Effect of alloying elements on copper and copper alloys
Oxygen is almost insoluble in copper. When the copper containing oxygen solidifies, oxygen is precipitated in the form of coprystalline, and distributed on the boundary of copper. When the oxygen content of as cast copper is very low, the subconcrystal, CO crystal and hypereutectic with Cu2O appear successively with the increase of oxygen content.
The co-existence of oxygen and other impurities has a very complex effect, such as the oxidation of trace impurities Fe, Sn, P in high purity copper by micro oxygen, so as to improve the conductivity of copper. If the impurity content is more, the effect of oxygen is not obvious.
Oxygen energy partially weakens the effect of sb and Cd on copper conductivity, but does not change the effect of as, s, Se, Te, Bi on copper conductivity.
P, CA, Si, Li, be, Al, Mg, Zn, Na, Sr, B can be used as deoxidizer of copper, among which p is the most commonly used. When the P content reaches 0.1%, the mechanical properties of copper are not affected, but the conductivity of copper is seriously reduced. For high conductivity copper, the phosphorus content should not be greater than 0.001%.
In some cases, a certain amount of oxygen is specially reserved in copper. On the one hand, it has little influence on copper properties. On the other hand, Cu2O can react with impurities such as Bi, Sb, as, and form spherical particles with high melting point distributed in the grains, eliminating the embrittlement of grain boundaries.
When the oxygen content is between 0.016% and 0.036%, the tensile strength of copper increases with the increase of oxygen content, but the plasticity and fatigue limit of copper will decrease, and the increase of oxygen content has little influence on copper conductivity.
When the oxygen content is 0.003% - 0.008%, and the iron content is between 0.06% and 2.09%, the conductivity and elongation of copper decrease with the increase of the two elements content, while the tensile strength and fatigue strength increase significantly.
When oxygen and arsenic coexist, it has no obvious effect on the mechanical properties of copper, but it can reduce the conductivity of copper.
The solubility of hydrogen in liquid-solid and solid copper increases with the increase of temperature. Hydrogen forms intermittent solid solution in solid copper, which improves the hardness of copper.
When the oxygen containing copper annealed in hydrogen, hydrogen can react with Cu2O in copper to produce high pressure water vapor, which makes copper rupture, which is commonly known as "hydrogen disease". The occurrence of hydrogen disease is related to the degree of harm and temperature. At 150 ℃, because the water vapor is in the condensed state, it will not cause hydrogen disease, and the oxygen containing copper can be put in hydrogen for 10 years and will not break; at 200 ℃, it can be placed for 1.5A, and only 70h in hydrogen at 400 ℃. No hydrogen disease occurs in copper deoxidized with mg or B.
The solubility of sulfur in room temperature copper is zero, and the dispersion particle of Cu2S is used in copper, which reduces the conductivity and thermal conductivity of copper, but greatly reduces the plasticity of copper and improves the cutting performance of copper.
The trace selenium in copper is in the form of cu2se compound, and the solubility of selenium in solid copper is very low, which has little influence on copper conductivity and thermal conductivity, but it significantly reduces the plasticity of copper and greatly improves the cutting performance of copper.
The solubility of tellurium in solid copper is very small, and the dispersion particle of cu2te has little influence on the conductivity and thermal conductivity of copper, but it can improve the machinability of copper.
Copper containing 0.06% - 0.70% te has been applied in industry. It is also used in quenching and processing state. Do not temper, so as to avoid cu2te precipitation along the grain boundary, which makes the material brittle.
The weldability of copper was significantly reduced by trace (0.003%) selenium and tellurium (0.0005% - 0.0030%).
The maximum solubility of phosphorus in copper (at 714 ℃ eutectic temperature) is 1.75%, and almost zero at room temperature, which significantly reduces the conductivity and thermal conductivity of copper, but has a good influence on the mechanical properties and welding properties of steel. Therefore, in the copper deoxidized with phosphorus, a certain amount of residual phosphorus is required. Phosphorus can improve the fluidity of copper melt.
