Die-cast AM50 Research Articles

Corrosion Behavior of Gravity Cast and High-Pressure Die-Cast AM60 Mg Alloys with Ca and Y Addition

In this study, the microstructure and related corrosion behavior of AM60 alloys with/without Ca and Y addition upon gravity casting (GC) and high-pressure die-casting (HPDC) are investigated by means of SEM/EDS characterization, immersion/salt spray test, hydrogen releasing, as well as electrochemistry examination. When utilizing GC, AM60 alloy with Ca and Y addition (named AZXW6000 alloy) has better corrosion resistance compared with AM60 alloy. Thanks to grain refinement and second phase networks introduced in HPDC, the anti-corrosion properties of the AM alloy seem much better than those of the GC counterpart. The corrosion mechanism of both GCed and HPDCed AM60-based alloys is also investigated in detail. The inspiration from present work can provide more thinking for developing high corrosion-resistant Mg alloys using different casting methods.

Upset Protrusion Joining (UPJ) characteristics of cast AM60 magnesium alloy to join with dissimilar material

Magnesium alloys have a significant benefit over the steel and aluminum alloys in manufacturing of components for many automotive and structural applications because of their extreme lightweight, low density, and high strength to weight ratio. However, one of the glaring impediments to the success of steels, aluminum, and magnesium-based multi-material integration for automotive industries is the ability to join these materials together without any cracking and corrosive damages during a performance. The present work aims to demonstrate a cost-effective, novel, and versatile joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly (1–2 s) join die-cast AM60 alloy to aluminum alloy sheet and evaluate its UPJ characteristics. Cast Mg plate has a cylindrical protrusion (11 mm diameter and 14 mm height) emanated perpendicular to its flat surface, and an aluminum sheet has a hole that accommodates the protrusion. Mg and Al alloy components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expanded circumferentially to fill the hole as well as the region above the hole, and entrapped the Al sheet between the deformed (in a mushroom shape) head and the Mg plate. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance is studied. The process demonstrated repeatability at given process conditions, and optimum process parameters were identified that produce visibly good joints (defect-free) and sufficient joint strengths when tested in the lap-shear mode under uniaxial tension. AM60 alloy showed a great promise as a candidate alloy to suit the UPJ method to adapt to automotive and other industrial manufacturing units to join with dissimilar wrought Al alloy sheets.

Analysis of local stress/strain fields in an HPDC AM60 plate containing pores with various characteristics

Casting pores are regarded as the main factor causing stress/strain concentrations, facilitating the initiation of microcracks and shortening the plasticity of a cast component. The influence of pore characteristics (i.e., size, morphology, and position) on local stress concentration in a High Pressure Die Cast (HPDC) AM60 sample is studied utilizing X-ray tomography (XRT) and image-based finite element (FE) techniques. Heterogeneous porosity distribution is identified in terms of volume fraction and projected area ratio per segment. Statistically results demonstrate that small pores (volume < 0.01 mm3) have higher number frequency and sphericity. In contrast, large pores (volume > 0.01 mm3) account for a very low number frequency (0.3%), and complex shape. The present study addresses the local stress/strain behavior in a cast-pore containing HPDC AM60 sample during tensile loading investigated using 3D image-based models which consider the actual size, morphology, and spatial distribution of pores based on XRT images and consider the actual material properties of the AM60 alloy. Simulation results show that the local stress/strain around a pore evolves progressively with deformation. The strain at a certain pore location may be amplified or reduced in the presence of other pores, depending on the specific location of the concerning pores. Also, the ratio between the projected area of a pore and its shortest distance to the free surface (PA/SD) could give a good indication of the max local stress concentration around the pore surface. The weakening of Ktpl values of pores found in defect bands are principally due to the pore orientation concerning the load direction. These findings may be extended to provide additional insight into the damage mechanisms in material containing casting pores and to enhance understanding of the ductility variation in terms of local deformation fields around pores and their interactions.

