International Annealed Copper Standard Research Articles

Microstructure Evolution and Properties Tailoring of Rheo-Extruded Al-Sc-Zr-Fe Conductor via Thermo-Mechanical Treatment.

Low-cost heat-resistant Al-Sc-Zr-Fe conductor wires were successfully manufactured by continuous rheo-extrusion process, and the mechanical and conductive properties of the materials were analyzed and compared after three different thermo-mechanical treatment methods. The coarse plate-shape Al3Fe phase transformed to small sized rod-like phase after solid solution treatment at 630 °C for 21 h. Direct aging treatment at 300 °C for 24 h led to the refinement and spheroidization of Al3Fe phase with a diameter of 200 nm. After the subsequent aging treatment at 300 °C for 24 h, the tensile strength and conductivity of the alloy wire significantly increased due to the homogeneous precipitation of the coherent spherical Al3(Sc, Zr) phase with an average size of 15 nm. The tensile strength, elongation, and conductivity of the alloy conductor wire after optimized thermo-mechanical treatment reached 165.7 MPa, 7.3%, and 60.26% International Annealed Copper Standard (IACS), respectively. The thermal resistance of the present alloy wire was superior to that of standard AT1 type alloy conductor according to IEC international standard.

Effect of ECAP Process and Subsequent Annealing on Microstructure and Properties of Cu-0.25Se-0.25Te Alloy

Cu-0.25Se-0.25Te alloy has been melted in a vacuum induction furnace and then heat treated. Afterwards, equal-channel angular pressing (ECAP) and subsequent annealing were carried out on the obtained samples. The effects of the ECAP process and subsequent annealing on the microstructure and properties of the alloy have also been investigated by scanning electron microscopy, Vickers microhardness testing, and eddy-current conductivity measurements. The results suggest a morphological evolution of the grains during the ECAP process. The equiaxed grains of the heat-treated alloy initially developed into shapes elongated along the shearing plane, then a series of smaller streamlined strip-like grains appeared and were eventually crushed into fine and equiaxed grains with a size of about 5 μm after different numbers of ECAP passes (one, two, four, or eight), along with a deformed strain e. Furthermore, the microhardness (HV) rose sharply from 68 N/mm2 to 140 N/mm2 and then climbed steadily to 169 N/mm2 under the comprehensive effect of e and the refinement of deformed grains. By contrast, the electrical conductivity decreased slowly from 96.2% international annealing copper standard (IACS) to 93.5% IACS. The microhardness and the electrical conductivity of the samples were found to vary contrarily with the change of annealing temperature and stabilized at 500°C. Notably, the electrical conductivity increased gradually, whereas the hardness of the alloys that were subject to a higher number of ECAP passes decreased remarkably with increasing annealing time at 300°C.

Effect of aging treatment on microstructure and mechanical properties of pure aluminum inoculated with Sc Zr element and graphene

Developing excellent performance conductors with high strength and electrical conductivity is a key issue in the electrical conductor industries. In this paper, an extruded composites containing trace amounts of Sc, Zr and graphene was prepared. Then all samples were extruded into round bars with a final diameter of 6.3 mm. Research results show that the UTS of one stage aging is 181 ± 2.7 MPa and the elongation is 21.4%. The hardness increases rapidly from 25.8HB(Brinell hardness) to 69.8HB within the first 12 h when the aging temperature at 280 °C. During the secondly stage aging, a peak electrical conductivity of 58.5%IACS(International annealed copper standard, 100%IACS = 58.0 MS m−1), which is obtained after a secondary aging at 380 °C for 48 h. A large number of nano-sized precipitates phase with smaller diameter are uniformly distributed throughout the matrix after aging at 280 °C for 24 h. With the increasing of aging time, the size of the precipitates phase increases significantly. This work also provides a good guideline for designing heat-resistant conductors.

