Alloys In As-cast Condition Research Articles

Response of the solidification microstructure of a high Nb containing TiAl alloy to an isothermal high-temperature heat treatment

Vacuum induction melting device combined with temperature control system was employed to investigate the effect of isothermal heat treatment (IHT) during solidification process on the microstructure evolution of a high Nb containing TiAl alloy. The microstructures of the alloy in as-cast condition and after IHT were studied. The results show that the as-cast microstructures exhibit a significant microstructural inhomogeneity with fine grains in dendrite core and coarse grains in interdendritic region. A new treatment approach by means of a short-term IHT within the β phase field during solidification process is proposed to obtain a uniform and refined microstructure. Compared with the as-cast alloy, IHT can reduce the tendency for crack. This phenomenon is attributed to the improvement of microstructural homogeneity by the elimination of peritectic α phase and the microstructure refinement by β → α transformation.

Influence of Nb addition on vacancy defects and magnetic properties of the nanocrystalline Nd–Fe–B permanent magnets

In present work, influence of Nb addition on vacancy defects and magnetic properties of nanocrystalline Nd–Fe–B permanent magnets, was investigated. Samples with composition (Nd,Fe,B)100−xNbx (where x=6,7,8) were studied in as-cast state and after annealing. Samples were prepared by arc-melting with high purity of constituent elements under Ar atmosphere. Ribbons were obtained by melt-spinning technique under low pressure of Ar. Ribbon samples in as-cast state had amorphous structure and soft magnetic properties. Positron annihilation lifetime spectroscopy PALS has been applied to detection of positron – trapping voids (vacancy defects). With increase of Nb in alloy increasing of vacancy defects concentration was observed. Heat treatment of the samples was carried out at various temperatures (from 923K to 1023K) for 5min, in order to obtain nanocrystalline structure. The aim of present work was to determine the influence of Nb addition and annealing conditions on the vacancy defects and magnetic properties of the Nd–Fe–B- type alloys in as-cast state and after heat treatment.

Microstructural Phenomena Occurring during Early Stages of Cavitation Erosion of Al-Si Aluminium Casting Alloys

The researches have concerned cavitation erosion of AlSi7Mg and AlSi11Mg aluminium casting alloys. The alloys have been investigated in the as-cast condition and after the precipitation hardening. The cavitation erosion tests were performed using vibratory cavitation erosion equipment in 5 minutes. Resistance to cavitation of tested materials was estimated by means of MDE (mean depth of erosion) parameter according to ASTM G32. After the cavitation tests eroded surface of the specimens has been observed by means of scanning electron microscopy. The roughness of the surface was measured on profile contact tester. The best resistance for cavitation erosion exhibited AlSi7Mg alloy after heat treatment, the weakest AlSi11Mg alloy in as-cast condition.

3D-Characterization of AlCu5Mg0.3Mn0.3 and AlCu7Mn0.4 Alloys

Abstract The three dimensional microstructural evolution of cast B206 (AlCu5Mg0.3Mn0.3) and AlCu7 (AlCu7Mn0.4) alloys is studied as a function of solution treatment time by synchrotron tomography. Both alloys are formed by an α-Al matrix, Al2Cu and Al7Cu2(FeMn). 3D microstructural parameters of the aluminides such as volume fraction and interconnectivity are presented for the alloys in as-cast condition and after 4 h, 8 h and 16 h of solution treatment at 530 °C. Morphological evolution is obtained from the mean and Gauss curvature distribution. Finally, target metallography is combined with energy dispersive x-ray analysis to identify the phases remaining after 16 h of solution treatment.

The effect of Ni and V trace elements on the mechanical properties of A356 aluminium foundry alloy in as-cast and T6 heat treated conditions

In this study, the tensile properties of unmodified A356 alloys with trace additions of Ni or V were investigated. The nominal concentrations of these elements were set at 600 and 1000ppm, respectively. Specimens obtained from sand and permanent mould casting in as-cast and T6 heat treated conditions were examined. It was found that the precipitation of Ni-rich intermetallics strongly influences the tensile properties of the sand cast A356 alloy in as-cast condition, leading to a reduction of both the yield strength (Rp0.2) and ultimate tensile strength (UTS) by 87% and 37%, respectively. Conversely, the V addition increased Rp0.2 and UTS by 42% and 25% due to a solid solution strengthening effect. After T6 heat treatment, the sand cast A356 alloys containing V exhibited slightly higher mechanical properties as compared to the A356 reference alloy (≈18%), whereas the detrimental effect of Ni was eliminated. The cooling rate became the main parameter influencing the mechanical properties of permanent mould cast alloys: no significant differences in mechanical properties were observed between the reference alloy and Ni- or V-containing alloys in both as-cast and T6 conditions.

