Die-cast Specimens Research Articles

Fatigue Life Assessment of Corroded AlSi10MgMn Specimens

This study investigates the influence of pre-corrosion damage on the fatigue behavior of AlSi10MgMn high-pressure die-cast specimens, using the statistical distribution of corrosion depths. The analysis is conducted on two different surface conditions: an unmachined rough surface (Ra=5.05μm) and a machined, polished surface (Ra=0.25μm). For the unmachined specimens, the corrosive damage manifests as homogeneously spread localized corrosion, whereas the polished specimens exhibit less uniform but deeper corrosion. The average corrosion depth of the polished specimens is found to be slightly higher (313 μm compared to 267 μm) with a broader depth distribution. Specimens are tested under a constant bending load amplitude in laboratory conditions at a stress ratio of R=0 until fracture. A fracture mechanics-based methodology is developed to assess the remaining fatigue life of corroded specimens, utilizing short and long crack fracture mechanical parameters derived from SENB specimens. This model incorporates a thickness reduction of the critical specimen cross-section based on the corrosion depth distribution and combines it with a small initial crack of the intrinsic defect size (aeff=14μm). Regardless of the surface condition, using the most frequent corrosion depth for thickness reduction provides a good estimate of the long-life fatigue strength, while using the 90th percentile depth allows for a conservative assessment.

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.

High-Temperature Behavior of High-Pressure Diecast Alloys Based on the Al-Si-Cu System: The Role Played by Chemical Composition

Al-Si-Cu foundry alloys are widely applied in the form of high-pressure diecast components. They feature hypo- or nearly eutectic compositions, such as AlSi9Cu3(Fe), AlSi11Cu2(Fe), and AlSi12Cu1(Fe) alloys, which are used in the present study. Diecast specimens, with a thickness of 3 mm, were used for tension tests. The short-term mechanical behavior was characterized at temperatures from 25 up to 450 °C. At temperatures above 200 °C, the tensile strength properties (YS and UTS) of the investigated alloys were severely affected by temperature, and less by chemical differences. Material hardness and ductility indexes better highlighted the differences in the mechanical behavior of these age-hardenable alloys and allowed us to relate them to the microstructure and its changes that took place at test temperatures. Thermodynamic calculations were found to be useful tools to predict phases formed during solidification, as well as those related to precipitation strengthening. By means of the performed comprehensive material characterization, deeper knowledge of the microstructural changes of Al-Si-Cu foundry alloys during short-term mechanical behavior was obtained. The gained knowledge can be used as input data for constitutive modeling of the investigated alloys.

Variation of microstructure and mechanical property of slurry die cast Al-Si-Mg-Fe alloy

Semi-solid metal processing technologies have been intensively studied in recent years. Gas Induced Semi-Solid (GISS) is a slurry preparation technique for producing non-dendritic or globular structures for cast alloys. In the present study, GISS technique was used in conjunction with conventional die cast process for casting Al–Si–Mg–Fe alloy. The shape of die cast specimen was designed as a simple flat plate. The variation of microstructures and tensile properties of specimens from different locations of cast plates was studied. The results show that the specimens from bottom location, near the gate section and the middle location of cast plates are stronger and more ductility than those from the top location. The microstructural examination reveals that the specimens from top location of cast plates contain more defects, such as shrinkage pores than those from the other locations. These defects are resulted in lower strength and ductility of the cast product.

Metallographic Assessment of Al-12Si High-Pressure Die Casting Escalator Steps

A microstructural characterization study was performed on high-pressure die cast specimens extracted from escalator steps manufactured from an Al-12 wt.% Si alloy designed for structural applications. Black and white, color light optical imaging and scanning electron microscopy techniques were used to conduct the microstructural analysis. Most regions in the samples studied contained globular-rosette primary α-Al grains surrounded by an Al-Si eutectic aggregate, while primary dendritic α-Al grains were present in the surface layer. This dendritic microstructure was observed in the regions where the melt did not impinge directly on the die surface during cavity filling. Consequently, microstructures in the surface layer were nonuniform. Utilizing physical metallurgy principles, these results were analyzed in terms of the applied pressure and filling velocity during high-pressure die casting. The effects of these parameters on solidification at different locations of the casting are discussed.

