Die-cast Plates Research Articles

Microstructural and tribological investigations of diecast and hard anodized AlSiCu alloys

This work is aimed to understand the impact of the surface characteristics of diecast Al-Si-Cu alloy on the hard-anodizing process. High-pressure die-cast plates made of AlSi9Cu3(Fe), AlSi11Cu2(Fe) and AlSi12Cu1(Fe) alloys were hard anodized in as-diecast condition and after sandblasting and surface milling operations.The thickness and morphology of the anodic layer were investigated using optical and electron microscopy, whereas the tribological properties were evaluated using a reciprocating sliding testing machine under ball-on-flat configuration. The removal of both external eutectic Si segregation and oxide passivating layer due to milling operation is beneficial to increase the thickness of the anodic film, independently of the investigated alloy. However, this leads to a decrease of the abrasion resistance due to the presence of coarser Si particles. Sandblasting removes lower amounts of material and its effect on the anodizing response is more affected by the initial chemical composition of the alloy. The thickness of the oxide layer over the as-diecast surfaces increases by increasing the eutectic fraction and decreasing the Cu content. The greater the amount of α-Al phase in the surface microstructure, the thicker the anodic layer will be. Fine and globular eutectic Si particles lead to a thicker hard anodic layer respect to coarser and plate-like ones. The anodizing response seems in any case to be more related to the amount of α-Al matrix than the shape of Si particles. Higher eutectic fraction with globular eutectic Si particles is useful to increase the tribological properties of the anodic film. Lower eutectic amounts lead to increase the thickness of the anodic film but also to decrease the abrasion resistance.

On the occurrence of weld bead porosity during laser vacuum welding of high pressure aluminium die castings

Due to porosity and incomplete fusion, aluminium high pressure die castings are materials that are known to be difficult to weld. Hereby porosity is mainly caused by hydrogen which is trapped within the weld bead during solidification as a result of insufficient degassing. To enhance degassing and to reduce the influence of surrounding air, laser vacuum welding was applied within the current study. The main goal was to investigate the occurrence of porosity during laser beam welding of aluminium high pressure die castings. To reach this aim, die casting plates were laser welded at varied ambient pressure and investigated by x-ray computed tomography. The analysis of the welds focuses on the size, position, amount and shape of the detected defects depending on the ambient pressure during welding. The results showed a dependency of the occurrence of porosity and the ambient pressure whilst welding.

Aluminum alloy foam core sandwich panels fabricated from die casting aluminum alloy by friction stir welding route

An aluminum foam sandwiches (AFSs) consisting of ADC12 Al–Si–Cu die casting aluminum alloy foam and ADC6 Al–Mg die casting aluminum alloy face plates were fabricated. Using ADC12 die casting plates containing large amounts of gases as the starting material of the foam, ADC12 foam can be fabricated without using a blowing agent. Using FSW, both the uniform dispersion of the segregated gases and pore stabilization powder in the ADC12 die casting plates used to fabricate a foamable ADC12 precursor and the bonding of the ADC12 precursor to the ADC6 plates can be simultaneously achieved. Namely, the AFS precursor is expected to be obtained in fewer processing steps. From the visual observation of the fabricated AFSs, no deformation of the ADC6 plates occurred and the ADC6 plates on both sides of the aluminum foam remained parallel. From the X-ray CT observation of the fabricated AFSs, good pore structures without the infiltration of ADC12 foam into the ADC6 plates can be obtained at a holding temperature of 948K and holding times of t=10 and 11min. In tensile tests on the fabricated AFSs, fracture occurred in the ADC12 foam parts but no fractures were observed at the bonding interface between the ADC12 foam and the ADC6 plates, that is, good bonding was obtained between the ADC12 foam and the ADC6 plates.

The Heat Treatment of Rheo-High Pressure Die Cast Al-Zn-Mg Alloy 7017

The CSIR rheocasting system was successfully used to produce high pressure die cast plates of medium-strength, weldable, wrought Al-Zn-Mg alloy 7017. A solution treatment at 450oC for 5 h leads to insufficient dissolution of Mg and Zn, resulting in inadequate T6 mechanical properties after artificial aging. However, a solution treatment at 470oC for 5 h, followed by water quenching and artificial aging at 120oC for 24 h results in tensile properties comparable to those of wrought alloy 7017 plate and extrusions. The alloy also shows a strong room temperature aging response, making it ideal to be used after welding without any further heat treatment.

