Pressure Die Cast Aluminum Alloy Research Articles

Numerical Determination of Initiation Fracture Toughness of High-Pressure Die Cast Aluminium Metal Matrix Composite Material Using FEM Analysis

The critical stress intensity factor for high-pressure die casted aluminium metal matrix composite material is rarely reported in the literature. The understanding of this parameter is very much essential for exploring the application of this material in automobile and aviation industries relying on light-weight materials. In the present study, critical stress intensity factor for pressure die cast aluminium alloy (ADC12) has been determined numerically, which compares well with experimental values. The variation due to fracture specimen thickness and relative crack size is also studied for the material.

Characterization and Analysis of Porosities in High Pressure Die Cast Aluminum by Using Metallography, X-Ray Radiography, and Micro-Computed Tomography.

Mechanical performance of cast aluminum alloys is strongly affected by the defects formed during solidification. For example, fractography studies of the fatigue specimens have shown that fatigue failure in aluminum castings containing defects is almost always initiated from defects, among which pores are most detrimental. However, elimination of these pores is neither always economically nor technically possible. This work characterizes defects in high pressure die cast aluminum alloy as an illustrative material, but the methods used can be applicable to other types of castings and defects. The defects were evaluated using metallography as well as micro-computed tomography techniques. The variability of defects between the specimens of two sizes as well as different porosity levels are studied statistically. The distributions of defects based on location within the specimens are also analyzed. Moreover, the maximum defect size within the specimens are estimated using extreme value statistics, which can be used as an input to fatigue life prediction models. Extreme value statistics is applied on both 2D and 3D defect data. The accuracy of each approach is verified by comparing the estimated maximum defect size within the specimens with the maximum observed defects on fracture surfaces of fatigue specimens.

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.

The Effect of Natural Pre-Ageing on the Mechanical Properties of Rheo-High Pressure Die Cast Aluminium Alloy 2139

Near-net shape casting of wrought aluminium alloys has proven to be difficult due to hot tearing. The Council for Scientific and Industrial Research (CSIR) has successfully processed wrought aluminium alloy 2139 into plate castings using the Rheo-high pressure die casting process (R-HPDC). Alloy 2139 is a Ag-containing aluminium alloy from the Al-Cu-Mg 2xxx series family. The addition of Ag enhances the age hardening response through the formation of co-clusters that act as precursors to the formation of plate-like Ω precipitates. These co-clusters typically form during natural ageing and 12-24 h of natural pre-ageing is normally specified before artificial ageing in Ag-containing Al-Cu-Mg alloys. The T6 hardness and tensile properties of R-HPDC 2139 alloy were investigated with and without natural pre-ageing. It is shown that there is no significant difference in both peak hardness and tensile properties in R-HPDC alloy 2139 with and without natural pre-ageing. The possible precipitation phenomena in both cases are discussed.

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

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.

A neural-network approach to describe the scatter of cyclic stress–strain curves

In order to predict a product’s durability in the early phases of development it is necessary to know the stress–strain behaviour of the material, its resistance to fatigue and the loading states in the material. These parameters, however, tend to exhibit a considerable degree of uncertainty. Due to a lack of knowledge of the actual circumstances in which the product is used, during the early development phase, simulations based on statistical methods are used. The results of the experiments show that the cyclic stress–strain curves demonstrate not only a large amount of scatter, but also a dependence on the temperature, the size of the cross-section, the content of alloying elements, the loading rate, etc. This article presents a method for modelling cyclic stress–strain curve scatter using a hybrid neural network for an arbitrary selection of the influencing factors. In an example of the measured data for a high pressure die-cast aluminium alloy it is clear that the suggested method is suitable for describing cyclic stress–strain curves. The main advantage of a hybrid neural network in comparison with a conventional method is the neural network’s ability to precisely describe the influence of various factors, and their combinations, based on the form and scatter of the cyclic stress–strain curve families. Defining the model parameters, i.e., training the neural network, is a procedure that does not require any additional user interventions; however, it enables us to gather knowledge that would otherwise require a lot of research. Thus, the trained neural network is a robust tool that can be used to predict cyclic stress–strain curves for random values of influencing factors. The capabilities of the presented method are only limited by the quantity of the measured data used for the neural-network training.

