Die-cast Alloy Research Articles

Anelastic Behaviour of Commercial Die-Cast Magnesium Alloys: Effect of Temperature and Alloy Composition.

The anelastic deformation, resulting from partial reversal of {102} twinning, is studied at room temperature to 150 °C on several commercial die-cast magnesium alloys for the first time. The magnitude of anelastic strain decreases with increasing temperature. For inter-alloy comparison, AZ91 shows the largest maximum anelastic strain, while AM40 and AM60 show similar maximum anelastic strain. The phenomenon is discussed in terms of solid solution softening and hardening of slip planes and how they influence twinning. T5-aged AE44 consistently shows smaller magnitude of anelasticity compared to as-cast AE44, suggesting that the precipitates formed during ageing may decrease the twin-boundary mobility and further suppress untwinning. Presence of anelasticity poses a challenge to yield strength measurement using the conventional 0.2% offset method, and a more accurate and consistent method of using a higher offset strain or a lower modulus is proposed in this study.

Elucidation of the Growth of Filiform Corrosion of AZ91D Mg Alloy in NaCl Solution

Magnesium (Mg) is the lightest structural metallic material with high specific strength. Mg alloys are highly expected to be applied in electronic, automotive vehicles and aerospace, etc. The most severe drawback of Mg and its alloys is corrosion susceptibility. When Mg alloys are used in chloride solutions, filiform corrosion sometimes occur. Being a common practice in the research of Mg corrosion, galvanostatic tests allow for easy comparison of the rate of hydrogen evolution with the applied current. But there are scarce studies reported about the in situ observation of filiform corrosion behavior of Mg alloys under galvanostatic polarization. The purpose of this study is to elucidate the growth of filiform corrosion of AZ91D Mg alloy in NaCl solutions by in situ observation.An ingot of AZ91D die-cast was cut into 25 mm × 30 mm × 5 mm sheets. The specimen surface was polished to 2000 grit with SiC paper and finished with a 0.25 µm diamond paste, followed by ultrasonically cleaning in ethanol. To confirm the metallographic structures, the sample was etched with a mixed reagent of 3 mL HNO3 and 80 mL of ethanol for 3 s. Galvanostatic polarization was performed using a micro electrochemical system with an in situ observation function. The electrolytes used were naturally aerated 0.1 M and 0.01 M NaCl (pH 8.0, adjusted with NaOH). The area of the electrode was about 0.01 mm2 or larger, the surfaces of the sample was covered with a silicone sealant except for the working electrode area. To start the experiments, an objective lens was put down to be immersed in the solution and clear view of the electrode area was attempted to obtain. After polarization, the specimen surface was assessed using OM, AES, FE-SEM and STEM.The AZ91D die-cast Mg alloys mainly consist of an α phase matrix (Mg solid solution) and β phases (Mg17Al12 intermetallic compounds). Lamellar (α + β) structures are also observed in the adjacent of β phases. Among these lamellar structures, some black dots are Mg-Al-Mn compounds. In the video of corrosion process, pits were observed in the boundaries of lamellar (α + β) structures and β phases. After polarization, EDS maps were taken. It was confirmed that filiform corrosion propagated in lamellar (α + β) structures and α phase matrix.

Effect of the microstructural characteristics of die-cast ADC12 alloy controlled by Na and Cu on the mechanical properties of the alloy

The mechanical properties of a die-cast Al–Si–Cu alloy (DC ADC12) were improved using new processing techniques that induce grain refinement and precipitation hardening. Several gravity-cast ADC12 (GC ADC12) samples with different microstructural sizes were also evaluated to better understand the material properties of DC ADC12. The material properties of DC ADC12 indicate that the alloy has both advantages (fine grains) and disadvantages (defects). The mechanical properties of ADC12 can be improved by adding Na before the T5 process. The grain refinement of ADC12 was achieved by introducing Na using benign and inexpensive NaHCO3 rather than metallic Na. The Na elements including sodium oxide retained in the melt cause fine spherical eutectic structures to form in the spherical α-Al matrix by interrupting the Si phase growth. The phenomenon can be detected via a three-dimensional atom probe tomography analysis. Precipitation hardening of the die-cast Al alloy was achieved by subjecting it to T5 treatment and a large amount of Cu, replacing the T6 treatment, for 3 h at 175 °C, because the die casting process can be replaced with the solid solution process in T6 owing to its high cooling rate. Precipitation hardening occurred in the grain-refined DC ADC12-Na sample during the T5 process, which was verified via in situ observation of its microstructure using laser microscopy during the heating and cooling processes. Al2MgCu, CuAl2, and fine Si particles, which were different from the precipitates obtained using the T6 process, were produced in the spherical α-Al phase. The demonstrated techniques resulted in remarkable improvements in the ultimate tensile strength and fracture strain of DC ADC12.

