High Pressure Die Casting Process Research Articles

Correlation of 3D defect-band morphologies and mechanical properties in high pressure die casting magnesium alloy

For understanding the processing-microstructure-properties correlation of high pressure die casting (HPDC) AZ91D alloy, 3D reconstruction was carried out to characterize the microstructural morphologies of castings produced by four designed HPDC processes. The influence of different parameters (vacuum, slow-shot speed, fast-shot speed) on porosity volume and morphology, defect band width and average externally solidified crystals (ESCs) size of castings were systematically studied. Microstructural characterization revealed that the defect band width was strongly related with the size and quantity of ESCs, rather than the porosity volume. Meanwhile, ESCs were mainly influenced by the slow-shot speed in shot sleeve (ESCs growth time) and fast-shot speed into the die cavity (shear stress of melt flow). Tensile fracture revealed that cracks easily propagated within the defect bands due to the accumulated ESCs and connected irregular pores, while the cracks were restrained in center zone. The mechanical properties of HPDC castings was inversely proportional to the defect band width, and is not dependent on the average volume fraction porosity.

Neutron Diffraction Analysis of Residual Strain in High-Pressure Die Cast A383 Engine Blocks

The residual strains in three high-pressure die cast A383 engine blocks were measured using neutron diffraction. Residual strains and stresses can be generated during high-pressure die casting process due to high thermal gradients and may cause fatigue failure or dimensional distortion. Neutron diffraction can measure the residual strain distributions deep inside castings with complex geometries, because neutrons can penetrate substantially more material than x-rays. In the present work, the residual strains (in the axial and hoop directions) along the whole cylinder bridge of high-pressure die cast A383 engine blocks in as-cast and heat-treated conditions were measured by neutron diffraction methods. The effect of heat treatment on the distribution and magnitude of residual strains was also investigated. The results indicate that the residual strain in the cylinder bridge is tensile in both the axial and hoop components for both the as-cast and the heat-treated engine blocks. The residual strain in the hoop direction is bigger in magnitude than the residual strain in the axial direction. Heat treatment significantly relaxes the residual strain in the axial direction but only slightly relaxes the residual strain in the hoop direction.

Microstructures refinement and mechanical properties enhancement of aluminum and magnesium alloys by combining distributary-confluence channel process for semisolid slurry preparation with high pressure die-casting

Abstract A simple and efficient semisolid slurry preparation technique, called distributary-confluence channel (DCC), was developed to prepare high-quality semisolid slurries of aluminum and magnesium alloys. The DCC process was coupled with the use of a high pressure die-casting (HPDC) machine to successfully achieve near-net forming and implement production applications with rheological high pressure die-casting (Rheo-HPDC) for various Al and Mg alloy castings. The changes in the flow state and in the physical field of the melt during the slurry preparation via the DCC technique were investigated by numerical simulations. The nucleation mechanism and the growth law of the primary grain during the DCC process were discussed. The microstructures, porosities, and mechanical properties of the aluminum and magnesium alloys prepared via DCC Rheo-HPDC were studied. The results show that semisolid slurries containing a large amount of primary grains with an average size 0.8, and uniformly dispersed in the liquid matrix can be prepared via DCC. The simulation results indicate that the melt exhibits opposite velocity vectors on the upper part and on the lower part of the DCC. Moreover, it encounters and collides at the confluence to generate convection, which is beneficial to obtain uniform melt temperature, composition fields, nuclei exfoliation, and spherical growth. The random particle tracking simulation results show that the DCC process improves the composition field of the slurry. The DCC process facilitates the melt nucleation by using multi-channel chilling and increasing the nucleation area. The self-stirring generated during the flow of the melt produces a large amount of free nuclei inside the melt. There exist two main mechanisms behind the formation of the spherical primary grains. The one is the mechanism of explosive nucleation and spheroidal growth, the other is the dendrite arm necking, fusing, grain ripening, and rounding. Furthermore, by comparing identical alloy castings produced via traditional HPDC and other Rheo-HPDC processes, the DCC Rheo-HPDC castings present finer and rounder grains, a lower porosity, and more performant mechanical properties.

