High Pressure Die Casting Research Articles

Correlation between segregation behavior and wall thickness in a rheological high pressure die-casting AC46000 aluminum alloy

The segregation behavior of a rheological high pressure die-casting (Rheo-HPDC) AC46000 aluminum alloy at positions with different wall thicknesses was studied. The results reveal that positions with different wall thicknesses exhibit different cooling rates that can result in distinctly different segregation characteristics. Segregation results in varying microstructure, elemental distribution, and hardness along the thickness of an alloy. The segregation in a Rheo-HPDC AC46000 alloy can be categorized as: cross-sectional segregation along the thickness and center segregation. As the distance from the alloy surface increases, the volume fraction of the primary phase increases, and the hardness of the microstructure and content of the eutectic Al-Si, Al2Cu, and α-(FeMn)3Si2Al15 phases decrease. As the alloy wall thickness increases, the differences in the volume fraction of the primary phase, elemental content, and hardness of the microstructure between the edge and center gradually decrease. Compared with the normal center microstructure, the volume fraction of the primary phase in the center segregation microstructure is lower, and the morphology is not round. The content of the eutectic Al-Si, Al2Cu, α-(FeMn)3Si2Al15, and Si phases is higher, and these phases are nonuniformly distributed. Center segregation is often accompanied by shrinkage cracks. As the alloy wall thickness increases, the center segregation area and crack size increase, and the more hard–brittle α-(FeMn)3Si2Al15 particles accumulate the crack. The hardness of the center segregation structure is higher than that of the normal center structure. With increasing alloy wall thickness, the hardness of the center segregation microstructure first increases and then decreases.

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.

Comparative study on the microstructures and hardness of the AlSi10.6CuMg alloy produced by sand casting and high pressure die casting

ABSTRACT This study compares the microstructures and hardness of an AlSi10.6CuMg alloy obtained by sand casting and high pressure die casting (HPDC). The results show that the morphology of HPDC dendrites was not uniformly distributed as in sand casting. HPDC refines the morphology of intermetallics and produces a modification of eutectic silicon. Chinese-script is the dominant iron intermetallic in sand casting, while primary polyhedral and secondary proeutectic particles are dominant in HPDC. The results of the X-ray diffraction show the presence of high residual stresses in the HPDC. Deep etching for HPDC samples reveals θ-Al2Cu phases in very thin compact dendrites. No evidence of twin plane re-entrant edge assistance was found in the growth of primary silicon. The primary silicon plate-like becomes unstable in HPDC, resulting in smooth and rounded outer surfaces. Hardness of HPDC alloy was about 11% higher than that of sand casting alloy.

Direct Observation of Filling Process and Porosity Prediction in High Pressure Die Casting.

Although numerical simulation accuracy makes progress rapidly, it is in an insufficient phase because of complicated phenomena of the filling process and difficulty of experimental verification in high pressure die casting (HPDC), especially in thin-wall complex die-castings. Therefore, in this paper, a flow visualization experiment is conducted, and the porosity at different locations is predicted under three different fast shot velocities. The differences in flow pattern between the actual filling process and the numerical simulation are compared. It shows that the flow visualization experiment can directly observe the actual and real-time filling process and could be an effective experimental verification method for the accuracy of the flow simulation model in HPDC. Moreover, significant differences start to appear in the flow pattern between the actual experiment and the Anycasting solution after the fragment or atomization formation. Finally, the fast shot velocity would determine the position at which the back flow meets the incoming flow. The junction of two streams of fluid would create more porosity than the other location. There is a transition in flow patterns due to drag crisis under high fast shot velocity around two staggered cylinders, which resulted in the porosity relationship also changing from R1 < R3 < R2 (0.88 m/s) to R1 < R2 < R3 (1.59 and 2.34 m/s).

Simulation Aspects of the High Pressure Die Casting Process

High pressure die casting (HPDC) is a manufacturing process for producing accurately dimensioned, sharply defined, smooth or textured surface metal parts. It is accomplished by injecting liquid metal at fast velocity and under high pressure into reusable steel dies. Compared to other casting processes, die casting is at the top end of both velocity and pressure. The high velocity translates into a very turbulent flow condition. The process is often described as the shortest distance between raw material and the finished product.