Real-time in situ observation of the corrosion process of die-cast AZ91D magnesium alloy in NaCl solutions under galvanostatic polarization

In situ observations of the filiform corrosion process of die-cast AZ91D magnesium alloy were carried out in 0.1 and 0.01 M NaCl solutions (pH 8.0) through a microscale polarization technique. The changes in morphology were observed in real-time using an optical microscope. Filiform corrosion proceeded in lamellar α + β structures adjacent to β phases and sometimes in the α phase grains. The β phases remained intact after filiform corrosion.

Re-evaluation of the mechanical properties and creep resistance of commercial magnesium die-casting alloy AE44

This paper presents a re-evaluation of the room temperature mechanical properties and high temperature creep resistance of magnesium die-casting alloy AE44 (Mg-4Al-4RE) in light of the influence of minor Mn addition. It is shown that the Mn-containing AE44 exhibits distinct age hardening response upon direct ageing (T5) due to the precipitation of nanoscale Al-Mn particles, as reported previously in a similar alloy. The T5 ageing leads to a significant improvement in strength with similar ductility. Consequently, the T5-aged AE44 has a remarkably better strength-ductility combination than most Mg die-casting alloys and even the Al die-casting alloy A380. Minor Mn addition is also shown to be critical for the creep resistance of AE44 whereas the influence of the RE constituent is not as significant as previously thought, which reaffirms that precipitation hardening of the α-Mg matrix is more important than grain boundary reinforcement by intermetallic phases for the creep resistance of die-cast Mg alloys. The findings in this work could provide new application perspectives for AE44, particularly in the automotive industry.

Prediction of Laminations in Zinc Alloy Die-Casting by Gas-Liquid Two-Phase Flow Simulation

Prediction of Laminations in Zinc Alloy Die-Casting by Gas-Liquid Two-Phase Flow Simulation

Microstructure and mechanical properties of high performance die cast Al-8Ce-3Y aluminum alloy containing Al4(Ce,Y) phase

The Al-8Ce-3Y high pressure die-casting alloy was investigated through characterization and first-principles simulation. The alloy shows excellent comprehensive mechanical properties among Al-Ce system alloys. Also it owns a tensile strength of 87 MPa at 350 °C after 200 h holding, which is much superior than Mahle piston Al alloys. Mechanical improvement is attributed to formation submicron Al4(Ce,Y) fiber with Y addition uniformly distributed. Al4(Ce,Y) phase is stable considering formation energy and mixing enthalpy. This study provides superior mechanical performance of Al-Ce alloy to alleviate the low strength at both room and high temperatures.

Microstructure and Mechanical Properties of AlSi12CuNi Alloy Fabricated by Laser Powder Bed Fusion Process

The microstructure and mechanical properties of the AlSi12CuNi alloy fabricated by the additive manufacturing technique, laser powder bed fusion (L-PBF), were investigated. Several laser irradiation conditions were examined to optimize the manufacturing process to obtain a high volume density of the fabricated alloy. Good fabricated samples with a relative density of 99% or higher were obtained with no cracks. The fabricated samples exhibited significantly good mechanical properties, such as ultimate tensile strength, breaking elongation, and micro-hardness, compared to the conventional die casting AlSi12CuNi alloy. Fine microstructures consisting of the α-Al phase and a nano-sized eutectic Al-Si network were observed. The dimensions of the microstructures were smaller than those of the conventional die-casting AlSi12CuNi alloy. The superior mechanical properties were attributed to the microstructure associated with the rapid solidification in the L-PBF process. Furthermore, the influence of the building direction on the mechanical properties of the fabricated samples was evaluated. The ultimate tensile strength and breaking elongation were significantly affected by the building direction; mechanical properties parallel to the roller moving direction were significantly better than those perpendicular to the roller moving direction. In conclusion, AlSi12CuNi alloys with good characteristics were successfully fabricated by the L-PBF process.

