High-pressure Die-cast Alloy Research Articles

Effect of chemical compositions on tensile behaviors of high pressure die-casting alloys Al-10Si-yCu-xMn-zFe

Effects of chemical compositions on the tensile properties, deformation behavior and fracture mechanism have been studied in a die-casting aluminum alloys Al-10Si-yCu-xMn-zFe. The test specimens were taken from the engine support brackets and tested at 20°C, 150°C and 300°C. Addition of Mn and Cu elements in the Al-10Si alloys can significantly increase the YS and UTS of the alloys. The as-cast Al-10Si-1.5Cu-0.8Mn-0.15Fe alloy exhibits the highest tensile properties (RT: YS of 190MPa and UTS of 308MPa, 150°C: YS of 176MPa and UTS of 249MPa, 300°C: YS of 94MPa and UTS of 111MPa). Increasing test temperature reduces the YS and UTS and improves the ductility of the alloys. Chemical compositions (such as Mn, Cu and Fe) do not significantly affect the work-hardening behavior of the alloys. Increasing test temperature significantly decreases the n and k values. Phase particles (both Si and (Fe/Mn)-rich) cracking and debonding determine the fracture mechanism of the alloys. Final failure of the alloys mainly depends on the global instability (HT, necking) and local instability (RT, shearing).

The influence of iron level on corrosion of high-pressure die-cast LM24 alloy

Iron is a detrimental alloying element for aluminium alloys; however, it is essential for facilitating die ejection in high-pressure die-casting process. Hence, studying the effect of iron on the corrosion performance of HPDC aluminium alloys is useful to find an optimal iron content for a specific alloy. Four LM24 alloys with 0.6 wt.% Fe, 0.8 wt.% Fe, 1.2 wt.% Fe and 2 wt.% Fe additions have been examined in this study. In addition to the differences in iron levels, the copper and manganese contents varied in two alloys. The corrosion performance of the alloy specimens was evaluated by electrochemical noise and electrochemical polarisation measurements, and scanning Kelvin probe force microscopy. The microstructures of the individual alloy specimens were observed by scanning electron microscopy prior to and after each corrosion evaluation experiment. The results show that more corrosion products accumulated in the alloys with higher iron additions, and this led to reduction of cathodic reaction rates in the aqueous aggressive chloride solution. An increased Mn/Fe ratio causes the distribution of iron-rich phase particles and cathodic sites across the surface of the alloy. Hence, the compositional potential gradient of the phases throughout the surface decreases. In addition, the potential gradient of the phases also depends on the surface roughness of the phase particles; therefore, the alloys with the larger iron-rich phase particles show the highest potential gradients.

Thermodynamics-Based Selection and Design of Creep-Resistant Cast Mg Alloys

Atomic level thermodynamics arguments that account for the generally weak age hardening response while suggesting that extending the athermal regime through short-range order (SRO) is a most feasible path to increasing the creep strength of many current alloys are presented. The tendency, or otherwise, of many solutes to develop SRO in dilute solid solutions rationalizes a number of observations in current multicomponent Mg alloys, and in particular the retention of linear strain hardening at high temperatures, while it disputes the viability of several micromechanisms often considered active, such as pinning of edge dislocations by mobile solute clouds, dynamic precipitation of thermally stable precipitates, or atomic size effects on the diffusivity. Potential solutes are sorted out and ranked based on the sign and value of the enthalpy of mixing of binary solid solutions using the Miedema phenomenological scheme. Due to their large negative energy of mixing and reasonable solubility (>1 at. pct) at ~473 K (~200 °C), Y and Gd appear as the best candidates to increase the creep strength through SRO, followed by Nd and Ca, in close agreement with data reported in the literature. The feasibility of enhancing the age hardening response through homogeneously nucleated, coherent precipitates, in some cases despite the negative energy of mixing of the alloy, or via internally ordered precipitates mimicking those present in Mg-Th alloys is considered by making parallels with the Al-Zn and the Al-Cu alloy systems. The possible optimization of the strengthening of high pressure die cast alloys combining SRO and intergranular eutectics or of heat-treatable cast alloys through internally ordered precipitates and SRO is 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.

