High Pressure Die Casting Research Articles

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 Al11Ce3 phase 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.

The Influence of Cooling Rate on Microstructure and Mechanical Properties of AlSi9Cu3

The aim of this study was to determine the correlation between the size and the distribution of microstructural constituents and their cooling rate, as well as the correlation between the mechanical properties and the cooling rate of AlSi9Cu3 aluminum alloy when cast in high-pressure die casting (HPDC) conditions. In other words, the ultimate goal of the research was to determine the mechanical properties for a casting at different cooling rates. Castings with different wall thicknesses were chosen, and different cooling rates were assumed for each one. Castings from industrial technological practice were systematically chosen, and probes were extracted from those castings for the characterization of their mechanical properties. Special non-standard cylinders were created on which compressive tests were carried out. The uniqueness of this research lies in the fact that the diameters of the designed cylinders were in direct correlation to the actual wall thickness of the castings. This is important because the solidification of metal in the die cavity is complex, in that the cooling rates are higher on the surface of the casting than in the center. Local in-casting cooling rates were determined using numerical simulations. It was discovered that with increasing cooling rates from 60 K/s to 125 K/s the values for strength at 5% deformation increased on average from 261 MPa to 335 MPa.

Microstructure and mechanical properties of high-strength high-pressure die-cast Mg–4Al–3La–1Ca–0.3Mn alloy

A new high-pressure die-cast (HPDC) Mg–4Al–3La–1Ca–0.3Mn (ALaX431) alloy with high strength has successfully been fabricated. This HPDC alloy in peak-aged state exhibits tensile yield strength (TYS) of 220 MPa at room temperature and TYS of 145 MPa at 250 °C, higher than the corresponding strength of HPDC Mg alloys reported so far. These high strengths are mainly due to the formation of fine grained structure, semi-continuous reticular structure consisting of stable Al3La and (Mg,Al)2Ca particles along grain boundaries and numerous nanoscale Al2Ca precipitates within grains. Due to its higher strength than existing HPDC Mg alloys, the new developed alloy has great application potential.

An Evaluation of the Effect of Ultrasonic Degassing on Components Produced by High Pressure Die Casting

Ultrasonic treatment is known to be efficient for aluminium melt degassing with the additional benefits of being both economical and environment friendly. This paper describes the effect of ultrasonic degassing on the preparation of an AlSi9Cu3(Fe) alloy for High Pressure Die Casting (HPDC). The degassing efficiency was assessed in terms of the indirect evaluation of the melt, by means of the reduced pressure test and the porosity evaluation of the cast parts. Additionally, the corresponding hydrogen content was estimated with an experimental equation reported in the literature. Ultrasonic degassing shows greater efficiency in terms of hydrogen removal from the melt than conventional N2 + Ar lance bubbling. Components produced by HPDC without degassing, with ultrasonic degassing and with lance degassing, were analysed by computed tomography and by metallography. The results show that the components produced by HPDC after ultrasonic degassing have a similar porosity level to components degassed with conventional lance bubbling, both showing an important improvement over components produced without degassing treatment. Hardness values were similar for all different treatment conditions and well over the minimum value established for the alloy by the corresponding standard.

Variable amplitude fatigue behavior and modeling of cast aluminum

AbstractMost of the research reported in the literature on cast aluminum alloys is related to constant amplitude loading, while in most applications such components are subjected to variable amplitude loading conditions. In this work, fatigue performance of high pressure die cast (HPDC) A356‐T6 aluminum alloy is evaluated using a real industrial load spectrum. Mean stress effect was also studied by conducting variable amplitude fatigue tests under two different mean stress conditions. Fatigue life estimations were performed following S‐N approach as well as fracture mechanics approach using direct summation method as well as FASTRAN program assuming the defects as initial cracks. The size of fatal defects measured from fracture surfaces as well as the maximum defect size estimated by extreme value statistics were used in fatigue life estimations. The results of life estimations are compared and discussed with reference to the experimental results.

