The Effect of Alloying Elements on Copper and Copper Alloys

Oxygen is almost insoluble in copper. When oxygen bearing copper solidifies, oxygen precipitates in the form of Cocrystal and distributes on the grain boundary of copper. When the oxygen content in cast oxygen containing copper is extremely low, as the oxygen content increases, sub eutectic, eutectic, and hypereutectic containing Cu2O appear in sequence.
When oxygen coexists with other impurities, the effect is extremely complex. For example, trace oxygen can oxidize trace impurities such as Fe, Sn, P, etc. in high-purity copper, improving the conductivity of copper. If the impurity content is high, the effect of oxygen is not significant.
Oxygen can partially weaken the influence of Sb and Cd on copper conductivity, but does not change the influence of As, S, Se, Te, Bi, etc. on copper conductivity.
P, Ca, Si, Li, Be, Al, Mg, Zn, Na, Sr, B, etc. can be used as the Oxygen scavenger of copper, of which P is the most commonly used. When the P content reaches 0.1%, although it does not affect the mechanical properties of copper, it seriously reduces the conductivity of copper. For high conductivity copper, the phosphorus content should not exceed 0.001%.
In some cases, a certain amount of oxygen is intentionally retained in red copper. On the one hand, it has little effect on the properties of copper, and on the other hand, Cu2O can react with impurities such as Bi, Sb, As, and form high melting point spherical particles distributed within the grains, eliminating grain boundary brittleness.
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 effect on the conductivity of copper.
When the oxygen content is 0.003%~0.008% and the iron content is between 0.06%~2.09%, the conductivity and elongation of copper significantly decrease with the increase of the two element contents, while the tensile strength and fatigue strength significantly increase.
When oxygen and arsenic coexist, there is no significant effect on the mechanical properties of copper, but it significantly reduces the conductivity of copper.
Hydrogen
The solubility of hydrogen in both liquid solid and solid copper increases with increasing temperature. Hydrogen forms intermittent Solid solution in solid copper to improve the hardness of copper.
When oxygen containing copper is annealed in hydrogen gas, hydrogen can react with Cu2O in the copper, producing high-pressure water vapor, causing the copper to rupture, commonly known as "hydrogen disease". The occurrence and severity of hydrogen disease are related to temperature. At 150 ℃, as the water vapor is in a condensed state, it does not cause hydrogen disease, and oxygen-containing copper does not break when left in hydrogen for 10 years; It can be stored for 1.5a at 200 ℃, and can only be stored for 70h in hydrogen at 400 ℃. Copper deoxidized with Mg or B does not undergo hydrogen disease.
Sulfur
The solubility of sulfur in room temperature copper is zero, and sulfur exists as a dispersed particle of Cu2S in copper, reducing the conductivity and thermal conductivity of copper, but greatly reducing the plasticity of copper and significantly improving its machinability.
Selenium
Trace selenium in copper exists in the form of Cu2Se compounds, and its solubility in solid copper is extremely low. It has little effect on the conductivity and thermal conductivity of copper, but significantly reduces its plasticity and significantly improves its machinability.
Tellurium
The solubility of tellurium in solid copper is very low, and it exists as a Cu2Te dispersed particle, which has little effect on the conductivity and thermal conductivity of copper. However, it can significantly improve the machinability of copper.
Copper containing 0.06% to 0.70% Te has been applied in industry and is used in quenched and processed states. Do not temper to avoid Cu2Te precipitation along grain boundaries, which can make the material brittle.
Trace amounts (0.003%) of selenium and tellurium (0.0005%~0.0030%) significantly reduce the solderability of copper.
Phosphorus
The maximum solubility of phosphorus in copper (at 714 ℃ eutectic temperature) is 1.75%, which is almost zero at room temperature, significantly reducing the conductivity and thermal conductivity of copper. However, it has a good effect on the mechanical properties and welding properties of steel. Therefore, in copper deoxidized with phosphorus, a certain amount of residual phosphorus is required. Phosphorus can improve the flowability of copper melt.
