Compression properties of cost-efficient porous expanded clay reinforced AA7075 syntactic foams fabricated by industrial-oriented die casting technology

In today’s manufacturing industries,hard competition between rival firms makes it compulsory for researchers to design lighter and cheaper machine components due to the megatrends of cost-effectiveness and anti-pollution.At this point,aluminum syntactic foams(ASFs)are new-generation engineering composites and come into the upfront as a problem-solver.Owing to their features like low density,sufficient elongation,and perfect energy absorption ability,these advanced foams have been considerably seductive for many industrial sectors nowadays.In this study,an industrial-oriented automatic die casting technology was used for the first time to manufacture the combination of AA7075/porous expanded clay(PEC).Micro evaluations(optical and FESEM)reveal that there is a homogenous particle distribution in the foam samples,and inspections are compatible with the other ASF studies.Additionally,T6 aging heat treatment was operated on one half of the produced foams to explore the probable impact of aging on the compressive responses.Attained results show that PEC particles can be an alternative to expensive hollow spheres used in the previous works.Besides,a favorable relationship is ascertained between the aging treatment and mechanical properties such as compression strength and plateau strength.

Effects of magnesium and copper additions on tensile properties of Al-Si-Cr die casting alloy under as-cast and T5 conditions

Aluminum high pressure die casting(HPDC)technology has evolved in the past decades,enabling stronger and larger one-piece casting with significant part consolidation.It also offers a higher design freedom for more mass-efficient thin-walled body structures.For body structures that require excellent ductility and fracture toughness to be joined with steel sheet via self-piercing riveting(for instance,shock towers and hinge pillars,etc.),a costly T7 heat treatment comprising a solution heat treatment at elevated temperatures(450℃-500℃)followed by an over-ageing heat treatment is needed to optimize microstructure for meeting product requirement.To enable cost-efficient mass production of HPDC body structures,it is important to eliminate the expensive T7 heat treatment without sacrificing mechanical properties.Optimizing die cast alloy chemistry is a potential solution to improve fracture toughness and ductility of the HPDC components.The present study intends to tailor the Mg and Cu additions for a new Al-Si-Cr type die casting alloy(registered as A379 with The Aluminum Association,USA)to achieve the desired tensile properties without using T7 heat treatment.It was found that Cu addition should be avoided,as it is not effective in enhancing strength while degrades tensile ductility.Mg addition is very effective in improving strength and has minor impact on tensile ductility.The investigated Al-Si-Cr alloy with a nominal composition of Al-8.5wt.%Si-0.3wt.%Cr-0.2wt.%Fe shows comparable tensile properties with the T7 treated AlSi10MnMg alloy which is currently used for manufacturing shock towers and hinge pillars.

Low cycle fatigue behavior of T4-treated Al-Zn-Mg-Cu alloys prepared by squeeze casting and gravity die casting

Gravity die casting(GC) and squeeze casting(SC) T4-treated Al-7.0Zn-2.5Mg-2.1Cu alloys were employed to investigate the microstructures,mechanical properties and low cycle fatigue(LCF) behavior.The results show that mechanical properties of SC specimens are significantly better than those of GC specimens due to less cast defects and smaller secondary dendrite arm spacing(SDAS).Excellent fatigue properties are obtained for the SC alloy compared with the GC alloy.GC and SC alloys both exhibit cyclic stabilization at low total strain amplitudes(less than 0.4%) and cyclic hardening at higher total strain amplitudes.The degree of cyclic hardening of SC samples is greater than that of GC samples.Fatigue cracks of GC samples dominantly initiate from shrinkage porosities and are easy to propagate along them,while the crack initiation sites for SC samples are slip bands,eutectic phases and inclusions at or near the free surface.