Effect of thermally stable Cu- and Mg-rich aluminides on the high temperature strength of an AlSi12CuMgNi alloy

The internal architecture of an AlSi12CuMgNi piston alloy, revealed by synchrotron tomography, consists of three dimensional interconnected hybrid networks of Cu-rich aluminides, Mg-rich aluminides and eutectic/primary Si embedded in an α-Al matrix. The strength at room temperature and at 300°C is studied as a function of solution treatment time at 490°C and compared with results previously reported for an AlSi12Ni alloy. The addition of 1wt% Cu and 1wt% Mg to AlSi12CuMgNi increases the room temperature strength by precipitation hardening while the strength at 300°C is similar for both alloys in as-cast condition. The strength of AlSi12CuMgNi decreases with solution treatment time and stabilizes at 4h solution treatment. The effect of solution treatment time on the strength of the AlSi12CuMgNi alloy is less pronounced than for the AlSi12Ni alloy both at room temperature and at 300°C.

Effects of Cu Content on Thermal Stability and Wear Behavior of Al-12.5Si-1.0Mg Alloy

This study investigates how Cu content affects thermal stability and wear behavior of Al-12.5Si-1.0Mg alloy, by adding 2.55 and 4.53 wt.% Cu. The low-Cu and high-Cu alloys were isothermally heat-treated at 300 °C for 100 h. The results indicated that the amount of eutectic Al2Cu and Al5Cu2Mg8Si6 particles in the high-Cu alloy was more than that in the low-Cu alloy. These hard particles retained in the Al matrices during isothermal heat treatment, maintaining a relatively stable hardness. Therefore, the hardness of the high-Cu alloy was superior to that of the low-Cu alloy in as-cast condition and after isothermal heat treatment. For wear behavior, both isothermal heat-treated alloys showed the same wear rate with 10 N normal load. The wear rate of Al-12.5Si-1.0Mg alloy was independent on the copper content under 10 N load, but the wear rate at a load of 40 N decreased with increasing Cu content in Al-12.5Si-1.0Mg alloy.

Analysis of Intermetallic Phases in 2024 Aluminium Alloy

The main objective of this study was to analyze the evolution of the microstructure (morphology, composition and distribution of intermetallic phases) in the 2024 aluminium alloy cooled with different cooling rates after solidification process. A few techniques: optical light microscopy (LM), scanning (SEM) electron microscopy combined with an energy dispersive X-ray microanalysis (EDS), X-ray diffraction (XRD) were used to identify intermetallics in the examined alloy. The results show that the microstructure of 2024 aluminum alloys in as-cast condition consisted following intermetallic phases: Al2Cu, Al2CuMg, Al7Cu2Fe, Al4Cu2Mg8Si7, AlCuFeMnSi and Mg2Si.

Hot deformation behavior of Mg–2Sn–2Ca alloy in as-cast condition and after homogenization

The hot deformation behavior of Mg–2Sn–2Ca (TX22) alloy has been characterized in the temperature range 300–500°C and strain rate range 0.0003–10s−1 using isothermal constant true strain rate tests. A processing map has been developed on the basis of flow stress data obtained as a function of temperature and strain rate, which revealed two windows or domains for hot working the alloy: (1) 300–370°C/0.0003–0.001s−1 and (2) 400–500°C/0.005–1s−1. Microstructural observations indicated that dynamic recrystallization occurs in both these windows with a finer resulting grain size in the first window. Apparent activation energy values of 183 and 178kJ/mole have been estimated in these windows, respectively and these are much higher than that for self-diffusion in Mg suggesting that considerable back stress is being generated due to the intermetallic particles (CaMgSn) present in the matrix. The mechanisms involving basal+prismatic slip and recovery by climb in the first domain and that of second order pyramidal slip and softening by cross-slip in the second domain are suggested to be occurring in these two domains. The processing map obtained on homogenized alloy is identical to that of the as-cast alloy suggesting that there is no benefit of homogenization treatment as regards hot workability and this is attributed to the thermal stability of the as-cast microstructure.