Effect of Intermetallic Compound Layer on Peel Strength and Crack Propagation Behavior in Cu/Al/Cu Clad Composites

The effects of interfacial modification in tri-layered Cu/Al/Cu composites by heat treatment on interface stability and crack propagation were investigated. In order to investigate the crack path during the peel test, the intermetallic compound layer with the propagating crack was examined using electron backscatter diffraction (EBSD) analyses. The increase of peel strength from 7.8 to 9.1 N/mm in the tri-layered Cu/Al/Cu composite in the presence of thin discontinuous intermetallic compounds with heat treatment at 200–300 °C was accompanied by the increase of electrical conductivity from 65.3% IACS (International Annealed Copper Standard) to 66.8% IACS. Continuous intermetallic layers consisting of Al2Cu, AlCu, and Al4Cu9 were found in Cu/Al/Cu heat-treated at temperatures above 350 °C and its thickness increased rapidly and reached up to 35.2 μm at 500 °C. The peel strength drastically decreased to 5.75 N/mm after heat treatment at 400 °C, and it gradually increased as the heat treatment temperature was increased to 450 °C (5.91 N/mm) and 500 °C (6.16 N/mm). The increased peel strengths after heat treatment at 450 and 500 °C were accompanied by pronounced serrations of the peel strength–displacement curves. The amplitude of serration increased substantially with increasing annealing temperature from 400 to 500 °C. The major crack along the interface propagated, mostly along the Al2Cu/AlCu boundary with some inclined cracks, propagated through the AlCu and Al4Cu9 intermetallic compound layers. The repetition of crack propagation along the interface and crack deflection through the intermetallic layer as an inclined crack induced the serrated surface on the peeled-off Cu plate, enhancing the interface toughening.

High strength and electrical conductivity of copper matrix composites reinforced by carbon nanotube-graphene oxide hybrids with hierarchical structure and nanoscale twins

Cu matrix composites reinforced with carbon nanotube (CNT)-reduced graphene oxide (RGO) hybrids were prepared by molecular-level mixing (MLM). Hierarchical structure consists of carbon-rich region and carbon-poor region are formed through the self-assemble process by controlling the pH value during MLM process, and nanoscale twins in the Cu matrix are also formed during reduction and sintering process. It was demonstrated that both the hierarchical structure and nanoscale twins contribute to the mechanical properties and electrical conductivity of the composites. The ultimate tensile strength of 2.5 vol% CNT-RGO/Cu composite is 601 MPa, much higher than that of 2.5 vol% RGO/Cu composite (450 MPa) and pure Cu (294 MPa). The obvious grain refinement effect and higher load-transfer efficiency of CNT-RGO hybrids were believed to contribute to the high strength of CNT-RGO/Cu composite. At the same time, satisfied electrical conductivity of 83% and 85% International Annealed Copper Standard (IACS) are retained in 2.5 vol% CNT-RGO/Cu and RGO/Cu composites, respectively. This work provides a better understanding of the architecture design of Cu composites with hierarchical structure and contributes to optimize their mechanical and electrical properties.

A property-oriented design strategy for high performance copper alloys via machine learning

Traditional strategies for designing new materials with targeted property including methods such as trial and error, and experiences of domain experts, are time and cost consuming. In the present study, we propose a machine learning design system involving three features of machine learning modeling, compositional design and property prediction, which can accelerate the discovery of new materials. We demonstrate better efficiency of on a rapid compositional design of high-performance copper alloys with a targeted ultimate tensile strength of 600–950 MPa and an electrical conductivity of 50.0% international annealed copper standard. There exists a good consistency between the predicted and measured values for three alloys from literatures and two newly made alloys with designed compositions. Our results provide a new recipe to realize the property-oriented compositional design for high-performance complex alloys via machine learning.

Accelerating heterogeneous nucleation to increase hardness and electrical conductivity by deformation prior to ageing for Cu-4 at.% Ti alloy

ABSTRACTDeformation bands, especially shear bands were intentionally formed in supersaturated Cu-4 at.% Ti alloy by groove-rolling with 75% area reduction. Cold deformation prior to the ageing process changed the precipitation behaviour of the alloy. The deformed structure with shear bands was maintained, without showing recovery and recrystallisation, even after prolonged ageing at 450°C for more than one day. The thermally stable shear bands act as nucleation initiation sites and prevent the expansion of discontinuous cellular precipitates. The hardness reached a value of 305 Hv and an electrical conductivity of 15% IACS (IACS = International Annealed Copper Standard. 100% IACS is defined as the conductivity corresponding to a volume resistivity at 20°C of 17.241 nΩ), compared to 283 Hv and 13% IACS for conventional solid-solutioned and peak-hardened alloy. In addition, the ageing time to reach the highest hardness was shortened from 720 to 180 min at 450°C.

