Experimental Research On Seawater Corrosion Behavior And Cathodic Protection Of High Damping Manganese Copper Alloy

Submarines and torpedoes serving in seawater have strict requirements for operational stability and"stealth",and propellers that produce noise and affect stability are important power structures.Therefore,the development of propeller materials with good corrosion resistance,vibration and noise reduction,or reasonable and effective protection of the propeller is the hot and focus of research for many years.Among them,Mn Cu Al-based damping alloys are widely used in submarines and torpedoes.The strength of Mn Cu Al alloys is slightly lower than that of other copper alloys,but the damping performance is very excellent,which can significantly reduce equipment vibration and noise.In the application process of Mn Cu Al alloy,it is found that due to the high Mn content of the alloy and the inevitable combined effect of oxidation and inclusions in the ordinary non-vacuum melting and casting process,its corrosion resistance is poor.Especially when it is used as a propeller,the resistance to cavitation corrosion,stress corrosion,and erosion corrosion is obviously poor.For this reason,this thesis has carried out experimental research on the corrosion behavior and cathodic protection of manganese-copper alloys for propellers.The manganese-copper alloy materials studied in the thesis were obtained by sampling from real boats,self-developed sand casting ingots and refining through electroslag remelting process.Using electrochemical workstation,scanning electron microscope and other equipment,the corrosion behavior,composition and morphology of the alloy in seawater were studied.The influence of the electroslag remelting process on the structure,corrosion behavior,surface morphology,etc.of this series of alloys was discussed,and the corrosion protection effects under different cathodic polarization potentials were tested and analyzed.After research,the following conclusions were obtained:Using Ca F₂:Na F:Na₃Al F₆=45:50:5 slag system to electroslag remelting sand casting manganese-copper alloy,the structure is more pure after refining,and the grain size is reduced;the manganese-copper alloy grows in the form of dendrites during solidification.The molten alloy structure is highly ordered.During the immersion process of manganese-copper alloys prepared by different processes in seawater,the potentials showed two stages:the potential rapidly increased from-700 m V to-450 m V at the initial stage of corrosion,and the potential fluctuated at-450 m V in the middle and late stages of the test.Since the corrosion potential rises rapidly and stabilizes for a period of time,it begins to fluctuate because the surface oxide film layer is formed rapidly in the initial stage,and the corrosion products appear to fall off as time goes by.In the 20-day weight loss experiment,it is found that the weight loss rate of the cast alloy is slightly lower than that of the remelted alloy,and the average corrosion rate of the remelted alloy after 1 year of actual sea corrosion is about 50%of the cast alloy.The corrosion resistance of the remelted alloy during long-term use has been significantly improved.For this manganese-copper alloy,the formation of the product layer under the protection potential of-750 m V is slow and cannot produce effective protection quickly.Applying-850 m V and-950 m V protection potentials can quickly form a more effective protective film in the early stage of polarization,and the film will continue to grow during the continuous polarization process.Among them,the-950 m V protection potential has the strongest ability to promote the formation of the calcareous layer,while the particle size of the calcareous layer formed under the-850 m V potential is the largest due to the unconstrained growth.The calcareous layer formed by cathodic protection is mainly composed of fine Mg(OH)₂-rich particles and larger spherical calcium particles.Among them,the calcium particles nucleate on the surface of the substrate and gradually grow up to form"cauliflower-shaped"large particles.With the extension of the polarization time,the calcium particles continue to increase and form a covering layer,which has a good protective effect on the base metal.