On the characterization of primary iron-rich phase in a high-pressure die-cast hypoeutectic Al-Si alloy

The morphological properties and distribution characteristics of primary iron-rich phase in a high-pressure die-cast hypoeutectic Al-Si alloy were investigated by synchrotron X-ray tomography technology. Attention was focused on the formation and evolution mechanism of primary iron-rich intermetallic compounds (IMCs) in high pressure die casting (HPDC). Results show that two different sizes of primary iron-rich phases included externally solidified primary iron-rich phase I ((P-IMC)I) and primary iron-rich phase II ((P-IMC)II). The morphology of (P-IMC)I was close to a hexahedron while (P-IMC)II was nearly a spherical particle. Both (P-IMC)I and (P-IMC)II enriched in the central area and their volume fraction maintained a high level from defect band to center. Phase calculation show that (P-IMC)I (601 °C) preferentially precipitated from liquid and its further growth led to the decrease of Mn/Fe ratio in the subsequent formed (P-IMC)II. In HPDC solidification process, (P-IMC)II exhibited a lateral growth pattern with the terminating surfaces determined to be {1 1 0} planes. In addition, the hexahedral (P-IMC)I in central ESCs-rich zone developed into a dendrite along its corner<100>direction.

Mechanical Properties of Selective Laser-Melted Components of Alsi10mg for Prototype Vehicles

Fabrication of aluminum alloy components by traditional high-pressure die casting (HPDC) requires cost- and time-consuming tooling of steel dies, which makes HPDC uneconomic for producing low-volume components or prototypes. In comparison, powder bed-based additive manufacturing, e.g. selective laser melting (SLM), enables rapid prototyping and production of even complex-shaped components directly from computer-aided design models without needing expensive tools. However, SLM prototype components must have almost identical mechanical properties to HPDC serial components in order to emulate their functionality under different load conditions. In this work uniaxial tensile properties of cast alloy AlSi10MnMg (EN AC-43500) in condition T7, i.e. with 120-170 MPa yield stress, 200-240 MPa tensile strength and 9-12 % strain at fracture, shall be attained using selective laser melting of powder alloy AlSi10Mg (EN AC-43000). These properties were achieved by tailored heat treatment. Furthermore, the effect of hot isostatic pressing (HIP) was investigated. The results of the tensile tests confirmed the basic feasibility of substituting HPDC components with SLM components for prototyping. In particular, similar tensile strength and uniform strain were achieved for SLM samples in condition O, i.e. for SLM samples which were only annealed.

Development of High Strength and Toughness Non-Heated Al–Mg–Si Alloys for High-Pressure Die-Casting

Based on the 3 factors and 3 levels orthogonal experiment method, compositional effects of Mg, Si, and Ti addition on the microstructures, tensile properties, and fracture behaviors of the high-pressure die-casting Al-xMg-ySi-zTi alloys have been investigated. The analysis of variance shows that both Mg and Si apparently influence the tensile properties of the alloys, while Ti does not. The tensile mechanical properties are comprehensively influenced by the amount of eutectic phase (α-Al + Mg2Si), the average grain size, and the content of Mg dissolved into α-Al matrix. The optimized alloy is Al-7.49 Mg-3.08Si-0.01Ti (wt%), which exhibits tensile yield strength of 219 MPa, ultimate tensile strength of 401 MPa, and elongation of 10.5%. Furthermore, contour maps, showing the relationship among compositions, microstructure characteristics, and the tensile properties are constructed, which provide guidelines for developing high strength and toughness Al–Mg–Si–Ti alloys for high-pressure die-casting.

Making Additively Manufactured Cores with Conformal Tooling Directly on a Die-base

Dies for high pressure die casting (HPDC) has traditionally been manufactured by machining from slabs of tool steel. Currently, the possibility of manufacturing them using additive manufacturing is being explored. This provides some advantages such as the possibility of making conformal cooling channels. However, the size of the dies is often larger than can be handled in most metal printers Still, it is possible to partly print the die by adding cores with intricate conformal cooling on a traditionally manufactured die base. In this paper, a feasibility study of using selective laser melting (SLM) to print cores of maraging steel directly onto a die base is explored. Results shows that the strength of the bond between the two metals is sufficient, and that the connection between the drilled and printed tooling channels can be made. The paper reasons on the expected impacts on the tooling industry showing potential for extended die life and recovery of die bases via re-manufacturing.

