Wt Pct Copper Research Articles

Benchmark Al-Cu Solidification Experiments in Microgravity and on Earth

Predicting macrosegregation and grain structure, including the columnar to equiaxed transition (CET), in alloy solidification is an ongoing challenge. Gravity-driven melt convection and transport of unattached solid grains complicate such efforts. Cylindrical samples of aluminum alloys containing 4, 10, and 18 wt pct copper are solidified from the bottom upwards on Earth and in microgravity conditions aboard the International Space Station. The chosen alloys possess primary solid densities that are greater than, equal to, and less than their melt densities promoting different gravity-driven solid transport phenomena. Significant differences in grain structure are observed between microgravity and terrestrial samples. All microgravity samples are entirely equiaxed, while the terrestrial samples exhibit a CET. The columnar grains near the cooled surface in the terrestrial samples can only be attributed to melt convection. The Al-4 wt pct Cu terrestrial sample shows evidence of grain sedimentation, while the Al-18 wt pct Cu terrestrial sample exhibits the effects of grain floatation. Measurements of eutectic fraction and solute concentration in the samples show inverse segregation due to shrinkage-driven flow in all samples. Terrestrially solidified samples have areas of high solute concentration that are not uniformly distributed over the diameter, indicating the presence of melt convection. The eutectic and macrosegregation measurements generally have good correspondence. Temperature, grain structure, eutectic fraction, and macrosegregation data are presented as benchmark data to validate future modeling efforts. Heat flux boundary conditions on the sample are determined using thermal modeling. Thermal process parameters are calculated for all samples.

Experimental Investigation on Metallic Droplet Behavior in Molten BOF Slag

In order to better understand the metallic droplet behavior during a slag treatment process, a physical modeling based on the similarity principle was performed in a transparent scaled-down vessel at room temperature. Paraffin oil, 20 wt pct copper sulfate solution, and compressed air were used to simulate the molten slag, metallic droplet, and carrier gas, respectively. The droplets injected into paraffin oil during the experiment were captured by a high speed camera and were analyzed by Image Pro Plus software to obtain the droplet size distribution. The critical droplet size in the physical modeling and slag treatment process is quantitatively correlated. The results show that droplet breakage phenomenon is dominant over its coalescence in the current industrial practice, and droplet breakage is enhanced with increasing gas flow rate and/or lance depth. No significant effect of the nozzle configuration was found on the droplet breakage and coalescence. The droplet size distribution varies with the lance position. Gas flow rate and lance depth are the most important factors for droplet breakage, the extent of which can be reduced through a proper selection of the operational conditions. A linear relationship between the droplet size and the input energy flux is obtained.

Finding the Most Efficient Way to Remove Residual Copper from Steel Scrap

The supply of end-of-life steel scrap is growing, but residual copper reduces its value. Once copper attaches during hammer shredding, no commercial process beyond hand-picking exists to extract it, yet high-value flat products require less than 0.1 wt pct copper to avoid metallurgical problems. Various techniques for copper separation have been explored in laboratory trials, but as yet no attempt has been made to provide an integrated assessment of all options. Therefore, for the first time, a framework is proposed to define the full range of separation routes and evaluate their potential to remove copper, while estimating their energy and material input requirements. The thermodynamic, kinetic, and technological constraints of the various techniques are analyzed to show that copper could be removed to below 0.1 wt pct with relatively low energy and material consumption. Higher-density shredding allows for greater physical separation, but requires proper incentivization. Vacuum distillation could be viable with a reactor that minimizes radiation heat losses. High-temperature solid scrap pre-treatments would be less energy intensive than melt treatments, but their efficacy with typical shredded scrap is yet unconfirmed. The framework developed here can be applied to other impurity-base metal systems to coordinate process innovation as the scrap supply expands.

Effects of Copper and Austempering on Corrosion Behavior of Ductile Iron in 3.5 Pct Sodium Chloride

Although alloying and heat treatments are common industrial practices to obtain ductile irons with desired mechanical properties, related information on how the two practices affect corrosion behavior is scarce. In this study, two ductile irons—with and without 1 wt pct copper addition—were austempered to obtain austempered ductile irons (ADIs). Polarization tests and salt spray tests were conducted to explore how both copper-alloying and austempering heat treatments influenced the corrosion behavior of ductile irons. The results showed that the corrosion resistance of 1 wt pct copper-alloyed ductile iron was better than that of the unalloyed one, while ADI had improved corrosion resistance compared with the as-cast. In particular, the ductile iron combined with the copper-alloying and austempering treatments increased the corrosion inhibition efficiency up to 84 pct as tested in 3.5 wt pct NaCl solution.

