Effects of primary phase morphology on mechanical properties of Al-Si-Mg-Fe alloy in semi-solid slurry casting process

The gas induced semi-solid(GISS) process was developed to create semi-solid slurry with fine and uniform globular structure.The combination of local rapid heat extraction and vigorous agitation by the injection of fine inert gas bubbles through a graphite diffuser in molten metal held at a temperature above its liquidus temperature changes the morphology of primary α(Al) from coarse dendritic to rosette-like and finally to fine globular.The GISS process produced semi-solid slurry at low solid fractions and then formed the slurry by a squeeze casting process to produce casting parts.The effects of primary phase morphology on the mechanical properties of Al-Si-Mg-Fe alloy were investigated.The results show that the ultimate tensile strength and elongation are affected by the shape factor and particle size of the primary α(Al).

Performance of Semi-solid Slurry Produced by Twin-screw Stirring Mixer and Rheo-diecasting Process of AZ91D Alloy

The microstructure of semi-solid slurry of AZ91D alloy, which was produced by twin-screw stirring mixer under the different parameters, was investigated.Rheoforming by cold chamber die casting process was performed thereafter. The results indicate that with decreasing of the barrel temperature of the mixer and the pouring temperature of molten Mg alloy, the solid fraction of semi-solid slurry increases and the size of non-dendritic grains becomes smaller. While the shear rate increases, the solid fraction of semi-solid slurry decreases. The tensile strength and elongation of metal rheoformed by die casting are higher by about 37% and 44% respectively than those produced by conventional liquid die casting.

Investigation of rheo-diecasting mold filling of semi-solid A380 aluminum alloy slurry

The rheo-diecasting mold filling capacity and the microstructure of the semi-solid A380 aluminum alloy slurry were investigated. The results show that the mold filling capacity was strengthened with increasing pouring temperature or increasing injection pressure. Under certain process parameters, the mold cavity was fully filled. However, the mold filling capacity decreased with increasing holding time. The mold filling capacity was improved with increasing shape factor of primary α(Al) grains; however, the solid fraction and the grain size significantly increased at the same time. In addition, the microstructures along the route of the spiral samples obviously differed. The grain size decreased gradually from the near-end to the far-end, whereas the shape factor increased gradually.

Rheo-squeeze casting of semi-solid A356 aluminum alloy slurry

The effect of pouring temperature, electromagnetic stirring power and holding process on semi-solid A356 aluminum alloy slurry was investigated, then the slurry was squeeze-cast. The results show that when the pouring temperatures are properly above the liquidus line, for example 630-650 ℃, the slurry with spherical primary α（Al） grains can be prepared under the stirring power of 1.27 kW. The slurry is then homogeneously held for a short time, and the primary α（Al） grains are further ripened and distributed evenly in the slurry. The results of the rheo-squeezed casting experiments show that the injection specific pressure has a great effect on the filling ability of the semi-solid A356 aluminum alloy slurry, and the higher the injection specific pressure is, the better the ability for the slurry to fill the mould cavity is. When the injection specific pressure is equal to or above 34 MPa, the whole and compact rheo-squeezed castings can be obtained. The microstructure of the castings indicates that the shape, size and numbers of the primary α（Al） grains in different parts of the castings are highly consistent. After being held at 535 ℃ for 5 h and then aged at 155 ℃ for 12 h, the ultimate strength of the rheo-squeezed castings can reach 300-320 MPa, the yield strength 230-255 MPa, and the elongation 11%-15%.

Microstructures and mechanical properties of semi-solid squeeze casting ZL104 connecting rod

Semi-solid squeeze casting（SSSC） and liquid squeeze casting（LSC） processes were used to fabricate a ZL104 connecting rod, and the influences of the process parameters on the microstructures and mechanical properties were investigated. Results showed that the tensile strength and elongation of the SSSC-fabricated rod were improved by 22% and 17%, respectively, compared with those of the LSC-fabricated rod. For SSSC, the average particle size（APS） and the shape factor（SF） increased with the increase of re-melting temperature（Tr）, whereas the tensile strength and elongation increased first and then decreased. The APS increased with increasing the mold temperature（Tm）, whereas the SF increased initially and then decreased, which caused the tensile strength and elongation to increase initially and then decrease. The APS decreased and the SF increased as squeezing pressure（ps） increased, and the mechanical properties were enhanced. Moreover, the optimal Tr, ps and Tm are 848 K, 100 MPa and 523 K, respectively.

