High Pressure Die Casting Research Articles

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.

Microstructural, microscratch and nanohardness mechanical characterization of secondary commercial HPDC AlSi9Cu3-type alloy

A key issue in producing high quality aluminum automotive components using High-Pressure Die Casting (HPDC) process is minimizing the amount of imperfections. In the present research work, by means of optical microscopy (OM), SEM, TEM and AFM characterization techniques, microstructural evolution of secondary commercial HPDC AlSi9Cu3-type alloy was studied. For this purpose, one Al-alloy called C1 containing nominal composition and a second one called C2 going out of specification were employed. In addition to metallographic characterization, Vickers and nanohardness and microscratch mechanical testing techniques were applied to analyze material behavior. Furthermore, complementary thermodynamic calculations were done to estimate alloy phases precipitation as function of temperature. Results indicate that globular and ramified dendrites are developed in C1 and C2 Al-alloys, respectively, due the major solidification time between them. In fact, gas porosity and shrinkage microporosity were detected. α-Fe particle increased in size but not in volume fraction, as Al2Cu and β-Fe intermetallics do. Mostly, it was found that α-Fe particle growth following a coring behavior, formed by nanospherical particles. Thus, main shrinkage microporosity is associated with Al2Cu precipitate, where shrinkage pores in alloy C2 present several nanoparticles located between dendrite arms, identify by SEM and TEM analysis. Finally, hardness of alloys differs in 30 HV values due intermetallics population, whereas nanohardness allowed measuring single value of each phase. Because no major nanohardness differences were observed, microscratch resistance behaves similar in both alloys. Hence, present microstructural/mechanical characterization results can be taken into account for redesign and improving commercial HPDC Al-components.

Effects of glass fiber size and content on microstructures and properties of KNO3-based water-soluble salt core for high pressure die casting

The water-soluble salt core with higher bending strength and toughness is necessary to withstand the high pressure needed to manufacture some complex parts by high pressure die casting (HPDC). In this paper, the effects of glass fiber size and content on microstructures and properties of KNO3-based (KNO3-30 mol%KCl) water-soluble salt core were systematically studied. The results showed that increasing the glass fiber content greatly improved the bending strength and impact toughness of the KNO3-based salt core, decreased the water solubility rate and increased the humidity resistance. In addition, increasing the glass fiber size sharply enhanced the impact toughness of the KNO3-based salt core, while decreasing the bending strength, water solubility rate and humidity resistance. The maximum bending strength and impact toughness of the reinforced KNO3-based salt core with the glass fiber were, respectively, 41.32 ± 0.38 MPa and 2.146 ± 0.108 kJ/m2, which were 55.9% and 315.1% higher than those of the unreinforced KNO3-based salt core, respectively. The microstructures show that the glass fibers were evenly distributed in the KNO3-based salt core, which significantly refined the KCl primary phases, especially for the 12.5-μm glass fiber. Meanwhile, many fiber pull-out holes were observed in the KNO3-based salt cores with 75-μm and 25-μm glass fiber. The grain refinement, fiber pull-out and crack deflection were the main mechanism for improving the strength and toughness of the KNO3-based salt core.

Effect of Material Segregations Due to Squeeze Parameters on Mechanical Properties of High Pressure Diecast Parts

Abstract This article is a research on the effect of material segregations due to squeeze parameters on mechanical properties of high pressure die cast parts. The technology of squeezing is applied in high pressure die casting technology with the aim to improve the internal material health of the castings from aluminium alloys, such as AlSi9Cu3(Fe), components incorporated in assemblies as mechanical and hydraulic parts. The objective of this article is to determinate the influence of the secondary effects of squeeze technology on the mechanical properties of parts produced from AlSi9Cu3(Fe) alloys, with HPDC technology.

Influence of porosity characteristics on the variability in mechanical properties of high pressure die casting (HPDC) AlSi7MgMn alloys

To reveal the influence of porosity on the variability in mechanical properties of HPDC Al alloys, micro computed tomography was employed to investigate the morphology and 3D distribution of porosity in the tensile samples. Experimental results show that the variability in mechanical properties of HPDC AlSi7MgMn alloy is related to the pore size and total volume of the porosity. The maximum pore size is inversely proportional to the elongation of the alloy with T6 heat treatment, while the total volume porosity was found to decline with increasing elongation. A maximum pore size of approx. 1.3 mm in diameter was found to correspond to an elongation of 6.4%. Once its maximum size reduced to less than 0.3 mm, the elongation was found to improve to 9%-13.5% for the alloy. Compared to the average value of 8.8%, 236.6 MPa, 296.0 MPa for elongation, yield strength and ultimate tensile strength respectively for the porosity-free AlSi7MgMn samples produced by gravity casting, the HPDC AlSi7MgMn alloy has the similar strength level and improved elongation to an average level of 11.5%. This indicates that the porosity level is a determined factor to the mechanical property variability and its size less than 0.3 mm has no significant adverse effect on the mechanical properties of the alloy. The elongation improvement in HPDC AlSi7MgMn alloy is attributed to the finer grain size with an average value of 10 μm compared to the average value of 500 μm for the gravity casting AlSi7MgMn alloy, and to the reduced size and uniform distribution of porosity resulting from the subsequent refinement in grain size.

