Die-cast Alloy Research Articles

On the formation mechanism of the ring-like microstructure of high-pressure die-cast A390 alloy

The microstructure of the A390 alloy during high pressure die casting (HPDC), including pores, primary silicon particles (PSPs) and Cu-rich phases was characterized using synchrotron X-ray tomography. On the cross section of the sample exhibited ring-like or band microstructure, which comprised multiple PSPs-free and PSPs-rich zones. The PSPs distributed evenly in both size and morphology regardless of the ring-like microstructure. The size of aluminum dendrites changed according to the location of the ring-like microstructure, and was highly dependent on the local latent heat released from the PSPs as well as the distribution of the ‘net’ Cu-rich phases. Along the radial direction of the sample exhibited an abrupt increase of pores, indicating a tendency for forming a defect band in but such tendency was inhibited because of the huge amount of latent heat released by the PSPs during solidification, which was quite different from that of either magnesium alloys or hypoeutectic aluminum alloys.

Microstructure and mechanical properties of a die-cast Mg-9Al alloy containing oxygen atoms

In this study, the microstructural features and mechanical properties of a high-pressure die-cast (DC) Mg-9Al alloy containing oxygen atoms (Mg-O-9Al alloy) were characterized. The oxygen atoms promoted the formation of nucleation sites of α-Mg under high pressure, including fine cells (12–13 μm), and reduced the number of defect bands compared to the DC Mg-9Al alloy (14–15 μm). The relation between hardness and phase spacing indicated that the dispersion strengthening of the β-phase was dominant. The DC Mg-O-9Al alloy exhibited enhanced tensile properties as compared to the DC Mg-9Al alloy.

Strengthening of Mg-Al-Ca Die-Cast Alloy with Fine C15-Al<sub>2</sub>Ca Precipitates

Strengthening of Mg-Al-Ca Die-Cast Alloy with Fine C15-Al<sub>2</sub>Ca Precipitates

ИССЛЕДОВАНИЕ ВЛИЯНИЯ СПОСОБА ЛИТЬЯ НА КОРРОЗИОННУЮ СТОЙКОСТЬ СПЛАВА АК12

The paper presents studies into the kinetics and mechanism of AS12 silumin produced by sand casting, chill-molding, and die casting in acidic and alkaline solutions. The research uses such methods as gravimetry, titrimetry, photometry, and microstructure analysis. Sand-cast specimen demonstrate a coarse-grained heterogeneous structure featuring needle-like silicon precipitates, while the die-cast alloy has a fine-grained and more homogeneous structure. The researchers have analyzed the kinetic dependencies of the corrosion process occurring in the alloy under consideration and describe the AS12 alloy corrosion in solutions of various pH values. It is proven that the silumin casting method does affect its corrosion resistance to various media, as the greater structural heterogeneity of sand-cast AS12 makes it more vulnerable to corrosion compared to its die-cast counterpart. The data are confirmed by the photometry and titration of AS12 silumin corrosion products. Notably, silumin corrosion in electrolyte solutions is an electrochemical process, where the silicon/silicon-oxide precipitates and impurities in the grain structure function as cathode areas. Emphasis is made on how the corrosive-medium composition affects the silumin corrosion process. It is found that the high oxidative activity of vanadates causes them to trigger the corrosion process in acidic media, which amplifies the depolarization of cathode areas, thus accelerating the corrosion. Regardless of the production method, AS12 is extremely unstable in alkaline media due to the amphoteric properties of aluminum. The paper demonstrates results of analyzing the alloy corrosion resistance as affected by inhibitory additives. It is shown that phosphates effectively protect AS12 silumin against the effects of acidic media while not inhibiting those of alkaline solutions.