Experimental and Numerical Study of an Automotive Component Produced with Innovative Ceramic Core in High Pressure Die Casting (HPDC)

Weight reduction and material substitution are increasing trends in the automotive industry. High pressure die casting (HPDC) is the conventional casting technology for the high volume production of light alloys; it has recently found wide application in the manufacturing of critical components, such as complex and thin geometry automotive parts. However, the major restriction of this affordable technology is the difficulty to design and realize hollow sections or components with undercuts. An innovative way to further increase the competitiveness of HPDC is to form complex undercut shaped parts through the use of new lost cores that are able endure the high pressures used in HPDC. This paper investigates the use of innovative ceramic lost cores in the production of a passenger car aluminum crossbeam by HPDC. Firstly, process and structural simulations were performed to improve the crossbeam design and check the technology features. The results led to the selection of the process parameters and the production of some prototypes that were finally characterized. These analyses demonstrate the feasibility of the production of hollow components by HPDC using ceramic cores.

Influence of steel preheat temperature and molten casting alloy AlSi9Cu3(Fe) impact speed on wear of X38CrMoV5-1 steel in high pressure die casting conditions

This paper is a part of experimental research in the area of high pressure die casting (HPDC) mould wear. Influence of mould preheat temperature and molten aluminium alloy impact speed on total mould wear was researched using novel laboratory die casting testing equipment. Testing parameters were set to simulate HPDC of aluminium alloy AlSi9Cu3(Fe). The specimens were made from X38CrMoV5-1 hot work steel (H11). Experiment was designed using central composite design. Following the experiment design, 13 specimens were heat treated and the surface was modified by “Tenifer” nitrocarburizing. Specimen wear was measured by a Mettler B5 scale (Küsnacht, Switzerland) and shown graphically by 3D scan before and after the experiment; the 3D scans were overlapped to determine main wear areas. Response surface was acquired. Most influential tribological wear mechanisms were determined by ANSYS CFX 17.2 analysis. It was found that preheat temperature and molten aluminium alloy impact speed directly affects total wear of the mould surface. An increase of preheat temperature decreases total wear, while an increase of molten aluminium alloy impact speed increases total wear. Conditions for minimum and maximum wear were quantified; most significant wear was observed on sharp edges of nitrided mould material specimens. ANSYS CFX 17.2 hard particle erosion rate simulation suggested erosion occurrence mostly at impact angles perpendicular to the specimen surface. Other ANSYS CFX 17.2 simulation suggested occurrence of cavitation erosion. SEM analysis indicated an occurrence of intermetallic compounds between molten alloy and hot work steel.

Predicting grain structure in high pressure die casting of aluminum alloys: A coupled cellular automaton and process model

Grain structure is one of the most important factors that affect the mechanical properties of metallic alloys. Accurate prediction of as-cast grain structure is critical in the design and manufacturing of metal castings using an integrated computational materials engineering (ICME) approach. In this paper, a three-dimensional (3-D) model based on cellular automaton (CA) and process simulation was developed for predicting grain size of components produced by high pressure die casting (HPDC) of aluminum alloys. The concurrent nucleation and growth of grains were considered in the model. A test specimen casting, consisting of different wall thicknesses, was simulated using a finite element based casting process simulation software ProCAST®. The thermal history of the simulated casting was extracted and used in subsequent mesoscale CA modeling. Different thermal conditions were used to simulate grain nucleation and growth during HPDC. The grain morphology, grain density and grain size were obtained by CA modeling. Electron backscatter diffraction (EBSD) analysis was performed on aluminum castings of different wall thicknesses under various cooling rates to validate the simulation results. The 3-D grain structure model is in excellent agreement with the experimental results, and can be used in ICME design and development of aluminum castings.