Phases in Austenitic Cast Steel

The paper presents the characteristics of intermetallic phases occurring in heat-resistant cast austenitic 0.3% C-30% Ni-18% Cr steel with additions of niobium and titanium. Five alloys were examined, in which the content of the examined elements was (wt.%) Nb 0.03, 0.55, 1.57 and 1.92, and Ti 0.03, 0.05, 0.30, 0.83 and 1.00. The phase composition of alloys in as-cast state and after annealing (temperature of 800°C and 900°C, time of up to 300 hrs) was examined by X-ray diffraction technique. Depending on the chemical composition of cast steel, carbides of MC type (NbC, TiC, (Nb,Ti)C), M23C6, titanium carbonitrides TiCN and G phase were identified in its microstructure. The phase morphology was examined on the polished sections and surfaces of metallographic specimens after deep etching by electrolytic extraction method. It was found that M23C6carbides assume the shape of rods, NbC carbides crystallise in the form of lamellae, and titanium carbonitrides TiCN in the form of cubes. An addition of both the stabilising elements favours the formation of double carbides (Nb,Ti)C of octahedral habit.

X-ray diffraction study of structural and phase states of a superplastic Sn-38 wt % Pb alloy and their variations under the effect of external mechanical stresses and aging

Structural and phase states of the eutectic alloy Sn-38 wt % Pb, which exhibits superplastic properties at room temperature, have been studied using samples that were cast, forged in a hydraulic press to ∼73%, aged in the as-cast state, as well as preliminarily forged samples and samples deformed in the regime of superplasticity. It has been shown that the phase state of the alloy in as-cast condition does not correspond to the equilibrium tin-lead phase diagram. The superplastic flow of the alloy occurs against the background of processes of decomposition of the supersaturated solid solution. In the preliminarily forged samples, the aging is accompanied by an increase in the concentration of lead in the surface layers. This is related, in particular, to the existence of tensile stresses in the tin-based phase and to their relaxation in the process of aging. In the structure of cast and preliminarily forged samples, an amorphous-crystalline component has been revealed, which most likely is located at grain boundaries. The experimental results agree well with the previously obtained results that are indicative of the nonequilibrium character of the initial structural phase state of the Sn-38 wt % Pb alloy and of the occurrence of structural-phase transformations under conditions of superplastic deformation, and substantially supplement them.

Structural Aspects of the Behavior of Lead-Free Solder in the Corrosive Solution

In oxidizing environments, most tin-based lead (Pb)-free alloys form a tin oxide that is easily eroded or mechanically damaged, affecting corrosion resistance and thus reliability of the soldered joints. In this study, the effect of microstructure heterogeneity on corrosion behavior of Pb-free solder candidate systems has been investigated on the example of as-cast and heat-treated alloys. The research was focused on a comparison between the corrosion resistance of binary Sn-Zn and ternary Sn-Zn-Cu alloys. Accelerated corrosion tests were performed by means of electrochemical methods in the sodium sulfate solution (VI), Na2SO4, of about 0.5 M concentration, pH adjusted to 2 by means of concentrated H2SO4 acid. In these tests, the corrosion potentials as well as polarization curves were determined for the selected alloys in as-cast state and after their heat treatment using different combinations of processing parameters. The measurements of basic electrochemical characteristics were made, i.e., the corrosion current (i corr μA/cm2) and Tafel coefficients, both cathodic (b c V/dec) and anodic (b a V/dec) ones. Detailed structural characterization of as-cast and heat-treated alloys before and after accelerated corrosion tests has been made under a wide range of magnifications using light microscopy and scanning electron microscopy observations. The results showed that structural heterogeneity of the examined alloys, attributed to the presence of secondary phases, and affected by their size and distribution, significantly influences the behavior of the examined Pb-free Sn-Zn-based alloys in the corrosive environment.