Fluidity of Alloys Under High-Pressure Die Casting Conditions: Flow-Choking Mechanisms

Theories on fluidity of alloys based on the solidification mode are not satisfactory in describing fluidity of alloys under high-pressure die casting (HPDC) conditions. To understand the flow-choking mechanisms under HPDC conditions, microstructure in the fluidity test coupons made using a 125-ton HPDC machine was characterized. Pre-solidified dendrites (PSDs), or externally solidified crystals (ESCs), which were formed in the shot sleeve, were found in the runners as well as in the fluidity casting. Surprisingly, a large amount of PSDs are collected in the runner adjacent to the in-gate, forming a PSD core with a thin layer of PSD-less or PSD-free region near the surfaces of the runner due to Magnus effect. Analytical calculations were performed to estimate the pressure drop for molten aluminum flowing through the mushy PSD zone. The results indicate that the pressure drop is comparable to the maximum pressure that was used for injecting molten metal to fill the casting. When the pressure drop is equal to the pressure driving the mold filling, the metal ceases to flow. Thus, it is the PSDs that are responsible for the choking of mold filling either mechanically at the in-gate or providing a pressure drop high enough to resistant fluid flow.

Multi-scale simulation of hybrid light metal structures produced by high pressure die casting

In modern automotive structural components, metal sheets are combined with casting parts to enable a light and mechanical stable structure. In this study, the bonding between steel metal sheets and aluminium casting parts are performed as part of the high pressure die casting (HPDC) process. In this way additional bonding steps like welding can be omitted, which saves time and energy. The combination of sheet metal and cast is achieved by a structured surface (ribs) of the sheet, which is filled in the casting process with the liquid aluminium alloy and leads to a mechanical connection after solidification. Coupled flow and solidification simulation is used to analyse the hybrid casting process with a focus on the rapid solidification inside the ribs. A high-resolution (mesoscale) simulation of the interface between metal sheet and aluminium alloy during filling and solidification can capture the details of melt flow and rapid solidification. By coupling the mesoscale flow and solidification simulations to multiphase field simulations on the microscale, the resulting microstructure can be calculated. The solidification conditions inside the ribs as result of the mesoscale simulation can be validated by comparing the calculated microstructure with experimental results found in real castings, performed on a cold-chamber HPDC machine.

Fatigue testing and non‐destructive characterization of AlSi9Cu3(Fe) die cast specimens by computer tomography

AbstractAlSi9Cu3(Fe) aluminum alloy fatigue test specimens were produced by high pressure die casting (HPDC) and vacuum‐assisted die casting (VPDC) techniques. Non‐destructive material tests (NDT) have been performed on cast specimens by computed tomography (CT). Uniaxial fatigue tests with two stress ratios of R = −1 and R = 0.1 have been performed in the high cycle fatigue (HCF) regime, and the CT results were reassigned after the fatigue test in order to identify the origin of the failure. The aim of this paper is to establish a relationship between the CT result and fatigue failure of die cast specimens. The location and the size of the casting defect determine the specimen fatigue life. It has also been found that the fatigue life is determined not only by the size of the defect but also by its location with respect to the position of the highly stressed area. The results can be used to judge the applicability of cast parts after non‐destructive testing.

Analysis of a Special, 3D Metal-Printed HPDC Tool Material

High Pressure Die Casting (HPDC) is still the most productive metal-casting method of our time, however the more demanding are the industrial expectations, the more challenging it becomes to ensure the creation of the difficult cavity geometries and the thermal balance of the die-cast tool. New perspective is required, thus we can utilize high heat-conductivity tool steels and additive manufacturing technology.