内部ガス量を変化させた ADC12 アルミニウム合金ダイカストの作製とそれらを用いた摩擦攪拌法によるポーラスアルミニウム

Various types of ADC12 aluminum alloy die casting plates containing different amounts and types of gases were fabricated by varying the die casting conditions. Porous aluminum without the use of a blowing agent was fabricated by friction stir processing using the gases contained in the fabricated ADC12 aluminum alloy die casting plates. The effect of the amount of gases contained in the die castings on the foaming efficiency and the pore structures of obtained porous aluminum observed by X-ray CT inspection were investigated. It was shown that, although the expansion efficiency of each type of gas was not clear, the total amount of gases and porosity of obtained porous aluminum has good correlation. A porosity of approximately 60% was obtained with small area of pores and highly spherical.

発泡剤不使用の摩擦攪拌法によるアルミニウム合金ダイカストを用いたポーラスアルミニウムの圧縮特性

Porous aluminum was fabricated without the use of a blowing agent by friction stir processing using the gases contained in ADC12 aluminum alloy die-casting plates. The compressive properties of the obtained porous aluminum were investigated. It was shown that a compressive test specimen with a porosity of approximately 70% was obtained that had pores with a relatively small area and high sphericity. Porous aluminum fabricated without the use of a blowing agent exhibited brittle fracture at a relatively high plateau stress and high absorption energy compared with those of ALPORAS.

りん酸塩電解液による陽極酸化処理を施した各種マグネシウム合金の防食機構

Corrosion resistance of anodized surfaces on high-purity magnesium (99.95 mass%), rolled sheets of ASTM AZ31B (Mg-2.9Al-0.85Zn) magnesium alloy and die-cast plates of ASTM AZ91D (Mg-9.1Al-0.75Zn) magnesium alloy has been studied. Anodization was conducted by environment-friendly electrolysis whose electrolyte consists of phosphate and ammonium salt. The anodized surface was covered with amorphous film, and showed only discoloration during salt spray test where formation of corrosion product (magnesium hydroxide) was well suppressed within 605 ks. Even when the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion was well suppressed by formation of new type of dense protective films for each substrate which consist of oxygen, magnesium, aluminum and phosphorus. Anodic polarization curves indicate that the anodized surfaces show sacrificial function due to the thermodynamically unstable state of phosphorus in the anodized layers and its resulting release of electrons. From the viewpoint of kinetics in corrosion on the anodzed surfaces, the curves show that the anodized layers dissolve quite slowly into the electrolyte compared with the case of the untreated substrates. The excellent corrosion protection obtained by the anodization is considered to be based on the formation of a dense protective film on the exposed area, as well as sacrificial function of the amorphous anodized layer.

Mechanism of Corrosion Protection of Anodized Magnesium Alloys

Corrosion resistance of anodized surfaces on high-purity magnesium (99.95 mass%), rolled sheets of ASTM AZ31B (Mg-2.9Al-0.85Zn) magnesium alloy and die-cast plates of ASTM AZ91D (Mg-9.1Al-0.75Zn) magnesium alloy has been studied. Anodization was conducted by environment-friendly electrolysis whose electrolyte consists of phosphate and ammonium salt. The anodized surface was covered with amorphous film, and showed only discoloration during salt spray test where formation of corrosion product (magnesium hydroxide) was well suppressed within 605 ks. Even when the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion was well suppressed by formation of new type of dense protective films for each substrate which consist of oxygen, magnesium, aluminum and phosphorus. Anodic polarization curves indicate that the anodized surfaces show sacrificial function due to the thermodynamically unstable state of phosphorus in the anodized layers and its resulting release of electrons. From the viewpoint of kinetics in corrosion on the anodzed surfaces, the curves show that the anodized layers dissolve quite slowly into the electrolyte compared with the case of the untreated substrates. The excellent corrosion protectivity obtained by the anodization is considered to be based on the formation of a dense protective film on the exposed area, as well as sacrificial function of the amorphous anodized layer.