Friction Stir Welding of Aluminium High Pressure Die Castings: Parameter Optimisation and Gap Bridgeability

It is well established that friction stir welding (FSW) allows joining of aluminium alloys which can hardly be fusion welded. A well-known limitation of weldability in aluminium alloys is high hot crack sensitivity, such as encountered in Al-Cu and Al-ZnMgCu alloys. The weldability of cast alloys containing a significant amount of gases with MIG, TIG or laser welding is however also significantly compromised due to the occurrence of porosity, blowholes and cracks in the fused metal. In this study, the high pressure die cast aluminium alloy EN AC-46000-F, which belongs to the latter category of alloys with strongly reduced weldability, is successfully joined with the FSW technique. The selection of optimum welding conditions is discussed as function of the tensile properties and salient microstructural features. Moreover, the gap bridging ability of the FSW process is highlighted, by demonstrating the influence of weld gap on joint strength and the occurrence of weld flaws.

615 疲労過程におけるADC12内部にある巨視的鋳造欠陥のX線CT観察(GS.F-3 疲労)

Aim of this study is to unravel the effect of macroscopic casting defects on fatigue life of pressure die cast aluminium alloy. Macroscopic casting defects are highly dependent on the product shape or casting process. Therefore, a methodology of fatigue design is strongly demanded to take account of casting defects specific to the product. In this study, observation of casting defects by X-ray CT and tension-compression fatigue test are carried out. Three-dimensional image processing visualizes actual shape and configuration of casting defects, such as porosities, in the specimen before fatigue test. Visualization of porosities during fatigue test or after failure can also be used to investigate the fracture process. We found that crack initiation is almost restricted to from surface or near-surface defects, and shrinkage porosities can accelerate the crack propagation and reduce the failure life. Moreover, a plane defect, which was hardly observed by the X-ray CT, extremely decreased the fatigue life notwithstanding its location.

Casting defects and fatigue strength of a die cast aluminium alloy: a comparison between standard specimens and production components

The influence of casting defects on static and fatigue strength is investigated for a high pressure die cast aluminium alloy. Defects exist in gas and shrinkage pores as well as cold fills, dross and alumina skins. For the three batches of specimens, differing for the sprue–runner design, the influence was straightforward, while no significant variation in the fatigue strength was observed when looking at batches of “acceptable” and “non-acceptable” components, as judged within the foundry quality control. In this case, defects count for their size and location, while quality control often takes no account for component working conditions. The Haigh diagram shows a good matching between the specimen reference material and the component fatigue data.

Influence of Cutting Parameters on Residual Stresses Induced by Milling in Pressure Die-Cast Aluminum Alloy Components

Residual stress states, induced by milling in a die cast aluminum alloy component, have been determined by means of X-ray diffraction. Samples have been cut from an automotive engine sump, fabricated by pressure die-casting. The X-ray experimental apparatus has been calibrated by detecting stresses on a sample bent under imposed external deformations. Different samples (cut from the sump) have been tested after milling operations with each one characterized by different cutting speed, feed speed and depth of cut in order to evaluate their influence on the final residual stress state. Results have been analyzed taking into account surface morphologies after milling, as revealed by scanning electron microscopy.

Fracture analysis of wheel hub fabricated from pressure die cast aluminum alloy

A catastrophic failure of wheel hub occurred during service. The nature of failure was a corner crack emanating from a spoke hole. An analytical investigation was carried out using the tool of Linear Elastic Fracture Mechanics to establish the cause of failure. The nonlinear behaviour is due to the presence of material inhomogeneities and micro-discontinuities. Plastic zone correction is made. The presence of material inhomogeneities and micro-discontinuities tend to alter the conditions near the crack tip. An analytical estimation was carried out in order to calculate the minimum number of cycles covered by the wheel hub in service. The initiation of crack growth is complex because of heterogeneity and morphology of the fracture surface. Fractographic and metallographic studies are carried out to assist the understanding of the corner cracking problem.