Semi-solid Compression Research Articles

Influence of Soaking Time and Loading Rate on Semi-solid Compression of Porous Al-4Cu-Mg Alloy

Influence of Soaking Time and Loading Rate on Semi-solid Compression of Porous Al-4Cu-Mg Alloy

Semi-Solid Deformation Behavior, Flow Stress Prediction and Deformed Microstructure of GH3536 Superalloy

In current work, the deformation behavior and deformed microstructures of GH3536 superalloy in semi-solid state were investigated, and the semi-solid flow stress was predicted by artificial neural network (ANN) model. The semi-solid compression deformation was carried out at 1320-1350 °C, and the solid deformation behavior at 1200 °C was tested for comparison. The peak stress under 0.01-1 s-1 semi-solid deformation was 45.6-161.9 MPa. The peak stress decreased with the increase of deformation temperature and the decrease of strain rate. The ANN model could well describe semi-solid flow stress. During semi-solid deformation, the apparent viscosity dropped as shear rate increased. At high temperature and low strain rate, more liquid phase was distributed at grain boundaries. The solid grains coarsened as deformation temperature increased.

Microstructure evolution of AZ80 magnesium alloy in semi-solid compression by molecular dynamics simulation

Molecular dynamics (MD) simulation and experiments were carried out in this work to probe the microstructure evolution in the semi-solid compression (SSC) of AZ80 magnesium alloy. The liquid phase flow, stress fluctuations, grain refinement, dislocation generation, and texture evolution were discussed. Results indicate that the liquid phase was squeezed out along the radial direction prior the solid phase at the beginning of compression. Stress-strain curve represented obvious fluctuation at lower strain rates. That resulted from stress reduction caused by more liquid evolving with a lower strain rate at an elevated temperature. Plastic deformation was detected in grains and the dislocations of 1/3<11¯00> dominated the deformation, while and 1/3<12¯10> just been activated at the beginning of SSC process. The results of EBSD showed the grains size was refined into about 38.8 μm from 92.3 μm after SSC process. During the process, grain refinement resulted in the increase of low-angle grain boundaries (LAGBs), and a strong (0001) basal plane texture evolved at the end. The higher the strain rates, the stronger the texture.

Microstructure and compression properties of semisolid CrCuFeMnNi high-entropy alloys

CrCuFeMnNi high-entropy alloys were investigated for semisolid processing due to their high compositional flexibility. They exhibited a highly globular semisolid microstructure, with small transformed solid globules. The alloys had a mixture of BCC and two FCC phases, with BCC fractions remaining almost constant while the fractions of both FCC phases changed with Cu content. Although the predicted and experimental equilibrium phase fractions differed, measured compositions were close to equilibrium. During semisolid compression, peak stresses decreased, and the deformation plateau increased with liquid fraction. Furthermore, the alloys behaved like a cohesionless granular material.

Deformation behavior and forming process simulation of semi-solid powder rolling based on the combined constitutive model

Semi-solid powder forming (SPF) as a novel technology has been widely used to prepare composite materials. However, most of the present models used to simulate the complicated SPF process are based on the constitutive relationship of single dense or porous material, which cannot well satisfy the actual conditions. In this study, the process of semi-solid powder rolling was simulated by the combined constitutive formula of sintered and dense Al-Cu-Mg alloy materials obtained from semi-solid compression experiments. The results show that the semi-solid compression curves of dense and sintered materials are similar, and their peak stresses increase with the decreasing porosities. The grain or particle size of sintered materials after semi-solid compression becomes finer as powders crushed, but the grain size of dense materials becomes larger due to grain coarsening and deformation, which is the key advantage of SPF with fine microstructures. The combined constitutive model of semi-solid powder materials was established and verified, and then the numerical simulation of semi-solid powder rolling based on the model was proved that can well describe the rolling process, which provides a guidance for process optimization.

Semi-solid compression of 2A14 alloy with high solid fraction: rheology, constitutive equation and microstructure

Semi-solid compression of 2A14 alloy with high solid fraction: rheology, constitutive equation and microstructure

Microstructural Evolution and Mechanical Properties of 7075 Aluminium Alloy during Semi-Solid Compression Deformation

Aluminium alloys are becoming increasingly popular due to the demands for high-performance lightweight components, and semi-solid metal processing (SSM) is a technique for forming near-net-shape and complex components with far fewer defects associated with turbulent filling. The deformation mechanisms of semi-solid 7075 aluminium alloy were studied through the direct partial re-melting method using as-extruded billets. It is found that inter-granular and intra-granular deformation occur simultaneously during compression under the semi-solid condition; the deformation of solid primary α-Al grains can compensate for the shrinkage of inter-granular liquid and increase the integrity of shaped parts. The intra-granular deformation at the final stage of SSM can change the morphology of spherical solid grains and induces sub-grain boundaries.

