Semi-solid Compression Research Articles

Compression Mechanical Behaviour of 7075 Aluminium Matrix Composite Reinforced with Nano-sized SiC Particles in Semisolid State

The 7075 aluminium matrix composite reinforced with nano-sized SiC particles was fabricated by ultrasonic assisted semisolid stirring method. The compression mechanical behaviour of the fabricated composite in semisolid state was investigated. The results show that the microstructure of the composite before semisolid compression consists of fine and spheroidal solid grains surrounded by liquid phase. Semisolid compression led to a nonuniform plastic deformation of solid grains. A slight plastic deformation occurred in the locations near the free surface due to the dependence of deformation on liquid flow and flow of liquid incorporating solid grains. However, obvious plastic deformation occurred in the central location and location contacting to die due to the contribution of plastic deformation of solid grains. The true stress–strain curve of the sample compressed at 500 °C consists of rapid increase of true stress and steady stage. However, rapid increase of true stress and decrease of true stress and steady stage are involved in the true stress–strain curves of the samples compressed at 550, 560, 570, 580 and 590 °C. The true stress–strain curve at 600 °C is similar to that at 500 °C. Apparent viscosity decreases with an increase of shear rate, indicating a shear thinning occurrence. When soaking time increases from 5 min to 15 min, the peak stress and steady stress decrease significantly. A further increase of the soaking time led to a slight change. Peak stress and steady stress increase with increasing volume fraction of SiC particles. A sudden increase or decrease of compression velocity led to a significant increase or decrease of the steady stress. The destruction of the samples compressed at solid state temperature mainly depends on cracks parallel to compression direction. However, the destruction forms of the samples compressed at semisolid temperatures consist of cracks parallel to compression direction and partial collapse. Increasing soaking time led to an obvious change of the destruction forms. Compression velocity affects slightly the macro appearance of the sample compressed at semisolid temperatures.

Application of the Eyring Equation in the Evaluation of Semi-Solid Forming-Induced Si Particle Refinement in the Hypereutectic Al-Si Alloys

On the basis of Eyring’s theory of absolute reaction rate, an approach to modeling Si particle refinement acceleration in the semi-solid forming of a hypereutectic Al-Si alloy has been developed. The acceleration variable data used in the present analysis were obtained from a semi-solid compression test using Al-25 mass pct Si alloy cylindrical specimens with a diameter of 15 mm and a height of 15 mm; the test conditions comprised a combination of compression displacements ∆h = 5, 10, and 12 mm; compression rates v = 5, 25, and 125 mm/min; and test temperatures T = 853 K and 863 K (580 °C and 590 °C). The coarse primary Si particle refinement depends on a complex interaction among variables, such as compression displacement, compression rate, and test temperature. The performance of Si particle refinement degraded under higher temperature, slower strain rates, and slower shear rates. The results of the Si particle size are suitably summarized by the Eyring equation as a function of the temperature and the shear rate. The baseline Si particle size and the baseline temperature of Si particle refinement, i.e., the reference temperature, were GN = 0.27 mm and TN = 866.4 K (593.4 °C), respectively. The calculated results using this equation correlated well with the observed results. An acceleration factor of Si particle refinement was successfully derived on the basis of this equation and indicated that operating at a higher shear rate and a temperature just above the melting point of eutectic Al-Si alloy are the optimum conditions for refining Si particles.

Microstructural evolution during partial melting and semisolid forming behaviors of two hot-rolled Cr–V–Mo tool steels

Using a multistage hot compression test machine, reheating experiments and semisolid compression tests were conducted on two commercial rolled Cr–V–Mo tool steels, SKD11 and SKD61. Austenization, grain growth, carbide dissolution, and partial melting took place during the reheating of the tool steels, and resulting in spherical semisolid slurries at certain temperatures (1300°C for SKD11, 1405°C for SKD61). The microstructural evolution of SKD11 and SKD61 tool steels during reheating and rapid cooling was found to be different owing to their different alloying element contents and the different distributions and morphologies of the carbides inside them. The forming characteristics of the two tool steels in the semisolid state were discussed on the basis of the results of compression tests.

In situ synchrotron tomographic quantification of granular and intragranular deformation during semi-solid compression of an equiaxed dendritic Al–Cu alloy

Semi-solid deformation mechanisms are important in a range of manufacturing and natural phenomena, which range from squeeze casting to magma flows. Using fast synchrotron X-ray tomography and a bespoke precision thermomechanical rig, we performed a four-dimensional (3-D plus time) quantitative investigation of the granular behaviour of equiaxed dendritic three-phase materials. This methodology produced new insights into the formation of damage during the isothermal semi-solid compression (∼30% liquid fraction) of an Al–15wt.%Cu alloy at both a macroscopic and microscopic level. Grain rearrangements, such as translation and rotation, were observed and lead to local dilatancy. The resulting flow of Cu-rich intergranular liquid into the dilated interstices gave rise to a local increase in liquid fraction, followed by rapid void growth above a critical axial strain of −6.4%. The local normal and shear strain distributions were quantified using digital volume correlation, identifying dilatant shear bands. At a microstructural level, the individual grains were also seen to undergo intragranular deformation, leading to bending and fragmentation of dendrites as grains interlock.