Microstructure of die cast and thixocast ZAEX10430 (Mg–10Zn–4Al–3Ce–0.3Ca) alloy

Abstract The microstructure and phase composition of die cast and thixocast ZAEX10430 (Mg–10Zn–4Al–3Ce–0.3Ca) alloy were studied. Two intermetallic phases were identified in both the die cast and the thixocast specimens: the τ-phase doped with calcium (Mg,Ca)32(Al,Zn)49 (or τ′-phase) and the (Al,Zn)xCe isomorphous phase with Al2CeZn2 and Al4Ce. In all of the specimens, the τ′-phase crystallized mostly as fine elongated particles and within a lamellar constituent. Needle-like (Al,Zn)xCe phase particles were visible in the die cast specimens, whereas coarse particles of various cross-sectional shapes (polygonal, elliptical, rod-like, etc.) were observed in the thixocast specimens. The difference in morphology of the intermetallic (Al,Zn)xCe particles in the matrix and the presence of large primary α-Mg grains in the thixocast specimens was used to explain the different creep behavior of die cast and thixocast ZAEX10430 alloy reported previously.

A Study on Surface Oxidation Coating Characteristic of Al-Si Casting Alloys

in this paper, it was aimed to improve understanding about the effects of physical melt treatment on the morphologies of eutectic silicon crystal size, and then the effects of these microstructural features on anodizing characteristics. A380 and A356 casting aluminum alloys were used in this experiment. A twin-screw melt-shearing process and an electro magnetic stirring process were utilized before high pressure die casting. In order to refine and homogenize the microstructure of the diecast Al-Si alloys, the melt-shearing process parameters were controlled and T6 heat treatment was carried out. A uniform microstructure over the whole thickness of the diecast specimens caused smaller difference in oxidation coating layer thickness between machined and non-machined surfaces. More uniform anodic coating layer was obtained by AC/DC coupled anodizing and PEO processes compared to conventional DC anodizing process.

Experimental investigation on the effect of applied pressure on microstructure and mechanical properties of squeeze cast AC2A aluminium alloy

This investigation focuses on the attempt made to prepare AC2A castings of a non-symmetrical component through squeeze casting process. Samples were produced to study the effect of squeeze pressures (0.1, 25, 50, 75, 100 and 125 MPa) on microstructure and mechanical properties of the alloy. Results of hardness and tensile tests indicated that squeeze cast specimens exhibited higher mechanical properties than gravity die cast specimens. This was mainly due to applied pressure which resulted in effective filling of the melt into die cavity, microstructural refinement and good heat transfer between the melt and the die. Pressure of 50 MPa was found to be sufficient for pore free castings and pressure of 100 MPa was noted for sound castings. From this study, the squeeze casting process is noted to be suitable for processing this alloy.

Effects of Heat Treatment on a High-Pressure Die-Cast Mg-La-Y Alloy

In this study effects of heat treatments on the creep resistance at 177°C/90MPa of a high-pressure die-cast Mg-2.70La-1.50Y (wt.%) alloy were examined. It was found that ageing at 160°C for 24 h (T5) or a solution treatment at 520°C for 1 h (T4) improved creep resistance and caused no blistering on the surface or dimensional changes to the die-cast specimens. TEM was used to characterize the microstructures of heat-treated samples. Improvements to creep resistance might be attributed to the pinning or otherwise retarding of dislocation motion by precipitates and/or solute atoms during creep.