Workability Characteristics and Deformation Mechanisms of Die-Cast AM60 and AZ91 Magnesium Alloys: Correlation with Processing Maps

Thermo-mechanical deformation behavior of the die-cast AM60 and AZ91 alloys was assessed by performing uniaxial compression tests on Gleeble 3800 simulator under different temperatures and strain rate conditions. Low-temperature deformation behavior of both alloys was accessed at 25, 100, and 150 °C, at the strain rates of 0.1 and 1 s−1. Processing maps at a true strain of 0.5 were generated to study the intrinsic hot workability of AM60 and AZ91 alloys. Optimum processing windows were identified, and the evolution of microstructures and textures was correlated with the imposed deformation conditions. The processing map for the AM60 alloy exhibited three dynamic recrystallization (DRX) domains in the ranges: (1) 320-400 °C and 0.2-1.5 s−1, (1A) 300-325 °C and 0.1-0.2 s−1, and (2) 360-400 °C and 3-5 s−1. In Domain 1, DRX occurred predominantly by pyramidal slip and recovery mechanisms by cross-slip as confirmed by the randomized textures. Deformation in Domain 1A is by the combination of basal and prismatic slip. In Domain 2, dynamic recovery was a softening mechanism controlled by the climb. The processing map for AZ91 alloy exhibited two DRX domains in the ranges: (1) 260-310 °C and 0.1-0.5 s−1 and (2) 325-350 °C and 0.8-3 s−1. The rate-controlling mechanism was climb by lattice self-diffusion in Domain 1 and by grain boundary self-diffusion in Domain 2. Both alloys exhibited flow instability at 200 and 250 °C, and therefore, they were unsuitable for processing at these temperatures.

Fatigue Analysis of Magnesium Alloys Components for Car Industry

Abstract The use of magnesium alloys in the automotive industry increased in the last decade because of their low weight and relative good mechanical properties. However, the variable loading conditions require a good fatigue behavior. This paper summaries the fatigue properties of magnesium alloys and presents new fatigue curve results for die cast AM50 magnesium alloy.

Assessing the Corrosion of Multi-Phase Mg-Al Alloys with High Al Content by Electrochemical Impedance, Mass Loss, Hydrogen Collection, and Inductively Coupled Plasma Optical Emission Spectrometry Solution Analysis

The corrosion behavior for several die-cast Mg-Al alloys (AM50, AM50, and AZ91) was compared to commercial purity Mg and AZ31B-H24 utilizing simultaneous measurement of electrochemical impedance spectroscopy (EIS), hydrogen gas collection over a 24 h immersion period, gravimetric mass loss, and inductively coupled plasma optical emission spectrometry (ICP-OES) solution analysis of the total Mg concentration released. Tests were conducted in three electrolytes, unbuffered 0.6 M NaCl, 0.1 M tris(hydroxymethyl)aminomethane (TRIS), and 0.6 M NaCl buffered with TRIS to a pH of 7. EIS derived polarization resistance was monitored periodically, as determined from EIS circuit modeling using data collected to 0.001 Hz, and considering the pseudo-inductive low-frequency impedance time constant. EIS derived corrosion rates and oxidation charge density were similar to charge density determined from cumulative mass loss, ICP-OES solution analysis, and the volume of hydrogen collected for the die-cast AM50, AM60, and A...

Friction stir welded AM50 and AZ31 Mg alloys: Microstructural evolution and improved corrosion resistance

One of the major drawbacks of Mg alloys is poor weldability, caused by porosity formation during conventional fusion welding processes. Friction Stir Welding (FSW) is promising technique in this context since it is a solid state technique. Contradicting results were published in the literature regarding the FSWed Mg alloys joint's properties. Current research was performed in order to investigate the microstructure and corrosion properties of FSWed Mg alloys, studying representatives of two commercial families: wrought AZ31-H24 and die cast AM50. It was found that in both alloys recrystallization occurred during the FSW. In AM50 the mechanism of the recrystallization was continuous, manifested by dislocation rearrangement into sub grain boundaries. In AZ31 discontinuous recrystallization had occurred through grain boundaries migration - twins rotated with respect to the matrix, turning into low angle grain boundaries. Corrosion resistance has improved during the FSW in both alloys to different extents. In the AM50 alloy, the nugget exhibited significantly higher surface potential than the base metal mainly due to the higher Al concentration in the matrix of the nugget, resulting from the dissolution of Al-enrichment and β-Mg17Al12 phase. In the AZ31 alloy, no change in Al concentration had occurred, and the surface potential measured in the nugget was only slightly higher than in the base metal. These results underline the appropriateness of the FSW for Mg alloys since during the conventional welding deterioration of the corrosion resistance occurs.

