Good in-depth article, do you know about the effects of rare earths on copper and copper alloys?
1.Rare earth copper
Copper and copper alloys have a series of special properties such as excellent electrical and thermal conductivity, good corrosion resistance, non-magnetism and anti-corrosion to microorganisms and algae in water, easy plastic processing and good weldability, and are easy to cast. It has become an important material in modern industry and is widely used in electronics, electromechanical, aviation, aerospace and other sectors.
Rare earth elements have typical metallic properties and are extremely active in chemical properties. They can interact with almost all elements except inert gases. They are the "monosodium glutamate" in the metallurgical industry.
The application of rare earths in copper and copper alloys has attracted widespread attention from scientific and technological workers in various countries in the 1950s, and has now become a research hotspot. my country began research on the application of rare earths in copper and copper alloys as early as the 1960s. Research at that time focused more on improving the hot and cold processing properties, corrosion resistance and wear resistance of copper and copper alloys, and achieved Some results of practical value have been obtained, but these studies have been progressing slowly, and there are not many areas of development and application.
2. Effect of rare earths on the structure of copper and copper alloys
01Purify tissue
There are two main ways to purify copper and copper alloy structures with rare earths:
(1) Rare earths have a strong affinity with oxygen and sulfur, forming rare earth compounds with higher melting points, strong thermal stability, and small specific gravity, thereby achieving the effects of desulfurization and deoxygenation; rare earth elements can easily react with atomic hydrogen. It acts to generate RH2 or RH3 type stable hydride (R represents rare earth metal). These hydrides are dissolved in the copper alloy in the form of solid solution, thereby eliminating the harmful effects of hydrogen.
(2) Rare earths and Pb, Bi and other elements generate high-melting intermetallic compounds with a higher melting point than copper. Therefore, during the copper melting and casting process, they can remain in a solid state and be eliminated from the liquid metal copper alloy together with the slag to achieve the removal of Pb, The purpose of Bi.
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02Refine the organization
The influence of rare earths on the microstructure of copper and copper alloys is mainly reflected in the refinement of grains, the reduction or elimination of columnar crystals, and the expansion of equiaxed grain areas.
There are three main views on the mechanism of rare earth refining the structure of copper and copper alloys:
(1) Form new crystal nuclei and inhibit grain growth.
(2) Microcrystallization.
(3) Alloying effect.
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03The influence of rare earths on inclusion structure
The influence of rare earths on the structure of inclusions is mainly to change the shape and distribution of impurities. Its main manifestations include the following four types:
(1) Reduce or eliminate dendrites and columnar crystals in the alloy structure.
(2) Make certain impurities in the alloy appear in the form of strips, sheets or even blocks, thus improving or enhancing the mechanical and processing properties of copper and its alloys.
(3) Redistributing certain harmful impurities in the alloy on the microscopic volume of the metal, or affecting the macrosegregation of certain impurities, leading to the improvement of various properties.
(4) Rare earth-containing compounds are adsorbed on the grain boundaries of metals or alloys, reducing the number of low-melting-point harmful impurities on the alloy grain boundaries, thereby weakening the high-temperature temper brittleness of the alloy.
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3. Effect of rare earths on the properties of copper and copper alloys
01Influence on processing performance
Adding an appropriate amount of rare earth metals to copper alloys can improve the casting properties of copper and copper alloys. For different types of copper alloys, the fluidity can be increased by 30% to 40% after adding rare earths.
Adding 0.01% to 0.03% mixed rare earths can significantly increase the high-temperature elongation of deformed lead brass, improve hot processing performance, and reduce or eliminate hot rolling cracking. The removal of impurities by rare earth elements increases the strength of grain boundaries and reduces the number of embrittlement phases, thereby increasing the high temperature σb and δ of copper alloys. Adding rare earth can reduce the residual stress value, and rare earth can improve the cold deformation ability of the material within a certain deformation range (<14%).
02Influence on wear resistance
Rare earth and copper elements can form intermetallic compounds with higher hardness and even distribution. These compounds become resistance to dislocation movement; and rare earth can effectively improve the existence form and distribution of inclusions, reduce the possibility of weakening grain boundaries, and reduce Reduces the chance of cracking along grain boundaries when subjected to load, thus improving wear resistance.
Cast brass containing rare earths has high hardness, good plasticity and toughness, which can shorten the running-in stage and extend the stable wear stage, thereby reducing wear and extending the service life of the workpiece. Adding Ce and B to high manganese aluminum bronze can reduce dry friction and wear by about 20% and lubrication friction and wear by about 50%.
03Effects on mechanical properties and electrical conductivity
The influence of rare earths on the mechanical properties of copper and copper alloys is mainly reflected in hardness, strength, plasticity, etc. When the rare earth content 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 mechanism of the influence of rare earths on the conductivity of copper and copper alloys is generally considered to be: on the one hand, the refining effect of rare earths refines copper grains, increases grain boundaries, and increases the probability of electrical scattering, resulting in an increase in resistivity and a decrease in conductivity. On the other hand, the purification effect of rare earths reduces impurities in copper, weakens lattice distortion, reduces the probability of electron scattering, and improves conductivity.
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4 Conclusion
Rare earths can purify the structure, refine the structure, and change the distribution of inclusions in copper and copper alloys, thereby improving their processing performance, corrosion and wear resistance, mechanical properties, and electrical conductivity. Therefore, rare earths can improve copper and copper alloys. performance has placed more expectations.
Although many rare earth-containing copper and copper alloy materials with industrial significance and practical value have been successfully developed, more copper and copper alloys have not yet used rare earths, so more rare earth-containing copper and copper alloys need to be developed. New alloy materials enable a wider range of applications of rare earths in copper and copper alloys, enabling industrial production. The types of rare earth additives or master alloy products need to be more serialized, and parameters such as adding methods and process conditions need to be more perfect.
At present, many studies are still in the experimental stage. The mechanism, influence rules, key process technologies and other issues of rare earth's ability to improve the properties of copper and copper alloys still need to be further explored. In order to give full play to the advantages of my country's rare earth resources, it is necessary to strengthen the application research and basic theoretical research of rare earths in copper and copper alloys, in order to promote the advancement of rare earth application technology and expand the application scope of rare earths.
