Study Of CrN_x Coatings Deposited On 2024 Aluminium Alloys By Multi-Arc Ion Plating

Zn/Ni/Cu/Cr/CrN_X coatings deposited on 2024 Aluminium Alloys by electrochemistry and magnetic filter pulse bias arc ion plating(PBAIP) technology are investigated.Al alloys are the most lightest materials with excellent properties such as high compare intensity,good heat conduction and conductance and easily machining etc,which are applied in many fields chiefly in automobile industry,aerospace industry and war industry.PBAIP has been extensively used to deposit various hard coatings especially on high-speed steel due to its higher ionization,higher deposition rate and stronger adhesion with substrate.But Aluminium Alloys'surface modification is hard to carry out due to its extreme lively chemical property,which are surrounded by a hard and crisp Oxide film quickly(20～30A). Moreover,the difference of expansion coefficient between CrN(22.9^*10^-6/K) and Al alloys (9.4^*10^-6/K) is very large.So a particular pretreatment and proper transitional layers are needed.Based on some scholars' research,a reasonable process is adopted to improve coatings-substrate adhesion that is composed of double dipping zinc,pre-electroless nickel and electroplate copper,followed by Cr/CrN_X coatings by PBAIP.In this paper,Scan electron microscope(SEM),X-ray diffraction(XRD),Electronic probe microanalysis(EPMA) and hardness tester are used to characterize the morphology,composition,structure and micro-hardness of the films respectively,The results show that:(1) Pretreatment technique of double dipping zinc and electroless nickel can resolve Al₂O₃ thin film completely and turn to easy plating material.Electroplate copper which stick Ni-P film with Cr/CrNx films relieve stress.Two-step electroless nickel can protect solution from poisoning by dissolving Zn and form a gradient P content.Such multilayer films of Zn/Ni/Cu/Cr/CrN_X decreased in compositions and properties and structure distributed by turns are beneficial to relieve stress and enhance adhesion.(2) Cr/CrNx coatings produced by PBAIP is consist of Cr,CrN and Cr₂N phases with CrN(220) major orientation,own glazed and compact performance.Ni-P film which possess high hardness strongly hold nitride film and contribute to surface hardness of 26 Gpa.(3) PBAIP with magnetic filter which reduce number and size of big grain with a good performance can weaken spot corrosion;toughness Cr and hard CrN_x coatings distributed by turns interrupt column structure and thick Ni-P film are good for bore corrosion;low stress and gradient electrochemistry property of Zn/Ni/Cu/Cr/CrN_X multilayer films also weaken phase corrosion speed,self-corrosion potential value shift positive 400mV,those improve 2024Al alloys corrosion resistance largerly.(4) frictional coefficient value of multilayer films is 0.4,CrNx performances and high hardness hold of Ni-P film are beneficial to good wear resistence.(5) Heat shaking law at 220℃for 20min and then cooling for 5min as a cycle,after 12 cycles without crack and flake,multilayer films have better film-substrate adhesion.Perfect CrNx coatings with higher hardness,higher wear resistance and good corrosion resistance can protect Aluminium Alloys and obtain industry applications widely in the future.