Semi-solid Magnesium Alloy Research Articles

Thixomolding Developments

Abstract Thixomolding is a method of molding semi-solid magnesium alloy pellets using equipment and processing methods similar to injection molding. Its commercial growth has been driven by its technical advantages, including enhanced precision, environmental cleanliness, and the ability to produce complex 3D shapes with high yields and minimal waste.

Development of High Strength and High Thermal Conductivity Semi-Solid Magnesium Alloy by Thixomolding Process

This paper investigates the influence of Cu addition on the microstructure, mechanical properties, and thermal conductivity of a semi-solid Mg-10Zn alloy produced by Thixomolding process. Microstructure of the Mg-10Zn alloy consists of α-Mg matrix and Mg2Zn second phase. The formation of Cu3Zn phase was found after the addition of Cu particles. Besides, the volume fraction of solid phase decreased in the Mg-Zn/Cu alloy compared with that of binary Mg-Zn alloy. The yield strength of the alloy was enhanced from 157MPa to 188MPa after Cu addition at the sacrifice of a small amount of ductility. Thermal conductivity, on the other hand, were kept the same level of 115-117 (W/m·K) in the Mg-10Zn alloy and Mg-10Zn/Cu alloy. This work demonstrates the potential for developing Mg alloys with high strength and high thermal conductivity via proper alloy design using Thixomolding process.

Investigation of Rheological Behaviour of Liquid and Semi-solid Magnesium Alloys of Mg–Zn–Al, Mg–Zn–RE Groups

In this study, in order to obtain more comprehensive characteristics of the magnesium alloys, rheological measurements were performed for the liquid and semi-solid state, taking into account the effect of thixotropy of the magnesium alloys tested. The hysteresis loop plotted shows the thixotropy of two examined alloys.

Mathematical Description of Semi-Solid Magnesium Alloys Behaviour by Using Rheological Models

This paper is a study of rheological analysis of magnesium alloys of groups Mg-Zn-Al and Mg-Zn-RE. It presents the results of high-temperature measurements of magnesium alloys, along with rheological analysis of their behaviour. Magnesium alloys are a very attractive material, due to their light weight and good plastic properties; on the other hand this material is very reactive in a liquid (semi-solid) state, which is challenging from a testing and forming perspective. The findings obtained were compared with five types of rheological models describing rheological characteristics of viscous systems. The analysis was carried out using Rheoplus software. As a result of the conducted work, the mathematical descriptions which are best for characterising rheological behaviour of semi-solid magnesium alloys containing 20% of the solid phase have been proposed.

Study of Semi-Solid Magnesium Alloys (With RE Elements) as a Non-Newtonian Fluid Described by Rheological Models

This paper includes the results of high-temperature rheological experiments on semi-solid magnesium alloys and the verification of different models describing the rheological behaviour of semi-solid magnesium alloys. Such information is key from the point of view of designing alloy forming processes in their semi-solid states. Magnesium alloys are a very attractive material, due to their light weight and good plastic properties; on the other hand, this material is very reactive in a liquid (semi-solid) state, which is challenging from a testing and forming perspective. Formulating/finding models for an accurate description of the rheological behaviour of semi-solid magnesium alloys seems to be key from the standpoint of developing and optimising forming processes for semi-solid magnesium alloys.

Time evolution of agglomerate size of semisolid magnesium alloy AZ91D during a real isothermal shearing

Abstract The present study attempts to discuss the time evolution of the slurry microstructure of semisolid magnesium alloy AZ91D so as to control the forming process more effectively. We calculated the instantaneous shear stress and the time evolution of average agglomerate size of a real isothermal shearing process containing increasing shear rate, holding the maximal shear rate and decreasing shear rate. The calculated results demonstrate that we should adopt as great a maximal shear rate as possible to achieve a finer slurry microstructure and reduce the resulting larger startup shear stress by increasing the time interval required to increase the shear rate to maximum. Moreover, we also should shorten the time interval required to decrease the shear rate to zero as far as possible, so as to weaken agglomeration during decreasing shear rate and achieve a better final slurry microstructure.