Particle Method Simulation for Formation and Flow of Cold Flakes in High-Pressure Die Casting

In high-pressure die casting (HPDC) processing of aluminum alloys, solidified layers generated in the sleeve of a die casting machine that flow into the mold cavity are known as “cold flakes.” The prediction and control of them are a crucially important issue for HPDC. This study developed a method to simulate their formation and flow using smoothed particle hydrodynamics. First, a solidified layer was modeled as a set of solid particles with behaviors defined by mechanical constitutive equations. Second, this study proposed an algorithm for ascertaining the phase of particles and for calculating liquid–solid particle interaction. Numerical results demonstrated that the method can predict the formations of solidified layers in the sleeve, their peeling and folding during the plunger movements, their inflow into the runner and the mold cavity, and flow disturbances caused by solidified layers trapped at the gate.

Aluminum Foam-Filled Steel Tube Fabricated from Aluminum Burrs of Die-Castings by Friction Stir Back Extrusion

A mixture of Al burrs of Al high-pressure die-castings and a blowing agent powder was used to fabricate Al foam-filled steel tubes by friction stir back extrusion (FSBE). It was shown that the mixture can be sufficiently consolidated to form an Al precursor that is coated on the inner surface of a steel tube by the plastic flow generated during FSBE. Namely, a precursor coated steel tube can be fabricated from Al burrs by FSBE. By heat treatment of the precursor coated steel tube, an Al foam-filled steel tube can be fabricated. Al foam was sufficiently filled in the steel tube, and the porosity was almost homogeneously distributed in the entire sample. In compression tests of the samples, the Al foam-filled steel tube fabricated from Al burrs exhibited similar compression properties to an Al foam-filled steel tube fabricated from the bulk Al precursor. Consequently, it was shown that an Al foam-filled steel tube cost-effectively fabricated from Al burrs by FSBE compares favorably with an Al foam-filled steel tube fabricated from the bulk Al precursor.

Influence of slow-shot speed on PSPs and porosity of AlSi17Cu2.5 alloy during high pressure die casting

The influence of slow-shot speed on primary silicon particles (PSPs) and porosity of AlSi17Cu2.5 alloy in high pressure die casting (HPDC) was investigated. Both PSPs and porosity were identified in the microstructure. It was found that variation of the slow-shot speed could generate significant influence on both volume fraction and distribution of the PSPs and porosity. The area fraction of PSPs reached a maximum of ˜0.19% when the slow-shot speed was 0.05 m/s. An increase of the slow-shot speed could reduce the PSPs content and increase the microstructure heterogeneity, e.g., multiple PSPs-rich and PSPs-free ring-shape regions formed. Detailed feature of the PSPs in casting was highly dependent on the PSPs formed in the shot sleeve. Affected by solidification shrinkage, the volume fraction of the porosity increased exponentially from the surface to the center of the sample. However, the precipitation of PSPs released large amount of latent heat and promoted local feeding of the melt. The porosity decreased abruptly at the PSPs-free region and reached a local minimum at a particular distance from the surface.

Research on Coatings and Infiltration to Strengthen Ceramic Lost Cores Used in High-Pressure Die Casting Processes

Lost cores used to manufacture complex aluminium components through high-pressure die casting (HPDC) processes need to withstand very high injection velocities and pressures. The conventional sand cores used in other casting processes, such as sand casting or low-pressure die casting, do not support the aggressive process parameters of the HPDC, so advanced ceramic cores must be used. These cores must be strong enough not to get broken during the casting process, but, at the same time, they must have a minimum porosity to be easily removed from the casting to obtain the finished part. Due to this porosity, the aluminium penetrates the core surface during the casting process. So, the criterion here is to find the necessary compromise between strength and porosity and to protect the core surface from the aluminium penetration. In this work, two research lines have been followed to address these challenges. On the one hand, different refractory coatings have been applied to the ceramic core surface with the aim of sealing it. Amongst the coatings analysed, boron nitride-based one has been found to be the most suitable and cost-effective solution to avoid aluminium penetration. On the other hand, silica has been proved to be a suitable infiltration agent to increase the strength of the core.

