High Pressure Die Cast Aluminum 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.

Defect Susceptibility of Tensile Properties to Microporosity Variation in High-Pressure Die-Cast Aluminium Alloy Controlled by Gas Bubbling Flotation Treatment

This study aims to investigate the variability in the tensile properties of high-pressure die-cast aluminium alloy controlled by the gas bubbling filtration or flotation (GBF) process in terms of the defect susceptibility of tensile properties to the variation in the overall microporosity level, including bifilm oxide and pre-existing microvoids. Test specimens were fabricated by adopting a high-pressure die-cast process of the cold chamber type at the production scale using A384.0 aluminium alloy. The volumetric porosity of cast specimens gradually decreased with GBF treatment, even though the fractographic porosity tended to decrease only under a specific GBF condition, with a remarkable microstructural refinement. The degassing treatment of 5 min could achieve a remarkable grain refinement, and further, this optimal condition could induce a practical improvement in the defect susceptibility of tensile properties to microporosity variation as well as the nominal level of tensile properties. The main reason for grain refinement in GBF treatment is the dispersion of small-sized pro-eutectic solid particles by fragmentation of abnormally big-sized dendrites, which are preferentially formed by an undercooling effect in a region around the impeller and gas inlet. Additionally, the improvement in melt quality by degassing action for dissolved hydrogen gas is practically nullified through the coarsening of pro-eutectic solid particles as well as the additional inclusion of bifilm oxide by excessive GBF treatment.

A Tool for Predicting the Effect of the Plunger Motion Profile on the Static Properties of Aluminium High Pressure Die Cast Components

The availability of tools for predicting quality in high pressure die casting is a challenging issue since a large amount of defects is detected in components with a consequent worsening of the mechanical behavior. In this paper, a tool for predicting the effect of the plunger motion on the properties of high pressure die cast aluminum alloys is explained and applied, by demonstrating its effectiveness. A comparison between two experiments executed through different cold chamber machines and the same geometry of the die and slightly different chemical compositions of the alloy is described. The effectiveness of the model is proved by showing the agreement between the prediction bounds and the measured data. The prediction model proposed is a general methodology independent of the machine and accounts for the effects of geometry and alloy through its coefficients.

Experimental and boundary element method study on the effect of stress on the polarization curve of cast aluminum alloy in sodium chloride solution

The effect of stress on the polarization curve of high pressure die cast aluminum alloy in sodium chloride solution was evaluated by mechano-electrochemical experiments and boundary element electrostatics simulations. The polarization curve was measured under a constant stress condition, and a decrease in natural potential due to stress was observed. A periodic arrangement of intact and damage surfaces was assumed in the mechanically damaged oxide film, and the polarization curve of the damage surface was identified. The simulation results showed that the decrease in natural potential is explained by the nucleation of the damage surface by plastic strain.

Investigation on the cold rolling and structuring of cold sprayed copper-coated steel sheets

A current driving force of research is lightweight design. One of the approaches to reduce the weight of a component without causing an overall stiffness decrease is the use of multi-material components. One of the main challenges of this approach is the low bonding strength between different materials. Focusing on steel-aluminum multi-material components, thermally sprayed copper coatings can come into use as a bonding agent between steel sheets and high pressure die cast aluminum to improve the bonding strength. This paper presents a combination of cold gas spraying of copper coatings and their subsequent structuring by rolling as surface pretreatment method of the steel inserts. Therefore, flat rolling experiments are performed with samples in “as sprayed” and heat treated conditions to determine the influence of the rolling process on the bond strength and the formability of the coating. Furthermore, the influence of the rolling on the roughness and the hardness of the coating was examined. In the next step, the coated surface was structured, to create a surface topology suited for a form closure connection in a subsequent high-pressure die casting process. No cracks were observed after the cold rolling process with a thickness reduction of up to ε = 14 % for heat treated samples. Structuring of heat treated samples could be realized without delamination and cracking.

Simultaneous Effect of Plunger Motion Profile, Pressure, and Temperature on the Quality of High-Pressure Die-Cast Aluminum Alloys

High-pressure die casting has been used widely to manufacture a large variety of products with high dimensional accuracy and productivity. Although this process has a considerably lower cycle time than the other metal forming processes, it is not yet optimized, due to the complexity of the process and the number of parameters to be controlled. Hence, the identification of the parameters affecting quality of castings is the current challenge toward efficient and effective production. In their previous work, the authors proposed and validated some novel kinematic parameters of the plunger, which explain and forecast both the static mechanical properties and the internal quality of castings. The present work extends such an approach by including two other meaningful parameters, which describe the effect of upset pressure and temperature on the final outcome. These parameters are here formulated and have been validated by means of a statistically significant sample manufactured with different plunger motion profiles, upset pressures, and temperatures of the melt and die. The quality of the castings was assessed through static mechanical properties and density measurements. As further proof, internal defects were analyzed on the fracture surfaces of some meaningful castings.