Corrosion protection of AZ91D magnesium alloy by anodization using phosphate electrolyte*

Mechanism of corrosion protection obtained by anodization for die-cast plates of ASTM AZ91D (Mg–9 mass%Al–0.7 mass%Zn) magnesium alloy has been studied. Anodization was conducted by conventional Dow17 which utilizes chromium oxide (VI), ammonium fluoride and phosphoric acid, and by environment-friendly Anomag whose electrolyte consists of phosphate and ammonium salt. The anodized surface obtained in Dow17 showed local corrosion in salt spray test (SST) after ~500 ks to form corrosion products consisting of magnesium hydroxides. On the other hand, the surface anodized in Anomag was covered with amorphous film, showed only discoloring in SST and corrosion product was scarcely observed. When the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion product was formed on the trench in the case of Dow17, but corrosion was well suppressed by formation of new type of protective film in the case of Anomag. Anodic polarization curves indicate that the surface anodized in Dow17 is protected by passive substances through which electrolyte can easily reach the substrate, and that in Anomag show sacrificial function where the anodized layer dissolves quite slowly into the electrolyte prior to the substrate. The excellent corrosion protectivity obtained in Anomag is considered to be based on the formation of a new type of protective film as well as sacrificial function of the original amorphous anodized layer.

Influence of Casting Defects on Tensile Properties of ADC12 Aluminum Alloy Die-Castings

Cold flakes, one of casting defects, were observed through acoustic microscopy in aluminum alloy die-cast plates (ADC12), and specimens having a cold flake of different sizes were prepared and subjected to the tensile testing. The tensile strength linearly decreased with the size of the cold flake, and the decreasing rate of the strength was greater for the specimen with the exposed cold flake than that with the embedded cold flake. The in-process ultrasonic measurement was carried out during tensile testing, and it was found that the oxide layer of the cold flake was

Effect of Environmentally Friendly Anodization on the Mechanical Properties and Microstructure of AZ91D Magnesium Alloy

Die-cast plates of ASTM (American Society for Testing and Materials) AZ91D magnesium alloy were anodized by DC or AC electrolysis in a solution of phosphate and ammonium salt in which the anodized layer is formed by local discharge, followed by rapid solidification. Salt spray tests of the anodized specimens showed that AC electrolysis increases corrosion resistance and the anodized layers become denser compared with that for DC electrolysis. Tensile strength, elongation, and hardness were also improved by anodization, but higher anodizing bias and the resulting heating caused grain coarsening and a decrease in these properties. For the specimens that displayed remarkable improvement in mechanical properties, a decrease in network precipitates of the β phase was observed. Improvement of mechanical properties is considered to be due to the fine precipitation of β inside the grains of the a phase at moderate temperature.

The Role of Microstructure on Ductility of Die-Cast AM50 and AM60 Magnesium Alloys

Die-cast AM50 and AM60 magnesium alloys have been examined to determine the fracture processes in bending and tension and to elucidate the influences of microstructure and porosity distribution on mechanical properties. The effect of section thickness has been explored using 2-, 6-, and 10-mm-thick die-cast plates. The processes of damage accumulation in terms of crack initiation, growth, and linkage leading to eventual failure have been studied qualitatively using progressive tensile straining experiments and three-point bend studies. The presence of a heterogeneous distribution of porosity played a critical role in the observed differences between strains to fracture in tension and in bending. More rapid damage accumulation at lower strains was observed in the high porosity regions with the rate of damage accumulation strongly dependent on the loading mode. Fracture processes at the microstructural level were characterized by scanning electron microscopy using an in-situ bending fixture. Crack initiation and growth occurred predominantly in the interdendritic eutectic regions, both in the presence of porosity and, to a lesser extent, in pore-free regions. The role of porosity volume fraction and distribution on ductility in these alloys has been examined using a modified Brown–Embury model. This model allows the prediction of fracture location in either loading mode by predicting the critical strains for the onset of cracking in differently strained regions of the test samples.

Corrosion Protection of AZ91D Magnesium Alloy by Anodization Using Phosphate Electrolyte

Mechanism of corrosion protection obtained by anodization for die-cast plates of ASTM AZ91D (Mg-9 mass%Al-0.7Zn) magnesium alloy has been studied. Anodization was conducted by conventional Dow 17 which utilizes chromium oxide (VI), ammonium fluoride and phosphoric acid, and by environment-friendly Anomag whose electrolyte consists of phosphate and ammonium salt. The anodized surface obtained in Dowl7 showed local corrosion in salt spray test (SST) after ∼500ks to form corrosion products consisting of magnesium hydroxides. On the other hand, the surface anodized in Anomag was covered with amorphous film, showed only discoloring in SST and corrosion product was scarcely observed. When the anodized surfaces were trenched with ceramic knife to form locally exposed substrate, corrosion product was formed on the trench in the case of Dow 17, but corrosion was well suppressed by formation of new type of protective film in the case of Anomag. Anodic polarization curves indicate that the surface anodized in Dowl7 is protected by passive substances through which electrolyte can easily reach the substrate, and that in Anomag show sacrificial function where the anodized layer dissolves quite slowly into the electrolyte prior to the substrate. The excellent corrosion protectivity obtained in Anomag is considered to be based on the formation of a new type of protective film as well as sacrificial function of the original amorphous anodized layer.