Semi-Solid Moulding of AZ91D Magnesium Alloy

AZ91D magnesium alloy is one of the most widely used magnesium alloys in the production of metal forming, which use the characteristics from liquid state to solid state of metal to form. The present status of the research and application of the semi-solid forming for AZ91D magnesium alloys at present was reviewed in this paper, including the microstructural characteristics, the thixotropic and rheological behavior, the forming process of semi-solid for AZ91D magnesium alloys and the mechanical properties of the parts made of semi-solid magnesium alloys. The developing prospects and the key points of the semi-solid forming for AZ91D magnesium alloys were forecasted, and the industrial application of the alloy were also discussed.

Influence of time evolution of particle shape on rheological behavior of semisolid slurries of magnesium alloy AZ91D

To gain the insights into the influence of the morphology of solid particles on rheological behavior of semisolid metal slurries, the time evolution of Hausdorff dimensionality describing the particle morphology is deduced in order to quantitatively analyze the time evolution of the particle morphology. In consideration of the role of the liquid entrapped by non-spherical solid particles, the non-spherical solid particles with the entrapped liquid are treated as spherical solid particles, and the equivalent solid volume fraction is defined as the sum of solid volume fraction and the volume fraction of the entrapped liquid. This model could be used to analyze the rheological behavior of the semisolid metal slurries containing the non-spherical particles with Hausdorff dimensionality less than 3. Moreover, the rheological behavior of semisolid magnesium alloy AZ91D is theoretically analyzed by this model during isothermal shearing and continuous cooling. The calculated results are found coinciding with the experimental results and the calculated results also reveal that the shear rate and cooling rate could influence the rheological behavior of semisolid metal slurries by changing the morphology of solid particles except by affecting agglomeration degree.

Effect of Holding Time on Rheological Characteristics of the Semisolid Magnesium Alloy

The semisolid shear rheological properties of AZ91D alloy were tested. The effect of holding time on the rheological characteristics was investigated. The results show that: during the shear rheological test at 570 °C, a critical shear stress and a maximum shear stress are happened. And with the holding time increasing, solid fraction decreasing and solid particles distributing more uniformly, the rheological rate increases, but the critical shear stress and the maximum shear stress decrease.

Microstructure and Residual Stress Formation during Friction-Stir Welding of Semi-Solid Cast ZK60-RE Magnesium Alloy

In this work, we report on the friction stir weldability of a semi-solid cast ZK60 alloy modified with 1.5 wt% mischmetall in the lap-joint configuration using a 120WV4 steel tool with concave shoulder and conical pin. The coarser solidification microstructure in the semi-solid cast ZK60-1.5%RE alloy requires low strain rates and increased heat input to produce lap-joints without inner defects. This was achieved with 250 rpm tool rotation and 50 mm/min welding speed. Friction stir welding results in a very fine grained microstructure in the stir zone probably due to dynamic recrystallization. In the thermomechanically affected zones dynamic recrystallization seems to occur within the solute enriched intergranular zones. The distribution of longitudinal residual stresses exhibit stress maxima at both thermomechanically affected zones. A compression peak is observed at the retreating side, whereas a tensile stress maximum occurs at the advancing side.

Comparison of Corrosion Resistance of High Pressure Die-Cast and Semi-Solid Cast AZ91, AM60, Alloys and Respective Anodic Oxides

A comparison of corrosion resistance of die-cast and semi-solid cast AZ91and AM60 magnesium alloys was performed in corrosive medium by measurement of the open circuit potential and potentiodynamic scans. Before testing, a heat treatment was carried out on the semi-solid cast alloys. Moreover, electrochemical measurements were performed on the four different substrates anodized in the micro-arc regime in an environment friendly alkaline aqueous solution. The results could be correlated to the different microstructures of the samples produced by the different processes and to the different compactness/porosity of the oxides.

