**I. Effect of Rare Earth on the Structure of Copper and Copper Alloys**
**1. Purification of the Material**
Industrial copper often contains various impurities, some of which are present in trace amounts, even below 0.001% (by mass). These impurities can significantly affect the processing properties of copper and its alloys, reducing electrical and thermal conductivity, as well as mechanical strength. Compounds like Cu₂O and Cu₂S are brittle and can cause cracks during cold drawing, lowering the alloy’s electrical performance, corrosion resistance, and weldability.
Rare earth elements help purify copper by forming stable compounds with oxygen and sulfur, which have high melting points and low density. This helps remove these harmful impurities from the melt. Additionally, rare earths react with hydrogen to form hydrides (RH₂ or RH₃), which dissolve in the alloy as solid solutions, eliminating the negative effects of hydrogen. They also form high-melting intermetallic compounds with lead and antimony, which are removed along with slag during casting, improving the purity of the final product.
**2. Refinement of Microstructure**
Rare earths play a key role in refining the grain structure of copper and its alloys. They reduce or eliminate columnar grains and expand the region of equiaxed grains. The mechanisms include:
- **Nucleation Enhancement**: Rare earths form fine, high-melting-point compounds that act as nucleation sites, promoting smaller and more uniform grains.
- **Microcrystallization**: Due to their larger atomic size compared to copper, rare earth atoms can occupy surface defects, hindering crystal growth and leading to finer grains.
- **Alloying Effects**: Although rare earths have limited solubility in copper, they form intermetallic compounds that disperse throughout the matrix, further refining the microstructure.
**3. Influence on Inclusion Structure**
Rare earths alter the shape and distribution of inclusions in copper alloys. They can transform dendritic or columnar structures into spherical forms, reducing the negative impact of impurities such as lead and bismuth. This improves mechanical and processing properties. Additionally, rare earth compounds adsorb at grain boundaries, reducing the amount of harmful impurities there and decreasing high-temperature embrittlement. For example, in bismuth-copper alloys, rare earths change the morphology of Cuâ‚‚O and Cuâ‚‚S from angular to spherical, enhancing overall performance.
**II. Effect of Rare Earth on the Properties of Copper and Copper Alloys**
**1. Improvement of Processing Properties**
Adding rare earth elements enhances the castability of copper alloys. It increases fluidity by 30–40%, improves hot workability, reduces cracking during hot rolling, and enhances machinability. It also improves the welding performance of copper alloys by reducing thermal cracking caused by impurities like Pb, Fe, Si, and Bi.
**2. Impact on Mechanical Properties and Electrical Conductivity**
The addition of rare earths can increase the hardness, strength, and plasticity of copper alloys. However, excessive rare earth may have a negative effect on strength. Regarding electrical conductivity, rare earths both refine grains (increasing resistivity) and reduce impurities (improving conductivity). The net effect depends on the amount added.
**3. Enhanced Oxidation and Corrosion Resistance**
Rare earths improve oxidation resistance without significantly reducing electrical conductivity. They also enhance corrosion resistance by purifying the matrix, forming protective oxide layers, and increasing the corrosion potential of the alloy. This makes them ideal for applications where both conductivity and durability are important.
**4. Improved Wear Resistance**
Rare earths form hard intermetallic compounds that improve wear resistance. They also refine inclusions and strengthen grain boundaries, reducing crack propagation under load. This leads to better performance in applications involving friction and wear.
**III. Rare Earth-Copper Intermediate Alloy**
Direct addition of rare earths during smelting is inefficient due to poor solubility and instability. A rare earth-copper intermediate alloy offers a better solution. It has good fluidity, is easy to mix, and ensures uniform distribution of rare earth elements, maximizing their beneficial effects on the properties of copper alloys.
*Label: Rare Earth Copper Alloy*
*Previous: (Europium (Eu)) Origin and Use of Rare Earth Element Name*
*Next: Application of Rare Earth in Aluminum Alloy*
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