The Evaluation of Weldability for AZ31B-H24 and AZ91C-F Mg Alloys in Friction Stir Welding

In the present study, an investigation has been carried out on the friction stir welding (FSW) of two magnesium alloys. Hot-rolled and Die-casting plates of AZ type magnesium alloys were successfully joined by friction stir welding. AZ31B-H24 and AZ91C-F plates with the thickness of 4mm were used, and the microstructural development in stir zone (SZ) was investigated using optical and scanning electron microscopes. Hardness of SZ in AZ31B-H24 alloy has been slightly decreased due to the coarse structure. On the other hand, Hardness of SZ in AZ91C-F alloy has been remarkably increased due to very fine recrystallized grain structure. The result of EPMA showed Al Solid solution hardening by Solid solution of β intermetallic compound to α-Mg. While tensile strength of the FSWelded AZ31B-H24 alloy showed about 80% values compare to Base metal, AZ91C-F showed about 68% values due to strongly affected by formation of the intermetallic compounds, β-Al12Mg17.

Acoustic visualization of cold flakes and crack propagation in aluminum alloy die-cast plate

Acoustic images received at different depths of aluminum alloy (ADC12) die-cast plates containing coarse cold flakes were compared with microstructures at the same depth. The bright and dark regions in the acoustic images coincided with the oxide layer on the initially solidified surface of the cold flake and the body of the cold flake, respectively. These results show the ability of nondestructive detection of cold flakes by the ultrasonic microscopy. The specimens were then fabricated to contain the cold flake at a center, and subjected to three-point bending test. When the coarse cold flake existed apart from the tensile side surface of the specimen, a crack initiated at a small cold flake on the side surface and propagated in the specimen. In this case the bending strength was almost the same as the tensile strength (285 MPa) of the die-cast plate. When the cold flake existed on the tensile side surface or at a position less than 0.5 mm inside the surface, the crack propagated along the oxide layer of the cold flake. In this case, the bending strength decreased from the tensile strength when the cold flake approached the side surface. A relation between the bending strength and the position of the cold flake in the specimen was discussed from the standpoint of the fracture mechanics.

Surface compositional inhomogeneity and subsurface microstructures in a thin-walled AZ91D plate formed by hot-chamber die casting

The accumulation of alloying elements and iron impurities in thin-wall AZ91D plate (300 mm × 240 mm × 1.4 mm) formed by hot-chamber die casting were investigated. Mold filling and temperature variation during casting were computationally simulated. The concentrations of alloy elements were examined using a glow discharge optical emission spectrometer (GD-OES). Glancing angle X-ray diffraction (GAXRD) and scanning electron microscopy (SEM) were employed to elucidate the microstructures of the samples. The results reveal that the concentrations of each alloying element and iron impurities in the die cast plate increased in the direction of filling of the melt—from the gate of the running system to the final position of the melt. Al, Zn, Mn and Fe accumulated in the final position where the melt had the lowest temperature and the solid fraction was highest. The chemical compositions at the surface of the die cast had higher concentrations than those in the interior. The subsurface as-cast microstructure and the [0 0 0 2] preferred orientation differed substantially among the positions on the die casting plate. In a position with a high concentration of alloying elements, the microstructures contain the equiaxed α-Mg grains and interdendritic Mg 17Al 12 β phase, and have a weakly preferred orientation. Near the gating system, where the concentration of alloying elements was low, the as-cast microstructure adjacent to the surface comprised columnar grains, exhibiting a relatively strongly preferred orientation. The simulation and experiments reveal that the concentrations of the alloying elements varied along the filling passage in the mold cavity. The size of the passage evidently affects the accumulation of the alloying elements.

