High purification
The main goal of high purification is to improve the electrical conductivity and thermal conductivity of the material as much as possible. For industrial copper containing 99.90% to 99.95% copper, and ultra-pure copper containing 99.99% (4 N) or higher copper, the impurity content requirements are more stringent, such as 99.9999% (6 N) copper. The oxygen content (O) is reduced from 0.01% to 0.05% to 0.001% to 0.006%, and to 0.0002% to 0.0003%. Minimize the impact of impurities on electrical and thermal conductivity. Typical application examples include high-purity copper for network transmission connection wires, high-purity oxygen-free copper for electric vacuum devices, precision guidance and high-fidelity signal transmission, and single crystal copper and ultra-pure copper for superconductors.
The tensile strength of single crystal copper is 24.71% lower than that of polycrystalline copper, the elongation is increased by 2.39 times, the cross-sectional shrinkage is 4.14 times, the resistivity is reduced by 31.7%, which is smaller than 1.72×10-8Ω·m, and its oxygen content is less than 5×10 -6, the hydrogen content is less than 0…5×10-6, and the density is greater than 8.92 t/m3.
Another manifestation of the development of copper-based alloy materials in the direction of high purification is that microalloyed copper alloys require high-purity purification of the copper alloy matrix to ensure that the material has a higher comprehensive performance.
Microalloying
The purpose of microalloying is to sacrifice the lowest thermal conductivity in exchange for other properties, such as a substantial increase in strength. Add about 0.1% of iron (Fe), magnesium (Mg), tellurium (Te), silicon (Si)), silver (Ag), titanium (Ti), chromium (Cr) or zirconium (Zr), rare earth elements, etc., It can improve its strength, hardness, softening temperature resistance or cutting ability. Microalloyed copper is one of the hot spots in the development of copper alloy materials.
The concept of oxygen-free copper is that relative to oxygen-free copper, the copper content of oxygen-free copper reaches more than 99.90%, which is equivalent to ordinary pure copper, but the oxygen content can be controlled between 0.005% and 0.02%, and can reach 100% at the same time The IACS conducts electricity. Because the right amount of oxygen has a certain oxidation effect on the impurity elements between the crystals, it can purify the matrix to a certain extent.
High-strength and high-conductivity copper alloys are favored by materials and science and technology at home and abroad because of their good comprehensive properties. They are the fastest-growing type of copper alloy in recent years. The main elements added after trace alloying are: P, Fe, Cr, Zr, Ni, Si, Ag, Sn, Al, etc. Typical alloy systems include Cu-P, Cu-Fe-P, Cu-Si, Cu-Cr series, Cu-Cr-Cr series, Cu-Ag, Cu-Ag-Cr, Cu-Ag-Zr series, Cu-Sn series, etc., as well as combinations of various alloys and rare earths. The total content of other components in the alloy is at least 0.01% to 0.1%, and generally the highest is not more than 3%. Generally speaking, materials have high strength and high conductivity.
Composite alloying
In order to further improve the strength, corrosion resistance, wear resistance and other properties of copper and its alloys, or to meet the requirements of some special applications, five yuan, six yuan, etc. are added to the existing bronze, brass, etc. A variety of components have realized the different functions of materials such as high elasticity, high wear resistance, high corrosion resistance, and easy cutting. The alloying of multiple components (four or more components) into copper alloys is another hot topic in the development of copper alloys. The composite alloys are endless. It has typical alloy types such as multi-manganese brass, silico-manganese brass, boron-added tin brass, and lead-free free-cutting copper. Its common feature is high toughness, and its tensile strength is generally above 600~700 MPa. Using this material to make automobile synchronous gear ring, high-pressure pump friction pair or electrode copper wedge, its service life is one to several times that of ordinary brass or bronze.
In recent years, as people's awareness of environmental protection has increased, environmental protection has become the theme of world civilization. Harmful elements such as lead, beryllium, cadmium, and arsenic have become more and more harmful to human health. The development of environmentally friendly copper alloy materials such as lead-free easy-cutting brass, beryllium-free high-elastic copper alloy, and arsenic-free corrosion-resistant copper alloy has become the development of copper alloy materials One of the important directions.
Composite materials
There are two main methods for preparing copper alloy materials, one is to introduce alloying elements to strengthen the copper matrix, and the other is to use a second strengthening phase to prepare composite materials. For example, dispersion-strengthened oxygen-free copper is a typical synthetic material, and commonly used dispersed particles are Al2O3, ZrO2, Y2O3, ThO2, etc. The artificial composite method refers to artificially adding second phase particles, whiskers or fibers to copper to strengthen the copper matrix. The copper is reinforced by introducing uniformly distributed, fine and thermally stable oxide particles into the copper matrix. Its second phase composition is generally less than 1% or less than 0.01%, but the strengthening effect on the material is very significant, especially the high temperature strength is greatly improved. For example, Cu-2.5%TiB2 (volume fraction) series alloys have a conductivity of 76% LACS and a tensile strength of 675 MPa; and Cu-0.5%Al2O3 (mass fraction) series alloys have a greenhouse strength of 500~800 MPa , The tensile strength is 85% LACS, the strength of the material can still reach 200~400 MPa after being burned with hydrogen at 900℃.
Another rapidly developing type is in-situ composite materials. In-situ composite materials refer to a type of composite material that is strengthened by exothermic reactions between elements or between elements and compounds in a copper matrix. In this composite material, the reinforcement does not have interface pollution, and has good interface compatibility with the matrix. While maintaining good toughness and high-temperature performance, the strength is also much higher than that of traditional artificial admixture composite materials.