Thermal Fatigue Testing of SiMoCr Compacted Graphite Cast Iron for HPDC Tooling Application

SiMoCr CGI (compacted graphite iron) has the potential to be a cost-effective replacement for some hot working tool steel parts like shot sleeve in HPDC (High-Pressure Die Casting) applications. Thermal fatigue testing of SiMoCr CGI cast alloy was performed on Gleeble 1500D machine. Cracks were evaluated on non-nitrided and nitrided samples at test temperatures of 400 and 600 °C, after 1000, 2000 and 4000 thermal cycles. Samples were heated to prescribed test temperature and afterward cooled in computer-guided cycles. After the test, all the samples were axially and radially sectioned and cracks on cross sections were evaluated. Length of all cracks which occurred was measured and statistically evaluated, i.e., the average length of cracks and distribution of crack lengths were determined. At nitrided samples, higher values for average crack lengths were obtained while density of cracks was lower in comparison with non-nitrided samples.

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.

Influence of pore characteristics and eutectic particles on the tensile properties of Al–Si–Mn–Mg high pressure die casting alloy

Heterogeneous microstructure and unpredictable porosity distribution in Al–Si high-pressure die-castings give rise to a significant variation in their mechanical properties. This study investigated the influence of porosity distribution, volume of the largest pore, eutectic phase morphology and Mn-containing intermetallics on the tensile properties of Al–Si–Mn–Mg high-pressure die-castings. The as-cast material has a “network” of fine coralloid eutectic Si as well as blocky AlSiFeMn intermetallics in interdendritic area. The solution treatment step of the T7 heat treatment spheroidized the eutectic silicon. Tensile samples were tested in both the as-cast and T7 conditions. The yield strength (YS), ultimate tensile strength (UTS) and elongation (%E) of as-cast samples were in the ranges of 129–146 MPa, 242–282 MPa and 2.6–4.7%, respectively. After T7 heat treatment the YS, UTS and %E had ranged from 124-142 MPa, 195–207 MPa and 4.6–12.1%, respectively. The T7 heat treatment had little effect on the YS but reduced the UTS considerably. The enhanced %E can be ascribed to the spheroidization of eutectic Si. The largest pore by volume in the sample also plays an important role in determining the ductility according to three-dimensional (3D) pore morphologies obtained via computed tomography (CT). The sample with largest pore by volume has the lowest %E, indicating the %E can be estimated prior to tensile test based on the size of the largest pore by volume in the sample.

Linear Elastic FE-Analysis of Porous, Laser Welded, Heat Treatable, Aluminium High Pressure Die Castings Based on X-Ray Computed Tomography Data.

The welding of aluminium high pressure die castings is a well known and broadly investigated challenge in various fields of industry and research. Prior research in this specific field mainly focused on the optimisation of the welding and the casting process and on the cause of the frequently occurring porosity and incomplete fusion phenomena, whereas the impacts of these defects have hardly been addressed. Therefore, the underlying study presents the investigation of weldments in EN AC-AlSi10MnMg high pressure aluminium die castings by linear elastic finite element analysis based on X-ray computed tomography as a novel approach. Hereby, four laser weldments with differing surfaces and pore contents were investigated by X-ray computed tomography and tensile testing. Based on the voxel datasets of the porous weldments, triangular finite element meshes were generated and a numerical finite element analysis was conducted. Good agreement of the stress–strain curves between the simulations and the experiments was achieved.

Al8Mn5 in High-Pressure Die Cast AZ91: Twinning, Morphology and Size Distributions

Manganese-bearing intermetallic compounds (IMCs) are important for limiting micro-galvanic corrosion of magnesium-aluminum alloys and can initiate cracks under tensile load. Here, we use electron backscatter diffraction (EBSD), deep etching, and focussed ion beam (FIB) tomography to investigate the types of Al-Mn phases present, their faceted growth crystallography, and their three-dimensional distribution at different locations in high-pressure die cast (HPDC) AZ91D. The Al-Mn particle size distributions were well-described by lognormal distributions but with an additional population of externally solidified crystals (ESCs) formed in the shot chamber analogous to α-Mg ESCs. The large Al8Mn5 particles were cyclic twinned. Differences in the particle size distributions and number density in the center compared with the HPDC skin are identified, and the spatial relationship between Mg17Al12 and Al-Mn particles is explored.

Die design and optimization of cooling channel position for cold chamber high pressure die casting machine

A well-designed gating system for pressure die casting has always been of great importance to achieve good quality castings. However, the cooling system employed in the die and its position has found to have a significant impact on the generation of stresses in the die. High stress concentrations contribute to the erosion of cavity surface thereby affecting the tool life and casting quality. The objective of this research work is to design a die and to analyse the effect of positioning of the cooling channels on the generation of stresses on the cavity surface. In this study, a runner gate system is designed for an ADC 12 aluminium alloy component that is to be cast on a Cold Chamber High Pressure Die Casting (HPDC) machine. Stress analysis and optimization of the cooling channel positionof the die is carried out using ANSYS Workbench. Flow simulation of the optimized design is carried using MAGMA software to understand the effect of cooling channel position on the flow characteristics. The results demonstrate the impact of cooling channel position on the stresses generated in the die and prove to be valuable in designing the die. Defect inspection and testing of porosity is carried out on the castings produced with the optimized design in operation to check if they are acceptable.