Low-cycle fatigue behavior of two magnesium alloys

Magnesium alloys possess many excellent performances, such as low density, high specific strength, excellent thermal conductivity, and machinability. Magnesium alloys, including Mg-Al alloy family, are increasingly considered for structural components, especially in automotive industry. AZ91 alloy with about 9 wt.% Al and 1 wt.% Zn is the most common magnesium die-casting alloy. It has excellent castability and good room-temperature mechanical properties. AE42 alloy with about 4 wt.% Al and 2.5 wt.% rare earth elements shows good creep resistance to 150 ◦C, and is often used for automotive engine components. For both AZ91 and AE42 alloys, few low-cycle fatigue data are available even though their monotonic tensile and creep properties have been well documented [1–6]. In this paper, the low-cycle fatigue behavior of two magnesium alloys including AZ91 and AE42 were investigated. The rectangular fatigue samples with dimensions 14 × 5 × 5 mm in gauge section were directly machined from die-cast plate of each alloy (designated F). Some fatigue samples were subjected to solution treatment in argon at 415 ◦C for 12 hr (designated T4). Fully-reversed pull-push fatigue tests were performed at room temperature in laboratory air under total strain amplitude control mode using Shimadzu servohydraulic testing machine. All tests were run to final separation of sample, and the corresponding cycling number was defined as low-cycle fatigue life. The fatigue life data (total strain amplitude, et/2, versus number of cycles to failure, Nf) of two alloys with F and T4 status are shown in Fig. 1a and b, respectively. It can be seen that at most of total strain amplitudes except for the lowest strain amplitude of 0.3%, the AZ91-T4 alloy gives greater resistance on strain cycling than the die-cast AZ91 alloy. On the other hand, the AE42 alloy subjected to solution treatment exhibits longer fatigue life than the die-cast AE42 alloy at all total strain amplitudes imposed in this investigation. The above-mentioned fact implies that solution treat-

Novel production for highly formable Mg alloy plate

The principle and advantages of multi-pass friction stir processing (FSP) for the production of a highly formable Mg alloy, and some convincing experimental results are reported in this paper. FSP is a solid state processing technique which involves plunging and traversing a cylindrical rotating FSP tool through the material. FSP achieved grain refinement and homogenization of the as-cast microstructure in Mg alloy AZ91D. Multi-pass FSP produced a fine homogeneous microstructure having a grain size of 2.7 μm throughout the plate. The plate containing this FSPed microstructure exhibited fracture limit major strains six times larger than the diecast plate in the fracture limit diagram (FLD). The present study shows that multi-pass FSP is an efficient production method for a large-scale plate of a highly formable Mg alloy.

Nondestructive Detection of Cold Flakes in Aluminum Alloy Die-Cast Plate with Ultrasonic Measurement

Aluminum alloy die-cast plates (ADC 12) were subjected to ultrasonic measurement to obtain a relation between the intensity distribution of the ultrasonic wave and positions of cold flakes appearing in the plate for developing a nondestructive method to detect cold flakes in the die-casts. Die-cast plates of 170 mm in length, 50 mm in width and 6.8 mm in thickness were produced with wider gates to introduce larger cold flakes in the plate. Then the ultrasonic measurement was carried out with the immersion method by using a probe generating a longitudinal wave of 20 MHz in frequency. Intensity distributions of the ultrasonic wave were obtained from the surface to the bottom. The cross section analysis was carried out to examine the distribution of the cold flake. From the cross section analysis, three types of cold flakes were observed: the type A with a straight boundary of initial solidification with oxide thin layer, the type B with a straight boundary without oxide layer, and the type C of an irregular and wavy boundary without oxide layer. In the case of the type C, the oxide layer was thought to be out of the observed section. The ultrasonic wave was slightly reflected from the front and rear boundaries between the cold flake and the matrix, and it was found that the position and the thickness of the cold flake can be detected by ultrasonic measurement.

コンパクト1 kg/h共面放電オゾナイザの開発

A compact coplanar discharge ozonizer, of which electrodes were set on stacked and water-cooled aluminum die-cast plates, was developed. We obtained 1 kg/h ozone gas production and over 300 g/Nm3 (20wt%) saturation concentration of ozone at the pressure of 0.17 MPa. The efficiency was 100g/kWh at 180g/Nm3 when 93% oxygen contents (PSA gas) were used. Moreover, we clarified the effects of gas pressure, feed oxygen gas concentration and gas gap on the ozonizer.