Nanostructured copper matrix composite with extraordinary strength and high electrical conductivity produced by asymmetric cryorolling

A novel method for fabricating nanostructured copper matrix composite with extraordinary strength and high electrical conductivity using casting, homogenization, and asymmetric cryorolling has been proposed. Microstructural observations were performed by optical microscopy (OM) and scanning electron microscopy (SEM) equipped by energy dispersive spectroscopy (EDS). A nanostructured (grain size < 100 nm) copper matrix composite due to the occurrence of discontinuous dynamic recrystallization (DDRX) and particle stimulated nucleation (PSN) mechanisms with a uniform dispersion of copper oxide particles achieved after 96% asymmetric cryorolling. The yield strength, ultimate tensile strength, and hardness of the 96% deformed copper matrix composite increased from 31.7 MPa, 206.2 MPa, and 29.4 HB (for the annealed sample) to 836.6 MPa, 841.7 MPa, and 103.4 HB, demonstrating 2539%, 308%, and 252% enhancement, respectively. The significant increase in strength and hardness was attributed to severe strain hardening, remarkable grain refinement, uniform dispersion of particles, and effective load transfer. At the same time, the improvement on yield and ultimate tensile strength did not cause serious deterioration in electrical conductivity so that the 96% deformed composite exhibited a high conductivity of 82.10% IACS (international annealed copper standard). Consequently, the copper matrix composite exhibited a good balance in strength and electrical conductivity. With increasing the thickness reduction, the number, and depth of dimples and the sharpness of tearing edges decreased and the failure mode changed from typical ductile fracture (for annealed, 30% and 60% rolled samples) to a combination of shear ductile and brittle fracture (for 90% and 96% deformed samples).

Comparative studies on microstructures and properties of Cu–Ni–M alloys controlled by strong interaction between elements

The heat resistance of copper alloys is desirable to improve while it services at high temperature as electrically and thermally conductive components. In present paper, the strengthening pattern of nickel-based superalloys is expected to be applied in copper alloys. Here the Cu50Ni37.5M12.5 (M = Al, Cr, Mo) alloys were prepared by vacuum arc melting and heat-treated in the corresponding conditions to obtain three different kinds of typical microstructure. The room temperature (RT) properties (hardness and resistivity) and high temperature properties (melting point, softening temperature and variable temperature resistivity) of the three alloys are contrasted and analyzed in detail. The Cu50Ni37.5Al12.5 alloy strengthened through the γ′ phase coherent precipitation shows the best conductivity and highest hardness (5.47 %IACS (International Annealed Copper Standard) and 310.1 HV). The splitting of the γ′ phase is contributing to hardening at high aging temperature. The resistivity-temperature behavior of the three alloys shows that the resistivity with rising temperature consists of the ideal lattice resistivity and the resistivity increment due to the defects. The Cu50Ni37.5Al12.5 alloy has the smallest room temperature resistivity and its resistivity maintains the lowest during the whole heating process (RT-1077K). Therefore, the coherent precipitated γ′ phase is expected to improve the heat resistance of the copper alloys while maintaining its electrical conductivity.

Heat Treatment Effect on the Microstructure and Properties of a High-Strength and High-Conductivity Cu–Nb–Cu Microcomposite

Cu–Nb–Cu microcomposite reinforced by Nb tube was successfully fabricated by accumulative drawing and bundling process. When the strength of the Cu–Nb–Cu composite reaches above 1 GPa, the conductivity can reach 67% International Annealed Copper Standard (IACS). The annealing effects on the microstructure and properties of the Cu–Nb–Cu microcomposite have been thoroughly discussed. Annealing temperature at 750 °C can lead to an obvious change of microstructures. Both the partial spheroidization and further coarsening of niobium filaments in Cu–Nb–Cu microcomposite have been revealed. The influences of the microstructure changes on the mechanical and electrical properties have also been analyzed.

Microstructure and properties of a Cu–Ni–Si–Co–Cr alloy with high strength and high conductivity

A novel Cu-1.01%Ni-0.28%Si-0.14%Co-0.45%Cr (mass percent) alloy with high strength and high conductivity was fabricated. Microstructure, mechanical and electrical properties of the alloy after multi-stage thermo-mechanical treatment were investigated in detail. The alloy has excellent comprehensive properties, with a tensile strength of 810 MPa, yield strength of 777 MPa, elongation of 3.4%, and electrical conductivity of 57.5%IACS (International Annealing Copper Standard). Three kinds of precipitates, (Cr,Co)2Si, (Ni,Co)2Si and Cr, form during aging treatment. Addition of Co element promotes the precipitation of Cr, Ni and Si solute elements from the matrix, while inhibits the growth of the (Cr,Co)2Si. The high strength of the alloy treated by multi-stage thermo-mechanical process is attributed to the dispersion strengthening, sub-structure strengthening, and work-hardening. The multi-aging process and addition of Co effectively improve the electrical conductivity of the studied alloy. The high strength and high conductivity of studied alloy make it as a potential candidate for lead frame materials in electrical and electronics industry.