The Effect of Vacuum on the Mechanical Properties of Die Cast Aluminum AlSi9Cu3(Fe) Alloy

High-pressure die casting (HPDC) is a widely used casting technology for product that is made of light metal such as aluminum alloy. During the die casting process, the molten metal is injected into a mold at high speed and solidified under high pressure. The amount of porosity in the cast part is an important question. Lots of technologies have been developed to minimize porosities, for example, vacuum-assisted high-pressure die casting process (VPDC). In this paper, AlSi9Cu3(Fe) aluminum alloy castings were produced by conventional HPDC with atmospheric venting and VPDC process under three different absolute cavity air pressures of 170 mbar, 90 mbar and 70 mbar at the cavity. The influence of absolute cavity air pressure on the porosity and on the mechanical properties of the castings was investigated and compared with conventional HPDC casting method. The results of the present study proved that the amount of porosity and the pore sizes in the castings can be significantly reduced from 1.10% at an atmospheric level to 0.47% at 70 mbar. This corresponds to 57% reduction. As a result, the mechanical properties are improved significantly, particularly, the tensile strength from 271.6 to 299.8 MPa, which corresponds to 10% increment and the elongation from 1.66 to 2.49%, which shows 50% increment. At lower absolute cavity air pressure, the entrapped gases become the final gas porosities in the die castings and show solidification shrinkage form inspected with scanning electron microscopy. In general, lower cavity air pressure contributes to reduce the pores, which improve the mechanical properties of die casting.

Evaluation of the corrosion resistance of a new AlSi10MnMg(Fe) secondary alloy

In this work the corrosion resistance of a new AlSi10MnMg(Fe) secondary alloy is evaluated as a function of the wall thickness obtained by high pressure die-casting (HPDC) in comparison with a primary alloy. The electrochemical tests have been performed at two different saline concentrations (0.03 and 0.5 M NaCl, respectively) in order to determine the corrosion rate. The experimental results indicate that there are not significant differences in the corrosion rate as well as pitting corrosion for both primary and secondary alloys. Finally, SEM/EDS microanalysis has confirmed that the corrosion mechanism is preferentially through the eutectic areas

Addition of Swarf to Produce a Semi-Solid Slurry during High Pressure Die-Casting of AS9U3 Aluminum Alloy

An internal cooling agent is used in rapid slurry forming (RSF) process to produce a high solid fraction slurry for a short period of time. In the process used in this research, the swarf which is known to be a low enthalpy material was added to the melt as the internal cooling agent. During the process, the swarf started to melt and a semi-solid slurry with a relatively high solid fraction was formed. This slurry was formed by exchanging the enthalpies between the low and high enthalpy materials. A commercial Al-Si-Cu alloy, i.e. AS9U3 Aluminum alloy, was used in this investigation. The microscopic examination showed that the Al-Si eutectic colonies start to melt during the melting process of swarf material resulting in the formation of globular Alpha-Al grains due to the multiplication of secondary dendrites arms. The fracture of dendrites arms and the subsequent spheroidization were suggested to be the origin of non-dendritic globular grains in the final microstructure. The amount of primary globular Alpha-phase was measured by the image analysis software. The results showed that during high pressure die-casting of AS9U3 Aluminum alloy using 4 mm thick samples, around 35 percent solid has been formed at the temperature of 580 oC.

Industrialized Application of Rheo-HPDC Process for the Production of Large Thin-Walled Aluminum Alloy Parts

A simplified and efficient process, namely air-cooled stirring rod (ACSR), was proposed to prepare semisolid slurry of aluminum alloys. An advanced integrated rheological high pressure die-casting (Rheo-HPDC) technology was established by combining the ACSR equipment with HPDC machines to produce high quality aluminum alloy products. Microstructures, surface qualities, mechanical properties, corrosion resistances and thermal conductivities of the Al-8Si alloy parts prepared by Rheo-HPDC were investigated and compared to those prepared by traditional HPDC. The results indicated that the Rheo-HPDC process can prepare aluminum alloy parts in which the primary particles are fine and spherical, and there is few shrinkage porosity. Multifarious high quality large thin-walled aluminum alloy parts, such as filter shells, cooling shells, antenna crates and mounting brackets for communication, were produced by the process. Rheo-HPDC alloys showed improved surface quality to those formed by traditional HPDC, and the surface roughness is small and avoid employing CNC to surface finish. Also, compared with HPDC alloys, the alloys prepared by Rheo-HPDC have an increased mechanical properties and thermal conductivity due to high density and refined microstructure. Furthermore, Rheo-HPDC aluminum alloys indicated a remarkable improvement in corrosion resistance as shown by the results of electrochemical and weight loss experiments.