The phosphorus content of oxygen free copper used for direct packaging of electric vacuum is better than 0.0003%, otherwise, the oxide film of boronizing treatment is easy to peel off, which can cause leakage of electronic tube. Si, Mg and so on also have similar effects with phosphorus.
The solubility of arsenic in copper can reach 6.77% at the eutectic temperature. A small amount of arsenic can improve the processing performance of oxygen containing copper, and the mechanical properties are very small. The recrystallization temperature of copper is significantly improved, and the conductivity and heat conductivity of copper are reduced.
As can react with Cu2O in copper to form copper arsenate with high melting point, eliminate Cu + Cu2O co crystal on the grain boundary, and improve the plasticity of copper.
Copper containing 0.15% - 0.50% arsenic can be used for the manufacture of components working in high temperature reduction atmosphere and low pressure water heater in power plant.
The solubility of antimony in copper can reach 9.5% at the eutectic temperature of 645 ℃, and it decreases rapidly with the decrease of temperature.
Antimony reduces the corrosion resistance, conductivity and thermal conductivity of copper. The Sb content of electrical copper shall not be greater than 0.02%. Antimony can react with Cu2O in oxygen containing copper to form spherical particles with high melting point, which are distributed in the grains, and can eliminate the Cu + Cu2O co crystals on the grain boundaries and improve the plasticity of copper.
The solubility of bismuth in copper is negligible, and the solubility of bismuth in copper is only 0.01% even at 800 ℃. The co crystal formed between bismuth and copper at 270 ℃ and the bismuth film distributed at the grain boundary, which seriously reduced the processing performance of copper. Therefore, the content of the product should not be greater than 0.002%.
The effect of Bi on the thermal conductivity and conductivity of copper is not significant. The copper of vacuum switch contact can contain 0.7% - 1.0% Bi. Because it has high conductivity, it can prevent the switch from sticking, improve its working life and ensure the safety of operation.
Lead is not solid soluble in copper, and it is distributed in fusible eutectic with black particle, and exists on the grain boundary.
PB has no significant influence on copper conductivity and thermal conductivity, and can also greatly improve the machinability of copper. Copper alloy containing 1.0% Pb is used to process high-speed cutting parts.
Pb seriously reduces the high temperature plasticity of Cu, that is, elongation δ and surface shrinkage ψ decrease sharply, and the high temperature brittle zone also increases with the increase of copper content.
The solubility of iron in copper can reach 3.5% at 1050 ℃ and 0.15% at 635 ℃. The beneficial effects of iron are: refining copper grains, delaying the recrystallization process of copper, and improving its strength and hardness.
Iron can reduce the plasticity, conductivity and thermal conductivity of copper.
If iron is independent in copper, copper has ferromagnetism.
Copper alloy containing 0.45% - 4.5% Fe has high strength and good heat resistance, conductivity, weldability and processability. It is a kind of electrical material which has been applied.
When assembling some electronic devices, the lead frame should be able to withstand 350 ℃ for several minutes and high temperature of up to 500 ℃ for several seconds. Therefore, the iron-bearing C19400 and c19500 alloys are selected as lead frame materials because of their good conductivity, strength and oxidation resistance.
The solubility of silver in copper is 7.9% at the eutectic temperature 780 ℃, but only about 0.1% at room temperature. However, the copper alloy containing 0.5% Ag may be a single solid solution in the actual production.
The conductivity and thermal conductivity of copper are not decreased much when the content of silver is small, and the effect on plasticity is also very small, and the recrystallization temperature and creep strength of copper are significantly improved. Therefore, the high copper alloy containing 0.03% - 0.25% Ag has become a kind of electrical materials with great practical value, such as C11300, c11400, c11500, c11600, c15500, etc. Silver containing copper belt is a widely used material for automobile water tank.
C15500 alloy (99.75cu-0.11ag-0.06p) containing Ag is a good lead frame material, which has high conductivity and high strength and softening resistance.
