Study On Preparation And Properties Of High Performance Coatings On Aluminum Alloy Wheel Surface

As an important load-bearing component in the vehicle driving system,aluminum alloy wheels have made an important contribution to the lightweighting of automobiles and have been widely used in civil,special operations,military and other fields.Automotive wheels should not only have sufficient overall strength and stiffness,but also need to have good surface properties.However,the surface of aluminum alloy wheels has low strength and hardness,poor wear resistance,and insufficient corrosion resistance in high salt,humid and hot environments,which greatly shortens the service life of the wheels and limits their application as wheels for heavy trucks and special vehicles in harsh environments.Therefore,it is very important to change the surface structure and improve the comprehensive surface properties by using surface treatment methods.In this paper,three surface modification methods were used to obtain reinforced coatings with different characteristics.The relationships between coating composition,phase structure,microstructure and mechanical properties,wear resistance,corrosion resistance were systematically investigated.Zr-based and Ni-based amorphous alloys were used as modified fillers to prepare polyurethane/amorphous alloy composite coatings.The results showed that the metal fillers had an effect on the reaction process of polyurethane,leading to a decrease in the content of hard segments on the surface of the coatings.The addition of amorphous alloys changed the intermolecular force between N-H bonds of the hard segments and the hydrogen bond strength of C=O bonds in the urea groups.Amorphous particles disrupted the original arrangement of the fillers and formed a near-ring structure,which generally has a positive effect on the overall properties of the coatings.Due to the synergistic effects of amorphous alloy properties and hydrogen bond strength,hardness and wear resistance increased with increasing amorphous content.The maximum increase in hardness is 1.66times and in wear resistance is 3.31 times.Wear mechanisms are dominated by abrasive wear and fatigue wear.The coatings have certain stealth performance,and the maximum bonding strength is 2.45 times that of the pure polyurethane coating.The addition of amorphous alloys can significantly improve corrosion resistance of the coatings.Among the polyurethane/amorphous alloy composite coatings,the one containing 50 vol%Zr-based amorphous alloy has the best overall performance.Using laser cladding technology to prepare cladding layers on the aluminum alloy surface,it was found that the defects could be reduced by using a small spot of 1.5 mm.Aluminum alloys with low melting point are easy to float up a lot in the molten pool,and the enthalpy of mixing between Al and other elements is negative,which easily leads to the formation of intermetallic compounds and deteriorates the coating quality.Therefore,high-entropy alloys with a high entropy effect were proposed as cladding materials.By determining the phase structure through theoretical calculations,the Fe Co Cr Ni-M（M=Mn,Cu,Ti,-）system was selected and designed for laser cladding on aluminum alloys.The optimal process parameters were given by combining multi-response process optimization and a double-layer cladding method.The dilution behavior of Al was basically suppressed,laying a foundation for the preparation of large area coatings.In Fe Co Cr Ni-M large area coatings,the addition of Mn and Cu did not change the single FCC phase,while the addition of Ti caused the formation of BCC,Laves and AB-type phases.Different elements caused different composition segregation and changes in grain size.Under the synergistic effects of solid solution strengthening,dispersion strengthening,precipitation strengthening and fine grain strengthening,the coatings can increase the hardness of the aluminum alloy substrate by up to 16 times and the wear resistance by up to 69 times.Wear mechanisms are dominated by abrasive wear and adhesive wear.Bonding strength of the coatings is much higher than that of the modified polyurethane coatings,and the addition of Cu can significantly improve the bonding strength.The high-entropy alloy coatings prepared by laser cladding can greatly improve corrosion resistance of the substrate,in which,the Fe Co Cr Ni Ti coating covered with compact passive film composed of Ti O₂ and Cr₂O₃ has the strongest corrosion resistance.High-entropy alloys deposition coatings were prepared by plasma spraying technique.The interface of the coatings is dominated by mechanical engagement,which can avoid Al floating up and entering the coatings.The coatings have a typical layered structure and mainly consist of the FCC phase and a certain number of oxides.Metallurgical bonding layer of micron size is present at the coating interface.Due to the different preparation methods of spraying powders,Cu and Ti mostly exist in the forms of simple substances and oxides,with a small part dissolved in the FCC phase.The coatings can increase the hardness of the aluminum alloy substrate by up to 8.4 times and the wear resistance by up to 62 times.Except for the Ti-added coating,the hardness and wear resistance of the other three coatings are higher than those of the laser cladding coatings with the same composition.Second phase strengthening is the main strengthening mechanism for the improvement of hardness and wear resistance.Wear mechanisms are dominated by adhesive wear,abrasive wear and oxidative wear.Bonding strength of the coatings is much higher than that of the modified polyurethane coatings,and is insensitive to changes of the elements.The high-entropy alloy coatings prepared by plasma spraying can obviously improve corrosion resistance of the substrate,in which,the FCC phase of the Fe Co Cr Ni Ti coating with some Ti gives the coating the best corrosion resistance.The polyurethane/amorphous alloy composite coatings have an advantage of the strongest corrosion resistance,and have good flexibility,stealth and aesthetics.Aluminum alloy wheels modified with polyurethane/amorphous alloy composite coatings are more suitable for service in an environment with high corrosion intensity.The laser cladding coatings have the highest bonding strength,as well as good mechanical properties,wear resistance and high corrosion resistance.Aluminum alloy wheels modified with laser cladding coatings are suitable for service in an environment where impact,scratch,wear and corrosion resistance are all required.The hardness and wear resistance of most plasma spraying coatings are higher than those of the laser cladding coatings,while the plasma spraying coatings also have good corrosion resistance.Aluminum alloy wheels modified with plasma spraying coatings are suitable for service in an environment with high requirements for impact and wear resistance and a certain demand for corrosion resistance.