Flow Behaviour of M2 Steel Alloy during Semi Solid Isothermal Rapid Compression

The key to all semisolid processes is spherical and non-dendritic particles suspended in a liquid matrix. This special kind of microstructure causes the semisolid material to behave like a non-Newtonian fluid dependent on time and shear rate. Semi solid metal processing gives less shrinkage and porosity, non-macro segregation, lower flow stress, good formability and increased die life compared with conventional production methods. Therefore, semi solid processing introduces a good option for massive forming of high temperature alloys. Here, by partial remelting of M2 tool steel alloy under rapid compression test, deformation mechanism of steel alloy and its correlation to rheological properties were investigated. Flow stress for M2 tool steel alloy corresponding to solid fraction above 55% derived at constant strain rate and holding time. In order to investigate the parameter involved in this process, in the second stage of experiments the ram speed and holding time are variable. The analysis of the derived curves shows that the semisolid slurries exhibit a pseudo plastic behavior dependent on stain rate and temperature. The classical power law model used to describe the rheological and thixotropic dependence.

Microscopic Characterization of Semi-Solid Ti14 Alloy

Abstract The microstructural evolution and the element distribution of Ti14 (a+Ti2Cu) alloy during semi-solid compression were investigated. Moreover, the Ti2Cu precipitate behaviors were discussed in detail. The results show that the microstructure, the number and distribution of Ti2Cu precipitates have significant dependence on the process parameters. More Ti2Cu will precipitate on grain boundaries at a higher deformation temperature, and/or a lower strain rate as well as deformation ratio, and finally a network structure is formed after deformation at 1100 °C. The precipitation on grain boundaries is found to be mainly controlled by peritectic reactions. The elevated temperatures resulted in more liquid along the prior grain boundaries, and a Cu-rich region is formed, finally. the “coarse” grain boundaries appear during re-solidification.

Constitutive Equation of ZL201 Alloy during the Semi-Solid Thixotropic Compression

Effects of deformation temperature and strain rate on deformation behavior of semi-solid ZL201 alloy were investigated on Gleeble3800 thermal-mechanical simulator. On basis of the experimental data of semi-solid ZL201, a model of was established to describe the relationship between the processing parameters and flow stress, which showed that the experimental results and calculation ones fitted well. The suitable conditions of this model for semi-solid ZL201 alloy were that the temperature range was 547°C-649°C and that of the strain rate was 0.1 s-1-5s-1.

Semi-Solid Deformation of Al-Fe Alloy Prepared by Electromagnetic Stirring

The semi-solid compression behaviors and the microstructure of Al-Fe alloy prepared by electromagnetic stirred were investigated in the strain rate range of 5×10-3 s-1 to 5×10-1 s-1 and the temperature range of 610 to 640°C on INSTRON-5500R materials testing machine. The experimental results showed that, during the semi-solid deformation of Al-Fe alloy，the peak value of true stress decreased with elevating deformation temperature. As the deformation increased, the stress peak value of the high solid fraction alloy was tending upwards, and that of the low solid fraction was tending downwards. The peak increased with increasing the strain rate. Al-Fe alloy was sensitive to strain rate during semi-solid compression. The strain softening phenomenon would happen. The smaller strain rate, the longer softening process, the stress falling was more slowly. The strain softening was a reason that the semi-solid alloy structure was instability during deformation. The semi-solid deformational behaviors of Al-Fe alloy was bound up with deformation temperature, strain rate, and deforming extent.

Microscopic characterization of semi-solid aluminium alloys

The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 (θ phase) precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformation temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.

Effect of Deformation Parameters on Deformation Behavior of Ti14 Alloy during Semi-Solid Compression

The effects of the process parameters on the deformation behavior of Ti14 alloy have been investigated by compressive tests, at temperature between 1000°C and 1150°C and with strain rates from 5×10-3 S-1 to 5S-1. The results revealed that deformation temperature and strain rate have significant effect on the peak flow stress, the flow stress decreases. The response time required by deformation was affected by the strain rates and liquid fraction was done by the temperature. At higher temperature, transforms deformation mechanism was changed from sliding between solid particles to flow of liquid incorporating solid particles by the change of the liquid fraction.