Beryllium is one of the effective deoxidizers of copper, but it is not used as deoxidizer because of its high price and difficult to add, but it is the main alloy element of beryllium bronze. The effect of beryllium as impurities on the mechanical properties and technological properties of copper is very small. The conductivity and thermal conductivity of copper are decreased, and the oxidation resistance of copper is improved obviously.
The micro aluminum solution as impurities has no obvious influence on the mechanical and technological properties of copper, but it can reduce the conductivity, thermal conductivity, brazing welding and tin plating performance of copper, and improve the oxygen resistance of copper.
At the eutectic temperature of 485 ℃, the solid solubility of magnesium in copper is 0.61%, and decreases sharply with the decrease of temperature. Therefore, the alloy with high magnesium content (2.5% - 3.5%) has precipitation hardening effect.
The magnesium content of the practical application Cu Mg alloy is less than 1%, for example, the copper alloy containing 0.3% - 1.0% Mg is used for processing conductive wire rod. These alloys have no aging effect and can only be strengthened by cold working. The conductivity of copper is decreased slightly by trace magnesium, and the oxidation resistance of copper is improved, and deoxidation is also achieved.
Lithium, boron, manganese, calcium
These elements deoxidize copper. Lithium, as impurities, can produce high melting point compounds with impurities such as bismuth in copper, which are distributed in the grains in fine dispersion state, which can improve the high temperature plastic residence of copper, and the micro lithium hardly affects the conductivity and thermal conductivity of copper.
The remaining 0.005% - 0.015% B as copper deoxidizer can refine the copper grains and improve the mechanical and technological properties of copper.
Manganese can be used as deoxidizer of copper. Generally, it contains 0.1% - 0.3% Mn in the deoxidized copper, which is solid soluble in copper. On the one hand, it can improve the softening temperature of copper, on the other hand, it is beneficial to the mechanical and technological properties of copper.
Calcium is almost insoluble in copper. As impurities, calcium can form high melting point compounds with impurities Bi, and distribute in the grains uniformly in the form of particle, so as to improve the high temperature plasticity of copper.
rare earth element
Rare earth elements are almost insoluble in copper, but a small amount of rare earth metals, whether alone or in mixed form, are beneficial to the mechanical properties of copper, but the effect on copper conductivity is not significant. These elements can form high melting point compounds with impurities such as lead and bismuth in copper, and they are distributed in the grains with fine spherical particles, which refine the grains and improve the high temperature plasticity of steel.
The process performance of copper can be improved by adding 0.008% rare earth to copper; when less than 0.l% y is added, the mechanical properties and technological properties of copper are improved; the mechanical properties, conductivity and softening resistance temperature of copper alloy containing 0.01% - 0.15% LA are better than that of cu-0.15ag alloy, which has been applied in industry.
Refractory metals and other metals
Tungsten, molybdenum, niobium, uranium, plutonium and other elements are almost insoluble in copper, while titanium, zirconium, chromium, cobalt and other elements are solubilized in copper in a small amount. However, they all refine copper grains to varying degrees, improve recrystallization temperature and neutralize the harmful effects of some fusible impurities, which is beneficial to improving high temperature plasticity.
Copper alloy containing a small amount of zirconium (cl5000, c15100, c18100), cobalt (c17110, C17500), chromium (c18400, c18200, c18500) has been applied in industry and has become a good electrical material.
The melting of iron in solid copper is very small, and the iron rich particle is distributed in α matrix, which has the function of refining grain. H60 brass added 0.3% - 0.6% Fe, which had strong grain refinement effect, but the iron content of the anti magnetic copper should be less than 0.3%.
The mechanical properties of brass were not affected by impurity iron.
Lead and bismuth
Lead and bismuth are harmful impurities in general brass, and bismuth is more harmful than lead.