Effect of heat treatment on microstructure and tensile properties of die-cast Al-Cu-Si-Mg alloys

The effects of T5 and T6 heat treatment on the microstructural development and mechanical properties of newly developed die-cast Al-xCu-2.2%Si-1.1%Mg (x=5, 6.6 and 10.6, in wt%) alloys were investigated. After T5 heat treatment to peak hardness, the main precipitates changes from β’’ in Al5Cu to β’’ and θ’ in Al6.6Cu and then to θ’ and Q’’-type precipitate in Al10.6Cu, due to the various Cu content in the α-Al matrix. The highest yield strength of 395±5 MPa and lowest elongation of 1.9±0.15% have been achieved in Al10.6Cu after peak-aged T5 condition as compared to other Al-Cu-Si-Mg alloy compositions. The solution treatment of Al-Cu-Si-Mg alloys for 30–60 min at 500 °C dissolves a sufficient quantity of Cu (~3 wt%), and spheridises the Al2Cu and Al5Cu2Mg8Si7 phases. A large number of θ’ and Q’’ coexist inside the α-Al matrix after T6 heat treatment, contributing to the exceptionally high mechanical strength. The T6 peak ageing time increased from 10 h in Al5Cu to 14 h in Al10.6Cu. These newly developed aluminium die-cast alloys having excellent mechanical properties that exceed those in existing aluminium die-cast alloys after heat treatment. Especially, the excellent yield strength of 427 MPa and 444 MPa, as well as elongation of 4.4% and 4.1%, were achieved in Al5Cu and Al6.6Cu after T6 heat treatment, respectively.

Synchronously Improving the Thermal Conductivity and Mechanical Properties of Al–Si–Fe–Mg–Cu–Zn Alloy Die Castings Through Ultrasonic-Assisted Rheoforming

Synchronously Improving the Thermal Conductivity and Mechanical Properties of Al–Si–Fe–Mg–Cu–Zn Alloy Die Castings Through Ultrasonic-Assisted Rheoforming

Casting Microstructure Inspection Using Computer Vision: Dendrite Spacing in Aluminum Alloys

This paper investigates the determination of secondary dendrite arm spacing (SDAS) using convolutional neural networks (CNNs). The aim was to build a Deep Learning (DL) model for SDAS prediction that has industrially acceptable prediction accuracy. The model was trained on images of polished samples of high-pressure die-cast alloy EN AC 46000 AlSi9Cu3(Fe), the gravity die cast alloy EN AC 51400 AlMg5(Si) and the alloy cast as ingots EN AC 42000 AlSi7Mg. Color images were converted to grayscale to reduce the number of training parameters. It is shown that a relatively simple CNN structure can predict various SDAS values with very high accuracy, with a R2 value of 91.5%. Additionally, the performance of the model is tested with materials not used during training; gravity die-cast EN AC 42200 AlSi7Mg0.6 alloy and EN AC 43400 AlSi10Mg(Fe) and EN AC 47100 Si12Cu1(Fe) high-pressure die-cast alloys. In this task, CNN performed slightly worse, but still within industrially acceptable standards. Consequently, CNN models can be used to determine SDAS values with industrially acceptable predictive accuracy.

Development, Microstructure, and Mechanical Properties of ALDC6-10Si Alloy for Spider Arm Component

The present work describes the development and characterization of mechanical properties of an Al-Mg based die-cast alloy (ALDC6-10Si) for spider arm components in washers. The effect of the addition of silicon (10 wt.%) and magnesium (2.7 wt.%) on the microstructure and mechanical properties of the developed ALDC6-10Si alloy was evaluated. The optical microscopy images and energy dispersive x-ray spectroscopy profiles reveal that the presence of Mg2Si in the ALDC6-10Si alloy is higher than that of commercial ALDC3 alloy. The hardness and tensile strength of the ALDC6-Si10 alloy were found to be improved due to the presence of intermetallic phases such as Mg2Si and π-Al8Si6Mg3Fe. Moreover, the formation of spheroidal primary α-Al and the refinement of the fine eutectic Si structure also enhanced the mechanical properties. In addition, a spider arm component was fabricated using the developed ALDC6-Si10 alloy and evaluated its microstructure and mechanical properties. The results indicated that ALDC6-Si10 alloy can be a better alternative for fabricating the spider arm component in washers.