A Study of Tightening Characteristics of Aluminum Alloy Bolt to Aluminum Die Cast Alloy

A Study of Tightening Characteristics of Aluminum Alloy Bolt to Aluminum Die Cast Alloy

Fatigue Evaluation on Splitted Surface of Aluminum Alloy Die-Cast Connecting Rod Fabricated by Fracture Splitting Method

Fatigue Evaluation on Splitted Surface of Aluminum Alloy Die-Cast Connecting Rod Fabricated by Fracture Splitting Method

Roundness Change of Big End Hole Fabricated of Aluminum Alloy Die-Cast Connecting Rod by the Fracture Splitting Method

There is a possibility that the roundness of the big end hole changes when the fracture splitting method is applied to the aluminum alloy die-cast connecting rod. In this study, it is examined by FEM analysis whether the roundness of the big end hole is kept by tightening the bolt after the process of the fracture splitting. As a result of the analysis, the big end hole was axially extended with the plastic deformation by the fracture splitting process. In addition, it became clear that the connecting rod was deformed by the bolting in elasticity and the big end hole shortened axially. As a result, the possibility that the fracture splitting method was able to be applied to the aluminum alloy die-cast connecting rod was shown.

Effect of as-cast microstructure heterogeneity on aging behavior of a high-pressure die-cast A380 alloy

Microstructure and hardness evolution of a vacuum-assistant die-cast A380 alloy during heat treatment were investigated. Both surface layer and central region of the casting component were analyzed in die-cast state, solutionized state and artificial age state. During the artificial age, the surface layer hardened more significantly than the central region due to faster precipitation and more refined hardening phases in the surface layer. Detailed analysis on the macro-segregation, microstructure morphology and grain size revealed that the different aging behaviors exhibiting in the surface and the central region were mainly attributed to a combining effect of the enrichment of Si and Cu at the surface layer, the fully-divorced morphology of eutectic in die-cast microstructure, and the presence of the externally solidified crystals at the central region. The presence of the Si particles, which exhibited quite different thermal expansion properties, changed the density and the distribution of the dislocations in the α-Al matrix, and consequently changed the precipitation of the hardening phases.

Dissimilar friction stir lap welding of magnesium to aluminum using plasma electrolytic oxidation interlayer

Joining the die-cast non-combustible magnesium alloy AMX602 to the die-cast aluminum alloy ADC12 via friction stir lap welding (FSLW) was investigated. The aluminum alloy on the top can more easily form a sound dissimilar joint than that on the bottom. Strong dissimilar joints were achieved after the magnesium alloy was subjected to a plasma electrolytic oxidation treatment. After the welding process, the plasma electrolytic oxidation interlayer was stirred and flowed into the aluminum alloy side. The growth of the intermetallic compound was restrained by the plasma electrolytic oxidation interlayer by reducing the reaction time of the magnesium alloy and aluminum alloy.

Improved degassing in laser beam welding of aluminum die casting by an electromagnetic field

An electromagnetic system was used to reduce the porosity in laser beam welding of aluminum die casting. The difference of electrical conductivities between gases and molten aluminum is used by an electromagnetic system to displace the included gases to the top during a laser beam welding process. It bases on generating Lorentz forces within the weld pool via an oscillating magnetic field. A partial penetration laser beam welding of standard die-cast aluminum alloy AC-AlSi9MnMg in flat position is used. An optimized laser beam process was taken to investigate the porosity content and the surface smoothing by applying an electromagnetic field. The produced weld seams were analyzed in cross section views, by x-ray imaging and by computer tomography (CT). Depending on the magnetic flux density, a significantly reduction of the porosity down to 75% can be achieved. Especially big pores can be removed successfully. A surface smoothing of up to 75% can also be reached by using this system.

Morphology transition of the primary silicon particles in a hypereutectic A390 alloy in high pressure die casting

The microstructure of a high-pressure die-cast hypereutectic A390 alloy, including PSPs, pores, α-Al grains and Cu-rich phases, was characterized using synchrotron X-ray tomography, together with SEM, TEM and EBSD. The Cu-rich phases exhibited a net morphology and distributed at the boundaries of the α-Al grains, which in turn surrounded the PSPs. Statistical analysis of the reconstructed 1000 PSPs showed that both equivalent diameter and shape factor of the PSPs exhibited a unimodal distribution with peaks corresponding to 25 μm and 0.78, respectively.) PSPs morphology with multiple twinning were observed and morphological or growth transition of the PSPs from regular octahedral shape (with a shape factor of 0.85 was mainly caused by the constraint of the Cu-rich phases. In particular, the presence of the Cu-rich phases restricted the growth of the α-Al grains, inducing stress on the internal silicon particles, which caused multiple twinning occurrence with higher growth potential and consequently led to growth transitions of the PSPs.