Lead is granular in the fusible eutectic at the grain boundary. If the lead content of α brass is more than 0.03%, the hot brittleness will appear, which has no obvious effect on the cold working performance. Lead has no great influence on the processing performance of duplex brass, and its allowable content can be slightly higher.
Bismuth is continuously brittle film distributed on the grain boundary in brass, which makes brass brittle during cold and hot working.
If the heating speed is too fast, the cold-rolled brass with lead and bismuth content exceeding the allowable limit will burst suddenly.
The brass containing lead and bismuth added a small amount of elements such as zirconium, which made them form high melting point compounds, which can eliminate their harm.
The solubility of antimony in copper decreases sharply with the decrease of temperature. When the content of antimony is less than 0.1%, Cu2Sb will be formed, which is distributed in the grain boundary in a net way, which makes the cold working performance of brass decrease greatly.
Antimony also makes copper alloy brittle.
The addition of lithium in brass can form a high melting point compound li3sb, which is distributed in the grains in small particles, thus eliminating the adverse effect of antimony.
Because of the high melting degree of antimony in copper at high temperature, the solid solution treatment can improve the cold working performance of antimony containing brass.
The solid solubility of P in α copper is very small, and a small amount of phosphorus has grain refinement effect, which improves the mechanical properties of brass. When the phosphorus content of brass is more than 0.05%, cu3p in brittle phase will be formed, which will reduce the processing performance of brass.
Phosphorus significantly increased recrystallization temperature of brass, which made recrystallization grains coarse and fine.
The solubility of arsenic in room temperature brass is less than 0.01%, and cu3as, which is a brittle phase compound, is formed when the content is large, which is distributed at the grain boundary, which reduces the processing performance of brass. The corrosion resistance of brass containing 0.02% - 0.05% as can be improved without dezincification.
The phosphorus content of tin bronze is generally less than 0.45%. When the phosphorus content is more than 0.5%, the eutectic cladding reaction will occur at 637 ℃ and the hot embrittlement will be caused. When the phosphorus content of the alloy is more than 0.3%, the coprystalline of copper and copper phosphates (cu3p) will appear in the structure.
Phosphorus is an effective deoxidizer for copper alloy, which improves the fluidity of tin bronze. The disadvantage is to increase the reverse segregation of ingots.
The grain size before cold working and annealing (180-300 ℃) after cold processing have a great influence on the mechanical properties of tin phosphor bronze. When the grains are fine, the strength, hardness, elastic modulus and fatigue strength of the materials are higher than that of coarse grain materials, but the plasticity is slightly lower.
After annealing at 200-260 ℃ for 1-2 hours, the strength, plasticity, elastic limit and elastic modulus of cold processed tin phosphor bronze are improved, and the elastic stability can be improved.
Zinc is one of the alloy elements of tin bronze, and its solubility in the solution of tin bronze α is large. Therefore, Cu Sn Zn bronze is a single-phase α solid solution. Zn improves the fluidity of the alloy, reduces the crystallization temperature range, reduces the reverse segregation, but has no significant influence on its structure and properties.
Zn content in tin bronze is generally not more than 5%.
Pb content in tin bronze is less than 5%, it is not solid soluble in phase a, and exists in free state, and it is distributed between branches and grains in black, but it is not evenly distributed.
Pb can reduce the friction coefficient, improve the wear resistance and cutting performance of tin bronze, but it can reduce the mechanical properties of the alloy.
Fe is a impurity of tin bronze, its maximum content is 0.05%, which can refine the grain, delay recrystallization process, improve the strength and hardness. But the content should not exceed the limit value, otherwise, too much iron rich phase will be formed, which will reduce the corrosion resistance and technological properties of the alloy.
Mn is one of the harmful impurities in tin bronze, and its content should be strictly controlled, and it should not be more than 0.002%.
Manganese is easy to oxidize to form oxides, which reduces the fluidity of alloy melt, and then distributes on the grain boundary after solidification, weakening the intergranular bonding and reducing the strength.
Ti can form a compound TISN with Sn, which is solid soluble in copper and has strong precipitation