Comparative study on performance and microstructure of composite water-soluble salt core material for manufacturing hollow zinc alloy castings

The water-soluble salt core material has been successfully used for manufacturing hollow aluminum and magnesium alloy castings. However, there is rare report about the water-soluble salt core being used for lower melting point and higher density hollow zinc alloy castings. In order to obtain a high-performance composite water-soluble salt core material (CWSSC) which is suitable for manufacturing hollow-structure zinc alloy castings via high pressure die casting process, the comparative study on performance and microstructure of the salt cores fabricated by gravity casting technology was investigated using KNO3 and KCl as the base salt material with the reinforcements of bauxite or glass-fiber powder. The results show that CWSSC strengthened by reinforcements possesses many advantages of good surface quality and water-solubility rate, high bending strength and impact toughness, low shrinkage and moisture-absorption rate, and CWSSC composed of KNO3-20 mol% KCl with 15 wt% bauxite powder and 15 wt% glass-fiber powder has the better comprehensive performance, whose surface roughness is 0.4758 μm, bending strength is 46.6 MPa, impact toughness is 21.72 kJ/m2, and water-solubility rate is 178.21 kg/(min·m2) in still water at 80 °C with relatively low shrinkage and 24 h moisture-absorption rate. The scanning electron microscope analysis shows that the strengthening-toughening mechanisms of CWSSC mainly include refinement of the grain and deflection of the crack caused by KCl dendritic crystal and the rigid enhanced powders. A practical casting test has been conducted to prove that the developed CWSSC can be used to manufacture hollow-structure zinc alloy castings.

Influence of B and Nb Additions and Heat Treatments on the Mechanical Properties of Cu-Ni-Co-Cr-Si Alloy for High Pressure Die Casting Applications

During the high pressure die casting process (HPDC), it is necessary to develop new designs and alloys for the copper plungers. In this research, two alloys Cu-9Ni-1Co-1.6Cr-2Si-1.3Fe-0.25B wt.% (A1) and Cu-9Ni-1Co-1.6Cr-2Si-0.1Fe-0.2Nb wt.% (A2) under different heat treatments (HT) were studied. Optical microscopy technique was applied to reveal the regions of dendritic morphology, also lower Secondary Dendrite Arm Spacing (SDAS); and different grain orientations. The results reveal that the solidification sequence is primary Cu dendrites and secondary intermetallics; heat treatments increase the redistribution of alloying elements in the interdendritic regions. During the heat treatments, some precipitates were found in the grain boundary after aging heat treatments for both alloys, which were determined by X-ray diffraction. Hardness test HRB presented a decrease with the solution heat treatment and an increase with the aging heat treatments proposed for both alloys. Finally, the wear resistances for both alloys were compared with a commercial alloy C17530, with decreased A1 with B additions having the best result in the as-cast condition 4.07 × 10−4 mm3/Nm, while for A2 with Nb additions wear resistance increased, with the best result in the one with aging heat treatment 1.69 × 10−4 mm3/Nm while for the C17530 alloy this was 2.74 × 10−4 mm3/Nm.

Effects of Ni and Cu Addition on Tensile Properties and Thermal Conductivity of High Pressure Die-cast Al-6Si Alloys

In this study, the effects of nickel and copper on the mechanical and thermal properties of Al-Si alloys were investigated, for different alloy compositions. Thermodynamic calculations were carried out to predict the alloys’ solidification behavior (solidification temperature, solid fraction and physical properties (density, thermal conductivity, elastic modulus, bulk modulus)). The aluminum alloys were produced by high pressure die-casting process with a 125 ton die-casting machine. Microstructures in the Al-Si-Ni alloys were characterized by optical microscopy and scanning electron microscopy. The mechanical properties were evaluated by tensile tests. Thermal conductivity was measured using a laser flash method. The addition of Ni and Cu improved the mechanical properties of the alloys by different strengthening mechanisms. Solution strengthening was the more effective method of improving mechanical properties, compared with strengthening by intermetallic compounds. The addition of an appropriate concentration of soluble alloying elements consistently improved alloy strength. However, addition of alloying elements decreased the thermal conductivity of the primary alpha aluminum phase. EDS analysis confirmed that soluble alloying elements like Cu not only can form intermetallic compounds, but can also change other kinds of compounds. Accordingly, careful consideration should be given to the chemical composition of soluble/insoluble alloying elements when attempting to improve mechanical properties and thermal conductivity at the same time.