Effects of Copper on the Hardenability of a Medium-Carbon Steel

Scrap-based steelmaking is gradually increasing the levels of residual copper present in modern steels. End-quench hardenability tests were conducted on medium-carbon steels containing up to 0.4 wt pct copper to evaluate if current methods are still accurate for predicting the ideal critical diameter as residual copper levels rise. The results indicate that copper’s contribution to hardenability, especially at lower concentrations, may be greater than conventional calculation methods indicate.

Effects of Small Additions of Copper and Copper + Nickel on the Oxidation Behavior of Iron

This study was undertaken to investigate the effect of small amounts of copper and copper + nickel additions on the oxidation rate and oxide/metal interface microstructure of iron. Three iron-based alloys were compared: 0.3 wt pct copper, 0.3 wt pct copper-0.1 wt pct nickel, and 0.3 wt pct copper-0.05 wt pct nickel. Alloy samples were oxidized in air at 1150 °C for 60, 300, and 600 seconds. Pure iron oxidized for 300 seconds was used as a reference material. The parabolic oxidation rate for the iron-copper alloy did not differ from that of pure iron, but the parabolic rate for the nickel-containing alloys decreased by a factor of 2. The microstructure of the iron-copper alloy consisted of a thin, copper-rich layer at the oxide/metal interface. Both nickel-containing alloys had perturbed oxide/metal interfaces consisting of alternating solid/liquid regions. The application of ternary alloy interface stability theories show that the perturbed interfaces arise from unequal diffusivities in the solid γ-iron phase. It is suggested that this perturbed interface microstructure causes the observed decrease in oxidation rate, by limiting the iron supply to the oxide.

Effects of Copper and Malleablizing Time on Mechanical Properties of Austempered Malleable Iron

In this study, both the unalloyed and 1 wt pct copper alloyed white irons were successively treated with a duplex heating process consisting of malleablizing and austempering, and then the effects of copper and processing variables on microstructure and mechanical properties of the austempered malleable iron (AMI) were investigated. The results showed that AMI could effectively shorten malleablizing time to obtain the constituents of irregular graphite, acicular ferrite, and retained austenite in the microstructure. Moreover, 1 pct Cu-AMI had a higher retained austenite content than unalloyed AMI. This is because copper is an austenite stabilizer and acts to delay the start of the transformation into ausferrite. In the case of mechanical properties, AMI increased tensile strength (1083 to 1190 MPa) and impact toughness (16 to 22 J) by 2 to 3 times after 930 °C–20 hours malleablizing treatment as compared to as-cast (572 to 580 MPa and 5 to 6 J). In particular, 1 pct Cu-AMI had better performance than unalloyed AMI except for hardness. In comparison with conventional malleable irons, AMI was found to possess better tensile and impact properties.

The relationship between microstructural and plastic instability in AI-4.0 Wt Pct Cu alloy

The investigation of the effect of plastic deformation on the stability of theθ′ precipitates in an aluminum-4.0 wt pct copper alloy was performed. The alloy was produced by directional solidification, with Ti added as a grain refiner. Hot compression tests were performed at 200 °C in the strain rate range of 10-3 to 10-5 s1 and equivalent strain up to 0.7 on specimens that had been initially heat treated, also at 200 °C, in order to obtain a uniform distribution of theθ0′ precipitates within the matrix. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of the plastically deformed specimens revealed a very heterogeneous distribution of strain. Also, the regions with localized strain contained randomly distributedθ precipitates of nearly equiaxed shape without any preferred orientation relationships to the matrix. Thus, the plastic deformation initiated the transformationθ′ →θ. The flow stress was reduced in the regions in which this transformation had occurred, which further accentuated the localization tendency of the strain. The combined process,θ′ →θ transformation/strain localization, thus developed in an avalanching way.