Microstructure evolution and densification of sintered porous 2024 aluminum alloy compressed in a semi-solid state

The semi-solid powder forming (SSPF) as a promising technology has a complicated process, but the formation mechanism of that remains unclear. The study of semi-solid compression of porous materials is an effective method to investigate the SSPF. Based on analyzing the influence of deformation strain, temperature, strain rate and initial relative density on microstructure evolution and relative density development of sintered porous 2024 aluminum alloy during semi-solid compression, the deformation mechanism and densification mechanism of semi-solid porous materials were proposed. The results show that main deformation mechanisms of porous materials during semi-solid compression are breakup of the solid skeleton or powders, and flowing of liquid with powders or fragments. Breakup mechanism is dominant at center area, whereas flowing mechanism dominates at the margin. With increasing strain and temperature and decreasing strain rate, breakup mechanism becomes primary. The densification mechanisms of porous materials during semi-solid compression are rearrangement of powders or fragments and filling of liquid, resulting from collapse of the solid skeleton or powders and flowing of liquid. The emergence of pores and densification occur simultaneously during semi-solid compression of porous materials.

Shear bands of as-cast and semi-solid Ti48Zr27Cu6Nb5Be14 bulk metallic glass matrix composites

The as-cast Ti48Zr27Cu6Nb5Be14 bulk metallic glass matrix composites (BMGMCs) were fabricated using a copper mold suction casting method. Then, the semi-solid BMGMC samples were obtained following an isothermal treatment (heating at 900 °C for 10 min, then cooling with water). The microstructure and compression property were investigated by scanning electronic microscopy (SEM) and universal mechanical tester. As a result of the isothermal treatment, the crystal shapes change from fine, granular, and dendritic to spherical or vermicular, and the average crystal size of the as-cast and semi-solid samples is 2.2 µm and 18.1 µm, respectively. The plasticity increases from 5.31% in the as-cast to 10.23% in the semi-solid samples, with an increase of 92.66%. The shear bands from different areas of the side surfaces of as-cast and semisolid compression fracture samples were observed. The characteristic changes of multiplicity, bend, branch and intersection of shear bands in different areas indicate that the deformation of as-cast and semi-solid samples is non-uniform during compression. It is found that poor plasticity of the as-cast samples or good plasticity of the semi-solid samples are reflected by characteristics of the shear bands. The semi-solid isothermal treatment improves the plasticity by forming large crystals which can block the expansion of shear bands and promote the multiplicity of shear bands.

Semi-solid compression of nano/micro-particle reinforced Al-Cu composites: An in situ synchrotron tomographic study

Four-dimensional fast synchrotron X-ray tomography has been used to investigate the semi-solid deformation of nano- and micro-particle reinforced aluminum-copper composites (Al-10 wt% Cu alloy with ~1.0 wt% Al2O3 nano and ~1.0 wt% Al2O3 micro particles). Quantitative image analysis of the semi-solid deformation behavior of three alloys (base, nano- and micro-particle reinforced) revealed the influence of the particulate size on both microstructural formation and dominant deformation mechanisms. The results showed that initial void closure and incubation period were present in the particle-free and nano-particle reinforced Al-Cu composite during semi-solid compression, while the micro-particle reinforced alloy only showed continual void growth and coalescence into cracks. The results suggest that the nano-particle reinforced composite has the best hot-tearing resistance amongst the three alloys. Improved hot-tear performance with nano-particulate reinforcement was attributed to the small liquid channel thickness, fine grain size which alters the distribution/morphology of the liquid channels, more viscous inter-dendritic liquid, and fewer initial voids.

Semisolid Compression Brazing of Al50Si Alloy Using Zn-Al-Cu Filler Metal Assisted by SiC Particles

Semisolid compression brazing of Al50Si alloy using Zn-Al-Cu filler metal assisted by SiC particles coating has been developed. The effects of the size and concentration of SiC particles on the microstructure and mechanical properties of the joints were studied. By using 1 μm SiC particles and the concentration of SiC particles increased to 3 g/m2, oxide film on the surface of base metal was completely disrupted and a good bonding strength was obtained. As SiC concentration further increased to 4 g/m2, colonies of SiC particle with nonwetting areas of filler metal formed at the interface, resulting in a decrease in the bonding strength. By using 5 μm SiC particles, the bonding strength was enhanced as SiC concentration increased from 1 g/m2 to 3 g/m2 due to the removal of the oxide film. By further increasing SiC concentration to 16 g/m2, the strength was constantly improved because of the dislocation strengthening effect generated at the SiC particle layer/filler metal interface. When SiC concentration increased to 32 g/m2, nonwetting area appeared inside the SiC particles layer, causing a decrease in the bonding strength.