Feasibility of semi-solid die casting of ADC12 aluminum alloy

The feasibility of semi-solid die casting of ADC12 aluminum alloy was studied. The effects of plunger speed, gate thickness, and solid fraction of the slurry on the defects were determined. The defects investigated are gas and shrinkage porosity. In the experiments, semi-solid slurry was prepared by the gas-induced semi-solid （GISS） technique. Then, the slurry was transferred to the shot sleeve and injected into the die. The die and shot sleeve temperatures were kept at 180 ℃ and 250 ℃, respectively. The results show that the samples produced by the GISS die casting give little porosity, no blister and uniform microstructure. From all the results, it can be concluded that the GISS process is feasible to apply in the ADC12 aluminum die casting process. In addition, the GISS process can give improved properties such as decreased porosity and increased microstructure uniformity.

Characterization of zirconia-based slurries with different binders for titanium investment casting

The materials and physical properties of primary slurry are crucial to the surface quality of the finished castings,especially for high reactivity titanium alloys.The aim of this study is to investigate the influence of different binders on the physical properties of primary slurry for titanium alloy investment casting.The zirconia-based slurries with different binders were evaluated by comparing the parameters:viscosity,bulk density,plate weight, suspensibility,gel velocity and strength.The results indicate that a higher viscosity of binder leads to a higher viscosity and suspensibility of slurry with the same powder/binder ratio.The retention rate and thickness of primary layer increase with an increase in the viscosity of the slurry,and a higher retention rate is associated with a thicker primary layer.The gel velocity of the slurry is correlated with the gel velocity of the binder.The green strength and the baked strength of the primary layer are determined by the properties of the binder after gel and by the production of the binder after fired,respectively.

Microstructural characteristics of near-liquidus cast AZ91D alloy during semi-solid die casting

Near-liquidus cast ingot was reheated to semi-solid firstly, and then a bracket of motor was prepared by die casting the semi-solid ingot into mould. The microstructural characteristics of AZ91D alloy in these processes were investigated. In the process of near-liquidus casting, primary α-Mg grains tend to be rosette-like because of the increase of plentiful quasi-solid atom clusters in molten alloy with the decrease of pouring temperature. These rosette-like a-Mg grains in ingots fabricated by near-liquidus casting are fused off and refined into near-globular structure owing to the solute diffusion mechanism and the minimum surface energy mechanism during reheating. After semi-solid die-casting, a-Mg grains, located in biscuit, impact and connect with each other; α-Mg grains, located in inner gate, congregate together; while α-Mg grains, located in component, distribute uniformly and become into globularity or strip. Because the inner gate limits the flowing of semi-solid slurry, and the pressure acted on the semi-solid slurry decreases gradually along the filling direction of semi-solid slurry in Cavity, microstructural segregation of unmelted a-Mg grains appears along this direction. Shrinkage holes in casting are caused by two different reasons. For biscuit, the shrinkage holes are caused by the blocked access of feeding liquid to the shrinkage zone for the agglomerated unmelted α-Mg grains. For component, the shrinkage holes are caused by the lack of feeding of liquid alloy.

Effect of heat treatment on microstructure and properties of semi-solid squeeze casting AZ91D

Semi-solid AZ91D magnesium alloy billets were prepared by near-liquidus heat holding.Semi-solid squeeze casting was conducted at 575,585 and 595℃,respectively,with 1 mm·s^-1 squeeze speed.The semisolid squeeze casting AZ91D samples were heat treated by T4(solution at 415℃for 24 h)and T6(solution at 415℃for 24 h+220℃for 8 h)processes,respectively.The microstructure and mechanical properties of the alloy in different states were investigated by means of OM,SEM and tensile testing machine.The results show that compared to as-cast alloy,the grain size of the semi-solid squeezed AZ91D decreased significantly,and with the increase of semi-solid squeeze temperature,the grain size of AZ91D increased.The grains of the alloy were refined by T4 treatment,and further refined by T6 treatment.T6 treatment greatly improved the tensile strength,elongation,and hardness,but did not significantly improve yield strength.After 575℃squeeze casting and T6 treatment,the ultimate tensile strength(UTS)reached 285 MPa,the elongation reached 13.36%,and the hardness also reached the maximum(106.8 HV),but the yield strength(YS)was only 180 MPa.During the process of semi-solid squeeze casting and heat treatment,the matrix grain was refined and a large number of precipitated and secondary precipitated phases of Mg17Al12 appeared.Both the average size of matrix grain and secondary precipitated phase decreased,while the volume fraction of secondary precipitated phase increased.All these resulted in high tensile strength,elongation and hardness.