Investigation for macro mechanical behavior explicitly for thin-walled parts of AlSi10Mg alloy using selective laser melting technique

Recently additive manufacturing of aluminum alloys by selective laser melting (SLM) is of research interest due to its potential benefits in manufacturing industries. The present work investigates the SLM-built AlSi10Mg thin-walled parts and their macro-mechanical behavior in correlation with relative densities. The superlative mechanical behavior of SLM parts was achieved by using the optimal parameters, i.e. 320 W of laser power, 900 mm/s of scanning speed, and 80 μm of hatch distance. The results showed that the SLMed AlSi10Mg thin-walled specimens attained the highest relative density of 99.86 % and 99.21 % for the wall thickness of 0.50 mm and 5.0 mm, respectively. For 0.50 mm wall thickness specimen, the tensile strength of 250.9 MPa, yield strength of 143.7 MPa, breakage elongation of 5.31 %, and microhardness of 116.8 HV were attained which would be comparable to those of the conventionally die-cast A360 alloy. The 364 MPa of tensile strength and 12.04 % of breakage were achieved for 5.0 mm thin-walled specimen. The fracture behavior of different thin-walled fabricated tensile specimens was also examined using a scanning electron microscope (SEM).

Tool Wear and Wear Mechanism of Carbide Tool in Cutting Al–Si Alloy Diecastings

Tool Wear and Wear Mechanism of Carbide Tool in Cutting Al–Si Alloy Diecastings

Cyanide-free environment-friendly alternative to copper electroplating for zinc die-cast alloys.

In this paper, a cyanide-free electroplating bath containing glutamate as a complexing agent is investigated as an environment-friendly alternative for copper plating on zinc die-cast alloys. Glutamate reacts with copper in an aqueous solution that exhibits similar copper cyanide properties by forming complexes. The electroplating bath pH is chosen from equilibrium diagrams to avoid the formation of insoluble complexes and oxides at varying copper-to-glutamate molar ratio. The plating bath's electrochemical response on a stationary electrode confirms that a 1:3 molar ratio between copper and glutamate at pH 8 exhibits better copper deposition onto the substrate, with its morphology characterized using SEM. The results suggest that the copper glutamate electroplating bath can be suitable for copper cyanide bath replacement without additives, allowing a one-step electroplating process. Moreover, the polarization and electrochemical impedance measurements suggest inhibition of the substrate's corrosion when copper was electroplated at a 1:3 copper-to-glutamate molar ratio. With the careful control of the concentration ratio, the process can provide adequate copper deposition and anti-corrosion capability suitable for green nanocoating applications.

Grain refinement promotes the formation of phosphate conversion coating on Mg alloy AZ91D with high corrosion resistance and low electrical contact resistance

The application of Mg and its alloys in 3C (i.e. Computer, Communication and Consumer Electronic) industries requires a strict combination of corrosion resistance and low electrical contact resistance (ECR). The conventional design of conversion coating relies on a thick and compact layer to offer active protectiveness but compromises the electric conductivity. In this work, phosphate conversion coatings (PCC) with low electrical contact resistance were prepared on the sand-cast and die-cast Mg alloy AZ91D, respectively. The microstructural differences, ECR and corrosion resistance were observed and compared. Results show that the PCCs on die-cast alloy have a thickness of 300-400 nm, and are more compact than those on sand-cast counterparts. Interestingly, PCCs of the die-cast exhibit lower ECR, which indicates a mild impact of the improved compactness on ECR. Meanwhile, corrosion resistance of the PCCs on die-cast alloy is greatly improved, which is attributed to the intensified micro-galvanic effect through the grain refinement of the die-cast alloy. It evidently promotes the electrochemical reactions during the conversion treatment to yield high quality PCC.