Microstructural evolution and mechanical properties of ZK60 magnesium alloy prepared by multi-axial forging during partial remelting

In order to improve the mechanical properties of ZK60 magnesium alloy components, the multi-axial forging (MAF) plus partial remelting route was used in this study. The effect of remelting temperature and holding time on microstructure of semi-solid ZK60 magnesium alloy was also studied. Furthermore, the tensile mechanical properties of ZK60 magnesium alloy components produced by multi-axial forging plus partial remelting route were compared at different thixoforging temperatures. The results showed that the multi-axial forging followed by partial remelting is an effective route to produce semi-solid ZK60 magnesium alloy for thixoforming. During the partial remelting, with prolonging the holding time and increasing the remelting temperatures, the solid grain size increased. With the increase of remelting temperature, the degree of spheroidization tended to be improved. With increasing the thixoforming temperature from 560 °C to 574 °C, the tensile mechanical properties of ZK60 magnesium alloy were improved.

Numerical Simulation of Thermal-Fluid Coupled Field in Casting Mouth During Rheocasting-Rolling of Semi-Solid Magnesium Alloy

In the initial stage of rheocasting-rolling of semi-solid AZ91D magnesium alloy, the semi-solid slurry was injected into the casting mouth. The whole process was investigated by the VOF model in this paper. The influents of the geometric shapes of casting mouth on temperature field and flow field in casting mouth was analyzed. The numerical simulation results showed that flow field was very chaotic in the casting mouth with rectangular section, air was involved in the slurry, quality of the strip was badly impacted. But flow field was very gentle in the casting mouth with arcuate cross-section. Coupled numerical simulation in steady stage of rheocasting-rolling of semi-solid AZ91D magnesium alloy was done under different inflow temperature, distribution of temperature field,Solid fraction in casting mouth of arcuate cross section was obtained. This provided the basis for optimizing the processing parameters in rheocasting-rolling of semi-solid AZ91D magnesium alloy.

Optimization of Thixomolding Process for Semisolid AM50 Magnesium Alloy by Numerical Simulation

To study the influence of barrel temperature, injection velocity, rotation speed and mold temperature on the quality and properties of products during molding process of thixomolding semisolid slurry, a series of thixomolding processes for semisolid AM50 products were simulated under different processing conditions. The results show that the key parameters of simulated results were influenced by the viscosity that was controlled by barrel temperature and rotation speed during preparation of semisolid slurry before injection. However, the results for different injection velocities demand on the role of shear process of injection nozzle and gate, while the mold temperature had a weak effect on the results. Through the analysis of simulated results, using the optimized parameters, the results of the numerical simulation of the filling process demonstrate that the cavity was filled smoothly and completely. The differences of the results were mainly located at the cold plug catcher of runner system, and the results were almost constants and the distributions are uniform at the shell. Optimal conditions were: barrel temperature 600°C, rotation speed 168 m/s, injection speed 2.09 m/s, mold temperature 230°C. The use of numerical simulation technology could efficiently predict filling defects in semi-solid thixomolding process, optimize the forming process, and provide a reference for mold designs. Microstructure evolution mechanism of AM50 was carefully analyzed.

Rheological behaviour of AZ91D magnesium alloy in semisolid state

The rheological characterisation of semisolid AZ91D magnesium alloy has been successfully studied using a Couette rheometer. Different applied regimes by varying the temperature and the shearing in semisolid state revealed the rheological behaviour of the alloy and were confirmed by microstructural evolution. The apparent viscosity was the critical parameter that was studied during the applied regimes. The change in the morphology of the solid phase during the thermomechanical treatment was the main cause of the evolution of the apparent viscosity. The evolution of the morphology of the solid phase, from dendritic to globular, due to the shearing, had a significant impact on the rheological behaviour of the slurry which was correlated to the operating conditions by an analytical model.L’étude de la caractérisation rhéologique de l’alliage de magnésium de type AZ91D à l’état semi-solide a révélé une étroite dépendance entre les conditions opératoires et les changements structuraux. Les régimes thermo-mécaniques choisis ont montré que la vitesse de refroidissement ainsi que le cisaillement imposé avaient un effet direct sur la viscosité apparente de l’alliage. Le passage d’une structure conventionnelle dendritique à une structure globulaire a réduit de manière significative la viscosité, tributaire de l’intensité ainsi que du temps de cisaillement selon un modèle analytique.

