With the increasing demand for automobiles, automobile brake discs are increasingly being used. The weight of traditional gray cast iron brake disc is 4-5 times that of aluminum alloy casting brake disc. Lightweight car design not only reduces energy consumption but also enable cars to achieve faster initial speeds. However, when excessive wear occurs on the surfaces of brake discs, the braking distance is significantly affected, which impairs driver safety. Compared with those of traditional gray cast iron brake discs, the hardness of aluminum alloy brake discs is low and the wear resistance is poor, and these are more likely to cause plastic deformation and other problems in cars. Thus, the application and development of aluminum alloys for use in car brake discs are greatly limited. As a new surface modification technology, laser cladding can be used to clad aluminum alloy brake disc surfaces with stronger mechanical and anti-wear properties. Not only can this technology reduce the weight of brake discs, it also can overcome the shortcomings of aluminum alloy brake discs and address actual working conditions. In this study, Al-Si-Ni-WC composite coating is prepared on the surface of the ZL108 aluminum alloy using laser cladding technology, where the hardness and wear resistance are greatly improved.

First, a ZL108 aluminum alloy sheet is used as the matrix material, which is prepared according to the proportions listed in Table 2. It is then placed in a ball mill for mixing for 6 h and dried in a drying oven for 5 h. The experiment is conducted using the fiber laser cladding equipment with a maximum laser power of 2 kW. After the coating is prepared on the Al alloy plate, it is cut along the direction perpendicular to the laser-scanning direction. After the sample is obtained, the surface is polished using SiC sandpapers. The polished sample is then placed in a prepared Kellers reagent for surface corrosion, and the surface microstructure is observed. The morphology is observed using scanning electron microscopy (SEM), and the phase composition of the substance and hardness of the cladding coating surface are measured using an X-ray diffractometer (XRD) and dimensional hardness tester, respectively. A friction and wear testing machine is used to test the friction and wear properties of the samples. A GCr15 steel ball with a hardness of 240 HV and diameter of 4.6 mm is used as the friction pair during the test. The load is 20 N and the wear time is 20 min. Finally, the substrate and coating materials are tested through electrochemical experiments using a NaCl solution at normal temperature to analyze their corrosion resistance.

Following the hardness test and friction and wear test on the cladding coating and substrate, it is found that the Al-18%-Si-30%-Ni-5%-WC composite coating forms a more uniform cladding surface. The main phases in the coating include AlNi, AlNi₃, WC, SiC, and other hard alloy phases, and the hard alloy phases generated in-situ are evenly distributed within the cladding layer. The substrate and coating bond tightly, and the grains inside the cladding coating are refined. In addition, the average hardness value of the cladding coating surface is found to be 272 HV when the mass fraction of Ni is 30%, which is 3.1 times the average hardness value of the ZL108 substrate surface, and the hardness values of the cladding coatings increase with an increase in Ni content. The wear volume of the composite coating is approximately 1/4.47 of that of the matrix, and the wear volume at high temperatures is lower than that at the normal temperature. The main reason for this is that Ni, which has strong high-temperature resistance, is added to the coating. Meanwhile, hard phases such as WC and SiC generated in situ also significantly improve the wear resistance of the coating.

Compared with that of the ZL108 aluminum alloy, the hardness of the coating prepared by laser cladding technology is greatly improved. NiAl, Ni₃Al, SiC, and other hard phases generated in situ inside the coating are evenly distributed inside the coating, thereby supporting and strengthening the coating. The main wear mechanisms of the substrate and cladding coating at room temperature are found to be abrasive wear. The wear mechanism of the substrate at high temperatures is adhesion wear and a small degree of oxidative wear, whereas the wear mechanism of the coating mainly consists of abrasion, oxidative, and adhesion wear. With an increase in ambient temperature, the thermal oxidation reactions are aggravated, and composite oxide films are generated by the coating, which alleviates the friction loss derived from adhesive and abrasive wear. This results in a lower wear volume at high temperatures than at room temperature. In the saturated NaCl solution, the corrosion resistance of the coating is significantly higher than that of the substrate. The improvement in corrosion resistance greatly increases the service life of the brake disc.