Deformation Behavior of Aluminum Alloy during Semi-Solid Compression

By semi-solid aluminum alloy compression test, deformation mechanism of semi-solid aluminum alloy was investigated, the thixotropic strength existing in semi-solid aluminum alloy was verified and the influences of temperature and strain rate on the deformation mechanism and thixotropic strength were discussed. The results show that there are 4 stages in the process of compression deformation for semi-solid aluminum alloy: stress swift growth stage, stress drop stage, steady stress stage and stress gradual growth stage. The semi-solid billet has a thixotropic strength, which is sensitive to temperature and strain rate. The higher the temperature or the higher the strain rate is, the smaller the thixotropic strength of the semi-solid alloy.

Experimental investigation and modelling of microstructural variables of Al–4Cu–Mg alloy

The effects of process parameters on microstructural evolution, including grain size and shape factor of the α solid particles during semisolid compression of an Al–4Cu–Mg alloy, were investigated. Experiments were conducted at deformation temperatures of 540, 560 and 580°C, strain rates of 0˙001, 0˙01, 0˙1 and 1 s–1, and height reductions of 20, 40 and 60%. All of the optical micrographs and quantitative metallography showed that deformation process parameters significantly affect the microstructure during semisolid compression of Al–4Cu–Mg alloy, which appears to have a fuzzy characteristic. According to the experimental results from the semisolid compression of Al–4Cu–Mg alloy, a model has been established to describe microstructural evolution by applying a fuzzy set and artificial neural network, which integrates the learning power of neural networks with fuzzy inference systems. The model presented in the present paper can be applied to predict the microstructural changes at deformation temperatures of 540–580°C and strain rates of 0˙001–1 s–1. The maximum relative difference of grain size is 9˙34%. The predicted results are in satisfactory agreement with the experimental results.

Compression behaviour of semisolid YL112 die casting aluminium alloy following isothermal heat treatment

The semisolid compression deformation behaviour of YL112 die casting aluminium alloy with the non-dendritic and dendritic structures has been compared in tests using a Gleeble-1500 thermomechanical simulator. The non-dendritic structure was obtained by isothermal treatment at 570°C for 120 min. In tests up to compressive strains of 0·8, the semisolid compression stress of the alloy with non-dendritic structure initially increases rapidly with increasing strain, then decreases, before reaching a plateau value. Under different deformation temperatures and deformation rates, the maximum compressive stresses are obtained in all cases at strain values of ∼0·07. The semisolid deformation stress decreases with increasing deformation temperature and increases with increasing deformation rate. The compression behaviour of the two types of alloy differs. The semisolid compression stress of the alloy with dendritic structure is higher than that of the alloy with non-dendritic structure; and for strains >0·07, the semisolid compression stress increases and decreases with increasing strain for alloys with dendritic and non-dendritic structures respectively.

Compression Deformation Behavior of AZ91D Magnesium Alloy in Semi-Solid State

The semi-solid compression deformation behavior of the AZ91D alloy with non-dendritic structure, which was obtained under the semi-solid isothermal treatment condition of 570°C×60min, was studied by means of Gleeble-1500 thermal-mechanical simulator. When the compression strain was lower than 0.7, along with the compression strain increasing, the compression stress firstly increased rapidly, then decreased rapidly, and finally kept a constant stress level gradually. Under the condition of different deformation temperatures and deformation rates, the maximum compression stress was obtained simultaneously when the compression strain value was 0.025 approximatively. Furthermore, when the deformation rate kept a constant, the compression stress decreased along with the deformation temperature increasing, and when the deformation temperature kept a constant, the compression stress increased along with the deformation rate increasing.

Mechanical Behavior of Processed AZ91D by Equal Channel Angular Extrusion during Semi-Solid Isothermal Compression

Mechanical behavior of processed AZ91D magnesium alloy by equal channel angular extrusion during semi-solid isothermal compression was investigated using semi-solid isothermal compression test. The results show that there are four stages, drastic increase of true stress, drastic falling of true stress, steady stage and increase of true stress. With the increase of holding time or deformation temperature, required true stress for obtaining same true strain falls evidently and peak stress and steady stress also fall in true stress-strain curve. With increasing strain rate, steady stress also increase. Peak stress will increase or decrease with the sudden increase or fall of strain rate. During semi-solid isothermal compression, plastic deformation of semi-solid billet mainly depends on plastic deformation of solid phases and their rotation and sliding. Coarse grains occur in upper position adjacent to compression die’s surface and fine grains occur in the central and free surface positions of billets.