Evaluation and Implementation of a Fundamental Model for Interfacial Heat Transfer Coefficient in High-Pressure Die-Casting

In the present study, the fundamental model for interfacial heat transfer coefficient (IHTC) in high-pressure die-casting (HPDC) developed by Hamasaiid et al. is re-examined using numerical simulations and established literature. The role of impact pressure on the peak IHTC is re-evaluated for the Aluminum alloy Al-9Si-3Cu and the magnesium alloy AZ91D. Currently, ANSYS FLUENT does not have a mesh independent model for air gap evolution at the die-casting boundary. To address this, an implementation of the Hamasaiid model is built for ANSYS FLUENT 18.1 and its results are compared to experimental work. All the derivations and code for the simulations are offered as open source under the GNU General Public License v3.0.

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.

ALCOA EZCAST 370

Abstract Alcoa EZCast 370 is a heat-treatable, aluminum-silicon-magnesium-manganese high-pressure die casting (HPDC) alloy which is widely used for thin-walled, crash-resistant, structural components for automotive applications. This datasheet provides information on composition, physical properties, and elasticity. It also includes information on joining. Filing Code: Al-461. Producer or source: Alcoa Corporation.

Automatically weighted high-resolution mapping of multi-criteria decision analysis for sustainable manufacturing systems

A common feature of Multi-Criteria Decision Analysis (MCDA) to evaluate sustainable manufacturing is the participation (to various extents) of Decision Makers (DMs) or experts (e.g. to define the importance, or “weight”, of each criterion). This is an undesirable requirement that can be time consuming and complex, but it can also lead to disagreement between multiple DMs. Another drawback of typical MCDA methods is the limited scope of weight sensitivity analyses that are usually performed for one criterion at the time or on an arbitrary basis, struggling to show the “big picture” of the decision making space that can be complex in many real-world cases.This work removes all the mentioned shortcomings implementing automatic weighting through an ordinal combinatorial ranking of criteria objectively set by four pre-defined weight distributions. Such solution provides the DM not only with a fast, rational and systematic method, but also with a broader and more accurate insight into the decision making space considered. Additionally, the entropy of information in the criteria can be used to adjust the weights and emphasise the differences between potentially close alternatives.The proposed methodology is derived generalising a problem of material selection of automotive parts in metal casting manufacturing systems. In particular, three typical aluminium, magnesium and zinc alloys in a High-Pressure Die Casting (HPDC) process are compared using the deterministic Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) combining 18 criteria organised in 4 main categories (cost, quality, time and environmental sustainability). A detailed and systematic approach to calculate the considered criteria is also provided and it includes Life Cycle Assessment (LCA) considerations. Results show that, although in most of the cases the aluminium alloy is the best option, there are a few areas in the decision making space where magnesium and zinc alloys score better without a simple correlation to categories. This shows how valuable the proposed mapping process is to understand the complex MCDA analyses. The methodology does not make specific assumptions about metal casting and can be applied to sustainable manufacturing in general.

Numerical and Experimental Analysis on Runner and Gate Positioning for Magnesium Alloy Die-Casted Test Piece

High Pressure Die Casting (HPDC) is a manufacturing process producing complex and precise products by injecting molten material into mold cavity at top speed and pressure. The quality of product is highly related with mold cavity design. Casting defects due to inappropriate mold design will affect mechanical properties, surface quality and product life cycle. Optimization of runner system is essential to manufacture complex and precision product design with minimal defects. The combination of runner and gating system is investigated in this paper. This paper investigated the effect of runner and gating optimization in reducing the gas porosity inside casting by evaluating the fluid and thermal distribution behavior in experimental and Computational Fluid Dynamic (CFD). The gas porosity generated in the molten magnesium alloy is due to the turbulent flow and the inconsistency of the fluid flow to push the gas bubble away from the main casting. This paper includes an X-ray of a sample product that shows correlation between gas porosity and CFD results. Results show that localize porosity gathered at the bottom of the main casting. Based on localized porosity position, runner and gating system is modified and numerical simulation is carried out for analysis. An inspection instrument step-type test piece is taken as an investigation sample to illustrate the technique of design modifications and improvements. Process parameters considered in this paper are injection speed, injection pressure, melt temperature and mold temperature. This paper proposed new runner designs that can generate balanced velocity and temperature distribution inside mold cavity, improving the solidification process aimed for reducing casting defects.