Effect of Process Parameters on Distortion and Residual Stress in High-Pressure Die Cast AZ91D Components After Clean Blasting and Painting

A high-pressure die-casting process was employed to produce AZ91D components. These cast components were exposed to three different post-treatments: (1) clean blasting, (2) clean blasting and painting, and (3) painting (without clean blasting). The influence of the process parameters first phase injection speed, temperature of fixed half of the die, cooling time, and intensification pressure on distortion and residual stress of the components after each post-treatment were investigated. The results showed that intensification pressure was the most significant factor among the four parameters.

A novel rheological high pressure die-casting process for preparing large thin-walled Al–Si–Fe–Mg–Sr alloy with high heat conductivity, high plasticity and medium strength

An air-cooled stirring rod (ACSR) process for efficiently preparing large volumes of semisolid slurry was introduced. A new low-cost casting Al–Si–Fe–Mg–Sr alloy was used to prepare large thin-walled heat-dissipating shells using both conventional HPDC and ACSR rheological high pressure die-casting (Rheo-HPDC) technologies. Their microstructures, thermal conductivities, elevated temperature and room temperature mechanical properties, and corrosion behaviors were compared. Furthermore, this work analyzed the mechanisms responsible for the microstructure refinement and performance enhancement in ACSR Rheo-HPDC alloys. The results showed that only 25 s was needed to prepare 32 kg of the semisolid slurry using ACSR process. The alloy prepared by ACSR Rheo-HPDC generated a large number of fine spherical primary α-Al particles with a volume fraction greater than 40%. The Rheo-HPDC alloy showed a moderate strength, high plasticity, and high heat conductivity. The heat conductivity, ultimate tensile strength and elongation of the Rheo-HPDC alloy were 184 W/(m.K), 264 MPa and 12.2% respectively, while those of the HPDC alloy were 167 W/(m.K), 228 MPa and 5.8% respectively. The improvement of heat conductivity of the alloy formed via ACSR Rheo-HPDC was mainly ascribed to the decrease of electron scattering by the refinement of eutectic silicons and Fe-rich intermetallics. This allowed the electron flow to pass through the eutectic Si region more easily. The refined and uniformly-distributed heat-resistant β-Al5FeSi intermetallics effectively prevented grain boundary sliding, so the Rheo-HPDC alloy showed superior high-temperature mechanical properties. The Rheo-HPDC alloy presented a more excellent corrosion resistance to the conventional HPDC alloy due to the refinement of iron-rich phase and eutectic silicons and the reduction in the potential difference between the matrix and the iron-rich phase.

Improvement in mechanical, thermal conductivity and corrosion performances of a new high-thermally conductive Al-Si-Fe alloy through a novel R-HPDC process

Abstract A low-cost, new casting Sr-modified Al-7.5Si-0.8Fe alloy with high-thermal conductivity was prepared into large thin-wall heat-dissipating shells for 5G communication base stations using a traditional high pressure die-casting (HPDC) process and a rheological HPDC (R-HPDC) technique. Their microstructure, tensile property, hardness, thermal conductivity, and corrosion behavior were analyzed. The R-HPDC Al-7.5Si-0.8Fe alloy shows a refined microstructure in terms of α1-Al particles, α2-Al grains, fibrous β-Al5FeSi, and granular eutectic silicons when compared to traditional HPDC alloys. The R-HPDC alloy has a thermal conductivity, elongation-to-failure value, ultimate tensile strength, yield strength, and Vickers hardness of 186 W/(m.K), 12.4 %, 235 MPa, 114 MPa, and 70 HV, respectively. These values are respectively 6 %, 91 %, 22 %, 14 %, and 11 % higher than those reported for conventional HPDC alloys. Moreover, the R-HPDC Al-Si-Fe alloy shows a superior corrosion resistance in comparison to HPDC alloys. This observation is supported by scanning Kelvin probe (SKP) measurements and electrochemical tests. The improved performances arise mostly from the refinement of the iron-rich intermetallics (β-Al5FeSi) and eutectic silicons, the increase in the area proportion of α2-Al grains relative to eutectic silicon, and the reduction in the potential difference between the aluminum matrices and the iron-rich intermetallics.