Plunger Kinematic Parameters Affecting Quality of High-Pressure Die-Cast Aluminum Alloys

The selection of the optimal process parameters in high-pressure die casting has been long recognized as a complex problem due to the involvement of a large number of interconnected variables. Among these variables, the effect of the plunger motion has been proved to play a prominent role, even if a thorough and exhaustive study is still missing in the literature. To overcome this gap, this work aims at identifying the most relevant plunger kinematic parameters and estimates their correlation with the casting quality, by means of a statistically significant sample manufactured with different plunger motion profiles. In particular, slow and fast shot velocities and switching position between two stages have been varied randomly in accordance with design of experiment methodology. The quality has been assessed through the static mechanical properties and porosity percentage. As a further proof, the percentage of oxides has been estimated on the fracture surfaces. These measurements have been correlated to novel parameters, representing the mechanical energy and the inertial force related to the plunger motion, that have been extracted from the time-history of the displacement curves. The application of statistical methods demonstrates that these novel parameters accurately explain and predict the overall quality of castings.

A Numerical and an Experimental Investigation of a High-Pressure Die-Casting Aluminum Alloy

In this paper, a computer simulation of a high-pressure die casting of aluminum alloy was performed using a commercially available software and also compared with the real castings of the same alloy. The commercial aluminum alloy was Etial 150 (AlSi12Cu) that is used for flange which is a washing machine part. Mold filling, solidification, temperature distribution, porosity, and velocity of the liquid metal during high-pressure die casting were investigated using the model through numerical simulation. The simulation results proved that the model values used in simulations were accurate in order to apply for experimental casting. After this numerical model, the flange part was cast experimentally according to the obtained optimum parameters from simulation results. Then, specimens from the experimental casting were tested for tensile, hardness, and microstructure analyses. Accordingly, the test results are rather sound which demonstrates that simulation provides profitable die casting. Consequently, it was observed from this study that simulation is not only useful for enhancing casting quality but also very economical and practical, which helps to reduce time spent on experiments. Moreover, simulation can reveal porosity and helps to minimize this defect. Thus, computer simulation should be used for casting applications more often, and simulation programs should be developed further.

Chemical pretreatment and adhesive bonding properties of high-pressure die cast aluminum alloy: AlSi10MnMg

High-pressure die cast (HPDC) aluminum components are increasingly integrated into the assembly of vehicles for weight-reduction. Adhesive bonding of HPDC aluminum alloys with other structural parts has been ever challenging in the hybrid construction of automobiles due to the inherent contamination of casting surfaces by die lubricants. In this study, the residual lubricant on HPDC AlSi10MnMg plates was quantitatively measured using surface sensitive techniques. Chemical pretreatment processes were designed and the effectiveness of pretreatment processes was evaluated by comparison of surface morphologies and chemical compositions, as well as adhesion properties before and after aging. It is found that the initial single lap-shear strength of the as-cast AlSi10MnMg plates shows a location-dependence and is influenced by casting parameters, particularly in the regions away from the melt-ingate of the die, where a high amount of residual lubricants is often measured. Chemical pretreatments including degreasing, deoxidation and deposition of titanium-oxide conversion coatings can improve the surface homogeneity through removal of residual lubricants from and replacement of oxide layers at the surface of HPDC AlSi10MnMg alloys. The chemical treatment process consisting of degreasing in alkaline solutions, deoxidation in fluoride-containing sulfuric acid solutions and dipping in hexafluorotitanic acid solutions has been identified to be the most effective pretreatment procedure by generating a rough surface in a micro-scale, and removing residual lubricants to a large extent from as well as inhibiting corrosion at the surface of HPDC AlSi10MnMg plates. The effectiveness of this pretreatment process was also confirmed by durability assessment of epoxy-bonded single lap-shear joints and wedge specimens after environment exposure to 70°C, 100% R. H. for 4 weeks.

