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Nickel-aluminum bronze for the propeller

Nickel-aluminum bronze for the propeller
Ni-al bronze has excellent mechanical properties, anti corrosion properties and cavitation resistance. It is one of the important materials for ship propeller. The rotor inertia of the Ni-Al bronze propeller is 15~19 % lower than that the brass propeller, increasing the bearing capacity of the propeller at the same power as the Marine engine. The tensile strength and corrosion fatigue strength of Ni-Al bronze are higher than that of high-strength brass. If the allowable stress of the propeller design more than 4.69 MPa (high-intensity brass is about 4.09 MPa), then the blade thickness can be thinned 8% - 10%, because of its small density than high-intensity brass 10%, consider if both at the same time, can make its reduce weight by 15%, and improve 20% the efficiency of the propeller shaft bearing wear, which save materialsl, reduce maintenance cost and fuel consumption, etc. The corrosion fatigue strength and cavitation resistance of Ni-Al bronze are better than that of high-strength brass, so the surface of propeller blade is coarsened slowly. Ni-al bronze has no stress corrosion tendency, corrosion fatigue strength is about twice as high as that of high-strength brass, and cavitation corrosion resistance is about 2-3 times higher than that of high-strength brass.
The decomodation corrosion of Ni-Al bronze in polluted seawater is less than that of high strength brass. However, the cost of the Ni-Al bronze propeller is 25%-30% more than that of the high-strength brass, but it has a longer service life and higher reliability. According to the literature, the service life of the high-strength brass propeller is about 10 years, and the service life of the Ni-Al bronze propeller can reach 17-20 years. In general, the Ni-Al bronze propeller is more economical.
Nickel-aluminum bronze contains 9-12% Al,6% Fe, 6% Ni, and 1% Mn. China Classification Society has made detailed provisions on the composition of nickel-aluminum bronze Marine propeller castings, requiring Cu 77-82,Al 7-11,Mn 0.5-4,Fe 2.0-6.0,Ni 3.0-6.0,Sn 0.1,Pb 0.03, mechanical properties & Sigma.b≥500MPa,σP0.2 & ge;At 245MPa, the elongation is not less than 14%. Ni and Fe in the alloy components avoid eutectoid transformation & Beta of simple Cu-Al binary alloy at 565℃.→ α+γ . Therefore, there is no slow cooling embrittlement. Fe can refine the effect of grains, but too much Fe will affect the corrosion resistance of the alloy. Ni is beneficial to improve the corrosion resistance and prevent the slow cooling brittleness of thick and large castings. Mn can improve the melt fluidity of Ni-Al bronze. In order to suppress the phase selective corrosion gamma;& lsquo; ’ Phase formation, Mn content should not exceed 1.3%. Small difference in alloying element content will cause changes in metallographic structure.FIG. 2 shows the microstructure transformation of Ni-Al bronze during casting.

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