock Produced by Different Routes

Thixoforming or Semi-Solid Metal (SSM) forming is a manufacturing route that relies on a non-dendritic microstructure, a structure that is retained after processing resulting in components of fine and uniform microstructures with enhanced mechanical properties as compared to conventional cast products. In this project, an investigation is conducted on the microstructural development of Aluminium A201 alloy in the semi-solid range, through a combination of variable time and temperature conditions. Using equilibrium and non-equilibrium (Scheil) curves, the solidus and the liquidus temperatures as well as the melting behaviour of this alloy are estimated. The temperature range for the thixoforming process typically lies within the 40-60% fraction liquid and this is found to be between 620oC to 637oC for this particular alloy. The aim is to heat treat specimens of this alloy within the semi-solid range (the process window) and observe the resulting microstructures to establish if they comprise of near-spheroidal solid phase particles surrounded by a liquid phase. This microstructure gives the material its thixotropic properties; i.e. the material flows like a liquid when sheared but thickens and behaves like a solid when it is allowed to stand. Three different routes for obtaining the non-dendritic microstructure necessary for thixoforming are investigated in this work: Magneto-Hydrodynamic (MHD) stirring, Strain Induced Melt Activated (SIMA) and Semi-Solid Rheocasting via Cooling Slope (SSR+CS) route. These routes are compared and their potential for future thixoforming applications studied.

Multi-pass friction stirred clad welding of dissimilar joined AA6061 aluminium alloy and brass

Tool steels are commonly used to cut metal materials due to their distinctive hardness, resistance to abrasion and deformation. However, tool steels are difficult to be joined using conventional fusion welding process. In this study, a thixotropic property of metal was utilised to butt-join an AISI D2 tool steel by using uncommon direct partial re-melting (DPRM) method. A high frequency of induction heating is used to apply the DPRM method. From the recent study, there are many methods in achieving the globular microstructure with the success of semi-solid joining process. Though, very less information on the microstructural effect of semi-solid joining on the mechanical properties was reported. This study aims to analyse the effect of uniaxial force on the microstructural evolution and mechanical properties of the thixo-joint of D2 tool steel. The microstructural analysis showed the diffusion occurred between the grains of the thixo-joint sample with 2.5 N uniaxial force. The maximum strength of the thixo-joint sample with force was 652 MPa. This was slightly higher than the as-received sample and the thixo-joint sample without force. The average hardness value of the thixo-joint sample was 400 HV due to the transformation of ferrite to the metastable austenite.

The Effect of Electromagnetic Stirrer on the Size and Morphology of Intermetallic Particles in Al-Si Metal Matrix Composite

The electromagnetic stirrer method was developed to overcome the problems caused by the presence of a mechanical stirrer in the slurry; this method is nowadays considered to be the most widely used and most useful method in the semi-solid processes. In this study, the structure of the intermetallic iron particles obtained in the aluminum matrix composites produced by the semi-solid method is compared with the traditional method. The results show that in semi-solid samples, the intermetallic particles are much smaller and more dispersed, so the stress concentration points in these samples are much smaller and less.

Microstructure, Mechanical Properties and Wear Behaviour of Semisolid Stir Casting SiC Reinforced Zn-40Al Based Composites

The Zn-40Al composites with various contents of SiC were fabricated by the semi-solid stir casting process. The influence of the SiC on the microstructure, mechanical properties and wear behavior of the composites were investigated. Microstructure analysis shows that the microstructures of as-cast Zn-Al alloys are refined by the addition of SiC. However, with the increase of SiC content, a number of shrinkage porosity occur. The hardness of the composites increases with the increase content of SiC. The tensile strength of the composites declines significantly with the increase content of SiC. The most effective strengthening achieves in Zn-40Al/0.5wt.% SiC, with a maximum increment of 20% in tensile strength compared to non-SiC addition alloy. The overall results reveal that the composites possess similar friction coefficients but the abrasion loss is reduced to less than a tenth after adding 0.5% SiC.