Study on Semi-solid Rheocasting Forming for Magnesium Alloy by Mechanical Stirring

In this paper the effect of pouring temperature of magnesium melt, preheating temperature of the barrel of screw mixer and shear rate on the solidified microstructures of semi-solid slurry was investigated by mechanical stirring method. The appropriate processing parameters of slurry preparation were obtained. The mold filling for thin walled casting was examined. Results indicated that the solid volume fraction of non-dendritic structure increased with decrease in pouring temperature of magnesium melt and the barrel preheating temperature of screw mixer. Also the grain size of primary α phase was reduced. Furthermore, the solid volume fraction of semi-solid non-dendritic structure decreased with the increase in shear rate. In the same time, grain size of primary α phase slightly changed. The fine-round granular solidified structure with 30～50 μm of prepared AZ91D magnesium semi-solid slurry was presented. Finally, it is successful to fabricate 1.0 mm extremely thin walled casting with clear contour and good soundness.

Semi-solid gravity sand casting using gas induced semi-solid process

The semi-solid metal forming using high pressures has been applied for several years.In contrast,low pressure casting,such as gravity sand casting,has not been widely studied even though it may help reduce porosity defects and offer a better casting yield.A semi-solid gravity sand casting process using the Gas Induced Semi-Solid process was investigated.The results show that the process can produce complete parts with no observable defects.The ultimate tensile strength and elongation data of semi-solid cast samples are higher than those of the liquid cast samples.In addition,the semi-solid sand casting process gives a better casting yield.It can be concluded that the semi-solid sand casting of an aluminum alloy using the GISS process is a feasible process.

To improve robustness of mechanical properties of semi-solid cast A356 alloy using taguchi design method

Mechanical properties of semi-solid casting are dependent on multiple processing parameters,and improper processing parameters will not only reduce mean data but also increase variations.The present study investigated the impact of parameters in slurry preparation and heat treatment on the yield strength and ductility of T6 heat-treated A356 Al-Si alloy using rapid slurry forming(RSF)semi-solid casting.The focus was primarily on the robustness of mechanical properties based on Taguchi design method.By analyzing signal-to-noise ratio and minimum value calculated from-3S,the optimum slurry preparation parameters and heat treatment parameters were determined to be no quench,enthalpy exchange material(EEM)temperature of 140℃,EEM-to-melt ratio of 6mass%,stirring time of 18 s,solution heat treated at 520℃ for 2 h,and ageing heat treated at 190℃ for 6 h.In a small batch validation,the-3S yield strength and-3S elongation reach 256.1 MPa and 5.03% respectively,showing a satisfactory robustness.The hardness and microstructure of heat-treated samples with the best and worst properties were characterized to gain insight into the underlying mechanisms affecting the mean value and variations of mechanical properties.

Microstructural evolution of Mg9AlZnY alloy with vibration in lost foam casting during semi-solid isothermal heat treatment

The nearly equiaxed grains of Mg9AlZnY alloy were obtained by vibrating solidification in lost foam casting(LFC) and the microstructure of Mg9AlZnY alloy was analyzed.On this basis,the morphology and size of α-Mg grains fabricated by semi-solid isothermal heat treatment(SSIT) at 530 ℃ and 570 ℃ holding different time were studied.The results show that the main constituent phases of Mg9AlZnY alloy are α-Mg,β-Mg17Al12 and Al2Y,and the Y can greatly refine α-Mg grains.The distribution of α-Mg grains equivalent diameters between 20 and 100 μm is up to 87%,and the average roundness of α-Mg grains reaches 1.37 in the specimen obtained at 570 ℃ and holding time 60 min.According to the analysis of solidification kinetics and thermodynamic,binary eutectic with low melting point melts firstly on SSIT process.As the liquid fraction increases with the solute diffusibility,both of the shape and size of α-Mg grains change ceaselessly.When the liquid fraction reaches equilibrium,the α-Mg grains are gradually spheroidized under the interfacial tension,and then the α-Mg grains begin to combine and grow.Evolution of α-Mg dendritic grains on SSIT process is obviously different from that of equiaxed grains.

Effects of process parameters on semi-solid squeeze casting performance of aluminum alloy scrolls for scroll compressors

The aluminum alloy scroll is one of the key parts of the scroll compressors widely used in the air-conditioning,refrigeration,and heat pump systems.In this work,the semi-solid squeeze casting(SSSC)process was used to fabricate the aluminum alloy scroll.The effects of process parameters including the pouring temperature,mold temperature,and squeezing velocity on the filling and solidification behaviors of the alloys were investigated through simulations based on the power law cut-off(PLCO)material model.Results show that there is a significant increase in the flow velocity of the slurry,and the area of the high-speed region enlarges with the increase of the pouring temperature.The homogeneity of the temperature and velocity fields in the slurry is improved with an increase in mold temperature.Both the filling time and its variation rate decrease with an increase in squeezing velocity.The maximum solidification time exhibits a linear variation with the increase in pouring temperature.The shrinkage area is decreased by increasing the mold temperature.The optimal process parameters of the SSSC process were obtained from simulation analysis,which are the pouring temperature of 595°C,mold temperature of 350°C,and squeezing velocity of 0.3 m·s-1.Moreover,the qualified scroll casting was fabricated using the SSSC process under the optimal process parameters.

