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Microstructure And Properties Of Laser Cladding Al+WC+La2O3 Composite Coating On Magnesium Alloy Surface

Posted on:2018-12-22Degree:MasterType:Thesis
Country:ChinaCandidate:S Y LiuFull Text:PDF
GTID:2311330518950928Subject:Full-time Engineering
Abstract/Summary:PDF Full Text Request
Because of its low density,high specific strength and specific stiffness,good thermal conductivity and electrical conductivity,magnesium alloys are widely used in aerospace,transportation,biomedicine,electronics and other fields.However,the low corrosion resistance and mechanical properties of magnesium alloys limit their practical application.Therefore,it is of great practical significance to use surface modification technology to improve the corrosion resistance and mechanical properties of magnesium alloy surface.In this paper,AZ91 D magnesium alloy was used as the research object,and the composite coating was prepared on the surface of magnesium alloy by laser cladding to improve its surface properties.Through the macro and micro comparison of the cladding layer,the appropriate laser processing parameters are obtained.The scanning speed is 150mm/min,the current is 120 A,and the spot overlap rate is 30%.Using this parameter,the Al+WC coatings with different ratios were coated on the surface of AZ91 D magnesium alloy.WC is dispersed in the cladding layer in the form of a dispersed phase,and the grains are refined.Part of the decomposition of WC and Al,Mg form of Al4C3,Al4 W,MgAl2C,Al18Mg3W2 and other intermetallic compounds play a role in precipitation strengthening.With the increase of WC content,the microstructure of the cladding layer is improved,the microhardness is increased and the corrosion resistance is improved.When the WC content is 15 wt.%,The cladding layer has the best overall performance.Al + WC + La2O3 coatings were prepared by adding 0 wt.%,0.8 wt.%,1.2 wt.%,1.6 wt.% La2O3 rare earth powder in 85 wt.% Al + 15 wt.% WC powder.Appropriate amount of rare earth can be added to refine the cladding layer to reduce the formation of microcracks in the cladding layer.The main phase of the cladding layer is Al12Mg17,Al3Mg2,Al4 W and LaAl3.When the rare earth content is 1.2wt.%,The average microhardness of the cladding layer is the best,and the corrosion resistance is the best.When the rare earth content exceeds 1.2 wt.%,the rare earth itself becomes an impurity,which reduces the flowability of the molten bath and becomes uneven in the cladding structure,thereby reducing the corrosion resistance and microhardness of the cladding layer.In this paper,the microstructure and properties of Al + WC cladding layer at 140 A current are analyzed.The microstructure of the cladding layer is Al12Mg17 + ?-Mg eutectic structure,Al12Mg17 intermetallic compounds are the main compounds in the above regions and the surface layer is mainly Al3Mg2 intermetallic compound.WC almost completely decomposed,part of W,C and Al,Mg elements formed tungsten Al4 W and carbide Mg Al2C2 and Al4C3.The cladding layer is increased by the dilution ratio of the magnesium alloy matrix,and the surface roughness is deteriorated.The microhardness and corrosion resistance of the cladding layer at high current were less than the cladding layer at low current.
Keywords/Search Tags:Laser cladding, WC, La2O3, Microhardness, Corrosion resistance
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