On the CFD Modelling of Slamming of the Metal Melt in High-Pressure Die Casting Involving Lost Cores

This paper uses computational fluid dynamics (CFD), in the form of the OpenFOAM software package, to investigate the forces on the salt core in high-pressure die casting (HPDC) when being exposed to the impact of the inflowing melt in the die filling stage, with particular respect to the moment of first impact—commonly known as slamming. The melt-air system is modelled via an Eulerian volume-of-fluid approach, treating the air as a compressible perfect gas. The turbulence is treated via a Reynolds-averaged Navier Stokes (RANS) approach. The RNG k-ε and the Menter SST k-ω models are both evaluated, with the use of the latter ultimately being adopted for batch computations. A study of the effect of the Courant number, with a view to establishing mesh independence, indicates that meshes which are finer, and time steps that are smaller, than those previously employed for HPDC simulations are required to capture the effect of slamming on the core properly, with respect to existing analytical models and empirical measurements. As a second step, it is then discussed what response should be expected when this force, with its spike-like morphology and small force-time integral, impacts the core. It is found that the displacement of the core due to the spike in the force is so small that, even though the force is high in value, the bending stress inside the core remains below the critical limit for fracture. It can therefore be concluded that, when assuming homogeneous crack-free material conditions, the spike in the force is not failure-critical.

Characterization of Nanostructures in the High Pressure Die Cast A383 Alloys

Several interesting nanostructures of high pressure die cast A383 alloys were characterized via transmission electron microscopy (TEM) and atom probe tomography (APT). The refinement of the eutectic Si, which was caused by Sr addition, was found to be associated with the formation of nano-Al particles (~5 nm), with Cu partitioning (up to 5 at. %) at the Al/Si interface, within the eutectic Si. Direct observation of Sr segregation (0.4 at. %) was achieved at the interface between the eutectic Al and refined eutectic Si using APT. It is proposed that Sr refines the eutectic Si by restricting the growth of Si. Interestingly, the segregation of Mg (10.2 at. %) and Cu (0.9 at. %) is also present at the interface between the eutectic Al and the refined eutectic Si. Moreover, the presence of nano-Si particles (~20 nm) in the primary Al was characterized in the primary Al via APT. Segregations of Mg (2.9 at. %) and Cu (2.8 at. %) were also found at the interface between the primary Al and the nano-Si particles. Density functional theory (DFT) was used to assess the driving force for the segregation behavior of Cu and Mg at the Al/Si interface. DFT results also suggest that the segregation of Cu and Mg slightly decreases the cohesive energy of Al/Si interface but is a function of the length scale of the interface.

Fatigue performance and life prediction of cast aluminum under axial, torsion, and multiaxial loadings

Many industrial components made of cast aluminum alloys are subjected to multiaxial loadings, while most of research on these materials are on uniaxial loading condition. This article investigates the fatigue performance of A356-T6 aluminum alloy produced by high pressure die cast (HPDC) under different loading conditions. In addition to obtaining monotonic and cyclic deformation behaviors, fatigue tests were performed under axial, torsion, in-phase and out-of-phase combined loadings. In order to study the fatigue crack growth mechanism, few tests were also conducted under cyclic torsion with static tension or compression. It was observed that the fatigue cracks in all specimens initiated from defects, mainly porosity, and grew on the plane of maximum principal stress. Smith-Watson-Topper (SWT) damage parameter was used to correlate the fatigue data. The experimental fatigue life data were predicted using small crack growth models and from the crack initiating defect on the fracture surfaces. The fatigue lives under different loading conditions were also predicted using the maximum defect size estimated by extreme value statistics. Very good agreements with the experimental lives under different loading conditions were obtained.