Vacuum assisted high-pressure die casting of AZ91D magnesium alloy at different slow shot speeds

The effects of vacuum assistance on the microstructure and mechanical properties of high-pressure die cast AZ91 D alloy at different slow shot speeds were evaluated. Plate-shaped castings of AZ91 D alloy were carried out on a TOYO BD-350V5 cold chamber die casting machine incorporated with a self-improved TOYO vacuum system. It was found that the vacuum pressure in the die cavity at the beginning of mold filling increases with the increase of slow shot speed, following a cubic polynomial curve, resulting in a decline in the porosity-reduction ability of vacuum assistance with the increase of slow shot speed. The externally solidified crystal（ESC） contents in conventional and vacuum die castings behave similar against the slow shot speed. The tensile properties of vacuum die castings were strongly influenced by the ESC content at relative low slow shot speeds. With the increase of slow shot speed, the influence of the gas porosity level in vacuum die castings would get prominent.

Focusing on Technology and Services, Competing in China Die Casting Market

The Asia-Pacific Die Casting Industry Exhibition 2005, organized by Foundry Institution of Chinese Mechanical Engineering Society （FICMES）, was held in INTEX Shanghai, China on August 14-17, 2005. On August 16th, the journalists of CHINA FOUNDRY journal visited five exhibitors on the spot of exhibition. They are： Mr. Roland FINK, General manager of Frech （Shanghai） Die Casting Machine Co. Ltd.; Mr. Thomas STROBL, General manager of Buhler Equipment Engineering （Wuxi） Co. Ltd., Switzerland; Mr. WANG Tong, Manager of ABB Engineering （Shanghai） Co. Ltd.; Ms. Karen LUO, National Sales Manager-Die Casting, Chem-Trend （Shanghai） Trading Co. Ltd.; and Mr. David ZHOU, Sales Supervisor of Acheson, the National Starch ＆ Chemical （Shanghai） Company.

Characterization of A390 aluminum alloy produced at different slow shot speeds using vacuum assisted high pressure die casting

The effects of vacuum assistance on the microstructure and mechanical properties of high pressure die cast A390alloy at different slow shot speeds were evaluated.Plate-shaped specimens of hypereutectic A390aluminum alloy were produced on a TOYO BD?350V5cold chamber die casting machine incorporated with a self-improved TOYO vacuum system.According to the results,the vacuum pressure inside the die cavity increased linearly with the increasing slow shot speed at the beginning of mold filling.Meanwhile,tensile properties of vacuum die castings were deteriorated by the porosity content.In addition,the average primary silicon size decreased from23to14μm when the slow shot speed increased from0.05to0.2m/s,which has a binary functional relationship with the slow shot speed.After heat treatment,microstructural morphologies revealed that needle-shaped and thin-flaked eutectic silicon particles became rounded while Al2Cu dissolved intoα(Al)matrix.Furthermore,the fractography revealed that the fracture mechanism has evolved from brittle transgranular fracture to a fracture mode with many dimples after heat treatment.

Study on Numerical Simulation of Mold Filling and Heat Transfer in Die Casting Process

A 3-D mathematical model considering turbulence phenomena has been established based on a computational fluid dynamics technique, so called 3-D SOLA-VOF (Solution Algorithm-Volume of Fluid), to simulate the fluid flow of mold filling process of die casting. In addition, the mathematical model for simulating the heat transfer in die casting process has also been established. The computation program has been developed by the authors with the finite difference method (FDM) recently. As verification, the mold filling process of a S-shaped die casting has been simulated and the simulation results coincide with that of the benchmark test. Finally, as a practical application, the gating design of a motorcycle component was modified by the mold filling simulation and the dies design of another motorcycle component was optimized by the heat transfer simulation. All the optimized designs were verified by the production practice.

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.

