Study On Microstructure And Properties Of Cu-18Pb-2Sn Laser Cladding Coating

In recent years,copper and Cu-based alloys have wider application in the industry.Among them,Cu-Pb alloy is widely used in machinery manufacturing industries because of its good wear resistance.Cu-Pb alloy manufactured by conventional casting methods is prone to generate component segregation,and the mechanical properties of parts which are made entirely of Cu-Pb alloys are difficult to satisfy the requirements.Therefore,how to produce a high performance Cu-Pb alloy coating becomes a very important issue.As an advanced surface strengthening method,laser cladding technology can prepare a cladding coating that forms metallurgical bond with the substrate with fine microstructure.On the other hand,laser remelting can reduce the number of defects in the cladding layer.In this paper,Cu-18Pb-2Sn alloy coatings were prepared using laser cladding under different process parameters,and laser remelting was also used.Variations of the microstructure and properties of the cladding layer were studied.The temperature of the molten pool during the cladding process was monitored using a pyrometer and;the microstructure and chemical composition analysis of the cladding layer were performed using optical microscope(OM)and scanning electron microscope;the porosity of the cladding layer was measured using ImageJ software;phase analysis of the cladding layer was performed using an X-ray diffractometer(XRD);microhardness of the cladding layer was measured using Vickers hardness tester;and the wear resistance test of the cladding layer was performed using friction and wear tester.Results indicate:(1)Porosity was observed in the cladding layer obtained under different laser cladding powers.Microstructure of cladding layer was composed of Cu phase matrix,with reticular Pb phase and punctate Pb phase dispersedly distributed on the matrix.The XRD results indicated that no Cu-Sn compound or oxides was formed in the layer.With the laser power increasing,the amount of reticular Pb phase deceased,while the microhardness of the layer became higher,which means better wear resistance of cladding layer.(2)The amount and volume of pores in cladding layer were obviously reduced after laser remelting,which means porosity of cladding layer decreased significantly.Less reticular Pb phase was found in the after-remelting layer,while the number of punctate Pb phase increased reversely.The phase composition of remelting layer was basically unchanged.After remelting the layer under different power,it was found that microhardness,average friction factor and abrasion loss were declined with the remelting power.(3)The maximum temperature of molten pool could reach 1200?at least.The evaporation of Pb and Sn caused by high temperature could be the reason for the formation of porosity.The temperature of molten pool during remelting is lower than that during cladding process,when the cladding power is relatively low.While the cladding power was 1500 W,the temperature of molten pool during remelting process was significantly increased,with higher cooling rate,which resulted in the increase of punctate Pb phase.