Steady-state cellular solidification of Al-Cu Reinforced with alumina fibers

The steady-state directional solidification of aluminum-4.5 wt pct copper and aluminum-1.0 wt pct copper alloys reinforced with parallel,continuous, closely spaced alumina fibers is investigated under growth conditions that produce a plane front or cells in corresponding unreinforced alloys. Specimens were designed to have a central reinforced region surrounded by unreinforced metal of the composite matrix composition. Each was produced by pressure infiltration, subsequently remelted, directionally solidified, and quenched to reveal the liquid/solid metal interface. Both unreinforced and composite sections were characterized to determine solidification front morphology and degree of microsegregation. In the unreinforced portion of the samples, the transition from plane-front to cellular solidification was observed to correspond to a coefficient of diffusion of copper in liquid aluminum of 5 − 10−9 m2 − s−1, in agreement with published values. Cell lengths, analyzed using a finite-difference model of microsegregation, are in agreement with the Bower-Brody-Flemings (BBF) model for cell tip undercooling. In the composite portion of the samples, the alloys solidify free of lateral microsegregation for all solidification conditions investigated, in agreement with theory. The shape of the liquid/solid metal interface near the fibers indicates a much lower fiber/liquid metal interfacial energy than fiber/solid metal interfacial energy. In the composite, plane front solidification is therefore not observed even when plane front solidification obtains in the unreinforced alloy. It is shown that geometrical constraint imposed on deep cells by the fibers causes significant increases in cell tip undercoolings, in agreement with current analyses of deep cell solidification.

Electron beam surface modification of a porous bronze-graphite composite

Elemental powders were mixed to obtain a 90 wt pct copper, 8 wt pct tin, and 2 wt pct graphite composite. The porosity level of the sintered specimens was reduced from 25 to 10 pct, which resulted in an increase in the macrohardness value from 17 Hv (90 MPa) to 67 Hv (355 MPa); the density of the sintered specimen was 7.80 g · cm−3. The synthesized material was then subjected to electron beam (EB) surface melting. The resultant surface was homogeneous and the microstructural features were refined. The segregation level and variation in the microhardness were drastically reduced. The morphology of the otherwise irregular pores changed to spherical, thereby reducing their interfacial energy. An intriguing modification in the EB melted layer had a density gradient with depth that is sensitive to the heating time of the material using EB. At a heating time of 250 ms, the upper region of the melted layer was dense and hard; the density and the hardness were 8.5 g · cm−3 and 103 ± 7 Hv, respectively, while the lower region had density of 6.7 g · cm−3 (porosity 22 pct). If the heating time was reduced to 17 ms, the distribution of pores was reversed; the density of upper and lower layers changed to 3.9 and 8.2 g · cm−3, respectively. In spite of the higher density of pores, the EB processed composite exhibited increased hardness, compressive strength, and tensile strength. The formation of pores in the lower EB melted region was explained using a qualitative fluid flow model. The combination of a dense substrate and porous surface was desirable, since the former improved the strength and the thermal conductivity of the composite and the latter could be impregnated with oil to achieve the required lubrication levels.

Electrical conductivity in directionally solidified lead-9 and -20 wt pct copper alloys

Composites consisting of aligned copper dendrites in a lead matrix have been produced by directional solidification processing for potential application as grids in lead-acid batteries. To promote a uniform composite of aligned copper dendrites in a protective lead matrix, two alloy compositions, Pb-9 and -20 wt pct Cu, have been directionally solidified through a temperature gradient,G l of 4.5 Kmm-1 at constant growth velocities which ranged from 1 to 100 µm s-1. With slow growth rates (≲10 µm s-1 ), the copper dendrites were generally columnar and continuous along the sample length; at higher velocities (≳60 µm s-1), they assumed an intricate and equiaxed morphology. In accordance with copper content and growth rate, the electrical conductivity of the directionally solidified composites was found to be as much as a 2.5 times that of pure lead. The results are compared with that predicted by a model based on a geometrical dendrite.

The development of plastic failure modes in crystalline materials: Shear bands in Fcc polycrystals

The structure and crystallography of shear bands formed in aluminum-3 wt pct copper polycrystals was studied by optical microscopy, electron microscopy, and convergent beam electron diffraction. The results are interpreted in light of recent finite element calculations. The importance of localized plastic deformation on material properties, particularly as a direct precursor to failure, is emphasized. Optical and electron microscopy showed that shear bands formed in aluminum-3 wt pct copper deformed in plane strain compression are not associated with microvoid formation or microfracture. Electron diffraction analyses and finite element simulations demonstrated that shear localization is promoted by local rotations of the crystal lattice that inducegeometrical softening. Regions acting as stress or strain concentrators, such as grain boundary triple points and specimen surfaces, were found to be preferential sites for shear band initiation. Texture formation promoted shear band propagation, in the sense that it reduced the misorientation between the shear band planes on each side of a grain boundary.