Correlation of microstructure and creep behaviour of MRI230D Mg alloy developed by two different casting technologies

The relationship between the as-cast microstructure and creep behaviour of the heat-resistant MRI230D Mg alloy produced by two different casting technologies is investigated. The alloy in both ingot-casting (IC) and high pressure die-casting (HPDC) conditions consists of α-Mg, C36 ((Mg,Al)2Ca), Al–Mn and Sn–Mg–Ca rich phases. However, the HPDC alloy resulted in relatively finer grain size and higher volume fraction of finer, denser network of eutectic C36 phase in the as-cast microstructure as compared to that of the IC alloy. The superior creep resistance exhibited by the HPDC alloy at all the stress levels and temperatures employed in the present investigation was attributed to the more effective dispersion strengthening effect caused by the presence of finer and denser network of the C36 phase. The increased amount of the eutectic C36 phase was the only change observed in the microstructures of both alloys following creep tests.

Predicting the Influence of Microporosity on the Mechanical Properties and Fracture Behavior of High-Pressure Die-Cast AM50 Magnesium Alloy

In this paper, experimental and finite element modeling methods were adopted to investigate the effects of microporosity on the tensile properties and fracture behavior of high-pressure die-casting (HPDC) AM50 alloy. By specimen-to-specimen fractographic analysis, the variability in tensile properties could be quantitatively correlated with the areal fraction of the porosity presented in the corresponding fracture surfaces by using a simple power law equation. Numerical models of synthetic microstructures with different pore sizes, areal fractions of pores and pore distributions were established. Based on the experimental and numerical simulation results, it could be concluded that the fracture will initially occur in the region where has the highest intensity of equivalent stress field (i.e., contains the most highly localized cluster of pores and shrinkage), and then, fracture crack will fast propagate through the adjacent regions which have the relatively high intensity of stress field.

Effect of Microporosity on the Tensile Properties of High-Pressure Die-Cast AM50 Magnesium Alloy

Cast Magnesium alloys often exhibit large variability in fracture related properties such as ductility. In this study, the characteristics of micro-voids in high-pressure die-cast (HPDC) AM50 alloy were investigated by microstructural detecting. Specimen-to-specimen fractographic analysis of tensile fractured surface was executed to summarize the relation between microporosity and tensile properties. The results indicated that the variability in tensile properties is quantitatively correlated to the areal fraction of porosity in the corresponding fracture surface, which could be expressed by a power law equation. All the results proved that the most highly localized cluster of micro-voids is most preferentially to be the origin of fracture, and then, fracture crack will preferentially propagate through the adjacent regions that with large porosity.

Homogeneous and heterogeneous precipitation mechanisms in a binary Mg–Nd alloy

Parallel modes of precipitation mechanisms in an Mg–Nd alloy were revealed by examining an isothermally annealed high pressure die cast alloy at 177 °C for up to 100 h. Broadly, precipitate evolution was observed to occur concurrently on dislocations and within the surrounding α-Mg matrix. However, it was observed that the presence of dislocation accelerated the precipitate formation kinetics significantly. In contrast to the accepted precipitation pathway in the Mg–Nd system, i.e., SSSS → GP zones → β″ → β′ → β1 → β → βe, dislocations were found to preferentially facilitate the formation of β′ and β1 precipitates even at the very early stages (5 h) of annealing. Within the same time frame, a homogeneous distribution of Nd-rich pockets was observed throughout the α-Mg matrix, along with the β′ and β1 precipitates decorating dislocation lines. Results further indicate that these Nd-rich regions initiated precipitation within the parent α-Mg matrix. The formation of these Nd-rich pockets was explained on the basis of a miscibility gap in the α-Mg phase at 177 °C. Our results demonstrate that the presence of dislocations influence strongly the phase-transformation pathways in Mg-rare earth alloys by facilitating the formation of selective precipitate phases.

Microstructural characterization of the Mg–Al alloy AM50 produced by a newly developed rheo-casting process

The microstructure of rheo-cast Mg-Al alloy AM50 produced by the RheoMetal process is investigated and compared with the same alloy produced by conventional high pressure die casting. The size and arrangement of microstructural constituents and pores are characterized quantitatively using image analyzing techniques. The nearest neighbor distribution of the intermetallic particles is determined. The area fraction of porosity in rheo-cast AM50 is about half that found in the high pressure die cast alloy. In rheo-cast material, the distribution of β phase (Mg17Al12) is relatively uniform throughout the cast. In contrast, the β phase particles tend to form macroscopic agglomerates in high pressure die cast material. The externally solidified grains in the rheo-cast material exhibit a smaller aluminum gradient than in the high pressure die cast alloy. This indicates that the solidification of the rheo-cast material is closer to equilibrium.