Combined Deformation and Solidification-Driven Porosity Formation in Aluminum Alloys

In die-casting processes, the high cooling rates and pressures affect the alloy solidification and deformation behavior, and thereby impact the final mechanical properties of cast components. In this study, isothermal semi-solid compression and subsequent cooling of aluminum die-cast alloy specimens were characterized using fast synchrotron tomography. This enabled the investigation and quantification of gas and shrinkage porosity evolution during deformation and solidification. The analysis of the 4D images (3D plus time) revealed two distinct mechanisms by which porosity formed; (i) deformation-induced growth due to the enrichment of local hydrogen content by the advective hydrogen transport, as well as a pressure drop in the dilatant shear bands, and (ii) diffusion-controlled growth during the solidification. The rates of pore growth were quantified throughout the process, and a Gaussian distribution function was found to represent the variation in the pore growth rate in both regimes. Using a one-dimensional diffusion model for hydrogen pore growth, the hydrogen flux required for driving pore growth during these regimes was estimated, providing a new insight into the role of advective transport associated with the deformation in the mushy region.

Effects of strain rate on hot tear formation in Al-Si-Cu alloys

The alloy casting process is one of the major manufacturing processes to produce near net shape components. The casing process is prone to a wide variety of defects, with hot tear being one of the most detrimental. The two main factors generally recognized as the primary cause for formation of hot tears are the mechanical response of the mush (which effects its permeability), and the solidification range (solidification time). The response of the mushy zone under deformation is mainly affected by the solid fraction, strain rate and grain morphology. Even though the science behind the formation of hot tear is understood, there is no general criterion to quantify the hot tear formation under varying casting conditions. The development of ultra-fast X-ray imaging has facilitated the means to quantify the effects of the critical parameters in-situ and develop better correlations for hot tear prediction. The in situ experiments will also provide insights into mush rheology, which has significant influence on hot tear formation. In this study, isothermal semi solid compression studies of Al-Si-Cu alloys were carried out using specially built thermo-mechanical rig. We studied the effects of the strain rate in the range of 2 × 10-4–0.02/s and solid fraction (∼0.6-0.9) on the mechanical response of the mushy zone. The sample were characterized before and after deformation using X-ray micro tomography. The data was subjected to an image processing routine and the amount of porosity and hot tear was quantified. The stress-strain curve of the semisolid alloys showed a characteristic strain softening behaviour for semi solid samples with ∼0.6-0.7 solid fraction, irrespective of loading rates, whereas the behaviour at higher fractions were that of constant flow stress. Additionally, in situ compression experiments were carried out, wherein the liquid channel thickness at various strain values were measured. Isolated liquid channels were formed under loading, from where the hot tears were found to nucleate. Hot tear susceptibility was found to increase with increasing strain rate and rheology of the mush, which is dependent on solid fraction.

The Current Status and Development of Semi-solid Powder Forming (SPF)

Semi-solid powder forming is a promising near-net-shaped forming technology, which has the advantages of powder metallurgy and semi-solid forming, such as fine grains, low forming pressure and short process flow. It was used to prepare wide solidification range alloys and its composites. Until now, there have been many studies on the parameters, microstructure and mechanical properties of this technology, but few on the forming principles. Because deformation, solidification and densification occur simultaneously, the forming mechanism is very complex. The liquid fraction is the key factor influencing the microstructure and mechanical properties. Semi-solid compression of porous materials was carried out to study the deformation mechanism of semi-solid powders. The combination mechanism and densification process for semi-solid powder rolling has been analyzed, and the compaction behavior of powders in the semi-solid state has been studied. Shima porous yield criterion and Doraivelu plastic yield criterion were applied in the simulation of semi-solid powder rolling. Based on the Fourier heat conduction equation and the related parameters of semi-solid powder, the rolling force and relative density were simulated by using the Marc finite element software platform. The simulation results are in agreement with the experimental results. Although some achievements have been made in the theoretical research and numerical simulation, the yield criteria and mathematical models suitable for semi-solid powder forming need to be further established. In addition, further optimization of this technology and its application in commercial applications should be the research direction.