Effect of Thermal Exposure Time on the Relaxation of Residual Stress in High Pressure Die Cast AM60

Effect of Thermal Exposure Time on the Relaxation of Residual Stress in High Pressure Die Cast AM60

2D and 3D characterization of pore defects in die cast AM60

The widespread application of die castings can be hampered due to the potential of large scale porosity to act as nucleation sites for fracture and fatigue. It is therefore important to develop robust approaches to the characterization of porosity providing parameters that can be linked to the material's mechanical properties. We have tackled this problem in a study of the AM60 die cast Mg alloy, using samples extracted from a prototype shock tower. A quantitative characterization of porosity has been undertaken, analyzing porosity in both 2D (using classical metallographic methods) and in 3D (using X-ray computed tomography (XCT)). Metallographic characterization results show that shrinkage pores and small gas pores can be distinguished based on their distinct geometrical features. Shrinkage pores are irregular with multiple arms, resulting in a form factor less than 0.4. In contrast, gas pores are generally more circular in shape yielding form factors larger than 0.6. XCT provides deeper insight into the shape of pores, although this understanding is limited by the resolution obtainable by laboratory based XCT. It also shows how 2D sectioning can produce artefacts as single complex pores are sectioned into multiple small pores.

Formation of Calcareous Deposition Layers on AM50 Magnesium Alloy in Presence of Ca2+ in De-Icing Salt Solutions: Immersion Vs. Salt Spray Test

The influence of the presence and absence of de-icing salt ingredient Ca2+ (CaCl2) on the corrosion behavior and morphology of calcareous deposition products on die cast AM50 magnesium alloy was investigated by using an electrolyte close to the de-icing salt composition (NaCl, MgCl2) with and without Ca2+ addition. The aim of the work is to point out the difference of corrosion mechanisms between the presence or absence of Ca2+ and between immersion and salt spray conditions. Electrochemical measurements (OCP, EIS, potentiostatic and potentiodynamic polarization) and several surface analysis techniques (FTIR, XRD, XPS, SEM / EDX) were used. During immersion experiments in the presence of Ca2+, a grey-white, voluminous and open-porous deposition layer has been formed on the surface of magnesium samples, which covered the whole surface after 12 days ­ with layer thicknesses above a tenth of a millimeter. XRD was used to identify Calcite (CaCO3) as a major component in the deposition layer. It has been shown previously by the authors [1, 2] that Ca2+ has an inhibiting effect on Mg alloy corrosion during short time immersion experiments (up to 4.5 h). The inhibiting effect of the Ca2+ in the first 4.5 h cannot be attributed to the incorporation of Ca2+ into the surface layer, which was shown by XPS. Further, an increase of the thickness of the corrosion product layer in presence of Ca2+ seems to be responsible for the inhibiting effect, shown by XPS depth profiling. After several days of immersion in the presence of Ca2+, the element Ca could be detected on the surface by EDX. XRD and FTIR proved the presence of calcite with layer thicknesses up to 155 µm, shown by SEM cross section investigations. The inhibiting effect of Ca2+is not present anymore as Calcite occurs in the surface layers at larger immersion times (> 4,5 h). Furthermore, the influence of the used testing method was investigated. In addition to immersion experiments, salt spray testing was performed up to 13 weeks which resulted in a different morphology of corrosion and deposition products (see Figure 1). Mass gain and mass loss measurements were carried out and showed a 5-times higher mass loss under immersion conditions in comparison to salt spray testing. The presence of a higher amount of carbonates after salt spray testing could be proven. Calcite is present in the surface layers in significant amounts after both testing methods. The increasing OH- concentration during Mg corrosion triggers the deposition of CaCO3 under conditions of low CO2 partial pressure, whilst the carbonate anion derives from the CO2 in the atmosphere.

Characterization of Pore Defects and Fatigue Cracks in Die Cast AM60 Using 3D X-ray Computed Tomography

AM60 high pressure die castings have been used in automobile applications to reduce the weight of vehicles. However, the pore defects that are inherent in die casting may negatively affect mechanical properties, especially the fatigue properties. Here we have studied damage (e.g., pore defects, fatigue cracks) during strained-controlled fatigue using 3-dimensional X-ray computed tomography (XCT). The fatigue test was interrupted every 2000 cycles and the specimen was removed to be scanned using a desktop micro-CT system. XCT reveals pore defects, cracks, and fracture surfaces. The results show that pores can be accurately measured and modeled in 3D. Defect bands are found to be made of pores under 50 µm (based on volume-equivalent sphere diameter). Larger pores are randomly distributed in the region between the defect bands. Observation of fatigue cracks by XCT is performed in three ways such that the 3D model gives the best illustration of crack–porosity interaction while the other two methods, with the cracks being viewed on transverse or longitudinal cross sections, have better detectability on crack initiation and crack tip observation. XCT is also of value in failure analysis on fracture surfaces. By assessing XCT data during fatigue testing and observing fracture surfaces on a 3D model, a better understanding on the crack initiation, crack–porosity interaction, and the morphology of fracture surface is achieved.