Three-dimensional rigid multiphase networks providing high-temperature strength to cast AlSi10Cu5Ni1-2 piston alloys

The three-dimensional (3-D) architecture of rigid multiphase networks present in AlSi10Cu5Ni1 and AlSi10Cu5Ni2 piston alloys in as-cast condition and after 4h spheroidization treatment is characterized by synchrotron tomography in terms of the volume fraction of rigid phases, interconnectivity, contiguity and morphology. The architecture of both alloys consists of α-Al matrix and a rigid long-range 3-D network of Al7Cu4Ni, Al4Cu2Mg8Si7, Al2Cu, Al15Si2(FeMn)3 and AlSiFeNiCu aluminides and Si. The investigated architectural parameters of both alloys studied are correlated with room-temperature and high-temperature (300°C) strengths as a function of solution treatment time. The AlSi10Cu5Ni1 and AlSi10Cu5Ni2 alloys behave like metal matrix composites with 16 and 20vol.% reinforcement, respectively. Both alloys have similar strengths in the as-cast condition, but the AlSi10Cu5Ni2 is able to retain ∼15% higher high temperature strength than the AlSi10Cu5Ni1 alloy after more than 4h of spheroidization treatment. This is due to the preservation of the 3-D interconnectivity and the morphology of the rigid network, which is governed by the higher degree of contiguity between aluminides and Si.

Microstructural Characterization of Al-Cu-Fe Alloys in the Quasicrystalline Composition Range

The microstructural changes of six Al-Cu-Fe alloys; A)Al62Cu25.5Fe12.5, B) Al65Cu20Fe15, C)Al68Cu20Fe12, D)Al61Cu26Fe13, E) Al65Cu22.5Fe12.5, F)Al64Cu25.5Fe13.5, where the icosahedral phase is present, have been experimentally studied in both as-cast and annealed conditions by X-ray diffractometry, optical metallography, scanning electron microscopy and hardness tests. The resulting microstructures were characterized to investigate the effect of chemical composition on percentage of icosahedral phase and the changes in hardness obtained in this composition range. It was found that the B) Al65Cu20Fe15alloy showed the microstructure with major amount of icosahedral phase in as-cast condition with a value of 50 area%, while the A) alloy showed the highest amount of icosahedral phase. The hardness of phases after heat treatment increased with respect to alloys in as-cast condition, the hardness of y-Al65Cu20Fe15phase increased between 20-25%, while the l-Al13Fe4 phase increased 9%.

Effect of rolling speed on microstructure and age-hardening behaviour of Al–Mg–Si alloy produced by twin roll casting process

In the present investigation the microstructure and age-hardening behaviour of Al–Mg–Si alloy prepared by twin roll casting (TRC), varying rolling speed (i.e., 3, 4, and 5 rpm), were studied. The as-cast samples were subjected to optical microscopy (OM) to understand the effect of rolling speed on the alloy microstructure. Significant difference in grain size and shape was observed for all the alloys in as-cast condition. The as-cast samples were solutionized at 540 °C for 2 h followed by isothermal heating at 180 °C for different time intervals. Thereafter, the as-cast and solutionized samples were subjected to scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Segregation of solute atoms at grain boundaries were observed for both as-cast as well as solutionized samples. Age-hardening results show that time to attain peak hardness decreases for the alloy produced by higher rolling speed.

Structure and Properties Investigation of a Magnesium Alloy Processed by Heat Treatment and Laser Surface Treatment

The goal of this paper is to present the structure and properties of the magnesium cast alloys in as-cast state and after heat treatment. Moreover the purpose of this paper is to extend a complex evaluation of magnesium alloys after laser surface treatment and the new methodology to determine thermal characteristics of magnesium alloy using the novel Universal Metallurgical Simulator and Analyzer Platform (UMSA). The presented results concern X-ray qualitative and quantitative microanalysis as well as qualitative X-ray diffraction method, light and scanning microscope.