Semi-solid squeeze casting process of a ZL109 alloy

The structure evolution of the ZL109 alloy in the process of semi-solid squeeze casting and the mechanical properties of the components were investigated. The results show that （1） the eutectic silicon phase in original billets is refined in the low super-heat casting process; （2） the eutectic structure in billets starts to fuse and the crystals of the eutectic silicon phase are refined further and sphericized in the remelting process of billets; （3） in the semi-solid squeeze casting process, the sphericity of the a phase and the refining of the silicon phase occur, owing to the friction between solid and liquid; （4） in the process of heat treatment, the eutectic a phase aggregates with the primary a phase and the eutectic silicon pieces aggregate together. The elongation of the semi-solid component after heat treatment rises to 1.42%.

Mechanical properties and microstructural evolution of rheocast A356 semi-solid slurry prepared by annular electromagnetic stirring

Nowadays,having an effective technique in preparing semi-solid slurries for rheocasting process seems to be an essential requirement.In this study,semi-solid slurry of A356 aluminum alloy was prepared by three-phase annular electromagnetic stirring(A-EMS)technique under different conditions.The effects of stirring current,pouring temperature and stirring time on microstructural evolution,mean particle size,shape factor and solid fraction were investigated.The rheocasting process was carried out by using a drop weight setup and to inject the prepared semi-solid slurry in optimal conditions into the step-die cavity.The filling behavior and mechanical properties of parts were studied.Microstructural evolution showed that the best semi-solid slurry which had fine spherical particles with the average size of~27μm and a shape factor of~0.8 was achieved at the stirring current of 70 A,melt pouring temperature of 670℃,and stirring time of 30 s.Under these conditions,the step-die cavity was completely filled at die preheating temperature of 470℃.The hardness increases by decreasing step thickness as well as die preheating temperature.Moreover,the tensile properties are improved at lower die preheating temperatures.The fracture surface,which consists of a complex topography,indicates a typical ductile fracture.

Microstructure characteristics and thermodynamic properties of A357-SiCp/A357 layered composites prepared by semi-solid vacuum stirring suction casting

A357-SiCp/A357 layered composites were prepared using a semi-solid vacuum stirring suction casting method.The microstructures,mechanical properties,and thermal conductivities of the composites fabricated under different suction casting processes were compared.Additionally,the microstructural evolution characteristics and performance enhancement mechanism of the A357-SiCp/A357 layered composites were discussed.The results demonstrate that suction casting at 610°C with a low solid phase ratio can significantly enhance the material density and reduce the agglomeration of SiCp.The A357-SiC_(p)/A357 interface is clear and straight with good bonding.With an increase in the suction casting temperature,the bending resistance and thermal conductivity of the A357-SiC_(p)/A357 layered composites exhibit a trend of significantly increase at first and then slowly decrease owing to casting defects,interface bonding,and SiCp distribution.Compared with SiCp/A357 composites,the bending strength,deflection,and thermal conductivity of the A357-SiCp/A357 layered composites increase from 257 MPa,1.07 mm,and 155.72 W·(m·K)^(-1) to 298 MPa,2.1 mm,and 169.86 W·(m·K)^(-1),respectively.This study provides a reference for improving the rheological casting of aluminum matrix layered composites.

Preparation of QTi4.3-4Graghite Composite by Semi-solid Casting Technology

The electromagnetic-mechanical stirring technology was employed for preparing QTi4.3-4 graghite composite slurry,and QTi4.3-4 graghite composite with uniform distribution of graphite particles was prepared uring the semi-solid casting technology successfully.The structure of this QTi4.3-4graphite composite was studied and the condition for uniform distribution of graphite particles was got.The experimental results show that there exists a linear relationship between the solid fraction and the stirring temperature of QTi4.3-4graphite slurry.With the decreasing of stirring temperature,the solid fraction of QTi4.3-4 graghite slurry increases constantly.In casting,with the increasing of solid fraction of QTi4.3-4 graphite slurry.the agglomeration of graphite particles is removed gradually.When the solid fraction is higher than 40%,graphite particles can distribute evenly in QTi4.3-4 graghite composite.

Two semi-solid die-casting production lines of Xuzhou Die- casting Technology Co., Ltd. officially put into operation

The two production lines for the first phase of the semi-solid die-casting high-end parts project were put into production in this October, and can monthly produce more than 30 thousand die casting parts.