Atmospheric corrosion of field-exposed AZ91D Mg alloys in a polluted environment

Abstract The atmospheric corrosion behaviour of cast and high pressure die-cast AZ91D alloy in a polluted environment were investigated by SEM, XRD and FTIR. The atmospheric corrosion rate of the ingot was higher than that of the die-cast specimen. SO 2 gas played an important role in atmospheric corrosion. The effects of dew condensation on the ingot were greater than that on the die-cast specimen. The corrosion was initiated in the less noble α phase of the samples. The β phase, on the other hand, remained and acted as a barrier to corrosion.

The effect of skin characteristics on the environmental behavior of die cast AZ91 magnesium alloy

The skin characteristics of die cast AZ91 magnesium alloys and their consequent environmental behavior were evaluated in correlation with die cast wall thickness. The metallurgical examination of the skins was carried out using scanning electron microscopy (SEM), SPX-surface analyses with ESCALAB 250 apparatus, and X-ray diffraction analysis. The corrosion behavior of the skins was evaluated by immersion tests and by potentiodynamic polarization measurements in 3.5% NaCl solution saturated with Mg (OH)2 at room temperature. The results show that the corrosion resistance of die cast specimens with relatively greater thickness was improved compared to the corrosion resistance of thin wall specimens. This was explained in light of the obtained skin characteristics, mainly in terms of aluminum content, β phase (Mg17Al12) quantity and morphology, and level of porosity.

In situ observation of tensile deformation of high-pressure die-cast specimens of AM50 alloy

In situ observation of HPDC AM50 alloy in the SEM chamber was performed to study the changes of the micro-voids and the β phase during tensile deformation. The results suggested that micro-voids had little change in the elastic region, opened linearly with increasing load in the plastic region and led to final fracture. The detachment of β phase from the interface was also observed in the plastic region and there was no evidence to suggest that the detachment led to the final fracture.

Effect of Prior Deformation on Creep Behavior of a Die-Cast Mg-Al-Ca Alloy

The creep of die-cast Mg-Al-Ca alloys is characterized by the pronounced decrease in creep rate during the transient region. Higher creep rates immediately after the stress application for the alloys can result in the degradation of bolt-load retention in the automotive powertrain applications. In this study, the effect of prior deformation on creep behavior was investigated for the Mg-Al-Ca AX51 (X representing calcium) die-cast alloy, where the prior deformation was introduced by using the creep machine at temperatures of 423 and 473 K. The creep curves of the specimens with the prior deformation were compared with that of the as die-cast specimen at the creep testing condition of 423 K and 80 MPa. It was found that the prior deformation introduced by the creep machine is not effective to decrease the creep rates for the alloy. The obtained results of creep behavior are discussed on the basis of dislocation movements during creep.

Corrosion Resistance of the Skin and Bulk of Die Cast and Thixocast AZ91D Alloy in Cl- Solution Using Electrochemical Techniques

The corrosion resistance of die cast and freely solidified or electromagnetically stirred thixocast AZ91D alloy has been studied using electrochemical noise technique and electrochemical impedance spectroscopy in a 0.05 M NaCl solution. Specimens polished at different depths were immersed in the solution in order to assess the influence of the microstructure on corrosion kinetics and morphology. At depths between 10 and 50 μm (skin), all specimens showed general non-uniform corrosion with the lowest corrosion resistance. Between 100 and 200 μm (interior skin), the observed corrosion was accompanied by superficial undefined pits due to metastable pitting. The corrosion form in the interior skins gave the best corrosion resistance. Stable pitting corrosion was observed beyond 400 μm deep on the bulk specimens. The skin of all thixocast specimens prepared from both types of billets showed a more corroded surface than that of die cast. On the other hand, the interior skin as well as the bulk of thixocast specimens showed better corrosion performance than that of the die cast specimens.

Deformation Behaviors of Aluminum Alloys for Automobile Parts Studied by Neutron Diffraction

In situ time of flight neutron diffraction measurements during tension test were performed for three Al-Si alloys with different microstructures including hot-forged (AHS 2), T 6 heat-treated (AHS 2-T 6) and die-cast (ACD 12) specimens. Strength and work-hardening behaviors of these specimens are investigated by evaluating phase stresses, i.e., stress partitioning between Si and the Al matrix as well as intergranular stresses of [hkl] oriented family grains in the component phases. It is revealed that Si particles embedded in the Al matrix play a role of the hard second phase. The size and shape of the Si particles affect work hardening and fracture of the alloys.