Six Sigma (DMAIC) Approach to Optimise Operation Variables in High Pressure Die Casting

Components manufactured by High Pressure Die Casting (HPDC) typically have excellent mechanical and metallurgical properties, and the process generally preferred for the manufacture of high-value-added products. This research paper focuses on the implementation of the Six Sigma philosophy to optimize the variables of the HPDC manufacturing process. As a systematic outline for quality improvement and achievement business excellence, the Six Sigma philosophy has become the model of the industrial world in recent years. The proposed work tries to simplify the phases of Six Sigma and categorizes the given tools/techniques for their utility. The work further validates its effectiveness by conducting a successful case study in an HPDC process. The five phases DMAIC (Define, Measurement, Analyse, Improve, and Control) use the following qualitative and quantitative tools. Examination of various critical process parameters and the interactions among them carried out with the help of Taguchi’s method of experimental design.

A digital twin approach to predict and compensate distortion in a High Pressure Die Casting (HPDC) process chain

The HPDC industry is changing, and E-mobility is one reason for this – power train components traditionally produced by HPDC are eliminated as the industry abolishes internal combustion engines (ICE). The casting industry reacts to this challenge by extending its product range towards structural automotive components - essentially large area/low thickness geometries prone to distortion as result of inhomogeneous cooling and similar effects. As corrective actions like mechanical alignment are costly, alternatives are required which can either eliminate or compensate effects promoting distortion. The alternative proposed here is based on analysis of the full HPDC process chain and identification of the main process steps that control distortion, allowing a correct prediction of distortion throughout the processing sequence via a “digital twin” approach. Components considered are assumed to undergo a solution heat treatment after casting, followed by quenching and precipitation hardening. As the subsequent quenching bears a potential for introducing distortion similar to solidification and cooling after casting, this step is selected to deliberately introduce inhomogeneous cooling designed to counteract the residual stresses and distortion brought in during the preceding process steps. Knowledge of the exact state of the casting immediately before quenching as provided by the “digital twin” approach for each individual part provides the basis for deriving a suitable distribution of heat extraction rates over the part surface. The present study presents and discusses the basic strategies on the level of part series and individual parts as well as aspects of their practical implementation via adaptive spray cooling systems. The task is complicated by the high thermal conductivity of the aluminum alloys studied and the need to arrive, after quenching, at microstructures supporting the required levels of strength after the final warm aging step, i.e. supersaturated solid solutions of the alloy-specific precipitate-forming chemical elements. The viability of the general concept is demonstrated based on initial numerical modeling and simulation of a component cooled under varied thermal conditions, highlighting the distortion and distortion compensation potential.

Effect of the Processing Parameters on the Shrinkage Defect Using A High-Pressure Die-Casting Process

Effects of the processing parameters of a high-pressure die-casting (HPDC) process on the shrinkage defect of housing block compressor (HBC) were examined in this research. Because of the reduction of defect can increase the productivity of HBC that representing a good quality product, the processing parameters determining the quality of product must be optimized. In this study, the processing parameter of high speed in the range of 3.97 to 4.97 m/s and that of fast start point in the range of 293 to 333 mm were calculated and then the HBC samples of using the Al alloy of ADC12 were produced through the HPDC process. The shrinkage defects on HBC were characterized by visual inspection, radiography testing and microstructure examination. The result showed that the best parameters for reducing shrinkage defect of HBC by the HPDC process are 4.97 m/s of high speed and 313 mm of fast start point. The optimum parameters of high speed and fast start point were verified to contribute to producing a high quality of the HBC for the applications in automotive engine.

Electrochemical Behavior of Conventional and Rheo-High-Pressure Die Cast Low Silicon Aluminum Alloys in NaCl Solutions

The electrochemical behavior of a low silicon aluminum alloy cast by the conventional and rheo-high-pressure die cast processes is evaluated using polarization test and electrochemical impedance spectroscopy in 0.01 M, 0.05 M, 0.1 M, and 0.6 M sodium chloride solutions. Compared to the conventional high-pressure die cast process, rheocasting introduces some alterations in the microstructure including the presence of aluminum grains with different sizes, formed at different solidification stages. According to the results of the anodic polarization test, conventional cast and rheocast samples show similar breakdown potentials. However, the rheocast samples present enhanced oxygen reduction kinetics compared to the conventional cast sample. Based on scanning electron microscopy examinations, localized microgalvanic corrosion is the main corrosion mechanism for both alloys and it initiates at the interface of aluminum with iron-rich intermetallic particles which are located inside the eutectic regions. The corrosion further develops into the eutectic area. Although the rate of the cathodic reaction can be influenced by the semisolid microstructure, according to the results of anodic polarization and electrochemical impedance spectroscopy tests, the corrosion behavior is not meaningfully affected by the casting process.