Kesan Pembentukan Tikso terhadap Mikrostruktur dan Sifat Mekanik Aloi Al-Si-Cu-Mg

Forming of metals in their semi-solid state is one of the options for producing near net shape parts. It can produce a strong and highly reliable product. Al-Si-Cu-Mg casting alloy is commonly used in automotive engine components which is now widely used in the semi-solid processing. The main physical properties of the aluminium alloy and alloying element content such as silicon, copper and magnesium, plays an important role in determining the mechanical properties of the alloy. In this paper, the effect of the formation process of Al-Si-Cu-Mg permanent die casting alloy and the thixoforming process has been investigated towards the evolution of microstructure and mechanical properties. Compound phases, shapes and morphology of the two processes were compared. The porosity effect was examined at permanent die castings and thixoforming process. The result of image analysis showed significant change of the thixoforming process of α-aluminum solid phase structure in spherical shape. Size and morphology, as well as the uniformity of the silicon eutectic phases and intermetallic compound distributions of Al2Cu, Al5Fe Si and Al15(Mn,Fe)3Si2 changed due to the compression during thixoforming process. Thixoforming process of the Al-Si-Cu-Mg alloy exhibit the lowest percentage and microporosity area thus proved that porosity issue significantly reduced during the aluminium alloy solidification process in thixoforming process . The tensile properties of thixoformed alloy improved significantly with its ultimate tensile strength, yield strength, and elongation to fracture at 193MPa, 163MPa and 1.6%,respectively.

Microstructural evolution and mechanical properties of thixoformed 7075 aluminum alloy prepared by conventional and new modified SIMA processes

Abstract The microstructural evolution during semi-solid processing and thixoformability of a 7075 alloy prepared by conventional and new modified strain induced melt activation (SIMA) processes were comparatively investigated in this paper. The semi-solid slurries were thixoformed at 600 °C, at which temperature the solid fraction was estimated to be 0.8. The coarsening process of the semi-solid samples was described using Lifshitz–Slyozov–Wagner theory and the effect of pre-deformation on the coarsening kinetics of the solid particles was discussed. The coarsening rate constant of the new modified SIMA sample showed a remarkable decrease compared to that of the conventional SIMA sample. Microstructural and mechanical investigations indicated that the sample with a near-equiaxed microstructure deforms through the plastic deformation of solid grains mechanism. However, the sliding of solid grains and flow of liquid incorporating solid grains mechanisms were dominant in the sample with a globular microstructure. Also, it was observed that the yield and ultimate strengths and hardness of the sample prepared by the new modified SIMA process after thixoforming and T6 heat treatment increased by about 15 %, 10 % and 25 % respectively, compared to those of the conventional SIMA sample.

The effects of ultrasonic treatments on the microstructure and mechanical properties of SAC0307 solder

The microstructures and physical properties of SAC0307 lead-free solder formed by an ultrasound-assisted semi-solid casting process were analyzed. The damages to a thin aluminium foil placed in the alloy melt at 226 °C showed strong effects of acoustic streaming. Significant erosion due to cavitation was found for powers higher than 450 W. Numerical simulations of a collapsing cavitation bubble obtained the highest peak pressure and temperature when the ultrasonic power was around 550 W. When the ultrasonic power was between 500 W and 600 W, sub-grains were observed and the crystal grains became equiaxed with the smallest average grain size of about 140 μm. The highest tensile strength found in this range was about 36.6 MPa. The density was 7.35 g/cm3. The elongation at break was about 60%, which was 40% higher than the value obtained by traditional casting techniques.