Experimental, theoretical and numerical fatigue damage estimation using a temperature modified Dirlik method

This article describes experimental, theoretical and numerical fatigue damage estimation using a temperature modified Dirlik method. The method enables an estimation of high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from power spectral analyses with the temperature effect. Preliminary investigations of high cycle fatigue properties of high pressure die-cast aluminium alloy AlSi9Cu3 have been carried out at elevated temperatures. Standard and non-standard fatigue tests have been performed to determine the temperature dependent S–N curves. Simultaneously, fatigue damage estimation was carried out numerically with commercial programmes Ansys Workbench and LMS Virtual.Lab using finite element methods. Finally, the numerical simulation results are compared with both experimental and theoretical results. The temperature modified Dirlik method enables a computationally fast fatigue damage estimation of random stress loadings and temperature histories.

GS0606-436 アルミニウム合金ダイカストの電気化学特性に対する応力と鋳肌の影響

GS0606-436 アルミニウム合金ダイカストの電気化学特性に対する応力と鋳肌の影響

Closed Chain Simulations of a Cast Aluminium Component - Incorporating Casting Process Simulation and Local Material Characterization into Stress-strain Simulations

The coupling between simulations of solidification, microstructure and local mechanical behaviour and simulation of stress-strain behaviour is studied by applying a recently developed simulation strategy to a high pressure die cast aluminium component. In the simulation strategy, named a closed chain of simulations for cast components, the mechanical behaviour throughout the component is determined locally by a casting process simulation. The entire casting process, including mould filling and solidification, is simulated to predict the formation of microstructure and residual stresses throughout the component, and material characterization models are applied to relate microstructural features to local elastic and plastic mechanical material behaviour. The local material behaviour is incorporated into a finite element method (FEM) stress-strain simulation of a realistic load case of the component in service.In the current contribution the influences of local variations in mechanical behaviour and residual stresses on the component behaviour are investigated. The simulation results for local microstructure and mechanical behaviour are compared to experimental results, and the predicted local mechanical behaviour is incorporated on an element level into the FEM simulation. The numerical effect of the variations in mechanical behaviour is quantified by comparing the results achieved using local behaviour and homogeneous behaviour. The influence of residual stresses predicted by the casting process simulation on the component behaviour is also studied.The casting process simulation is found to accurately predict the local variations in microstructure throughout the component, and the local variations in mechanical behaviour are well described. The numerical results show that casting process simulation and modelling of microstructure formation, material behaviour and residual stresses are important contributions to correctly predict the behaviour of a cast aluminium component in service. This motivates the use of the proposed simulation strategy, and show the importance of incorporating materials science and casting process simulations into structural analyses of cast components. It is discussed that integration of these areas, e.g. using the closed chain of simulations, is important in order to increase the accuracy of FEM simulations and the product development efficiency in the future.

GS01 塩水中引張応力下におけるAl合金ダイカストの腐食特性

Effect of tensile stress on the corrosion potential of high pressure die cast aluminum alloy was examined by the tensile test in a corrosive environment with the electrochemical measurement. The aluminum alloy has an oxide film as a corrosion barrier, but the oxide film may partially break by the mechanical stress and the damage leads to a local corrosion such as pitting corrosion by the effect of local cell. To qualitatively evaluate the strength of corrosion fatigue or stress corrosion cracking, the effect of stress on the electrochemical property has to be clarified. The spontaneous potential difference was measured by the three-electrode system during the tensile test, and the relationship between the spontaneous potential and the tensile stress was evaluated. The results showed that the spontaneous potential certainly decreased within the elastic region and saturated after the yielding. The effect of casting skin was also examined, and the spontaneous potential decreased due to the deletion of the casting skin.

Validation of temperature modified Dirlik method

The paper presents the validation of a temperature modified Dirlik method. This method enables an estimation of high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from a known power spectral analysis with the temperature effect. High cycle fatigue properties of high pressure die-cast aluminium alloy AlSi9Cu3 are investigated at elevated temperatures. Standard fatigue tests are performed to determine the temperature dependent S–N curves. In the next step special fatigue tests are developed and performed to validate the temperature modified Dirlik method. Finally, the numerical simulation results are compared with the experimental results. The temperature modified Dirlik method is tested successfully. Besides, it enables a computationally fast fatigue damage estimation of random stress loadings and temperature histories.

Influence of Aging Temperatures and Times on Mechanical Properties of Vacuum High Pressure Die Cast Aluminum Alloy A356

In this study a number of thermal treatment schemes over a wide range of temperatures between 120˚ to 350˚ C and times (30 120 minutes) have been experimented in an effort to understand the effect of thermal treatment on tensile properties of vacuum die cast modified aluminum alloy A356. The results show that, the morphology of eutectic silicon has a sound effect on the tensile properties of the tested alloy. The content of magnesium-based intermetallic phases, their morphology and distribution throughout the matrix affect the mechanical properties of the aged alloy as well. The reduction in the strengths of the alloy treated at 350°C for two hours should be at least attributed partly to the absence of the magnesium-based intermetallic phase. However the presence of sufficient amount of magnesium intermetallic phase had played important role in strengthening the alloy thermally treated at 200°C for 90 minutes.