Investigation on Sub-Rapid Solidification Behavior of Semi-Solid Magnesium Alloy Metal

In order to investigate sub-rapid solidification behavior of semi-solid magnesium alloy metal, a novel semi-solid processing technique, called new vacuum suction casting (NVSC), is used to manufacture thin castings of AZ91D Mg-alloy directly from a liquid metal. The resulting microstructures of castings are characterized in detail and linked to the solidification behavior. In the microstructure of the sub-rapidly solidified SSM sheet, the “preexisting” primary solid particles, with the morphology of near-globules or rosettes, disperse in the homogeneous matrix consisting of fine near-equiaxed secondary α-Mg grains and fine precipitates of β-Mg17Al12 intermetallics. Owing to rapid solidification rate, the volume fraction of the β phase in the sub-rapidly solidified SSM sheets is much lower than that in the as-cast ingot. In addition, the content of alloying elements of Al and Zn was higher in the grain boundaries and the eutectic structure than that in the primary solid particles and in the second α-grains.

Orthogonal Experiment in Rheocasting-Rolling for Semi-Solid Magnesium Alloy Used by Slope and Mechanical Stirring

The experiment of the rheocasting-rolling for semi-solid magnesium was carried out on the equipment made by ourselves in our laboratory. Semi-solid AZ91D magnesium slurry was prepared by cooling slope and mchanical sirring The evolution of microstructure under different technological parameters were studied. The results show that the technological parameters have great influence on the microstructure of the semi-solid magnesium slurry. The results show that the optimum parameters of slope method were: pouring temperature 630 degrees�� angle of slope 60°�� length of slope 0.570m. the optimum parameters of slope method were: stirring rate 500r/min ; holding time 10min; stirring time 15min; casting temperature 560 degrees.

Numerical Analysis on Thermal Field in Rheocasting-Rolling of Semi-Solid Magnesium

The process on rheocasting-rolling of semi-solid AZ91D magnesium alloy was investigated by the finite element method from the aspect of fluid mechanics .The mathematical model of the casting-rolling zone was built based on the analysis on the heat transfer mode and boundary conditions of the casting-rolling zone. The numerical simulations were carried out by different casting-rolling parameters to observe the full solidification point and find the best pouring temperature. The numerical simulation results showed that when the semi-solid slurry temperature was 584°C, magnesium strips with good structure and performance could be obtained by rheocasting-rolling. This simulation provided a valid evidence to determine the optimal process parameters.

Study on Rheocasting-Rolling of Semi-Solid AZ31B Magnesium Alloy

Analysis on microstructure of semi-solid AZ31B magnesium alloy produced under different technological parameters were done, hot rolling experiments of AZ31B magnesium alloy semi-solid strips were carried out on the rheocasting-rolling machine which was developed by ourselves. The result shows that the strips after the rheocasting-rolling of AZ31B semi-solid magnesium alloy have good plasticity and rolling properties, this offers theory basis for reprocessing of AZ31B.

Study on Filling Capacity of Semi-Solid Magnesium Alloy

The Semi-Solid Processing technology is an innovation manufacturing process. The filling capacity of the semi-solid metal has very important effects on the properties and qualities of the work pieces. Lots of heat factors have effects on the filling capacity of semi-solid metal. The filling capacity of semi-solid AZ91D magnesium alloy has been studied by means of fluidity test. The results indicate that the filling length increases with the increasing of the temperature and the filling capacity of semi-solid magnesium alloy with shearing is better than that of without shearing. The lower temperature, the more obvious the effect of shearing on the filling capacity is. However, if the temperature is very low, the flow of the slurry is poor and the effect of shearing on filling capacity decreases. The microstructures of semi-solid magnesium alloy after shearing is spherical and homogeneous.