Uncertainty Propagation Through a Simulation of Industrial High Pressure Die Casting

Abstract While numerical models are often used in industry to evaluate the transport phenomena in solidification processes, the uncertainty in the results propagated from uncertain input parameters is rarely considered. In this work, in order to investigate the effects of input uncertainty on the outputs of high pressure die casting (HPDC) simulations, the Center for Prediction of Reliability, Integrity, and Survivability of Microsystems (PRISM) uncertainty quantification (PUQ) framework was applied. Three uncertainty propagation trials investigate the impact of uncertainty in metal material properties, thermal boundary conditions, and a modeling parameter on outputs of interest, such as fraction liquid at different times in the process cycle and shrinkage porosity volume, in an industrial A380 aluminum alloy HPDC process. This quantification of the output uncertainty establishes the reliability of the simulation results and can inform process design choices, such as the determination of the part ejection time. The results are most sensitive to the uncertainty in the interfacial heat transfer (for both outputs of interest) and the feeding effectivity (FE) (a model parameter controlling porosity formation determination), while the other heat transfer boundary conditions, model parameters, and all the properties play a secondary role in output uncertainty.

Two-phase flow modeling of air entrapment in high pressure die casting considering air compressibility and surface tension

Air entrapment is a serious defect in HPDC (high pressure die casting) process. In this paper a two-phase flow numerical model aimed at predicting this defect is developed. Two important physical factors are firstly considered in the modeling of HPDC process, namely air compressibility and surface tension. An ESOLA (Extended SOLA) algorithm is derived to solve the Navier–Stokes equation of compressible air. An interface capturing approach VOSET (coupled volume of fluid and level set) using geometric operation for level set function is adopted for capturing the melt/air interface evolvement and calculation of surface tension. The proposed model allows calculations with non-orthogonal mesh. The capability of the model is verified by comparing simulation results with analytical and experimental results.

Degating of AlSi10Cu2Fe High-Pressure Die Casting Component Using Resonance Vibration Technique

The high-pressure die casting process is meant for high volume production rate mainly used in the automotive industry. An efficient method to separate the die-cast components from the main sprue and runner system is crucial to improving the productivity of the manufacturing processes. Conventionally casting components are often separated with the use of a grinding wheel machine, trimming machine or pneumatic hammer. Often these techniques require customized machine design in trimming the cast part as each die casting gate design might be different from one another, especially when there is a change in production cast model. This may incur higher set-up cost and additional configuration time. It is unfavourable in the manufacturing production line that handles small batch high variation of casting model in the small/medium casting industry. Thus, this paper introduced an alternative degating technique with the use of a shaker machine to match the resonance of the casting component natural frequency to separate the die-cast component from the casting tree. The proposed method can overcome the drawback of the conventional method by eliminating the additional configuration time required when there is a change in different casting part design. Die casting parts employed in this study were constructed by AlSi10Cu2Fe aluminium alloy. Experimental modal analysis was performed to verify the natural frequency calculated through finite element analysis. The correlated finite element model was then employed for harmonic response analysis to compute the frequency response of input excitation location against output stress response at the gate. The results from the analysis showed that the first natural frequency mode could induce a bending mode at the gate and created the highest stress concentration at the location. Next, an experiment was carried out by exciting the first natural frequency to the casting part using a shaker machine. In the experiment, the die-cast components were able to break away within 0.31 s at its first natural frequency. This observation was found to be in agreement with the simulation results, whereby the degating time of 0.27 s was obtained. Therefore, the present study has shown that an efficient degating of casting components process can be achieved via introducing a correct mode of vibration excitation.