Investigating the characteristics of AZ61 magnesium alloy on the hot and semi-solid compression test

The characteristics of magnesium AZ61 in semi-solid state have been investigated to understand the changes in its stress-strain in the compression process, the effects on its strain under different processing temperatures, and the consequence of the change of peak stress. First, the AZ61 magnesium alloy is heated to 660 °C and sustained at that temperature for 5 min. Then by natural cooling, the cooling curve is acquired. This natural cooling experiment immediately reveals the semi-solid temperature range of AZ61 magnesium alloy. On this temperature range, the study of its semi-solid characteristics and the observation of microstructure can be carried out. After that, the observed results determine the experimental conditions of semi-solid compression. The compression experiment primarily has two parts. One is to understand the changes of AZ61 magnesium alloy from normal temperature to 400 °C, and the other is to carry out the compression experiment of AZ61 magnesium alloy under semi-solid temperature. Upon completion of the experiment, this research explores their microstructures, and compares the structural change of AZ61 magnesium alloy in a hot chamber within the semi-solid temperature range.

Deformation behavior and microstructural evolution during the semi-solid compression of Al–4Cu–Mg alloy

The effects of the process parameters, including deformation temperature and strain rate, on the deformation behavior and microstructure of an Al–4Cu–Mg alloy, have been investigated through isothermal compression. Experiments were conducted at deformation temperatures of 540 °C, 560 °C, and 580 °C, strain rates of 1 s −1, 1×10 −1 s −1, 1×10 −2 s −1, and 1×10 −3 s −1, and height reductions of 20%, 40%, and 60%. The experimental results show that deformation temperature and strain rate have significant effect on the peak flow stress. The flow stress decreases with an increase of deformation temperature and/or a decrease of the strain rate. Above a critical value of the deformation temperature, the flow stress quickly reaches a steady value. Experimental materials A and B have equiaxed and irregular grains, respectively, prior to deformation. The microstructures vary with the process parameters in the semi-solid state. For material B, the irregular grains transform to equiaxed grains in the process of semi-solid deformation, which improves the deformation behavior.

Structure evolution and compressive behavior of semi-solid Al–Si hypoeutectic alloy with re-melting heat treatment

This paper presents a new method—a re-melting heat treatment method—to fabricate a semi-solid billet of Al–Si hypoeutectic alloy and examines the effect of re-melting temperature, holding temperature and holding time on the semi-solid structural evolution. Semi-solid compression tests are carried out to investigate the deformation behavior and deformation mechanism using a semi-solid billet fabricated by the re-melting heat treatment method. Semi-solid compressive deformation is described using a simple hexagon model. In the compression forming of a semi-solid billet the liquid flow leads to motion or rotation of solid particles, which results in the appearing of some “vacancy” among the primary phase. This makes it easy for solid particles nearby to move to the position of “vacancy” to reach a new arrangement. Semi-solid compressive deformation involves liquid flow, motion or rotation and plastic deformation of solid particles. The solid fraction will affect the practical deformation manner. For a low solid fraction the rotation or motion of solid particles and liquid flow will take a dominant role, whilst for a high solid fraction the solid particles tend to contact each other, so that plastic deformation of solid particles is the main manner. This compressive deformation model is verified by experimental results.

Effects of compression parameters on deformation behaviors of semi-solid ZA27 alloys

An investigation was performed on the effects of semi-solid compression parameters, such as strain rate, compression temperature and heating time at these temperatures on deformation behaviors of two kinds of ZA27 alloys, one was modified by Zr and the other was unmodified. The results indicate that with the increasing of the strain, the stress of the modified composite first sharply increases to a peak value, then dramatically decreases to a peakeau value, and again increases till the end of deformation. But for the unmodified, after being up to a peak value, the stress only decreases slowly. As the compression temperature or the heating time decreases, or the strain rate increases, the stress level and the cracking degree of these two kinds of alloys increase. Under the same deformation conditions, the stress level and the cracking degree of the unmodified alloy are higher than those of the modified one. But there is an exception that the stress level of the unmodified alloy is minimum and smaller than that of them modified one when deformed at the low temperature of 450°C. These phenomena were mainly discussed through analyzing the microstructures under different conditions and the deformation mechanisms at different deformation stages.

The apparent viscosity of fine particle reinforced composite melt

In order to obtain better mechanical properties, fine particles in several micron or submicron diameter are used as reinforcement to reduce stress concentration which are usually induced by larger particles. Zn–22% Al matrix composites with fine alumina particulate reinforcement are fabricated by high intensity ultrasonic treatment. The particulate sizes are chosen with the minimum 0.5 μm. Comparing the height change of composite samples before and after remelted, which have been degassed with semisolid compression, the relation between apparent viscosity and reinforcement diameter is obtained. Experimental results show that there is no interface reactive product involved in the apparent viscosity change. With smaller particulate size, the viscous force is enhanced. That is the dominating reason for the composite melt apparent viscosity increment. An additional reason is the gas introduced with the particulates.