Effect of gas-induced semisolid process on solidification parameters and dendrite coherency point of Al–4.3Cu alloy using thermal analysis

Semisolid processing of Al–4.3%Cu (A206) alloy was carried out using gas-induced semisolid (GISS) process in different conditions. The flow rate of inert gas, 1, 2, and 4 L min−1, starting temperature for gas purging (the temperature of superheated melt), 670, 660, and 650 °C, and the duration of gas purging, 10, 20, and 30 s, were three key process variables which were changed during this investigation. Thermal analysis was successfully implemented through CA-CCTA technique for GISS samples as well as conventionally cast sample. The two-thermocouple thermal analysis technique was utilized to determine the dendrite coherency point of GISS sample and conventionally cast sample. The results showed that gas purging into the melt led to temperature drop of the melt to its liquidus temperature. In fact, copious nucleation is induced by cooling effect of inert gas bubbles. GISS process delays the dendrite coherency point from 644.2 to 637.3 °C which leads to increase the solid percentage from 9 to 21% at this point and therefore enhance the casting characteristics. It is found that inert gas purging into the molten metal, regardless of the process parameters, leads to the microstructural modification from fully dendritic to globular structure. Microstructural evaluation showed that the best sample which included fine grains of 76 μm in average size and with high level of globularity of 0.86 was achieved from a semisolid sample in which the gas purging started at 670 °C and its duration time was 20 s with the gas flow rate of 4 L min−1.

Effect of processing routes on structure-property correlationship of ADC 12 Al alloy

The present work focuses primarily on the effect of processing routes on structure-property correlationship of ADC 12 Al alloy. Both conventional processing (Gravity cast and pressure die cast) and Semi Solid processing techniques (cooling slope and Rheo-Pressure Die Cast; RPDC) were attempted to bring out the correlationship between their microstructures and mechanical properties of ADC 12 Al alloy. Gravity cast experiment was done on ingots of ADC12 Al melted in an resistance furnace and poured at temperature 585 °C in a copper mould. In the Pressure Die-Casting process, ingots of ADC12 Al alloy were melted in an resistance furnace and the liquid metal was poured in the mould of the pressure die casting system. Semi-solid metal processing was carried out using cooling slope experiments in a developed in-house set up and effect of rheocasting on the semi solid microstructure was studied. Rheo pressure die cast experiments were carried out in an integrated set-up of cooling slope and pressure die-cast system. The obtained result of gravity cast material reveals dendritic morphology of primary Al phase and elongated eutectic phase; upon using pressure in a pressure die cast system, the structure of primary Al phase changes to large size dendrites along with rosette shaped morphology. The cooling slope technique to generate semi-solid structure yields nearly globular and fine grains; whereas the rheo pressure die casting experiments reveal nearly globular shape primary Al exhibit that distribute relatively uniformly in the matrix compared to the all three above the processing routes. From The best mechanical properties are also obtained in Rheo-pressure die cast system with tensile strength (223 MPa), elongation (6.5%), and hardness (87 VH) compared to all other processing routes. Explanations of fracture micro mechanisms are supplement to the investigation.

Effect of solid fraction on microstructures and mechanical properties of a Mg-Al-La-Ca alloy processed by rheocasting

Morphological evolution of microstructures and tensile properties in Mg-Al alloy containing La and Ca (Mg-6Al-3La-1Ca) processed by rheocasting with different solid fractions (fs) were investigated at this paper. An apparatus for semisolid metal alloy processing was used to melt and to obtain the rheocast material. Isothermal mechanical stirring experiments were carried out with fs = 0.30, 0.49 and 0.61 at 950 rpm for 10 min. A conventional casting (no stirring) was also obtained for comparisons. Results showed that microstructure in conventional casting is composed by α-Mg dendritic matrix and Al11La3, (Al,Mg)2Ca and Mg2Ca compounds. Non-dendritic and globular microstructures were observed in the rheocasting. For fs = 0.30 the acicular Al11La3 phase precipitated at globule boundaries, while for the fs = 0.49 and fs = 0.61 the acicular phase precipitated both inside and at globule boundaries. The ideal rheocasting condition was achieved fs = 0.30 due to the improvement of 76% for the ultimate tensile strength (UTS) and 80% in the strain to fracture when compared to the conventional casting. Fracture surface analysis pointed to a mixed ductile-brittle fracture mode containing dimples and quasi-cleavage facets for the lowest solid fraction (fs = 0.3), and a fully brittle fracture mode consisting exclusively of cleavage planes for the highest solid fraction (fs = 0.61).