Simulation of mold filling and prediction of gas entrapment on practical high pressure die castings

Element parameters including volume filled ratio,surface dimensionless distance,and surface filled ratio for DFDM(direct finite difference method)were proposed to describe shape and location of free surfaces in casting mold filling processes.A mathematical model of the filling process was proposed specially considering the mass,momentum and heat transfer in the vicinity of free surfaces.Furthermore,a method for gas entrapment was established by tracking flow of entrapped gas.The model and method were applied to practical ADC1 high pressure die castings.The gas entrapment prediction was compared with the fraction and maximum size of porosities in the different casting parts.The comparison shows validity of the proposed model and method.The study indicates that final porosities in high pressure die castings are dependent on both gas entrapment during mold filling process and pressure transfer within solidification period.

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.

Temperature change and stress distribution analysis of die surface in Al-alloy die casting process and experimental study on die heat check

The temperature change of the die surface in practical aluminum alloy die casting process was analyzed,and a 2D model was formulated on the basis of a deep concave round cavity without sliding core to analyze thestress distributions along the die surface in detail. Equipment was designed to test the thermal state of the die steelin different thermal loading conditions. The results of stress analysis showed that, the value of thermal stress (maximum1.5 GPa) caused in the die filling and die spraying stages was larger than the mechanical stress (maximum 85 MPa)caused in the die locking stage. The results of the thermal check experiment showed that there were three stages ofdie dissolving, and that the stress distribution shown by the samples' cracking routine was close to the die surfacestress analysis.

Characterization on the formation of porosity and tensile properties prediction in die casting Mg alloys

The 3D visualization of the porosity in high-pressure die casting(HPDC)Mg alloys AZ91D and Mg4Ce2Al0.5Mn(EA42)was investigated by X-ray computed tomography.It was demonstrated that the volumetric porosity at the near-gate location for alloy EA42 was significantly higher than that far from the gate location.This difference resulted from the low valid time during intensified casting pressure conditions.Specimens of alloy EA42 exhibited a narrow pore distribution in the side view(~0.5 mm)compared to the wide distribution(~1.8 mm)of alloy AZ91D,which was mainly attributed to the formation mechanism of the defect band.The formation of microporosity in the defect band of alloy EA42 was inhibited because of the significant latent heat released by a large amount of the Al11Ce3phase segregated in the defect band during solidification.Additionally,an effective estimator(Z-Propagation)was introduced,which is proposed to predict the projected area fraction of the porosity(f)involved during tensile failure with better effectiveness compared with traditional methods based on the actual fractured surface.By coupling the Z-Propagation method with the critical local strain model,the logarithmic fracture strain and true fracture stress of the specimens were predicted within 3.03%and 1.65%of the absolute value of the average relative error(AARE),respectively.

Effects of combined addition of Y and Ca on microstructure and mechanical properties of die casting AZ91 alloy

A series of die casting heat-resistant magnesium alloys based on Mg-Al system were developed for automotive application by adding Y and various amounts of Ca. The mechanical properties and microstructures of die casting AZ91 alloy with combined addition of Y and Ca were investigated by optical microscopy, scanning electronic microscopy, X-ray diffractometry and mechanical property test. The results show that the combined addition of Y and Ca can refine the as-die-cast microstructure, result in the formation of Al2Ca phase and Al2Y phase, and inhibit the precipitation of Mg17Al12 phase. The combined addition of Y and small amount of Ca has little influence on the ambient temperature tensile properties, but increasing the content of Ca can improve significantly the tensile strength at both ambient and elevated temperatures. It is found that for AZ91-1Y-xCa alloy, the hardness and the elevated temperature tensile strength increase, while the elongation decreases with increasing the addition of Ca. The mechanism of mechanical properties improvement caused by the combined addition of Y and Ca was also discussed.

Determination of interfacial heat transfer coefficient and its application in high pressure die casting process

In this paper,the research progress of the interfacial heat transfer in high pressure die casting(HPDC)is reviewed.Results including determination of the interfacial heat transfer coefficient(IHTC),influence of casting thickness,process parameters and casting alloys on the IHTC are summarized and discussed.A thermal boundary condition model was developed based on the two correlations:(a)IHTC and casting solid fraction and(b)IHTC peak value and initial die surface temperature.The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.

