I. Effect of rare earth on the structure of copper and copper alloys
1. Purify tissue
Industrial copper often contains a variety of impurities, although some impurities are very low, even less than 0.001% (mass fraction, the same below), but these impurities will seriously affect the processing properties of copper and copper alloy, reduce conductivity and heat conduction Sex. Brittle compounds such as oxygen, sulfur and copper (Cu2O and Cu2S) can reduce the plasticity of copper. These brittle compounds also produce burrs when cold drawn and reduce the electrical conductivity, corrosion resistance and weldability of copper. There are two main ways to purify copper and copper alloys by rare earths: (1) The affinity of rare earths with oxygen and sulfur is very strong, and the rare earth compounds with higher melting point, strong thermal stability and small specific gravity are formed, so as to achieve desulfurization and deoxidation. Rare earth elements are easily reacted with atomic hydrogen to form RH2 or RH3 type stable hydrides (R stands for rare earth metals). These hydrides are dissolved in the copper alloy in the form of solid solutions, thereby eliminating the harmful effects of hydrogen. (2) Rare earths and elements such as lead and antimony form high-melting intermetallic compounds with a higher melting point than copper. Therefore, in the process of copper casting, they can maintain a solid state and are removed from the liquid metal copper alloy together with the slag to achieve lead removal. The purpose of é“‹.
2, refine the organization
The influence of rare earth on the microstructure of copper and copper alloy is mainly reflected in refining crystal grains, reducing or eliminating columnar crystals and expanding the role of equiaxed crystal regions. There are three main mechanisms for the action of rare earth refined copper and copper alloys: (1) Formation of new crystal nuclei to suppress grain growth. Rare earths can react with some elements in copper and its alloys to form high melting point compounds, often suspended in the melt with very fine particles, which become a dispersed crystalline core, which makes the grains more and smaller, and from the solidification principle and thermodynamics. From the point of view, since the rare earth is concentrated in the liquid phase at the front of the solid-liquid interface, the composition is supercooled when the alloy is solidified, solidified and grown in a dendritic manner, and at the same time, a neck is formed at the branching node, and the melting is increased, and the crystal is increased. The core, thus refining the grains. (2) Microcrystallization. Since the atomic radius of the rare earth element (0.174 nm to 0.204 nm) is 36% to 60% larger than the atomic radius of copper (0.127 nm), the rare earth atom can easily fill the grain new phase of the growing copper or copper alloy. Surface defects, forming a film that hinders the continued growth of crystal grains, thereby refining into crystallites; (3) alloying. The solubility of rare earths in copper is small, generally only a few parts per thousand to a few ten thousandths, but rare earths and copper can form a variety of intermetallic compounds. These intermetallic compounds are dispersed in the matrix to refine the grains.
3. Effect of rare earth on inclusion structure
The influence of rare earth on the inclusion structure is mainly to change the shape and distribution of impurities. There are four main manifestations: (1) Reducing or eliminating dendritic crystals and columnar crystals in the alloy structure, which is related to the fact that rare earths form refractory compounds with certain impurities and are in a dispersed state. (2) Some of the alloys in the form of strips, flakes or even blocks (such as lead, antimony, etc., some of which can form low-melting eutectic) turn into spots or spheres, thereby improving or improving copper The mechanical and processing properties of its alloys, which are due to the strong activity of rare earth metals, can make the wettability of copper with some impurities such as lead sharply reduced. These impurities make the volume greatly under the action of their own surface tension. Zoom out. (3) Some harmful impurities in the alloy are distributed between the dendrites or grain boundaries, and are more uniformly distributed throughout the crystal, so that the impurities are redistributed on the microscopic volume of the metal, or for certain impurities. Macro segregation has an impact, resulting in improved performance. (4) The rare earth-containing compound is adsorbed on the grain boundary of the metal or alloy to reduce the amount of low-melting harmful impurities on the grain boundary of the alloy, thereby weakening the high-temperature temper brittleness of the alloy. For example, in the case of bismuth copper alloy, the inclusions are mostly irregularly angular Cu2O and Cu2S. After adding appropriate amount of rare earth, the inclusions are all spheroidized, and the rare earth inclusions replace Cu2O and Cu2S, so that the inclusions are solid solution. The state changes to the precipitation of a rare earth compound.