Experimental characterization, material modeling, identification and finite element simulation of the thermo-mechanical behavior of a zinc die-casting alloy

Many industrially manufactured parts consist of a zinc die-cast material. Since classical constitutive models cannot predict the thermo-mechanical structural behavior of such a material – which exhibits highly non-linear rate-dependent effects, distinct aging properties as well a size-dependence of thin-walled parts –, it is necessary to carry out mechanical experiments under varying conditions as a basis for constitutive modeling. In this article, one major goal is the investigation of the rate-dependence at different temperatures of a zinc die-casting alloy. On the basis of several experiments on thin-walled, cylindrical tubes of Zamak 5, a thermo-mechanically consistent thermo-viscoplasticity model without a yield surface is proposed. Moreover, a concept of material parameter identification is provided and the implementation of the model into a finite element program is shown. Finally, the applicability of the model is proven by comparing an experiment of a complex component part with finite element simulations.

Different aging behaviors at surface layer and central region of a die-casting A380 alloy during heat treatment

Microstructural and hardness evolutions of a vacuum-assistant die-cast A380 (Al-8.67wt.%Si-3.27wt.%Cu) alloy during heat treatment were investigated. Isothermal DSC test at 200 °C revealed that the precipitation reaction in the surface layer was faster than that in the central region. This corresponded with the hardness evolution that the surface layer hardened faster. The hardness increment in the surface layer was higher than that in the central region. Further experimental evidences indicated that the differences were due to the different amounts of heterogeneous nucleation sites for precipitation in the two parts. The influence of the characteristic as-cast microstructure on the artificial aging process is analyzed and discussed in detail.

Influence of Sr and TiB on the Microstructure and Eutectic Temperature of Al-12Si Die-Cast Alloys

In order to develop a new commercial Al-12%Si casting alloy with improved physical properties, we investigated the effect of adding Sr and TiB to the alloy. Al-12%Si alloys were prepared by die casting at $660^{\circ}C$ . The eutectic temperature of the Sr-modified Al-12%Si alloy decreased to $9^...

Application of a Force Model Adapted for the Precise Turning of Various Metallic Materials

The knowledge of cutting forces is critical. They might affect the load of the machine and, in the case of fine turning, the deformation of thin and slim workpieces. The generated forces depend not only on material properties (hardness, tensile strength) and on cutting parameters, but also on the tool edge geometry, that strongly determines the geometry of the chip (thickness and width). This article deals with the application of a force model adapted for precise turning technology. Three different types of materials widely used in mass production were taken into consideration (C45 and KO36 steel types and AS12 die-cast aluminium alloy). The components of cutting force were measured in three directions (Fc , Ff , Fp ) and the specific cutting forces were calculated. The main values of specific cutting forces were introduced for precision turning (k1, 0.1); using this, a new force model was constructed based on the theoretical parameters of the non-deformed chip cross-section (heq is equivalent chip thickness and leff effective length of the edge of the tool) in case of all three examined materials. Investigations revealed that the influence of leff on specific cutting force components is not negligible; however, it has the least effect on kc and is the most influential in case of kp. The errors of the constructed new force models follow Gaussian distribution with low values of standard deviation. Thereby, the models can be applied to estimate cutting force components during the technological process planning procedure with adequate accuracy.