Electrochemical Study of AXJ530 Magnesium Alloy Behavior in Alkaline NaCl Solution

The corrosion behavior of AXJ530 magnesium alloy has been investigated. Die-cast and thixocast specimens were tested using potentiodynamic polarization, electrochemical noise analysis (ENA), electrochemical impedance spectroscopy (EIS) and immersion tests. These tests showed that all specimens were passive in that solution. However, the passive film formed on thixocast specimens was found to be more protective and resistant to localized corrosion than that of die-cast specimens.

Influence of elevated temperatures on the cyclic deformation behaviour of the magnesium die-cast alloys AZ91D and MRI 230D

The magnesium alloys AZ91D and MRI 230D were investigated in form of die-cast specimens with a cast skin. The fine-grained microstructure consists of a dendritic magnesium solid solution and interdentritic precipitates. The cyclic deformation behaviour was characterised in stress-controlled load increase tests and constant amplitude tests by means of mechanical stress–strain hysteresis measurements at room temperature and at T = 150 °C. The MRI alloy leads to higher plastic strain amplitudes and nevertheless higher lifetimes for both temperatures. Load increase tests allow a reliable short-time estimation of the endurance limit under both, room and elevated temperatures. With the physically based fatigue life calculation method “PHYBAL” the lifetime of the magnesium alloys can be calculated on the basis of cyclic deformation data determined in one load increase test and two constant amplitude tests in excellent agreement with the conventionally determined S– N curve.

Cyclic deformation behaviour and lifetime calculation of the magnesium die-cast alloys AZ91D, MRI 153M and MRI 230D

Abstract The magnesium alloys AZ91D, MRI 153M and MRI 230D were investigated in the form of die-cast specimens with a cast-skin. The fine-grained microstructure consists of a dendritic magnesium solid solution and interdentritic precipitates. The cyclic deformation behaviour was characterised in stress-controlled load increase and single step tests by means of mechanical stress – strain hysteresis and temperature measurements. Load increase tests allow a reliable short-time estimation of the endurance limit. With the physically based lifetime calculation method “PHYBAL”, the lifetime of the magnesium alloys can be precisely calculated on the basis of the plastic strain amplitude and the change of the specimen temperature due to cyclic plastic deformation with three experiments. Lifetimes calculated according to “PHYBAL” agree excellently with experimentally determined data.

Manufacturing and Plasma Electrolytic Oxide Coatings on the Thin-Wall Aluminum Notebook PC Case

The silicon-based aluminum casting alloy and 2 different types of gate designs were used to investigate experimentally the fabrication feasibility of sound thin-wall case casting by diecasting process. While split type gate design had no defect, tangential type gate design resulted in cracks in the all obtained specimens. Electrolytic Oxide (PEO) coating was performed as a surface treatment process. Before the PEO coating treatments some die cast specimens were heat treated at the temperature of 323K and N2 atmosphere for 1hr to evaluate the effect of heat treatment. The result showed that hardness was improved after PEO coating, however, the effect of heat treatment was not significant.

The correlation between wall thickness and properties of HPDC Magnesium alloys

A systematic study was carried out to evaluate the correlation between high pressure die casting (HPDC) parameters and the mechanical properties of Magnesium alloys. The tested alloys included two conventional alloys: AZ91D and AM50A and a newly developed alloy, MRI153M. The nature of the above correlations was semi-empiric, based on computer simulation of the die casting process using MAGMA ® simulation software and actual measurements of mechanical properties. This was combined with microstructure analysis with the aim of understanding the interaction between high pressure die casting and the obtained properties. Special attention was also given to the complex effect of the wall thickness of die cast specimens and their subsequent porosity level.