Microstructure And Properties Of Chrome/Nitriding Diffused Composite Layer On Aluminum Alloy Surface

Cr/N coatings have been widely studied and innovated by material workers in recent years because of their high hardness,high toughness,high wear resistance,and good corrosion resistance.Because of its light weight,high specific strength,excellent heat resistance and high fatigue strength,aluminum alloy is widely used in aerospace,automotive,building materials and other industries,and has become the second largest metal in use after steel material.However,the low hardness,poor wear resistance,and non-corrosion resistance limit the use of aluminum alloys.In order to improve the performance of aluminum alloys,the application of surface treatment technology to aluminum alloys has become a new research hotspot.Therefore,in order to meet the new requirements for improving the hardness and wear resistance of the 2024 aluminum alloy surface,this article has adopted a combination of magnetron sputtering technology and plasma nitriding technology to prepare Cr/N-Cr/Al on the aluminum alloy surface.Composite modified layer.Unbalanced magnetron sputtering ion plating technology was used to change the substrate bias and target power sputtering parameters,and a nanoscale elemental Cr film was deposited on the surface of 2024 aluminum alloy.XRD results show that the Cr film with a body-centered cubic structure(bcc)has a preferred orientation of(110),and the grains exhibit a typical columnar crystal structure.The substrate bias voltage increased from-10 V to-110 V,and the grain size increased from 178 nm to 353 nm.With the increase of the target power(0.2 k W to 1.6 k W),the film thickness increased,and the grain size increased from 50nm to 290 nm.The indentation test showed that the surface hardness of the film reached 4.58 GPa at-10 V,and H/E(crack resistance)and H³/E²(plastic deformation resistance)decreased with increasing substrate bias and target power.The film-based bonding force of the film is the best at-10 V,and the critical load is 53.83 N.After the pre-plated elemental Cr film is subjected to plasma nitriding,the surface becomes denser and a multi-layer structure is formed on the surface.The phases from the surface to the substrate are Cr N,Al₄Cr,Al₁₈Cr₂Mg₃and other intermetallic compounds.The thickness of the Al₄Cr,Al₁₈Cr₂Mg₃composite modified layer is greatly affected by changes in plasma nitriding temperature.Below 430?,the growth of the composite modified layer is not obvious.At 480?,the Al₁₈Cr₂Mg₃layer thickens to 14.5?m.The composite modified layer significantly improved the hardness and wear resistance of the 2024 aluminum alloy surface.The surface hardness after nitriding treatment reached9.39 GPa and the elastic modulus was 175 GPa.Compared with the aluminum alloy substrate hardness(1.57 GPa),the hardness of the film layer is significantly improved,and the H/E crack resistance(0.0604)and H³/E²plastic deformation coefficient(0.0342)are significantly improved.The surface friction coefficient of aluminum alloy decreased from0.72 to 0.32,and the wear mechanism of the composite modified layer was mainly adhesive wear at the beginning,and abrasive wear was the main part in the stable stage,and it was always accompanied by oxidation wear.