Numerical simulation of fluid flow, solidification and defects in high pressure die casting (HPDC) process

The high pressure die casting process is extensively used to manufacture light metal parts with high productivity. A major drawback of the process is the relatively high variability in mechanical properties and poor repeatability between casting cycles, limiting the achievement of weight reduction through lighter design. Although it has been established that mechanical properties are adversely affected by casting defects, the origin of the relatively high randomness in the HPDC process is not well understood. Numerical simulation is a powerful and cost-effective tool to address this question, as it gives access to quantities that are difficult to obtain experimentally. A numerical simulation approach based on the finite element casting software ProCAST has been developed. The model was applied to the casting of aluminium tensile test samples, which were used to measure the tensile properties of the alloy. Simulation permitted the study of fluid flow, solidification and defect formation during each stage of the HPDC process: pouring, injection and cooling. Air entrapment and porosity distribution in the cast part were predicted. The results were compared with temperature measurements, porosity observations and solid distribution in the sleeve prior to injection. Although the results are still very preliminary, some trends could be established between the level of turbulence of the melt during injection and reduced elongation.

The combined effects of Sr additions and heat treatment on the microstructure and mechanical properties of high pressure die cast A383 alloy

The microstructures and mechanical properties of high pressure die cast A383 alloys under four conditions (with and without Sr additions and heat treatment) were investigated. Sr addition is responsible for the increase in the elongation of high pressure die cast A383 alloys by refining the eutectic Si particles from long, needle-like morphologies to fine, fibrous ones. High cooling rates, as generated in the high pressure die casting process, also significantly contribute to the microstructural refinement of the eutectic Si particles. However, there was almost no relationship between the morphologies (size and roundness) of the eutectic Si particles and the yield strength of high pressure die cast A383 alloys. Heat treatment (aging without solution treatment) increased the yield strength of high pressure die cast A383 alloys. Sr addition combined with heat treatment was found to refine the size of aging precipitates and therefore improve the yield strength beyond the levels observed for heat treatment alone. The sludge characteristics (size, roundness and fraction) were not affected by the different heat treatments and Sr additions and had no discernible effect on the change in mechanical properties.

Analysis design of the gating system on high-pressure die casting process for production effectiveness

The purpose of this study is to improve the efficiency of production time for the manufacture of radiator components by performing gating system design optimization. The production data obtained is used as data to examine cases that occur on the production floor. The method of analysis is used to perform simulations on the design of the gating system that already exists, and then compare the results with the new design. The existing gating system design has two cavities while the new design has one cavity. Based on the simulation results, the two cavity gating system has a cooling time of 5 seconds longer than gating one cavity. As a result of longer cooling time, the product can be attached to the mould so difficult removable and can lead to defective products. The percentage of air trapped in the new design is 3.12%, whereas, from the previous design 19.29%, this can cause a reduction in potential defects in porosity in the product.

Dissolution and erosion behavior of AISI H13 shot sleeve in high pressure die casting process

In high-pressure die casting process (HPDC), shot sleeve undergoes erosion, wear and soldering due to cyclic thermo-mechanical exposure by the molten casting alloy stream with high temperature and high velocity. Gradual deterioration of sleeve surface during service affects the quality of resultant casting, lives of piston and sleeve. It also results in increased cost and downtime. Objective of this work is to study and reduce sleeve surface damage while casting the components weighing between 20 and 40 kg. As initial survey, the worn-out sleeve was used to perform failure analysis to understand erosion mechanism. Simulation study was conducted to estimate impact force of liquid metal stream on sleeve surface at various sprout angles. Dummy pins were made from same steel that of the sleeve - AISI H13 and their erosion response to different surface conditions such as surface roughness, nitrided case depth, and coating chemistry was investigated. Erosion performance of a dummy pin made from steel with increased molybdenum and reduced silicon content was compared with the pins of AISI H13 steel. The pins were observed intermittently for size, weight loss and any crater formation on the surface. All the pins were characterized after subjecting to a maximum number of 4500 casting made. The pins were characterized for microstructure, chemical composition, and phase analysis. Surface roughness and micro-hardness were also measured. Pin made of DIN 1.2367 steel showed increased resistance against erosion, comparative to the pin made of AISI H13 steel under similar testing condition. TiAlN coated pin outperform all other pins in terms of resistance against erosion. Mechanism of progression of erosion in actual shot sleeve is proposed based on experimental design.