It is recommended that the phosphorus content of oxygen free copper used for direct encapsulation of electric vacuum should not exceed 0.0003%, otherwise the boron treated oxide film may easily peel off and cause electronic tube leakage. Si, Mg, etc. also have similar effects as phosphorus.
Arsenic
At eutectic temperature, the solubility of arsenic in copper can reach 6.77%. A small amount of arsenic can improve the processing performance of oxygen-containing copper, with little impact on mechanical properties. It significantly increases the recrystallization temperature of copper and reduces its conductivity and thermal conductivity.
As can react with Cu2O in copper to form copper arsenate particles with high melting point, eliminating Cu+Cu2O Cocrystal on the grain boundary, thus improving the plasticity of copper.
Copper containing 0.15%~0.50% arsenic can be used to manufacture parts and components working in high temperature reducing atmosphere and low-pressure feed water heaters in power plants.
Antimony
At a eutectic temperature of 645 ℃, the solubility of antimony in copper can reach 9.5%, and it rapidly decreases with the decrease of temperature.
Antimony reduces the corrosion resistance, conductivity, and thermal conductivity of copper. The Sb content of electrical copper shall not exceed 0.02%. Antimony can react with Cu2O in oxygen bearing copper to form spherical particles with high melting point, which are distributed in the grain, and can eliminate Cu+Cu2O Cocrystal on the grain boundary, thus improving the plasticity of copper.
Bismuth
The solubility of bismuth in copper is negligible, with a solubility of only 0.01% even at 800 ℃. Bismuth and copper form Cocrystal at 270 ℃, in which bismuth is distributed in the grain boundary as a thin film, seriously reducing the processability of copper. Therefore, its content should not exceed 0.002%.
Bi has little effect on the thermal conductivity and conductivity of copper, and vacuum switch contact copper can contain 0.7%~1.0% Bi. Because it has high conductivity and can prevent switch bonding, improve its working life and ensure safe operation.
Lead
Lead is insoluble in copper, distributed as black particles in the fusible Cocrystal, and exists on the grain boundary.
Pb has no significant effect on the conductivity and thermal conductivity of copper, and can significantly improve the machinability of copper. Copper alloy containing 1.0% Pb is used for machining high-speed cutting parts.
Pb severely reduces the high-temperature plasticity, i.e. elongation, of Cu δ Face shrinkage ψ Intense decrease, while the high-temperature brittle zone also expands with the increase of copper content.
Iron
At 1050 ℃, the solubility of iron in copper can reach 3.5%, while at 635 ℃, the solubility decreases to 0.15%. The beneficial effect of iron is to refine copper grains, delay the recrystallization process of copper, and improve its strength and hardness.
Iron can reduce the plasticity, conductivity, and thermal conductivity of copper.
If iron forms an independent phase in copper, then copper has ferromagnetism.
Copper alloys containing 0.45% to 4.5% Fe have high strength, good heat resistance, conductivity, weldability, and processability, making them a widely used electrical material.
When assembling certain electronic devices, the lead frame must be able to withstand high temperatures of 350 ℃ for several minutes and up to 500 ℃ for several seconds. Therefore, C19400 and C19500 alloys containing iron were selected as lead frame materials due to their good conductivity, strength, and oxidation resistance.
Silver
At a eutectic temperature of 780 ℃, the solubility of silver in copper is 7.9%, but at room temperature, the solubility is only about 0.1%. However, the copper alloy containing 0.5% Ag may still be a single Solid solution in actual production.
Silver is different from the soluble Cu element. When the silver content is low, the decrease in copper conductivity and thermal conductivity is not significant, and the effect on plasticity is also minimal. It significantly increases the recrystallization temperature and creep strength of copper. Therefore, high copper alloys containing 0.03% to 0.25% Ag have become a class of practical electrical materials, such as C11300, C11400, C11500, C11600, C15500, etc. Silver containing copper strip is a widely used material for automotive water tanks.