Effect of SPD Processing on the Strength and Conductivity of AA6061 Alloy

The extruded and artificially aged at 177 °C high strength commercial alloy AA6061‐T651 is subjected to severe plastic deformation (SPD) by cyclic extrusion up to 1000% of the true strain at 400 °C. Unexpectedly, the electrical conductivity of the deformed alloy increased by 10% International Annealed Copper Standard (IACS), while the hardness dropped by only 40 HV. Further, it is shown that low temperature aging at 130 °C after SPD results in the following phenomena: the hardness of the alloy is restored almost to the initial level, with a slight decrease in conductivity, which still remained higher than in the original state. All microstructural parameters of the alloy including aluminum matrix composition, grain size, grain boundaries fraction, and morphology of the precipitates are characterized and correlated with the observed effect of SPD on the strength and electrical conductivity of alloy AA6061.

Evolution of Microstructure and Mechanical Properties in a Single-Stage Aged 7075 Aluminum Alloy Pulse Variable Polarity Plasma Arc Welded Joint

A 7075 aluminum alloy was successfully welded by pulsed variable polarity plasma arc welding (PVPPAW) and the single-stage aging behavior of the 7075 aluminum alloy PVPPAW joint was systematically investigated. The results demonstrated that the tensile strength of the welded joints initially increased and then decreased with the increase of the single-stage aging temperature and time. After single-stage aging at 490 °C for 80 min and at 130 °C for 24 h, the tensile strength of the welded joint was 551 MPa, which was increased by 38.5% compared to the as-welded joint. Moreover, the conductivity was 25% international annealed copper standard (IACS) at room temperature, and the resistance to stress corrosion was improved. The main strengthening phases of the weld center were η′ and η phase. The average precipitate size slightly increased with the increase of the single-stage aging temperature, but no obvious change was observed with the increase of the single-stage aging time. The area fraction was initially increased and then decreased with the increase of the single-stage aging temperature and time.

Effect of Deep Cryogenic Treatment on Microstructure and Properties of Pure Copper Processed by Equal Channel Angular Pressing

A new process combing equal channel angular pressing (ECAP) and deep cryogenic treatment (DCT) is proposed to balance the tensile strength and electrical conductivity of pure copper. The effect of the DCT on the microstructure and properties of pure copper processed by the ECAP is investigated. The optical microscopy (OM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) analyses are used to investigate the microstructure evolution. It shows that as a result of the ECAP, the shear bands are developed, the grains are obviously refined and the dislocation density increases. After the subsequent DCT, the grains are further refined and a large number of dislocations appear. With the increase of ECAP passes, the microhardness and tensile strength increase, however, the elongation to failure and electrical conductivity are degraded. The microhardness, tensile strength, elongation to failure, and electrical conductivity are enhanced by the DCT. The combination of tensile strength ≈423 MPa and electrical conductivity ≈97.9% international annealed copper standard (IACS) is simultaneously achieved after the ECAP (four passes) and DCT (24 h). Tensile properties can be improved by the DCT due to the increase of dislocation density and the grain refinement.

Preparation and electrical conductivity of graphitic carbon-infused copper alloys

Abstract

Influence of selective laser melting process parameters on texture evolution in pure copper

In the present work, Crack-Free pure copper parts with relative densities exceeding 98% are processed by selective laser melting (SLM) using a high-power fiber laser. The influence of different laser scan parameters such as hatch spacing, laser power and scan speed on the texture evolution in the manufactured parts is determined. On the top surfaces, a clear interrelationship between laser scan parameters and crystallographic texture is established. This shows that the texture at the top surface can be very strong especially when a high laser power and a low scanning speed is used. However, a random texture exists in the core of the sample due to successive re-melting and altered heat gradients induced by the application of a 90° scan rotation between subsequent layers. A maximum electrical conductivity of 88% of the International Annealed Copper Standard (IACS) is achieved in the as-built state. Damage to the optical mirror of the SLM machine is observed and recommendations for sustainable up-scalability are proposed.