Effect of Artificial Ageing on the Defect Susceptibility of Tensile Properties to Porosity Variation in A356 Aluminium Alloys

The present study aims to estimate the dependence of the tensile properties on microporosity variation in low-pressure die-cast A356 aluminium alloys with respect to various T6 treatment conditions and to investigate the relative contribution of the strain-hardening exponent and damage evolution of eutectic Si particles in terms of the defect susceptibility of the tensile properties to effective void area fraction. The solution treatment was performed for 3, 6 and 12 h at 540 °C, and the artificial ageing was conducted for 4, 16 and 48 h at 140–180 °C. The defect susceptibility of the tensile properties to microporosity variation depends practically upon the ageing time, whereas the solutionising time has a minor effect on the variability in the defect susceptibility. Additionally, the maximum value of the ultimate tensile strength (UTS) achievable in a defect-free condition remarkably increases with the ageing treatment, and it also slightly increases with the solutionising time. The maximum value of the tensile elongation for a defect-free condition depends practically upon the solutionising time, even though it generally decreases with ageing treatment. The main reason that the UTS and elongation exhibit different responses with regard to the solutionising and ageing treatments is the variation in the strain-hardening exponents associated with the T6 treatment. The frequency of the damage evolution of eutectic Si particles by the cracking mode is considerably decreased with the ageing treatment, and this transition under ageing treatment has additional contributions to the variation in the defect susceptibility of tensile properties to effective void area fraction.

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...

Evolution of microstructure and mechanical properties of A356 aluminium alloy processed by hot spinning process

The evolution of microstructure and mechanical properties of A356 aluminum alloy subjected to hot spinning process has been investigated. The results indicated that the deformation process homogenized microstructure and improved mechanical properties of the A356 aluminum alloy. During the hot spinning process, eutectic Si particles and Fe-rich phases were fragmented, and porosities were eliminated. In addition, recrystallization of Al matrix and precipitation of AlSiTi phases occurred. The mechanical property testing results indicated that there was a significant increase of ductility and a decrease of average microhardness in deformed alloy over die-cast alloy. This is attributed to uniform distribution of finer spherical eutectic Si particles, the elimination of casting defects and to the recrystallized finer grain structure.

Evaluation of Elastoplasticity-Dependent Creep Property of Magnesium Alloy With Indentation Method: A Reverse Numerical Algorithm and Experimental Validation

Magnesium (Mg) alloys have been widely used in automotive and aerospace industries due to its merits of exceptional lightweight, super strong specific strength, and high corrosion-resistance, where intermetallic compounds with a small volume are very critical to achieve these excellent performance. This study proposes a reverse analysis that can be employed to extract elastoplasticity-dependent creep property of commercial die-cast Mg alloys and their intermetallic compounds from instrumented indentation with two sharp indenters. First, the creep deformation that obeys the Norton's law (ε˙ = Aσn) is studied, and the parameters of A and n are determined from two indentation experiments conducted with different sharp indenters. Then, a numerical algorithm and dimensional function developed is extended to extract the elastoplasticity of various metallic materials by focusing on the loading stage of indentation experiments. By considering the full loading history with both linear increase and holding stages of loads, we propose a framework of reverse analysis to determine both elastoplasticity and creep properties simultaneously. Parallel indentation experiments on pure magnesium and aluminum and Mg alloys are performed, and the results agree well with the numerical predictions.

Ductile fracture of an Al-Si-Mg die-casting aluminum alloy

Abstract The anisotropic plastic flow and ductile fracture of Al-Si-Mg die-cast aluminum alloy (trade name, Aural2) is investigated using a combination of experiments and analysis. The material is in the form of a 2 mm thick sheet and was received in the –T7 temper. The plasticity of the material is probed using uniaxial tension and plane-strain tension experiments at 3 angles to the material direction, and disc-compression experiments. Good repeatability is obtained in every case. These experiments are used to calibrate the Yld2004-18p anisotropic yield function. This function is flexible enough so that very good fitting of the experiments is obtained. The ductile fracture of the alloy is then probed using notched-tension (with 6 mm and 20 mm notch radii) and central-hole experiments. Each of these specimens is designed so that it provides a different stress triaxiality in the region of rupture, while still requiring only a universal testing machine. Digital Image Correlation is used throughout the experimental work to assess the surface strain fields. However, since the sheet is relatively thick, rupture did not necessarily initiate at the surface. For this reason, fully-3D finite element simulations, using the Yld2004-18p yield function and 3 post-necking hardening models (Swift, Voce and combined) are performed. The surface strains predicted by the simulations depend strongly on the material model adopted. Hence the predicted fracture strains reported here underscore the fact that the plasticity of the material needs to be carefully established before any fracture study is undertaken.