Alloying elements affecting the comprehensive properties of Ni-Al bronze

In order to improve the slow cooling brittleness of aluminum bronze, a certain amount of nickel is added to aluminum bronze alloy to make nickel aluminum bronze, mainly by changing the ratio between α and (α+γ2) phase by nickel, the phase dissolution limit moves to the high aluminum side, expanding the α phase region, to prevent the slow cooling brittleness. Nickel-aluminum bronze has excellent properties of corrosion cracking resistance, corrosion fatigue resistance, cavitation corrosion resistance, erosion resistance and Marine biological fouling resistance. Nickel-al bronze is much better than stainless steel and brass in seawater corrosion fatigue than manganese bronze, and nickel-al bronze is much better than brass in erosion resistance. Nickel can not only improve the corrosion resistance of castings, but also prevent the "slow cooling brittleness" of thick castings, increase the nickel content, and the corrosion potential of the alloy moves to the positive direction.

High manganese aluminum bronze has low melting point and good fluidity, but high sensitivity to overheating. Although mn can be added to aluminum bronze, the α phase can be reduced, but the eutectoid transition temperature of β phase can be significantly reduced, thus the stability of β phase can be improved, and the "slow cooling brittleness" of aluminum bronze can be greatly weakened. Mn can also be dissolved in α solid solution, which has a certain strengthening effect of solution. Therefore, the addition of Mn can further improve the corrosion resistance of aluminum bronze while increasing the strength and reducing the plasticity

The solid solubility of iron in copper is low, and it only has a certain solid solubility at high temperature, and will precipitate with the decrease of temperature. The addition of appropriate amount of iron is beneficial to grain refinement and precipitates into metal compounds with aluminum and nickel. Moreover, Fe and Ni can improve the mechanical properties and corrosion resistance of the alloy. Adding enough fe or Ni to ordinary aluminum bronze can not only inhibit the formation and netting of γ2 phase, but also refine the grain size. When the fe content reaches 2%, the γ2 phase network structure can be prevented in the casting with the cross section diameter less than 75mm. However, excessive iron content will reduce the corrosion potential, thus affecting the corrosion performance. Because Fe can refine the grain, it has good strength and plasticity. Therefore, in high manganese aluminum bronze, Fe and Ni should be added in proportion, and the content of Mn should be considered. It is beneficial to improve the performance of the alloy by controlling the Fe in 2% ~ 4% and Ni in 0 ~ 2%, respectively. Iron can slow down the diffusion rate of atoms in aluminum bronze and increase the stability of the β phase. The effect of iron on the eutectoid transformation rate at 525℃ is not as significant as that at lower temperature range, but the phenomenon of "self-annealing" which causes the brittleness of the alloy can be inhibited and the brittleness of the alloy can be significantly reduced.