Influence of Aging Temperatures and Times on Mechanical Properties of Vacuum High Pressure Die Cast Aluminum Alloy A356

In this study a number of thermal treatment schemes over a wide range of temperatures between 120˚ to 350˚ C and times (30 120 minutes) have been experimented in an effort to understand the effect of thermal treatment on tensile properties of vacuum die cast modified aluminum alloy A356. The results show that, the morphology of eutectic silicon has a sound effect on the tensile properties of the tested alloy. The content of magnesium-based intermetallic phases, their morphology and distribution throughout the matrix affect the mechanical properties of the aged alloy as well. The reduction in the strengths of the alloy treated at 350°C for two hours should be at least attributed partly to the absence of the magnesium-based intermetallic phase. However the presence of sufficient amount of magnesium intermetallic phase had played important role in strengthening the alloy thermally treated at 200°C for 90 minutes.

Frequency based fatigue analysis and temperature effect

This paper proposes a temperature modified Dirlik method to estimate the high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from a power spectral analysis. Besides, the methodology for combining the frequency based fatigue analysis with the temperature effect is represented. This approach is based on a new definition of loading as a random Gaussian process. The fatigue damage estimation of the high pressure die-cast aluminium alloy AlSi 9Cu 3 is investigated at elevated temperatures. Finally, numerical simulations on the known power spectral densities with different shapes at different temperatures are performed in order to establish proper dependence between the temperature modified Dirlik method, the rainflow cycle counting, the linear cumulative fatigue damage and the spectral bandwidth parameters. The proposed method enables computationally fast fatigue damage estimation for the random loadings and the temperature histories.

Quantitative Evaluation of Porosity Effect on Fatigue Strength of High Pressure Die Cast Aluminum Alloy (Part 2, Fatigue Strength Prediction Based on Elastic Stress Field around Pores)

An empirical prediction method for the fatigue strength considering the effect of porosity was proposed. We prepared six types of specimen of ADC12 high pressure die cast aluminum alloy, where the casting condition was different to each other, and obtained the S-N curve for each specimen type from the fatigue test. The porosity volume fraction for all specimens was calculated using the X-ray CT images. The image-based finite element analysis was also carried out for all specimens to evaluate the maximum first principal stress corresponding to the nominal stress amplitude in the fatigue test. The maximum stress was referred to as the local stress amplitude, and its ratio to the nominal stress amplitude was defined as the local stress concentration factor. We modified the S-N data by using the local stress amplitude instead of the nominal stress amplitude, and obtained a single master S-N curve. From the statistical investigation, the local stress concentration factor was found to be determined empirically by the porosity volume fraction. The relationship was identified by the least-square approximation. Consequently, we found that the fatigue strength was predicted from the porosity volume fraction via the local stress amplitude and the master S-N curve.

Quantitative Evaluation of Porosity Effect on Fatigue Strength of High Pressure Die Cast Aluminum Alloy (Part 1, Experimental Investigation for Effect of Porosity and Casting Surface)

Effect of casting defects on the fatigue strength of die cast aluminum alloy was addressed through the tension-compression fatigue test and the X-ray CT inspection, which revealed the amount of porosity included in the specimen. Six types of casting condition were employed to examine the effect of different porosity. Most of fatigue crack sources were the pores. The porosity volume fraction was calculated for all specimens from the three-dimensional X-ray CT images. The fatigue limit of each specimen type was estimated from the fatigue test results. The correlations among fatigue limit, porosity volume fraction, Vickers hardness, and dendrite arm spacing were evaluated, and the result showed that the porosity volume fraction most dominantly affected the fatigue limit in the averaged sense.

Equivalent Elastic Property of Cast Aluminum Alloy around Clustered Shrinkage Pores

The mechanical properties of the clustered shrinkage pores in high-pressure die cast aluminum alloy ADC12 were evaluated through the serial sectioning experiment and the image-based finite element analyses. We have investigated the effect of pores on the fatigue strength, and found a mechanical significance of the clustered shrinkage pores, which considerably undermines the fatigue strength of die cast aluminum alloys. In this study, we constructed twenty three unit cell models for the homogenization analysis based on the three-dimensional image of a clustered shrinkage pore. From the homogenization analysis and uniaxial extension analysis, we obtained the equivalent elastic constants and the micro stress concentration factor as a function with respect to the porosity volume fraction.