Fatigue crack initiation and propagation behaviors of solution-treated and air-cooled Cu-6Ni-1.5Si alloy strengthened by precipitation hardening

Fatigue tests were conducted on round bar specimens of a solution-treated and air-cooled Cu-Ni-Si alloy with high solute concentrations of 6% Ni and 1.5% Si. This alloy was strengthened by disc-shaped Ni2Si precipitates, a few tens of nanometers in diameter, formed during air cooling. The results were compared with those of a conventional solution-treated Cu-Ni-Si alloy cooled by water quenching. The correlation between the tensile and fatigue strengths of the two alloys differed completely from the general tendency that enhanced tensile strength brings an increase in fatigue strength. Indeed, the fatigue strength of the air-cooled Cu-Ni-Si alloy was 1.1 times higher than that of the water-quenched alloy, while the tensile strength was only 75% that of the water-quenched alloy. Moreover, the electrical conductivity of the air-cooled specimens in International Annealed Copper Standard (IACS) percentage points was 1.7 times higher than that of the water-quenched specimens. The physical background for the superior fatigue strength of the air-cooled Cu-Ni-Si alloy, including the role of microstructure, is discussed.

Enhancing the oxidation resistance and electrical conductivity of alumina reinforced copper-based composites via introducing Ag and annealing treatment

Alumina-reinforced copper matrix composites with Ag addition were fabricated by internal oxidation. The effects of slight Ag addition (0.92 at%) on electrical conductivity (EC) and oxidation resistance of internal-oxidized copper alumina composites were investigated. The annealing treatments were carried out to promote the diffusion of Ag in copper matrix. Ag was observed to segregate at Cu/Al2O3 interface after being annealed, which may lead to the lower interfacial energy between Al2O3 and copper matrix. The EC increased more than 7.8% after Ag was added. Moreover, annealing CuAl2O3Ag composite at 500 °C for 10 h results in the improvements of both oxidation resistance and EC. The initial oxidation temperature increased from 169 °C to 189 °C and the EC increased from 81.98 ± 0.56% International Annealed Copper Standard (IACS) to 88.19 ± 0.27%IACS. While the EC of CuAl2O3 composites always remained ∼76%IACS which suggests that the annealing treatment has insignificant impacts on EC of CuAl2O3 without Ag.

Microstructure and Enhanced Properties of Copper-Vanadium Nanocomposites Obtained by Powder Metallurgy.

Cu-2.4 wt.%V nanocomposite has been prepared by mechanical alloy and vacuum hot-pressed sintering technology. The composites were sintered at 800 °C, 850 °C, 900 °C, and 950 °C respectively. The microstructure and properties of composites were investigated. The results show that the Cu-2.4 wt.%V composite presents high strength and high electrical conductivity. The composite sintered at 900 °C has a microhardness of 205 HV, a yield strength of 404.41 MPa, and an electrical conductivity of 79.5% International Annealed Copper Standard (IACS); the microhardness and yield strength reduce gradually with the increasing consolidation temperature, which is mainly due to the growth of copper grain size. After sintering, copper grain size and V nanoparticle both maintain in nanoscale; the strengthening mechanism is related to grain boundary strengthening and dispersion strengthening, while the grain boundary strengthening mechanism plays the most important role. This study indicates that the addition of small amounts of V element could enhance the copper matrix markedly with the little sacrifice of electrical conductivity.

The Impact of Particle Reinforcement with Al2O3, TiB2, and TiC and Severe Plastic Deformation Treatment on the Combination of Strength and Electrical Conductivity of Pure Aluminum

It has been found that a high electrical conductivity of 63.1%, the International Annealed Copper Standard (IACS), and high mechanical properties are achieved by the initial aluminum alloy after undergoing four cycles of the severe plastic deformation (SPD) process. It has been found that when TiB2 particles are introduced into aluminum and the samples are subject to SPD, the mechanical characteristics of the aluminum alloy are improved. Microhardness (HV) increases from 329 to 665 MPa, yield strength (YS) increases from 38 to 103 MPa, and ultimate tensile strength (UTS) increases from 73 to 165 MPa while maintaining the initial electrical conductivity of cast aluminum without reinforcing particles (53.9–54.1% IACS).