Mechanical Properties of Al-10 Mass % Si-Mg High-Pressure Die-Casting Alloy with Different Mg Content

The influence of Mg content on Al-10 mass % Si-0.05, 0.30 and 0.60 mass % Mg alloys castings were produced by high-pressure die-casting process, used by microstructure observation and evaluation of mechanical properties. With increasing Mg content, the main constituent phases (primary α-Al phase and eutectic phase) were not changed, but a small amount of phases crystallized at last stage of solidification (β-Al5FeSi, π-Al8Si6Mg3Fe and Mg2Si) were changed in the kind and the volume. In the mechanical property, 0.2%PS and UTS were increased, elongation and absorbed energy were decreased with increasing Mg content or difference of heat treatment. Because the fracture mode in primary α-Al phase was changed from ductile to brittle by precipitation strengthening.

Microstructure and corrosion behavior of die-cast AM60B magnesium alloys in a complex salt solution: A slow positron beam study

The microstructure and corrosion behavior of high pressure die-cast (HPDC) and super vacuum die-cast (SVDC) AM60B magnesium alloys were investigated in a complex salt solution using slow positron beam technique and potentiodynamic polarization tests. The experiments revealed that a CaCO3 film was formed on the surface of the alloys and that the rate of CaCO3 formation for the SVDC alloy with immersion time was slower than that of the HPDC alloy. The larger volume fraction of β-phase in the skin layer of the SVDC alloy than that of the HPDC alloy was responsible for the better corrosion resistance.

Influence of Process Parameters on the Fluidity of High Pressure Die-Casting Al-Si Alloys

It is generally known that silicon influences the fluidity of aluminum alloys. There are several techniques to evaluate the fluidity of aluminum for gravity casting such as using spiral or serpentine type mold and vacuum suction test. However, fluidity of aluminum in high pressure die-casting has not been sufficiently studied. Therefore, in this study, the relationship between the fluidity and superheat of pouring aluminum alloy as well as injection speed was studied. A serpentine and step type die for evaluating the fluidity of aluminum alloys was designed and actual experiments were conducted for aluminum by varying many parameters such as pouring and injection speed and the content of silicon. The results showed that fluidity of aluminum in die-casting was quite similar to the gravity casting. Under high pressure die casting conditions, increased fluidity was measured as the silicon content, superheat, G.B.F treatment time and injection speed were increased.

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.

Microstructure characterization of early corrosion behavior of AM60B magnesium alloys

The microstructures and corrosion behavior of AM60B magnesium alloys, produced by both high-pressure die casting (HPDC) and super vacuum die casting (SVDC) processes, were investigated by a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), and slow positron beam technique. XRD confirmed that calcium carbonate (CaCO3) deposited on the surface of alloys during the early stages of corrosion, and the deposition rate of CaCO3 for SVDC with corrosion time was slower than that of HPDC. SEM observation found that the β-phases in the skin surface of SVDC alloy had a greater volume fraction and more continuous distribution than that of HPDC alloy, leading to lower volume fraction of CaCO3 deposited on surface of SVDC alloy for the same corrosion time. The slow positron beam Doppler broadening measurement revealed that the thickness of surface corrosion layer increased with corrosion time. Compared with HPDC alloy, the increase rate of thickness for SVDC alloy is slower, which implied that SVDC alloy exhibited a better corrosion resistance than HPDC alloy.

