Microstructure And Properties Of Laser Cladded Aluminum Bronze Coating On Carbon Steel

There are many marine steel facilities in China,most of which are made by low carbon steel or low alloy steel.However,they are vulnerable to corrosion in the sea environment.Aluminum bronze?AB?has good mechanical property,corrosion resistance and anti-microbial property,therefore,it has been widely used in marine engineering,such as propeller of the ship.Due to high price of aluminum bronze,it cannot totally take place of steel.Relevant researches show that,corrosion resistance of some aluminum bronze is better than that of pure copper,let alone the carbon steel.Therefore,the surface of marine structural steel can be modified by cladding aluminum bronze coating on it,furthermore,other alloy elements can be added to improve properties of the coating.At present,there are few studies on copper alloy cladding on steels.Most of the literature studies the microstructure and properties of pure copper/steel dissimilar welding.At the same time,the research on copper alloy coatings mainly focuses on in-situ composite systems.Aluminum bronze powder,as the cladding material,is seldom studied,together with the copper contamination phenomenon at the interface.To this end,aluminum bronze powder was used to repair the marine structural steel and improve its surface properties.AB,AB?5%Ni?and AB?5%Ni,5%Co?powders were mixed by ball milling,then cladded on Q235 substrate.Microstructure and phases of the claddings were investigated by OM,SEM,EDS and XRD.The upper region of the cladding was fine equiaxed crystal,the middle region was equiaxed crystal and part of dendrites,and the bottom was coarse dendrites.At the same time,"liquid separation"was found.This was because the solubility of copper and iron was very small,and separation occurred at high temperatures.The cooling rate was fast enough to form the iron-rich phases which embedded in the copper-rich matrix.Meanwhile,in the iron-rich phases,many fine copper-rich particles precipitated due to supersaturation of copper.Copper contamination phenomenon occurred at the interface between the aluminum bronze cladding and the carbon steel substrate.A set of three-factor and two-level orthogonal experiments was designed and it found that the contamination phenomenon was most sensitive to laser power.The microhardness,friction and wear properties and electrochemical corrosion property of three aluminum bronze claddings were tested and analyzed.Among them,AB?5%Ni,5%Co?cladding had the best overall performance.The addition of?5%Ni?,?5%Ni,5%Co?caused a certain increase in the microhardness of cladding.In general,the friction coefficients of the three cladding layers were all around 0.55.The wear mechanism of AB cladding layer was adhesive wear,while others were abrasive wear.The addition of Ni element improved corrosion resistance of cladding.Ni element would aggregate in the Cu₂O passivation film and improve its stability.However,decrease of grain size would increase the rate of corrosion by adding Ni element.The corrosion resistance of AB?5%Ni,5%Co?cladding was the best.This was because simultaneous addition of Ni element and Co element inhibited the supersaturation and desolvation of the copper-rich phases in the iron-rich phase,which led to the tendency of the original phase to be uniformly transformed into a single phase.Therefore,the galvanic corrosion tendency between the different phases was reduced,together with the preferential corrosion path.Therefore,the corrosion performance was improved.