The effect of semicoherent precipitation on void swelling in Al-Cu alloys

Aluminum-4 wt pct copper alloys previously heat treated (50 h at 473 K) to contain semi-coherent θ′ precipitate were neutron irradiated to a fast fluence of 2.8 × 1026 n/m2 (E > 0.1 MeV) at 328 K to determine the effect of the precipitate on void swelling relative to swelling observed in elemental aluminum under the same irradiation conditions. The ob-served void swelling values were ∼1 and ∼12 pct for the alloy and elemental aluminum, respectively. The broad faces of the θ′ precipitate underwent at least partial coherency loss, the matrix dislocation density increased somewhat, and some of the transmutation-formed silicon segregated to θ′ interfaces and some voids during the irradiation. The θ′ particle size distribution did not change significantly during the irradiation. The swell-ing behavior of the alloy under irradiation was analyzed by extending the rate theory of swelling to include reduction of irradiation-caused point defect concentration by indirect recombination, a result of trapping free point defects at θ′ interfaces. Calculated swell-ing in the alloy using the model agreed well with the experimental observation. Accord-ing to the model the suppression of swelling by θ′ precipitates under the irradiation con-ditions used occurs by extension of the knee of the swelling curve, not by changing the dose exponent for swelling.

Mechanical behavior of cast single phase alloys solidified from undercooled melts

Several ingots (0.0254 m in diam × 0.10 m long) of nickel-30 wt pct copper, nickel-10 wt pct cobalt and iron-25 wt pct nickel were solidified with various undercoolings up to about 200 K, prior to nucleation of the solid. The materials were mechanically tested in the ascast condition. In nickel-30 wt pct copper and iron-25 wt pct nickel alloys the 0.2 pct offset yield strength, ductility and fatigue strength increased with undercooling. A linear relationship was established between 0.2 pct offset yield strength and the square root of secondary dendrite arm spacing in dendritic alloys (undercooled less than 170 K) or that of grain diameter in nondendritic alloys (undercooled more than 170 K). In iron-25 wt pct nickel limited testing indicated improvements in Charpy V-notch impact strength and in fracture toughness with undercooling. No improvement of tensile properties with undercooling was observed in nickel-10 wt pct cobalt, an alloy which solidified normally with very low microsegregation.

Structure and strength of Al, Cu-Al3Ni directionally solidified composites

A series of Al3Ni fiber reinforced composites with a matrix composition varying from pure aluminum to Al-3.3 wt pct Cu were prepared by directional solidification of Al-Ni-Cu alloys. The solidification conditions were kept constant in all cases atG/R ≃ 104 °C · s/mm2 (G is the temperature gradient andR is the growth rate). The mechanical properties of the composites were studied in the as grown and in the heat treated conditions and the results were discussed in terms of the structure and composition. With the techniques used, it was possible to preserve the Al-Al3Ni eutectic composite structure while strengthening the matrix by copper addition. The addition of 1 wt copper to the matrix caused a considerable increase in the mechanical strength, especially after heat treatment, without affecting the ductility. Strength values of the order of 530 MN/m2 were reached in the heat treated composites which is higher than predicted by the rule of mixtures. This is attributed to the high work hardening capacity of the matrix especially in the presence of θ’ phase. Massive Al3Ni rods and dendrites caused premature fracture and reduction in the strength of the composites containing 2 and 3 wt pct copper. Eliminating these defects by using higherG/R values can produce composites with exceptionally high strength.

The effect of solidification microstructure on the corrosion behavior of a columnar aluminum-copper alloy

The morphological and kinetic nature of corrosion of directionally solidified aluminum-4.5 wt pct copper alloy in the as-cast, solutionized and solutionized-and-aged conditions in air-saturated aqueous 3.5 wt pct NaCl solution were evaluated. In the solutionized and solutionized-and-aged conditions the intergranular attack and pitting are similar to those occurring in solutionized wrought alloys; the extent of attack at long times increases with increasing severity of solidification rate. The as-cast alloy exhibits a cored dendritic structure with significant formation of interdendritic nonequilibrium eutectic. Extensive inter dendritic corrosion of the α-phase containing more than 3.2 wt pct copper is seen; α containing less than 3.2 wt pct copper and the θ-Al2Cu phase are cathodic. Corrosion of the as-cast alloy is parabolic with time and increases with increasing severity of solidification rate in proportion to the amount of nonequilibrium second phase.