It is inevitable for trace elements to enter copper. Due to the different characteristics of elements, they can not be dissolved in copper, trace solid solution, large amount of solid solution, infinite mutual solution, the solid solubility decreases sharply with the decrease of temperature, and there is a complex phase transition under the solid phase. Therefore, the effects on the properties of copper vary greatly.

hydrogen

The behavior of hydrogen in copper is a subject that people are studying. Hydrogen and copper do not form hydride. The solubility of hydrogen in liquid and solid copper increases with the increase of temperature, especially in liquid copper. During solidification, pores will be formed in copper, resulting in brittleness and surface peeling of copper products;

In solid copper, hydrogen exists in the form of proton. The electrons of hydrogen fill the S-layer orbit of copper atoms to form a proton type solid solution. Although hydrogen has little effect on the properties of copper, hydrogen is harmful to copper and copper alloys. Oxygen containing copper will produce cracks when annealed in hydrogen, i.e. "hydrogen disease", because cu2o+h2 ? 2cu+h2o reaction occurs, and the resulting water vapor will cause pores and cracks;

Various elements have different effects on the solubility of hydrogen in copper. Among them, Ni, Mn and other elements cause the increase of solubility, while P, Si and other elements reduce the solubility of hydrogen in copper. The hydrogen content in copper can be reduced by reducing smelting time, adjusting composition, controlling the hydrogen content in furnace charge, and covering the melt surface with charcoal.

oxygen

Oxygen is inevitable in the production of copper, and its influence is also very important. Oxygen is rarely dissolved in copper, which is 0.06% at 1065 ℃ and 0.002% at 600 ℃ (weight ratio); Oxygen in copper exists in the form of Cu2O except that it is rarely soluble in solid solution. Copper oxide is not soluble in copper and presents cu+cu2o eutectic structure, which is distributed at the grain boundary. The eutectic reaction is: l oxygen content 0.39% 1065 ℃ α The oxygen content is 0.01%+cu2o. The oxygen content in Hypoeutectic copper is directly proportional to the eutectic content. The oxygen content in copper can be accurately determined by comparing it with the standard picture under the microscope.

The effect of oxygen on the properties of copper and its alloys is complex. Trace oxygen has little effect on the conductivity and mechanical properties of copper. Industrial copper has high conductivity because oxygen, as a detergent, can remove many harmful impurities from copper and enter the slag in the form of oxide. In particular, it can remove arsenic, antimony, bismuth and other elements. The conductivity of copper containing a small amount of oxygen can reach 100-103% ± ACS, High purity copper, such as 6N copper, has very low resistance under cryogenic conditions.

The content of oxygen in copper used for electric vacuum components shall be strictly controlled. The reason is that the electric vacuum devices need to be sealed in hydrogen. The presence of oxygen in copper will lead to hydrogen disease and damage to the high vacuum environment of the devices. Therefore, the copper used for electric vacuum should be oxygen free copper. The oxygen content in oxygen free copper is less than 20ppm in Chinese national standards and 3ppm in American ASTM standards. In order to control the oxygen content, In the production of oxygen free copper, high-quality electrolytic copper raw materials should be selected. In the smelting process, reducing atmosphere should be adopted to strengthen the surface coverage of the molten pool, and charcoal protection is generally used;

Generally, deoxidation should be carried out during smelting of copper and copper alloys. Deoxidizers include phosphorus, boron, magnesium, etc. they are added in the form of master alloy. Phosphorus is the most effective deoxidizer. However, the residual amount of phosphorus should be strictly controlled because it can strongly reduce the conductivity of copper and alloys.

phosphorus

The binary solid phase of copper and phosphorus shows that there is eutectic reaction at 714 ℃: l8.4% → α 1.75%+cu3p, as the temperature decreases, the solid solution of phosphorus in copper decreases rapidly, which is 0.6% at 300 ℃ and 0.4% at 200 ℃; Phosphorus dissolved in copper significantly reduced its conductivity. The conductivity of the soft band containing p0.014% was 94%iacs, and the conductivity of the soft band containing p0.14% was only 45.2%;

Phosphorus is the most effective deoxidizer with the lowest cost. The existence of trace phosphorus can improve the fluidity of the melt, improve the welding performance, corrosion resistance and softening resistance of copper and its alloys. Therefore, phosphorus is a valuable additive element of copper and its alloys. Phosphorus copper alloys containing p0.015-0.04% are widely used in the production of building waterway pipes, cooling pipes of refrigeration and air conditioners, and seawater pipelines of ships;

Low phosphorus copper alloy plate and strip are widely used in electronic and chemical industries, and low phosphorus copper alloy is also widely used in integrated circuit lead frame copper strip; Phosphorus copper alloy with eutectic composition is an excellent welding material. High phosphorus copper alloy has superplasticity between 580-620 ℃ and can be hot extruded φ 3- φ 5mm welding wire is an important material for welding copper, copper alloy, steel and copper parts.

Effect of other metal elements on copper

Magnesium, lithium and calcium are limited in solid solution to copper, and manganese and copper are infinitely miscible. These four elements can all be used as deoxidizers for copper; Manganese can improve the strength of copper. Low manganese copper alloy has high strength and corrosion resistance, which is used in chemical engineering. Manganese copper resistance temperature system is very few, so it is an excellent resistance alloy; The transformation of Cu Mn alloy in the solid state is very complicated due to the isomorphic and heteromorphic transformation. In the solid state, it has the processes of amplitude modulation decomposition and crystal transformation, and has the performance of vibration and noise reduction. It is a famous damping material.

Rare earth elements represented by cerium are almost insoluble in copper. Their role in copper is to modify and purify, desulfurize and deoxidize, form high melting point compounds with low melting point impurities, eliminate harmful effects, and improve the plasticity of copper and alloys. Adding rare earth elements to up cast wire blanks can improve plasticity and reduce cold working cracks.

Source: tongxinbao

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