C15500 alloy containing Ag (99.75Cu-0.11Ag-0.06P) is a good lead frame material, which has both high conductivity and considerable strength and softening resistance.
Beryllium
Beryllium is one of the effective Oxygen scavenger for copper, but because it is expensive and difficult to add, it is not used as a Oxygen scavenger, but as the main alloy element of beryllium bronze. The trace amount of beryllium, as an impurity, solidly dissolves in copper and has little effect on the mechanical and technological properties of copper. It slightly reduces the conductivity and thermal conductivity of copper and significantly improves its high-temperature oxidation resistance.
aluminium
The trace amount of aluminum, as an impurity, solidly dissolves in copper and has no significant effect on the mechanical and technological properties of copper. However, it reduces the conductivity, thermal conductivity, brazing and soldering performance, and tin plating performance of copper, improving its oxygen resistance.
Magnesium
At a eutectic temperature of 485 ℃, the solid solubility of magnesium in copper is 0.61%, which sharply decreases with the decrease of temperature. Therefore, alloys with high magnesium content (2.5%~3.5%) have precipitation hardening effect.
The magnesium content of Cu-Mg alloys used in practical applications is less than 1%, such as copper alloys containing 0.3%~1.0% Mg used for processing conductive wires. These alloys have no aging effect and can only be strengthened through cold working. Trace magnesium slightly reduces the conductivity of copper, improves its high-temperature oxidation resistance, and also has a deoxygenation effect on copper.
Lithium, boron, manganese, calcium
These elements have a deoxygenation effect on copper. Lithium, as an impurity, can form high melting point compounds with impurities such as bismuth in copper, which are distributed in a refined and dispersed state within the grains, improving the high-temperature plasticity of copper. Trace amounts of lithium almost do not affect the conductivity and thermal conductivity of copper.
The residual 0.005%~0.015% B as a copper Oxygen scavenger can refine copper grains and improve the mechanical and technological properties of copper.
Manganese can be used as a Oxygen scavenger for copper. The copper deoxidized by manganese generally contains 0.1%~0.3% Mn, 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, and as an impurity, calcium can form high melting point compounds with impurities such as Bi, which are uniformly distributed in the grain in the form of particles, improving the high-temperature plasticity of copper.
Rare earth elements
Rare earth elements are generally almost insoluble in copper, but a small amount of rare earth metals, whether added alone or in a mixed form, are beneficial to the mechanical properties of copper, and have little effect on its conductivity. These elements can form high melting point compounds with impurities such as lead and bismuth in copper, forming small spherical particles uniformly distributed within the grains, refining the grains and improving the high-temperature plasticity of steel.
Adding 0.008% mixed rare earths to copper can significantly improve its processing performance; When less than 0.1% Y is added, the mechanical and technological properties of copper are improved; The mechanical properties, conductivity, and softening resistance of copper alloys containing 0.01%~0.15% La are superior to Cu-0.15Ag alloys, and have been applied in industry.
Refractory metals and other metals
Elements such as tungsten, molybdenum, niobium, uranium, and plutonium are almost insoluble in copper, while elements such as titanium, zirconium, chromium, and cobalt are slightly soluble in copper. However, they all refine copper grains to varying degrees, increase their recrystallization temperature, neutralize the harmful effects of some fusible impurities, and are beneficial for improving high-temperature plasticity.
Copper alloys containing small amounts of zirconium (Cl5000, C15100, C18100), cobalt (C17110, C17500), and chromium (C18400, C18200, C18500) have been applied in industry and have become good electrical materials.
Brass
Iron
The melting of iron in solid copper is extremely small, and it is distributed as iron rich phase particles α In the matrix, there is a grain refinement effect. The addition of 0.3%~0.6% Fe to H60 brass has a strong grain refinement effect, but the iron content of the diamagnetic copper material should be less than 0.3%.
Impurity iron has no significant effect on the mechanical properties of brass.
Lead and bismuth
Lead and bismuth are harmful impurities in general brass, and bismuth is more harmful than lead.