Microstructures and creep properties of Mg–4Al–(1–4) La alloys produced by different casting techniques

The microstructures, mechanical properties and creep resistance of Mg–4Al–(1–4) La alloys produced by permanent mold casting and high pressure die casting (HPDC) were investigated. In addition to solute atoms in α-Mg matrix, Al element may exist in the form of three different intermetallic phases in the present alloys depending on the experimental conditions. In both casting states, the increase of La addition results in a rise in the volume fraction of Al11La3 eutectic, and simultaneously Mg17Al12 phase, including divorced eutectic in as-cast state and discontinuous precipitation after creep, is suppressed until completely disappears. This leads to a gradual increase in creep resistance. The formation of more Mg17Al12 phase in HPDC alloys is considered a major factor in causing their worse creep properties by comparison with that of the permanent mold casting alloys when La content is in a lower level below 2wt.%. By contrast, the HPDC alloys show better creep resistance with La content added above 2wt.% owing to the formation of denser network distribution of Al11La3 phase along grain/dendrite boundaries as a result of more rapid solidification rate and higher solidification pressure. For the alloys studied, grain/dendrite boundary sliding is suggested to be a possible controlling mechanism responsible for creep deformation at elevated temperatures.

Insights into microstructure based corrosion mechanism of high pressure die cast AM50 alloy

Corrosion mechanism of high pressure die cast (HPDC) AM50 magnesium alloy from a planar microstructure context is discussed. The progress of corrosion is mapped by means of electrochemical impedance spectroscopy, microscopy, and by elemental composition distribution analysis. Corrosion resistance of the alloy surface increased on prolonged exposure to the electrolyte (1.6wt.% NaCl solution), which is attributed to the selective dissolution of Mg-rich alpha phase, and to the evolution of Al-rich surface comprising of Mg17Al12 (beta) and Al-containing eutectic phases. A comparative study between HPDC and sand cast AM50 alloys revealed superior corrosion performance of die cast alloy.

Influence of Elevated Temperature and Stress Ratio on the Fatigue Response of AM60B Magnesium Alloy

The fatigue response of a high pressure die-cast AM60B Mg alloy is studied at room and elevated temperatures. The fatigue tests are conducted with stress ratio of R = 0.1 and frequency of 30 Hz. The main objective is to determine whether elevated temperature would affect the fatigue response of the alloy. In addition, fatigue crack growth characteristics of the alloy is investigated at room temperature. The purpose of this test is to ascertain the capability and accuracy of a finite element approach coupled with the Walker model in assessing the life cycle of the alloy, in consideration of the influence of stress ratio.

Design of Secondary Alloy Compositions for High Performance Aluminium Pressure Diecastings

High pressure die-casting (HPDC) is a widely used production technique for metal components that are required to have close dimensional tolerances and smooth surface finishes. Approximately 50% of the aluminium castings produced globally are manufactured by HPDC from secondary alloy and these are dominant in the automotive sector where they account for the majority of aluminium components present in each vehicle manufactured. Recently, it has been shown that industrially produced aluminium alloy high pressure diecastings (HPDC’s) can be successfully heat treated without encountering problems with surface blistering or dimensional instability. These processes may significantly improve the properties which develop from the alloys, thereby significantly increasing the scope of applications that may be realized. HPDC alloys however have not been developed specifically for heat treatment or the optimization of specific properties. In particular, recent work in Al-Si-Cu HPDC alloys has identified composition ranges of alloys for a) achieving yield strengths exceeding 400 MPa, b), rapid heat treatment that minimizes cost / cycle times, and c) high strength combined with elevated ductility levels. The role of alloying elements, composition limits and effects on mechanical property development are discussed.

An Evaluation of Quality Parameters for High Pressure Die Castings

Several techniques for examining casting “quality” as it relates to high pressure diecast alloy A380 have been evaluated in the as-cast condition. The roles of three simple parameters were considered: a) metal velocity at the gate, b) the effect of increased Cu or Zn content, and c) the effect of rotary degassing on a recycled melt. It was shown that tensile failure in high pressure die casting (HPDC) specimens is influenced by complex defect clusters and the interaction of a variety of casting defects. The two major defect cluster types identified in the current work were comprised of a dispersed foam-like shrinkage defect, and/or large oxide films present on the fracture surfaces. The removal of hydrogen had little effect on average tensile properties which was a surprising result, but rotary degassing did appear to remove a portion of the oxides present in the melt, thereby improving casting quality. It is shown that of the different analyses conducted, all could differentiate a degree of casting quality, but some techniques (i.e., Weibull statistics combined with flow curve derivations based on the Ludwik-Holloman equation) are particularly useful. It is proposed that complex strain localization and failure occurs in HPDC specimens, which results in a proportionately large fraction of defects appearing on the fracture surface.

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.