Softening Behavior of Cold-Sprayed Aluminum-Based Coatings AA1200 and AA7075 During Annealing

For lightweight constructions, joining dissimilar metals is often indispensable to achieve exceptional properties. A common challenge is the bonding of steel and aluminum parts. The use of cold-sprayed coatings as a bonding agent is an innovative approach for high pressure die casting (HPDC) aluminum-steel hybrid components in order to achieve a metallurgical bonding, although it comes with high requirements in terms of coating adhesive and cohesive strength. Therefore, the main aim of this study is the optimization of a post-processing treatment of cold-sprayed coatings in order to improve the cohesive strength to help the introduced coatings withstand the mechanical and thermal stresses during HPDC. The effect of the heat treatment on the mechanical properties of the cold-sprayed Al99.0 and AA7075 coatings was investigated. Freestanding coatings were heat-treated at a temperature of T = 400 °C for different dwell times in order to analyze the recrystallization kinetics through hardness measurements. Two different heat treatment states along with an as-sprayed condition were chosen to investigate the evolution of the mechanical properties of the coatings by means of 3-point bending tests. Besides the softening of the coatings during the heat treatment, sintering effects at splat boundaries and their impact on fracture mechanisms were investigated using electron microscopy.

The Metallurgy of Aluminum Alloys for Structural High-Pressure Die Castings

Aluminum alloys for high-pressure die casting (HPDC) usually contain sufficient quantities of dissolved iron to reduce die wear and soldering. Unfortunately, iron reduces ductility, making the product unsuitable for crash-resistant automotive components. Recent improvements in machine design and new alloys allow the production of high ductility, structural HPDC components. This paper details the chemical and metallurgical factors underlying this development .

A complete computer aided engineering (CAE) modelling and optimization of high pressure die casting (HPDC) process

The application of computer aided engineering (CAE) has become a trend in manufacture industry due to its great efficiency and reliability. In casting industries, numerical modelling of the casting process based on CAE has replaced traditional trial-and-error R&D procedures in many aspects. With advanced parallel computing techniques and numerous calculation models, the fluid flow, heat transfer, solidification and defect formation behaviours under different casting conditions may be examined in detail. Based on this idea, component design and the optimization of casting parameters may be carried out to produce products for subsequent microstructural and mechanical characterization. In this way, a direct link between process condition, casting quality, and cast mechanical properties may be established in a manner that is practical, economical and energy efficient for such processes as gravity die casting, high pressure die casting (HPDC) and continuous casting.

Residual stress, microstructure, and mechanical properties analysis of HPDC aluminum engine block with cast-in iron liners

During the manufacturing of cast aluminum (Al) engine blocks with iron (Fe) cylinder liners, the mismatch of thermal expansion/contraction coefficients between the Al cylinder wall and the Fe liners results in the development of high residual strains/stresses. This evolution of residual stress can surpass the strength of the currently used alloys and can lead to the premature failure of the engine block. Thus, improving the mechanical properties of the engine block alloys reduces the number of failures and allows automotive manufacturers to increase the operating pressures and, therefore, efficiency. High-pressure die casting (HPDC) has been shown to provide increased cooling rates in the casting as compared to sand casting, and therefore manufacturers commonly use this method for improving not just the efficiency of the high-volume production, but also mechanical properties of the cast components. Hence, investigating the impacts of the HPDC process on the evolution of residual stress in engine blocks with Fe liners and, consequently, their durability is of great importance. The present study includes a microstructural, mechanical property, and residual strain analysis on an inline-4 HPDC Al engine block with cast-in Fe liners. The results indicate that the yield and tensile strength at the top of the cylinder were ∼15 % and ∼8 % greater than the bottom, respectively. This trend was primarily attributed to the higher cooling rate experienced by the top region. Moreover, the top and bottom of the Fe liner experienced 450 MPa of compressive residual stress in the axial direction, which is counterbalanced by tensile stresses in the Al cylinder bridge (CB), which reaches approximately 70 % of the alloy’s yield strength. The findings of this study provide automotive industries with important insights on the combined impacts of the HPDC process and cast-in Fe liner on the as-manufactured properties of engine blocks and will assist them in developing the next generation of engine blocks.

