Effect of Alloy Elements on Tin Bronze
Tin bronze is a copper alloy with copper as the base element and tin as the main element. There are many grades of tin bronze alloy, which are suitable for use under different working conditions. The difference between grades lies in the different addition amounts of elements. Different addition amounts of elements can make tin bronze alloy achieve different properties and be applied to different use requirements. Below we will introduce in detail the effects of various element additions on the performance of tin bronze.
Phosphorus P
1. The phosphorus content of tin bronze generally does not exceed 0.45%. When the phosphorus content is greater than 0.5%, the eutectic-peritectonic reaction L+αβ+Cu3P will occur at around 637, causing hot brittleness. When the phosphorus content of the alloy is greater than 0.3%, a eutectic composed of copper and copper phosphide (Cu3P) will appear in the organization.
2. Phosphorus is an effective deoxidizer for copper alloys and improves the fluidity of tin bronze. The disadvantage is to increase the reverse segregation of the ingot.
3. The grain size of the material before cold working and the low-temperature annealing (180~300) after processing have a 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 the coarse grain material, but the plasticity is slightly lower. 4. After cold-processed tin-phosphor bronze is annealed at 200~260 for 1~2h, its strength, plasticity, elastic limit and elastic modulus are all improved, and the elastic stability can also be improved.
Zinc Zn
1. Zinc is one of the alloying elements of tin bronze, and zinc has a large solubility in the α solid solution of tin bronze. Therefore, Cu-Sn-Zn processed bronze is a single-phase α solid solution. Zn improves the fluidity of the alloy, narrows the crystallization temperature range, and reduces reverse segregation, but has no significant effect on its structure and properties.
2. The content of Zn in processed tin bronze is generally not more than 5%.
Lead Pb
1. The content of Pb in tin bronze does not exceed 5%. It is not dissolved in the α phase and exists in a free state. It is distributed between dendrites as black particles, but the distribution is uneven.
2. Pb can reduce the friction coefficient of tin bronze, improve wear resistance, and increase machinability, but slightly reduce the mechanical properties of the alloy.
Manganese Mn
1. Mn is one of the harmful impurities of tin bronze, and its content should be strictly controlled and should not exceed 0.002%. 2. Manganese is easily oxidized to form oxides, which reduces the fluidity of the alloy melt, and after solidification, it is distributed on the grain boundaries, weakening the intercrystalline bonding and reducing the strength.
Iron Fe
Fe is an impurity of tin bronze, with a maximum content of 0.05%. It has the effect of refining grains, delaying the recrystallization process, and improving strength and hardness. However, the content must not exceed the limit value, otherwise too much iron-rich phase will be formed, reducing the corrosion resistance and process performance of the alloy.
Aluminum Al, magnesium Mg, silicon Si
1. A small amount can be dissolved in the α solid solution to improve the mechanical properties of the alloy, but during the melting process, it is easy to oxidize to produce refractory oxides, thereby reducing the fluidity and strength of tin bronze.
2. The content of aluminum in Sn bronze should not be greater than 0.002%, and the content of Mg should also be strictly controlled, because their oxides will reduce the strength of the alloy and the fluidity of the melt. Some tin bronzes containing Al and Mg have been developed abroad, which not only have high strength, but also good corrosion resistance. For example, Cu-5Sn-7Al alloy has high corrosion resistance and strength, and Cu-5Sn-1Mg tin bronze has a strength of 900 MPa and 30 HRC after aging treatment, and a conductivity of 30%~35% IACS, which can be used to manufacture components with high strength, high corrosion resistance and good conductivity.