Evolutions of Mechanical Properties and Macro Textures of AZ91D sheets by Hot Rolling and Subsequent Annealing

The mechanical properties and textures of 75% hot unidirectionally rolled and cross rolled commercial magnesium die-casting alloy AZ91D sheets were investigated for the different rolling temperatures 623K and 673K, respectively. As for mechanical properties, tensile testing results show total elongations of both as-unidirectional and as-cross-rolled sheets are enhanced by the repetition of rolling passes and inter-pass heating. The planar anisotropy of tensile strengths and elongations of cross-rolled at 673K are the smallest among the rolling conditions employed in the present study. Annealed sheets demonstrate the significant elongation to failure due to the static recrystallisation at 623K. Macro textures of the as-unidirectional-rolled sheets show typical double-peak (0001) basal textures with inclined peaks towards ±15° in RD. Contrastingly, macro textures of the as-cross-rolled sheets show the significant (0001) basal textures having double peaks at ±10° in TD and concentrically broader orientation distribution in RD and TD.

Development of a laboratory-scale Upset Protrusion Joining (UPJ) system for dissimilar materials

Magnesium alloys have a significant benefit over steel and aluminum alloys in manufacturing components for many automotive and structural applications because of their higher light-weighting potential, lowest density, and higher strength to weight ratio. However, one of the impediments to the success of multi-material integration of the above materials for automotive manufacturing is joining these materials together without any cracking or corrosion during in-service use. The present work aims to develop and demonstrate a cost-effective, novel, and versatile mechanical joining technique, named Upset Protrusion Joining (UPJ), to mechanically and rapidly join a cast magnesium component to an aluminum alloy sheet. The process involves a cylindrical protrusion emanating perpendicular to the flat surface of a cast plate that fits through a hole in an aluminum sheet. The two components are then clamped together, electrically heated, and compressed perpendicular to the protrusion axis. During compression, the protrusion expands circumferentially to fill the hole as well as the region above the hole, thus entrapping the sheet metal between the mushroomed head and the casting. The effect of different UPJ process parameters such as applied current, current duration, compression loading rate, and compression distance were studied through experimentation on die-cast magnesium alloy, with protrusion of 11 mm diameter and 14 mm height. Material-specific process window was identified to achieve a satisfactory joint quality in terms of post-UPJ joint strength with appearance. UPJ method shows a great promise to implement in automotive and other industrial manufacturing environments for fastening cast components to a similar or dissimilar wrought sheet component.

On the characterization of primary iron-rich phase in a high-pressure die-cast hypoeutectic Al-Si alloy

The morphological properties and distribution characteristics of primary iron-rich phase in a high-pressure die-cast hypoeutectic Al-Si alloy were investigated by synchrotron X-ray tomography technology. Attention was focused on the formation and evolution mechanism of primary iron-rich intermetallic compounds (IMCs) in high pressure die casting (HPDC). Results show that two different sizes of primary iron-rich phases included externally solidified primary iron-rich phase I ((P-IMC)I) and primary iron-rich phase II ((P-IMC)II). The morphology of (P-IMC)I was close to a hexahedron while (P-IMC)II was nearly a spherical particle. Both (P-IMC)I and (P-IMC)II enriched in the central area and their volume fraction maintained a high level from defect band to center. Phase calculation show that (P-IMC)I (601 °C) preferentially precipitated from liquid and its further growth led to the decrease of Mn/Fe ratio in the subsequent formed (P-IMC)II. In HPDC solidification process, (P-IMC)II exhibited a lateral growth pattern with the terminating surfaces determined to be {1 1 0} planes. In addition, the hexahedral (P-IMC)I in central ESCs-rich zone developed into a dendrite along its corner<100>direction.

Improved Corrosion Resistance of AZ91D Mg Alloy by Cerium-Based Films. Formation of a Duplex Coating with Polypyrrole

In order to improve the corrosion resistance of die-cast AZ91D magnesium alloy in simulated physiological solution, two cerium-based coatings were synthesized. The coatings were electrodeposited from solutions containing Ce(NO3)3, H2O2 and C6H8O7 or C4H4O6Na2. The influence of the presence of sodium tartrate and citric acid in the preparation solution on the morphology, composition and anticorrosive performance of the generated coatings was evaluated. The corrosion properties were examined in Ringer solution by polarization studies, open circuit measurements and faradaic impedance spectroscopy. Results showed that the incorporation of additives improves the anticorrosive properties of the films formed without sodium tartrate or citric acid. The coating formed in the presence of sodium tartrate showed the best anticorrosive performance. Subsequently, the possibility of forming duplex coatings employing the cerium-based films as inner layers and polypyrrole as top coating was evaluated. At this point, it was found that polypyrrole can be electropolymerized on top of the formed cerium-based film modified with sodium tartrate.