Effect of Heat Treatment on Microstructure and Mechanical Properties of NF6357A Cast Alloy for Wear Resistance Application

The solidification structure of the as-cast consists of the matrix structure that is predominantly austenite and precipitated chromium carbide along the grain boundary. Under these circumstances and where the level of impact is relatively modest, such alloys in as-cast condition will perform. However, at higher levels of impact energy, a point is reached where excessive stress are built up within the component and eventually the materials strength is exceeded and the outcome is complete failure in a characteristic stress fracture mode. If this is to be prevented, it is therefore imperative that the casting be subjected to appropriate heat treatment, to obtain a structure which consist of Cr7C3 carbide and martensite at a hardness range of 650-750HB. The microstructure of NF6357A cast chromium steel containing 2.59% C- 0.7%Si-0.91%Mn-18.54%Cr-0.019%P-0.01%S- balance–Fe after appropriate heat treatment such as quenching and tempering process have been characterised by means of optical microscope, micro hardness tester, optical emission spectrometer and charpy testing machine. The results show that oil quenched samples were found to retained microstructural consistency for casting thicker than 120mm section. For economic argument, air quenched castings of less than 120mm thickness is not only cheaper alternative, but it is also environment friendly. The fracture toughness was found to be fairly consistent between 2.4-2.6%C range. However, at higher carbon level, the fracture process is dominated by the presence of segregated carbide network which act as a weak link in the microstructure. This weak link encourages dislocation pile-up and impaired material toughness.

Pit nucleation on as-cast aluminiuim alloy AW-5083 in 0.01M NaCl

The use of aluminium alloys in a wide range of technical applications is related mostly to the two facts: they facilitate weight saving of final products (if compared to the steel) and they are prone to spontaneous passivity due to the coherent surface oxide layer which impedes further reaction of aluminium with the environment. Among the commercial Al alloys, EN AW-5083 alloy is a representative non-heat treatable Al-Mg based alloy which possesses many interesting characteristics as a structural material, such as low price, moderately high strength, high formability in conjunction with superplasticity and good corrosion resistance in marine atmospheres. Aiming to enhance the knowledge of possible interactions of studied alloy EN AW-5083 in as-cast condition with chloride media, electrochemical measurements were used to follow the pitting behaviour in 0.01 M NaCl. The results of tests have shown that susceptibility of alloy to pitting corrosion is strongly influenced by the microstructural constituents of the alloy in as-cast condition.

Effects of Ce-rich RE additions and heat treatment on the microstructure and tensile properties of Mg–Li–Al–Zn-based alloy

As-cast Mg–5Li–3Al–2Zn– xRE ( x = 0–2.5 wt.%) alloys were prepared under the ambient of pure argon, and the effects of Ce-rich rare earths (RE) and heat treatment on the microstructure and mechanical properties of Mg–Li–Al–Zn-based alloy were investigated. The results show that the main phase compositions of Mg–5Li–3Al–2Zn (LAZ532) alloy consist of α-Mg and AlLi. With the addition of RE, Al-RE precipitate forms, and increases gradually, whereas AlLi phase decreases. The room temperature tensile test reveals that the addition of RE could clearly improves the mechanical properties of alloys which are further improved after heat treatment. In more detail, excellent tensile strength and ductility are obtained in 1.5 wt.% RE containing alloy in as-cast state. After heat treatment, the 1.0 wt.% RE containing alloy attains superior tensile strength. The differences in tensile strength are related to the morphology, distribution of second phases and solid–solution strengthening in different alloy systems. In addition, the fracture pattern of the alloy is predominantly brittle cleavage and tends to be quasi-cleavage with RE addition.

3D Interpenetrating Hybrid Network of Rigid Phases in an AlSi10Cu5NiFe Piston Alloy

Abstract The three dimensional architecture of an AlSi10Cu5NiFe piston alloy in as-cast condition is characterized qualitatively and quantitatively by means of synchrotron tomography and light optical tomography. The same sample is used to correlate and combine the results obtained using both techniques. Synchrotron tomography reveals the long-range interconnectivity, volume fraction and shape of different aluminides present in the studied alloy. The morphology of individual aluminides and their contiguity between each other as well as with the eutectic Si is studied by light optical tomography. The eutectic Si and the Fe-aluminides show a considerable fraction of regions with platelet-like morphologies while the Cu-aluminides and Ni-aluminides show a large fraction of region with convex saddle and convex cylindrical morphologies. The aluminides and the eutectic Si form ≈ 18 vol. % three dimensional hybrid network with a long-range contiguity and interconnectivity located in the interdendritic space.