Second, the effect of rare earth on the properties of copper and copper alloys
1. Effect of rare earth on the processing properties of copper and copper alloy
Adding an appropriate amount of rare earth metal to the copper alloy can improve the casting properties of copper and copper alloy. For different types of copper alloys, the fluidity can be increased by 30% to 40% after the addition of rare earth. For high manganese aluminum bronze, when the amount of rare earth added is not more than 0.15%, the fluidity increases as the amount of rare earth added increases. Adding 0.5% to 1.0% mixed rare earth in high-lead bronze (ZQPb25 - 5) and 0.04% to 0.05% mixed rare earth in HPb59 - 1 lead brass can improve the segregation or reverse segregation of the alloy. The addition of 0.01%-0.03% mixed rare earth can significantly improve the high temperature elongation of the deformed lead brass, improve the hot workability, and reduce or eliminate the hot rolling cracking phenomenon. The addition of rare earth can reduce the residual stress value, and the rare earth can improve the cold deformation ability of the material within a certain deformation range (< 14 %). The addition of 0.03% to 0.05% rare earth in the deformed lead brass can greatly improve the machinability, especially the surface roughness, burrs and tool wear. Rare earth additives have a good effect on improving the welding process performance of copper and its alloys. Impurities in the weld metal such as trace amounts of Pb, Fe, Si and Bi can cause thermal cracking, and the addition of rare earth elements will effectively prevent this tendency.
2. Effect of rare earth on mechanical properties and electrical conductivity of copper and copper alloys
The influence of rare earth on the mechanical properties of copper and copper alloy is mainly manifested in hardness, strength and plasticity. When the content of rare earth in pure copper is 0.1% to 0.2%, the strength increases greatly, and when it is higher than 0.2%, the strength increases slowly. The effect of rare earth on the strength of H68 brass has a dual effect: on the one hand, the solid solution strengthening and purification of rare earth increases the strength of the material; on the other hand, when the amount of rare earth exceeds a certain value, the harmful effect of rare earth masks A favorable effect, the macro performance is the decline in strength.
The mechanism of the influence of rare earth on the conductivity of copper and copper alloy is: on the one hand, the refinement of rare earth causes the grain of copper to refine, the grain boundary increases, the probability of electro-scattering increases, resulting in an increase in electrical resistivity and a decrease in electrical conductivity; On the one hand, the purification of rare earth reduces the impurities in copper, the lattice distortion is weakened, the probability of electron scattering is reduced, and the conductivity is improved. These two factors that counteract the conductivity simultaneously exist, and the influence varies with the amount of rare earth added.
3. Effect of rare earth on oxidation resistance and corrosion resistance of copper and copper alloy
In order to solve the contradiction between oxidation resistance and high electrical conductivity, rare earth metals are added as alloying elements of copper and copper alloys. It was found that when the amount was properly added, the conductivity did not decrease but increased slightly, and it was also found that rare earth was added to the copper.
Can significantly improve the oxidation resistance. The corrosion resistance of rare earths added to copper and copper alloys has been improved to some extent. The explanations for this phenomenon are as follows: (1) Purification of rare earths to eliminate impurities in copper matrix. (2) Forming a dense oxide layer on the surface of copper and copper alloys to prevent outward diffusion of matrix atoms and inward diffusion of external atoms. (3) Improve the corrosion potential of copper and copper alloys. (4) The addition of rare earth reduces the crystallization temperature range of the copper alloy.
The addition of mixed rare earth can not only improve the corrosion resistance of tin brass, but also change the corrosion morphology of tin brass, which not only reduces the thickness of the easy-to-peel layer, but also greatly reduces the thickness of the permeation layer.
4. Effect of rare earth on wear resistance of copper and copper alloy
Rare earth and copper elements can form intermetallic compounds with high hardness and uniform distribution. These compounds become the resistance to dislocation motion; and rare earth can effectively improve the existence form and distribution of inclusions, reduce the possibility of weakening grain boundaries, and reduce the possibility of reducing the grain boundary. The probability of cracking along the grain boundary when subjected to load, thus improving the wear resistance. Casting brass containing rare earth has high hardness and good plasticity and toughness, which can shorten the running-in time and prolong the stage of stable wear, thereby reducing wear and prolonging the service life of the workpiece. Adding rare earth to high manganese aluminum bronze can reduce dry friction and wear by about 20%, and reduce friction and wear by about 50%.
Third, rare earth-copper intermediate alloy
In the practical industrial application of rare earth in copper and copper alloys, the difference in atomic radius between rare earth and copper is not conducive to solid solution, and the fluidity is poor. Adding rare earth directly in the smelting process of copper and copper alloy will cause a large amount of burning. The slag phase is damaged and it is difficult to control the stability and uniformity of the distribution of rare earth elements in copper and copper alloys, which seriously affects the improvement effect of rare earth on various properties of copper and copper alloy.
Rare earth-copper intermediate alloy is a eutectic alloy body of rare earth and copper. It retains the characteristics of rare earths and has good solid solubility in copper and copper alloys. Therefore, it has strong fluidity and is easy to join. The mastery of the quantity and the uniformity of the stirring control can greatly exert the beneficial properties of the rare earth in copper and copper alloy.
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Label: Rare Earth Copper Alloy
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