Effect of runner design on the externally solidified crystals in vacuum die-cast Mg-3.0Nd-0.3Zn-0.6Zr alloy

The microstructure and tensile properties of a vacuum-assist high-pressure die casting (HPDC) Mg-3.0Nd-0.3Zn-0.6 Zr alloy and the effect of runner design on the externally solidified crystals (ESCs) were investigated. The microstructure of the alloy mainly comprised ESCs (large primary α-Mg grains) formed in the chamber, small primary α-Mg grains crystalized in the cavity, divorced eutectic Mg12Nd and a small amount of Mg12(NdxZn1-x) or Mg12(NdxZnyZr1-x-y) phases in the region near the shrinkage. The average ESCs grain size decreased as the distance from the center increased remarkably. The employment of ESCs collector contributed to the depression of ESCs grain size, particularly in center region. On the contrary, the grain size of small primary α-Mg has overall slightly downward trend from center to skin region, and the size difference was small. The employment of an ESCs collector effectively decreased the number and size of the ESCs, and accordingly both strength and elongation of the alloy were improved. This specially design ESCs collector improve the runner system and optimize the mold design. The elongation of the alloy approached 10%.

The Effects of Silicon Addition on the Microstructure and Mechanical Properties of a Mg-Al-Sn Alloy Produced by Vacuum Assisted High Pressure Die Casting

In this paper, the effects of a small addition of Si (about 0.4 wt pct) on the microstructure and mechanical properties of a Mg-Al-Sn alloy produced with vacuum assisted high pressure die casting (HPDC) are reported. CALculation of PHase Diagrams-based modeling was used to design the heat treatment schedules to optimize the precipitation of Mg2Sn and Mg17Al12 in the Mg-7Al-2Sn-0.4Si alloy (in wt pct, designated as ATS). The HPDC test specimens were studied in the as-cast condition as well as in multiple heat-treated conditions to improve their tensile properties. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were used to characterize the microstructure in each condition. The results suggest that the small addition of Si is effective in enhancing and accelerating the precipitation hardening of Mg-7Al-2Sn alloy AT72, due to enhanced precipitation of Mg17Al12 and Mg2Sn phases as well as the precipitation of Mg2Si phase. In as-cast conditions, the new ATS alloy has similar strengths but significantly improved ductility compared with AZ91D, and significantly improved strength but reduced ductility compared with AM60B. The ATS-T6 after a one-stage solution treatment provides further improvement of mechanical properties: yield strength 151 MPa, ultimate tensile strength 253 MPa, and elongation 4.9 pct.

The effect of vacuum degree on the porosity and mechanical properties of die cast AlSi9Cu3(Fe) alloy

AlSi9Cu3(Fe) aluminum alloy specimens were produced by conventional high-pressure die casting (HPDC) and vacuum-assisted high-pressure die casting (VPDC) processes under atmospheric and 3 different...

Gating system optimization of high pressure die casting thin-wall AlSi10MnMg longitudinal loadbearing beam based on numerical simulation

High pressure die casting (HPDC) is a kind of near net shape manufacturing method. However, air entrapment in HPDC parts has serious effects upon the casting quality. In order to reduce the air entrapment defects in a AlSi10MnMg alloy thin-wall longitudinal load-bearing beam produced by HPDC, different gating systems were designed and simulated by software Flow-3D to evaluate the entrapped air. Simulation results showed that when the beam is produced by the original designed gating system with a middle ingate, there exist obvious air entrapments in the critical area; the volume of air entrapment was reduced by replacing the middle ingate to an overflow well, and the filling of molten metal became more stable. When the middle ingate was removed for further improvement, the volume of air entrapment was decreased drastically. The parts with glossy surface and good microstructure have been successfully produced by using the final optimized gating system based on simulation results.