Effect of different casting techniques on the microstructure and mechanical properties of AE44-2 magnesium alloy

AE44-2 magnesium (Mg) alloys were fabricated by gravity casting (GC), high pressure die casting (HPDC), and high vacuum assisted high pressure die casting (HVHPDC). The effect of these three different casting techniques on the microstructure evolution, texture, and mechanical properties of the AE44-2 alloy was investigated. The results showed that the different cooling rates in these three different casting techniques led to the different distribution and morphology of the precipitated phases, and rapid cooling contributed to a dense network distribution of the phases as well as grain refinement. In addition, the faster cooling rate resulted in a decrease of the dislocation accumulation. The addition of vacuum assistance in the HPDC process increased texture strength. The average grain size of the HPDC alloy was reduced by 90.4% compared to the GC alloy and the yield strength increased by 85.7 MPa due to rapid cooling. The elongation of the HVHPDC alloy increased by 2.3% compared to the HPDC alloy due to vacuum assistance. Moreover, the mechanical properties improved for the alloys in the order of GC < HPDC < HVHPDC because of gran refinement caused by the faster cooling rate. Based on the analysis of the strengthening mechanisms, the rapid cooling process of the HPDC alloy led to better strengthening compared to the GC alloy. In addition, grain refinement contributed to 82.1% of the strengthening mechanism.

Characteristics of Al-Si Alloys with High Melting Point Elements for High Pressure Die Casting.

This paper is devoted to the possibility of increasing the mechanical properties (tensile strength, yield strength, elongation and hardness) of high pressure die casting (HPDC) hypoeutectic Al-Si alloys by high melting point elements: chromium, molybdenum, vanadium and tungsten. EN AC-46000 alloy was used as a base alloy. The paper presents the effect of Cr, Mo, V and W on the crystallization process and the microstructure of HPDC aluminum alloy as well as an alloy from the shell mold. Thermal and derivative analysis was used to study the crystallization process. The possibility of increasing the mechanical properties of HPDC hypoeutectic alloy by addition of high-melting point elements has been demonstrated.

Optimizing process parameters to reduce blowholes in high pressure die casting using Taguchi methodology

Products manufactured from every manufacturing process exhibit some defects. To supply quality products to the customer these defects must be reduced. The motivation for this work is to reduce defects in end products reaching customers, thereby increasing productivity. The objective of present work is to reduce the rejection of parts due to blowhole defects that arise during High Pressure Die Casting (HPDC) process. The casting product selected for this study is rack housing made of aluminium alloy (ADC 12) connected with steering column of automobiles. The process parameters taken for study are Limit Switch Position, Intensification Pressure, Phase-1 Velocity and Phase-2 Velocity. Density of casting is chosen as the response factor for the parameters taken for study. Taguchi parameter design approach is used to optimize the process parameters. By varying the selected process parameters with various levels obtained through Taguchi method different experiments were conducted. The experiments are conducted based on L25 orthogonal array. To determine the percent contribution of various process parameters ANOVA have been performed. The optimum process parameters were obtained for minimum blowhole in HPDC of ADC 12 alloy. The optimum process parameters level obtained using Taguchi technique to minimize castings defects for Limit Switch Position, Intensification Pressure, Phase-1 Velocity and Phase-2 Velocity are 170 mm, 300 kg/cm2, 1 m/s and 4 m/s respectively.

New Insights into the Formation Mechanism of Solid-Liquid Segregation in the Semi-Solid Processing: Macro-Micro Linkage Theory

Solid-liquid segregation is a typical problem in multiphase flow, especially in the die casting of metallic alloys. The avoidance of phase segregation in High Pressure Die Casting (HPDC), and Semi-solid Processing (SSP) for suspended flow is a benefit for improving product performance. At present, there is not a unified statement on the cause of the solid-liquid segregation defect. The formation mechanism of phase segregation is investigated by theoretical analysis from the perspective of hydrodynamic and rheology. The relationship between hydrodynamic parameters and characteristic rheological index is established. Maps of critical velocity, power-law index n, and consistency coefficient k are depicted for the semi-solid slurries. Then experiments and corresponding multiphase simulations were conducted to verify this theory. The macroscopic and microscopic linkage mechanism was proposed based on the theoretical discussion. This investigation not only provides important insights into the flow map of the semi-solid slurry, but also offers a key criterion of filling velocity for the avoiding of phase segregation for shear-thinning non-Newtonian fluids.