Design and Verification of an Auxiliary System for High Vacuum Die Casting

Vacuum die casting is the optimal method to produce high quality aluminum alloy components.At present,there are still very few systematic studies on vacuum die casting theory and equipment design.On the basis of the existing theories of the vacuum die casting pumping and venting systems,a simplified model is established in this research.The model has an aggregate unit consisted of ＂vacuum pump ＋ buffer tank＂ and a cylindrical container（including the shot sleeve,cavity and exhaust channel）.The theoretical analysis is carried out between the cavity pressure and the pumping time under different volume models.An auxiliary system for high vacuum die casting is designed based on the above analysis.This system is composed of a vacuum control machine and a new vacuum stop valve.The machine has a human-computer control mode with ＂programmable logic controller（PLC） ＋ touch screen＂ and a real-time monitoring function of vacuum degree for buffer tank and die cavity.The vacuum stop valve with the ＂compressed gas ＋ piston rod ＋ labyrinth groove＂ structure can realize the function of whole-process vacuum venting.The new system shows great advantages on vacuuming the cavity with a much faster speed by making tests on an existing die casting mold and a 250 t die casting machine.A die cavity pressure less than 10 kPa can be reached within 0.8 s in the experiment and the porosity of castings can be greatly decreased.The systematic studies on vacuum die casting theory and equipment have a great guiding significance for high vacuum die casting,and can also be applied to other high vacuum forming in related theoretical and practical research.

Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1mm. Therefore, in this study, thin-walled die casting of aluminum （Al-Si-Cu alloy： ALDC 12） in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation （MAGMA soft） and actual casting experiment （Buhler Evolution B 53D）. Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.

High thermal conductivity and high strength magnesium alloy for high pressure die casting ultrathin-walled components

With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry alloys(such as Mg-9wt%-1wt%Zn)are still relatively low.In this study,we developed a high-thermal-conductivity Mg-4Al-4Zn-4RE-1Ca(wt%,AZEX4441)alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting(HPDC).The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure(average grain size of 2.8μm)with granular Al_(11)RE_(3),fibrous Al_(2)REZn_(2),and networked Ca_(6)Mg_(2)Zn_(3) phases distributed at the grain boundaries.The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m^(-1)·K^(-1),which was much higher than 53.7 W·m^(-1)·K^(-1) of the HPDC AZ91D alloy.Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al_(11)RE_(3),Al_(2)REZn_(2),and Ca_(2)Mg_(6)Zn_(3) phases because of the addition of RE and Ca.Therefore,the lattice distortion induced by solute atoms of the AZEX4441 alloy(0.171%)was much lower than that of the AZ91D alloy(0.441%),which was responsible for the high thermal conductivity of the AZEX4441 alloy.The AZEX4441 alloy exhibited a high yield strength of~185 MPa,an ultimate tensile strength of~233 MPa,and an elongation of~4.2%.This result indicated that the tensile properties were comparable with those of the AZ91D alloy.Therefore,this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity,high strength,and good castability.

Characteristics and formation mechanisms of defect bands in vacuum-assisted high-pressure die casting AE44 alloy

The microstructure in vacuum-assisted high-pressure die casting(HPDC) Mg-4Al-4RE(AE44) alloy was studied. Special attention was paid to the characteristics of defect bands and their formation mechanisms. Since double defect bands are commonly observed, the cross section of die cast samples is divided into five parts with different grain morphologies and size distributions. The inner defect band is much wider than the outer one. Both the defect bands are solute segregation bands, resulting in a higher area fraction of Al;RE;phase than that in the adjacent regions. No obvious aggregation of porosities is observed in the defect bands of AE44 alloy. This may be due to a narrow solidification temperature range of AE44 alloy and a large amount of latent heat released during the precipitation of intermetallic phases. The formation of the defect bands is related to the shear stress acting upon the partially solidified alloy, which can lead to collapse of the grain network. However, the generation mechanisms of shear stress in the outer and inner defect bands are quite different.