Effect of alloying elements on aluminum bronze
Aluminum bronze alloys are based on copper and aluminum. In order to improve and enhance the performance of aluminum bronze, some other alloying elements are generally added. The reasonable addition of alloying elements plays a key role in improving the performance of materials, such as better corrosion resistance, higher hardness, better toughness, etc. At the same time, excessive addition of some elements will also bring some adverse consequences, such as reduced strength, increased brittleness, reduced corrosion resistance, etc. This article introduces the role of the main alloying elements added to aluminum bronze.
Iron Fe
1. A small amount of Fe can be dissolved in the α solid solution of Cu-Al alloy. If it is excessive, it will form needle-shaped FeAl3, which will reduce the mechanical properties and corrosion resistance of the alloy. Therefore, the Fe content in the alloy should not exceed 5%.
2. If the content of Ni, Mn, and Al in the alloy increases, the solubility of Fe in the solid solution will be further reduced. Iron can slow down the atomic diffusion rate in aluminum bronze and increase the stability of the β phase, thereby inhibiting the "self-annealing" phenomenon that causes the alloy to become brittle, greatly reducing the brittleness of the alloy.
3. Appropriate amount of iron can refine the casting and recrystallization grains of aluminum bronze and improve mechanical properties. Adding 0.5%~1.0 can significantly refine the grains.
Nickel Ni
1. Nickel has a certain solid solubility in Cu-Al alloy. When the Ni content exceeds the maximum solid solubility, K phase NiAl phase will be formed. Ni increases the eutectoid transformation temperature of aluminum bronze on the one hand, and moves the eutectoid point composition in the direction of temperature increase on the other hand, and can also change the morphology of α phase. When the Ni content is low, the α phase is needle-shaped, and when the nickel content reaches 3%, it turns into a flake.
2. When Mn is added to Cu-Al-Ni alloy, there is a tendency to form granular structure when the β phase undergoes eutectoid transformation.
3. Ni can significantly improve the strength, hardness, thermal stability and corrosion resistance of aluminum bronze. Cu-Al-Ni-Fe alloy containing a certain amount of Ni does not need to be solution treated and quenched after hot working, and can be directly aged.
4. Adding Ni and Fe to aluminum bronze at the same time can obtain better comprehensive performance. In Cu-A1-Ni-Fe alloy, the precipitation morphology of κ phase has a great influence on its mechanical properties.
5. The optimal content ratio of Ni to Fe is 0.9~1.1.
Manganese Mn
1. Mn has a large solubility in the α solid solution of Cu-Al alloy, but reduces the solid solubility of aluminum in α. Manganese stabilizes the decomposition of β phase, reduces the starting temperature of phase transformation, and delays eutectoid transformation.
2. The Mn content in aluminum bronze does not exceed the maximum solubility limit, which is beneficial to the mechanical properties and corrosion resistance of the alloy, and they have good processing and forming properties.
3. Binary aluminum bronze containing 0.3%~0.5% Mn has quite good hot working properties, and the cracking tendency during hot rolling is significantly reduced.
4. A certain amount of Fe is added to aluminum bronze containing Mn, and the performance of the alloy is further improved, because Fe can refine the grains, but iron will weaken the stabilizing effect of Mn on the β phase.
Tin and chromium
1. Adding ≤0.2% Sn to aluminum bronze can improve the alloy's ability to resist stress corrosion cracking in steam and slightly acidic atmospheres.
2. Chromium can improve the mechanical properties of binary Cu-Al alloys, inhibit grain growth during alloy annealing, and increase the hardness of annealed materials.
Zinc and silicon
1. Zinc dissolves in Cu-Al alloy α to a limited extent, expanding the α phase region. However, Zn will reduce the iron-rich phase particles of Cu-Al-Ni-Fe alloys, reducing wear resistance. The maximum content of impurity zinc in processed aluminum bronze is 1.0%.
2. Silicon is an impurity in aluminum bronze, and its content must not exceed 0.2%, and for most aluminum bronzes must not exceed 0.1%, otherwise it will reduce the mechanical properties and process properties of the alloy, but it can improve the machinability of the alloy.