Influence of heat treatments and Ca additions on the passivation behaviour of high‐pressure die cast AM50

The influence of heat treatments and Ca additions on the corrosion behaviour of HPDC AM50 was studied using potentiodynamic polarisation technique in bi‐distilled water at pH=8. Heat treatments caused a considerable modification of the polarisation behaviour, which manifested itself in a wide range of passivity in the anodic branch. During heat treatments, the Mg solid solution was enriched from 2 wt.% to 4 wt.% Al due to the partial dissolution of the β‐phase. This enabled the comprehensive formation of a double‐structured passive layer during polarisation. Only minor effect of Ca additions (0.7 wt.%) on the corrosion behaviour of AM50 was observed.

Corrosion fatigue behavior of AM60 magnesium alloy with anodizing layer and chemical-conversion-coating layer

The status of poor corrosion resistance of die cast AM60 magnesium (Mg) alloys can be improved by applying various types of surface coatings above them. However, coating can sometimes alter the fatigue properties and initiation mechanism, which is not reported so far for this group of alloy. Present study focuses on this issue investigating influence of anodizing layer and chemical-conversion-coating layer on corrosion fatigue properties of Mg alloy, AM60. Coating performance was assessed in two different corrosive environments: high humidity (50 °C, 80% RH) and 5 wt% NaCl medium. The key observation for humid environment was that the chemical-conversion-coating without a painting layer showed better corrosion resistance than that of the anodized layer without a painting layer. Moreover, chemical-conversion-coating with a painting layer can effectively protect the underlying AM60 alloy even under the most severe corrosive environments (5 wt% NaCl). Our results show, for the first time, that chemical conversion coating can be successfully used in machine parts loaded in aggressive medium without severely compromising the fatigue strength.

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.

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.

Influence of Ca2+in Deicing Salt on the Corrosion Behavior of AM50 Magnesium Alloy

To lower the freezing point of deicing salt, calcium chloride (CaCl2) is commonly used. The influence of the presence and absence of the deicing salt ingredient Ca2+ on the corrosion behavior of die-cast AM50 magnesium alloy was investigated using an electrolyte close to the deicing salt composition with and without Ca2+ addition. The goal of the work was to point out the differences in the corrosion mechanism with and with-out Ca2+ addition by electrochemical investigations, H2 evolution, and weight-loss characterization. Under polarizing conditions the resulting current densities are significantly lower in the presence of Ca2+. Electrochemical impedance spectroscopy (EIS) measurements up to 4.5 h showed an increasing polarization resistance, RP, with time, and after 4.5 h, a breakdown of RP values in the presence of Ca2+ combined with the appearance of an inductive loop. Mass-gain, mass-loss, and hydrogen evolution measurements confirmed the inhibiting behavior in the presence of Ca2+ up to 1 day. Durin...

Corrosion Characterization of Magnesium Alloys – The Role of Process Parameters

The present work presents a comparative study of FSW die cast AM50 Mg alloy. The main focus is the effect of the FSW metallurgy on the corrosion behavior of the alloy. AC and DC polarization tests were carried out on the FSW Mg alloys. The microstructure was examined using electron microscopy (SEM).

Influence of Ce addition on microstructure and mechanical properties of high pressure die cast AM50 magnesium alloy

The influence of Ce addition on the microstructure and mechanical properties of AM50 magnesium alloy was investigated to improve its mechanical properties. The results show that the addition of Ce to AM50 alloy results in the grain refinement and the mechanical properties of the Ce-modified AM50 at room and elevated temperatures are remarkably improved. AM50 magnesium alloy containing 1% Ce (mass fraction) shows better refinement and mechanical properties compared with the AM50 magnesium alloy with 0.5% Ce and even AM50 alloy without any Ce.

Influence of cerium additions on the corrosion behaviour of high pressure die cast AM50 alloy

The influence of Ce additions to AM50 magnesium alloy prepared by high pressure die casting on the microstructure and corrosion behaviour has been investigated. The corrosion behaviour was evaluated by hydrogen evolution, salt spray, potentiodynamic polarization and electrochemical impedance experiments. The results show that Ce addition promotes the formation of Al11Ce3 phase and reduces the amount of β-phase (Mg17Al12). The corrosion resistance is improved with increasing Ce content which can be attributed to the formation of Al11Ce3 phase, reduction of β-phase (reduced galvanic effects) and higher purity of AME50X alloys (melt cleaning effects).

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.