Effect of T6 Heat Treatment on the Microstructure and Hardness of Secondary AlSi9Cu3(Fe) Alloys Produced by Semi-Solid SEED Process

The effect of the T6 heat treatment on the microstructure and hardness of a secondary semi-solid AlSi9Cu3(Fe) alloy have been investigated by using optical, scanning and transmission electron microscopy and hardness testing. The semi-solid alloy was produced using the swirled enthalpy equilibration device (SEED). The solution heat treatments were performed at 450, 470 and 490 °C for 1 to 6 h followed by water quenching and artificial ageing at 160, 180 and 220 °C for holding times ranging from 1 to 30 h. The microstructural investigations have revealed the spheroidization of the eutectic Si and the dissolution of the majority of Cu-rich compounds after all the solution heat treatments; moreover, the greater the solution temperature and time, the higher the hardness of the alloy. Unacceptable surface blistering has been observed for severe solution condition, 490 °C for 3 and 6 h. The artificial ageing at 160 °C for 24 h has led to the highest alloy strengthening thanks to the precipitation of β” and Q’ (or L) phases within the α-Al matrix. The hardening peaks at higher temperatures have been early achieved due to faster hardening kinetic; however, the lower number density of β” and Q’ (or L) phases and the presence of coarser θ’ precipitates result in a reduction of hardness values for peak aged condition at 180 and 220 °C, respectively.

Effect of the Parameters of Semi-Solid Processing on the Elimination of Sharp-Edged Primary Chromium Carbides from Tool Steel

Although conventional tool steels have been heat treated on a routine basis for decades, the search continues for new ways to eliminate their troublesome sharp-edged primary chromium carbides, which impair toughness. One of the available techniques is semi-solid processing, which involves partial melting of the workpiece. The structure after semi-solid processing consisted of a austenite and carbide-austenite network. The network can be broken up and its fragments distributed uniformly by subsequent forming with appropriate parameters. In this experimental study, X210Cr12 tool steel was heated to a semi-solid state, and after cooling to a solid state, worked in a hydraulic press. Suitable soaking temperatures were sought within an interval between 1200 °C and 1280 °C. The workpieces were quenched from the forming temperature in water or oil. In order to improve formability and reduce hardness, tempering was tested as well. Additional experimental regimes included conventional quenching and tempering. Once the appropriate parameters were chosen, the elimination of primary chromium carbides was successful. The resultant microstructures were fine and consisted of M-A constituent with a size of approximately 1 μm, and very fine Fe3C and Cr7C3 carbides. The hardness was in excess of 800 HV10. They were examined using optical and scanning electron microscopes. The carbides were characterized on transparent foils in a transmission electron microscope. Mechanical characteristics were determined in micro-tensile tests.

A novel graphene-stimulated semi-solid processing to fabricate advanced aluminium matrix nanocomposites

This study reveals an unprecedented capacity of flake graphene sheets in manipulating semi-solid deformation of aluminium matrix nanocomposites by restricting the grain growth of the nanograins during the reheating process to significantly enhance (173%) the yield strength of the fabricated composites. The graphene sheets with onion shape have also shown the unique capability in alleviating the agglomeration of SiC nanoparticles, attributed to the manipulated Hamaker constant of these particles as a result of wrapping graphene sheets. A devised mathematical approach has authenticated, for the first time, the effect of wrapping graphene sheets on subtle adjusting the Hamaker constant of SiC nanoparticles to stimulate engulfment of these nanoparticles within solidifying matrix rather than agglomeration at grain boundaries. This, therefore, has resulted in diminishing the porosity and stimulating multi-scaled micro/nano grains, thereby significantly enhancing the tensile properties of the fabricated composites.