Microstructure And Properties Of NiAl Composite Coating By Laser Cladding On Al Alloy

Aluminum alloy has many advantages such as low density,high thermal conductivity,good corrosion resistance,easy forming,low cost and renewable.It is widely used in aerospace,transportation,electronic communication,construction and other fields.Nowadays,it has become a key material for industrial development.However,the low hardness and poor wear resistance of the aluminum alloy lead to the abrasion and failure easily occured on the surface resulting in the failure of the full parts during the actual working process.In order to solove the serious problems that the low hardness and wear resistance of aluminum alloy in practical application,the Ni Al composite coating was fabricated by laser cladding technology on the surface of 6061 aluminum alloy in this paper.The optical microscope,X-ray diffractometer,scanning electron microscope and the energy disperse spectroscopy were used to analyse the macroforming quality,phase composition,microstructure and elements distribution of the cladding coating.The microhardness and wear resistance of the cladding coating were tested by HVS-1000 microhardness tester and high speed friction wear tester.The influence of laser process parameters on the macroscopic morphology and size of the cladding coating were discussed,and the effects of Al₂O₃-TiO₂ composite ceramics and different mass fraction of CeO₂ on the structure and properties of NiAl composite coating was studied.The results show that:?1?By investigating the effects of scanning speed and current strength on the forming quality and macro morphology of single-channel cladding coating,the optimal process parameters of laser cladding NiAl coating is obtained:current 200A,scanning speed 250mm·min^-1,frequency 8Hz,pulse width 4.0 ms,spot diameter 2mm,protective gas flow 15L·min^-1,overlapping rate 35%.?2?Due to the high brittleness of NiAl intermetallic compounds and the difference of physical properties between alloy powder and aluminum alloy,there are obvious cracks and pores forming in the NiAl cladding coating.The cladding coating is mainly composed of?-Al solid solution and NiAl,Ni₂Al₃ and NiAl₃intermetallic compounds.The average hardness of the coating can reach 350HV_0.2,which is about 4.5 times of the substrate.The wear resistance is 5.81 times of the6061 aluminum alloy matrix.?3?On the basis of the NiAl mixed powder with a molar ratio of 1:1,the different mass fraction of CeO₂?2%,5%,8%,and 10%.?were added.The results show that the microstructure morphology and wear resistance of NiAl cladding coating are improved effectively with the addition of CeO₂,and the cladding coating with better forming quality is obtained.The content of Ni Al₃ and Ni₂Al₃intermetallic compounds in the cladding coating is increasing,while it has the new phase of CeNi₅ is forming in the cladding coating.What's more,the microstructure of cladding coating is effectively refined and get more uniform and denser.In the grain boundary,the rare earth element Ce has obvious enrichment.The hardness and wear resistance of the cladding coating were improved by the addition of different amounts of rare earth CeO₂.When the content of CeO₂ is 8%added into NiAl coating,the performance of the NiAl coating has the most significant effect.?4?Adding 10wt%Al₂O₃-TiO₂ composite ceramics into the NiAl mixed powder that content is molar ratio 1:1 can improve the macroscopic morphology of the cladding coating to some extent.The phase of the cladding coating is mainly composed of NiAl₃,Ni₂Al₃ intermetallic compound,?-Al solid solution and a small amount of Al₂O₃,NiTi and TiO₂.From the surface to the bottom,a dense and fine small dendrites,columnar dendrite,petal equiaxed dendrite and dendrite mixed structure are formed.The average hardness of the NiAl/Al₂O₃-TiO₂ composite coating is 650HV_0.2,increases by 300HV_0.2.2 compared with Ni Al coating.and the relative wear resistance is 9 times that of aluminum alloy substrate,increased 35%of the NiAl coating.?5?The addition of 5wt%CeO₂ in Ni Al/Al₂O₃-TiO₂ can effectively inhibit the defects formation of cracks and porosity in the cladding coating.Additionaly,the microstrure of the cladding coating is more uniform and refinement.The addition of CeO₂ has little influence on the composition of the cladding coating,except the composition of NiAl/Al₂O₃-TiO₂ composite coating,a small amount of CeNi₅ rare earth compounds is formed in the cladding coating.The hardness and wear resistance of NiAl/Al₂O₃-TiO₂ is improved.When the addition of CeO₂ is 5wt%,the NiAl/Al₂O₃-TiO₂ cladding has the best performance of microhardness and the wear resistance.