Microstructural Evolution during Partial Melting and Semisolid Forming Behaviors of Two Hot-Extruded Magnesium-Rare Earth Alloys

Reheating experiments and semisolid compression tests were conducted on two hot-extruded magnesium-rare earth (Mg-RE) alloys, Mg-8.20Gd-4.48Y-0.36Zr-3.34Zn and Mg-3.75Gd-5.15Y-0.75Zr-3.05Zn by using a multistage hot compression test machine. Dissolution of eutectic compounds, growth of grains, and partial melting took place during the reheating of these Mg-RE alloys and resulted in spherical semisolid slurries at certain temperatures (580 °C for Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr, 560 °C for Mg-3.75Gd-5.15Y-0.75Zr-3.05Zn). Owing to the different alloying element contents of these two Mg-RE alloys, eutectic compounds with different morphologies were found inside them after reheating and rapid cooling processes. The forming characteristics of these two Mg-RE alloys in semisolid state were discussed based on the results of compression tests.

Partial melting behavior and thixoforming properties of extruded magnesium alloy AZ91 with and without addition of SiC particles with a volume fraction of 15%

A series of reheating-isothermal holding experiments and compression tests were conducted on pristine magnesium alloy AZ91 extruded by equal channel angular extrusion (ECAE) and SiC particles (a volume fraction of 15%) reinforced AZ91 composite (AZ91-SiCp) by regular extrusion. Dissolution of eutectic compounds and partial melting of the α-Mg matrix occurred during the reheating of these materials. Spherical semisolid slurries of these materials were obtained when the reheating temperature and isothermal holding time were 550°C and 20s, respectively. The presence of SiCp in AZ91-SiCp not only caused lower liquid fractions of semisolid slurries but also resulted in higher values of flow stress during semisolid compression tests. Both AZ91 alloy and AZ91-SiCp composite exhibited better thixoforming properties at high temperatures. Segregation of SiCp did not occur during thixoforming of AZ91-SiCp composite after an isothermal holding at semisolid temperatures for 20s.

Deformation Behavior and Microstructure Evolution of 9Cr18 Alloy During Semi-Solid Compression

Deformation Behavior and Microstructure Evolution of 9Cr18 Alloy During Semi-Solid Compression

Effects of reheating and subsequent rapid cooling on microstructural evolution and semisolid forming behaviors of extruded Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy

Reheating and rapid cooling experiments, and semisolid compression tests were conducted on extruded Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy using a multistage hot compression test machine. Affected by reheating temperature, heating rate and isothermal holding time, dissolution of eutectic compounds and partial melting occurred during reheating, dynamic arrangement of alloying elements and phase transformation took place during subsequent rapid cooling. These microstructural behaviors not only changed the anisotropy in microstructural morphology of the extruded Mg–8.20Gd–4.48Y–3.34Zn–0.36Zr alloy, but also affected the anisotropy in forming properties of it. When this alloy was reheated to 580°C with a heating rate of 20°C/s and held isothermally for 20s, semisolid slurry without anisotropy in microstructural morphology and forming properties, exhibiting a homogeneous spherical microstructure was obtained.

Effect of Temperature on Deformation Behavior of Sintered Porous AA2024 During Semisolid Compression

Semisolid processing as a promising manufacturing route has recently gained wide use for dense materials. Nevertheless, very few investigations on porous materials or powders were reported and the effect of temperature on deformation behavior of porous materials or powders remains unclear. Sintered porous AA2024 specimens with initial relative density of 83% were compressed at a semisolid state. The liquid volume fraction of gas-atomized AA2024 powders at a semisolid state was determined by the Thermo-calc prediction, the differential scanning calorimetry (DSC) experiment, and metallographic analysis. The results show that the DSC experiment is the best suitable method in this study. As temperature increases, two opposite effects simultaneously act on the microstructure: More powders of samples after compression are broken up, making grains finer, whereas the surface energy decreases, making grains more spherical and coarser. The relative density increases with the increasing temperature because more powders crush and more liquid flows. Thus, the deformation resistance of sintered porous materials decreases, which makes true stress decrease with the increasing temperature. Therefore, the effect of temperature on deformation behavior of sintered porous materials at a semisolid state is attributed to the liquid fraction, which significantly affects the breakup of solid skeleton or powders and the flowing of liquid.

Compression deformation behavior of semisolid Al2O3np reinforced 7075 aluminum matrix composites with high solid fraction

Abstract