Lead exists in the fusible Cocrystal on the grain boundary in granular form, α If the lead content of brass exceeds 0.03%, it will exhibit thermal brittleness and have no significant impact on cold working performance. Lead has no significant impact on the processing performance of duplex brass, and its allowable content can be slightly higher.
Bismuth is distributed on the grain boundary as a continuous brittle film in brass, which makes brass brittle during cold and Hot working.
Cold rolled brass containing lead and bismuth exceeding the allowable limit may experience "fire cracking" or sudden bursting during the annealing process if the heating speed is too fast.
Adding a small amount of elements such as zirconium to brass containing lead and bismuth can form high melting point compounds and eliminate their harm.
Antimony
The solubility of antimony in copper decreases sharply with the decrease of temperature. When its content is less than 0.1%, Cu2Sb forms and is distributed in a network at grain boundaries, greatly reducing the cold working performance of brass.
Antimony also causes thermal brittleness in copper alloys.
Adding trace amounts of lithium to brass can form a high melting point compound Li3Sb, which is uniformly distributed in the grains as small particles, thereby eliminating the adverse effects of antimony.
Due to the high melting degree of antimony in copper at high temperatures, solid solution treatment can improve the cold working performance of antimony containing brass.
Phosphorus
Phosphorus in α The solid solubility in copper is very low, and a small amount of phosphorus has a grain refinement effect, improving the mechanical properties of brass. When the phosphorus content in brass exceeds 0.05%, brittle phase Cu3P will be formed, reducing the processing performance of brass.
Phosphorus significantly increases the recrystallization temperature of brass, resulting in uneven grain size.
Arsenic
The solubility of arsenic in room temperature brass is less than 0.01%, and when the content is high, it forms a brittle phase compound Cu3As, which is distributed at grain boundaries and reduces the processing performance of brass. The corrosion resistance of brass containing 0.02%~0.05% As can be improved without dezincification.
Bronze
Tin bronze
Phosphorus
The phosphorus content of tin bronze generally does not exceed 0.45%. When the phosphorus content is greater than 0.5%, eutectic peritectic reaction will occur at around 637 ℃+ α ⇄ β+ Cu3P, causing heat embrittlement. When the phosphorus content of the alloy is greater than 0.3%, there will be Cocrystal composed of copper and copper Phosphide (Cu3P) in the structure.
Phosphorus is an effective Oxygen scavenger for copper alloys, improving the fluidity of tin bronze. The disadvantage is to increase the reverse segregation of the ingot.
The grain size before cold working and the low temperature annealing (180~300 ℃) after cold working have great influence on the mechanical properties of tin Phosphor bronze. When the grain size is small, the strength, hardness, elastic modulus, and fatigue strength of the material are higher than those of coarse-grained materials, but the plasticity is slightly lower.
After annealing at 200~260 ℃ for 1~2h, the strength, plasticity, Elastic Limit and elastic modulus of cold worked tin Phosphor bronze are improved, and the elastic stability is also improved.
Zinc
Zinc is one of the alloying elements in tin bronze, and zinc in tin bronze α The solubility in Solid solution is high. Therefore, Cu Sn Zn processing bronze is single-phase α The Solid solution, Zn, improves the fluidity of the alloy, narrows the crystallization temperature range, and reduces the reverse segregation, but has no significant effect on its structure and properties.
The content of Zn in processed tin bronze is generally not more than 5%.
Lead
The content of Pb in tin bronze does not exceed 5%, and it is not solidly soluble in α The phase exists in a free state, with black particles distributed between the dendrites, but the distribution is uneven.
Pb can reduce the friction coefficient of tin bronze, improve wear resistance, and improve machinability, but slightly reduce the mechanical properties of the alloy.
Iron
Fe is an impurity in tin bronze, with a maximum content of 0.05%. It has the function of refining grains, delaying the recrystallization process, and improving strength and hardness. However, the content should not exceed the limit value, otherwise excessive iron rich phases will form, reducing the corrosion resistance and process performance of the alloy.
Manganese
Mn is a harmful impurity in tin bronze