In order to improve the hardness, corrosion resistance and wear resistance of aluminum alloy materials, a Ti/TiC composite coating material was prepared on the surface of ZL101 aluminum alloy by laser cladding process, and its performance was studied. The results show that with the increase of TiC powder content, the hardness of the material increases, and the corrosion resistance and wear resistance are enhanced. When the TiC powder content is 0%, the corrosion resistance of the coating material with laser cladding Ti powder alone decreases compared with the aluminum alloy substrate. The Ti/TiC composite coating material prepared by laser cladding with 88% Ti powder and 12% TiC powder has good comprehensive performance, and its microhardness reaches 685 HV, which is about 7 times higher than that of the aluminum alloy substrate. The electrochemical corrosion current density is 3.549e’-005A/cm’2, which is one order of magnitude higher than that of the aluminum alloy substrate, and the corrosion resistance is good. The average friction coefficient is only 0.238, which is 52.6% lower than that of the aluminum alloy substrate, and the wear resistance is good.
In order to enhance the application performance of aluminum alloy materials, surface modification technologies such as laser cladding and micro-arc oxidation are often used to improve the hardness, wear resistance and corrosion resistance of aluminum alloys. For example, on the surface of 7075 aluminum alloy, an Al-Cr composite coating was studied by laser cladding process, and the performance of the coating material was analyzed [1]. Ni-based composite coating was prepared on the surface of aluminum alloy by mechanical spheroidal graphite process, and the coating performance was studied [2]. In addition, a cerium vanadate (CeVO4) nanofiller was prepared by hydrothermal synthesis, and then the filler was dispersed in epoxy resin to prepare a coating material for aluminum alloy surface modification [3]. Based on this, in order to improve the comprehensive performance of ZL101 aluminum alloy, a Ti/TiC composite coating material was prepared on its surface by laser cladding process, and the performance of the composite coating material was studied.
1 Experimental part
1.1 Materials and equipment
Main materials: ZL101 aluminum alloy (industrial pure, Zhengren mold steel); TiC powder (industrial pure, Xunlai Metal Materials); Ti (B, C, N) powder (industrial pure, Zheming New Materials);
Main equipment: HVS-5ZD hardness tester (Zhongte Precision Instrument); LDF 4000-100 laser (Lecong Electromechanical); YM-4A planetary ball mill (Yuming Instrument); CS350H electrochemical workstation (Zhenming Keji); MRH-3G friction and wear tester (Kece Testing Technology).
1.2 Experimental method
1.2.1 Laser cladding process parameters
The substrate material used in the experiment is ZL101 aluminum alloy. A Ti/TiC composite coating material is prepared on the substrate by laser cladding. Table 1 shows the laser cladding process parameters.
1.2.2 Laser cladding powder ratio
The test mainly tests different TiC powder contents in the process. Table 2 shows the laser cladding powder ratio.
1.2.3 Pretreatment of raw materials
(1) According to the ratio of Ti powder and TiC powder in 1.2.2, use an electronic balance to weigh appropriate amounts of T powder and TiC powder and add them into the ball mill. Set the speed of the ball mill to 200 mmin, mix the Ti powder and TC powder for 1 hour, then take out the mixture and set aside;
(2) In the laser cladding test of aluminum alloy, the oxide film on the surface of the aluminum alloy substrate will increase the number of pores in the cladding layer and reduce the quality of laser cladding. Therefore, the aluminum alloy substrate needs to be pretreated. First, remove the oxide film on the surface of the aluminum alloy substrate by mechanical grinding. Then, clean it with anhydrous ethanol. Then put the aluminum alloy substrate into a drying oven and dry it until there is no moisture on the surface. Take out the aluminum alloy substrate and start laser cladding treatment immediately.
1.2.4 Laser cladding test
In the process of laser cladding Ti/TiC composite coating material on the surface of ZL aluminum alloy, the coaxial powder feeding method is adopted. The specific steps are as follows:
(1) Load the mixture of Ti powder and TiC powder pretreated in 1.2.3 into the powder feeder, and place the aluminum alloy substrate material with the oxide film removed on the workbench;
(2) Check the equipment and confirm that it is safe. Then, under the laser cladding process parameter settings in 1.2.1, feed the powder and send the mixture of Ti powder and TiC powder to the focus of the laser beam for laser rapid heating and rapid cooling. Note that during laser cladding, argon gas needs to be continuously introduced from the side;
(3) After the laser cladding is completed, turn off the equipment. After the laser cladding Ti/TiC composite coating material is naturally cooled, use a cutting machine and a hot mounting machine to prepare the samples required for subsequent performance testing for standby use.
1.3 Performance test
1.3.1 Hardness test
Before the hardness test, the sample was first metallographically processed. The cross section of the sample was polished with coarse and fine sandpaper in turn. Then a small amount of polishing agent was applied to the cross section of the sample and polished. After that, it was corroded for 10s, and the corrosion solution was immediately rinsed with alcohol and blown dry. The hardness of the cladding layer of the cross section of the sample and the aluminum alloy material matrix was tested by a hardness tester, and the microhardness was analyzed. Among them, the test load and loading time were 200 g and 15 s respectively.
1.3.2 Corrosion resistance
The test was conducted by using an electrochemical workstation and a standard three-electrode system to test the corrosion resistance of the Ti/TiC composite coating material laser-melted on the surface of the aluminum alloy. In addition, the electrochemical reaction solution was a 3.5% NaCl aqueous solution at a constant temperature of 25 ℃. Before the electrochemical corrosion test, the sample was first polished and cleaned, and the surface of the sample was coated with epoxy resin glue several times, and a 1mmx1 mm test area was left. Then it was wrapped with a copper wire. After the electrochemical corrosion test, the sample data was processed by Origin software to obtain the polarization curve and analyze the electrochemical corrosion test data of the sample.
1.3.3 Wear resistance
The Ti/TiC composite coating material sample laser clad on the aluminum alloy surface was placed on a friction and wear tester for 20 min wear resistance test. Among them, the test load and friction frequency were 5 N and 2 Hz respectively. Note that the sample mass was weighed with an electronic balance before and after the friction loss test, and the sample wear loss and average friction coefficient were analyzed.
2 Results and analysis
2.1 Hardness analysis
The hardness test was carried out on the Ti/TiC composite coating material laser clad on the aluminum alloy surface with different TiC powder contents, and the specific results are shown in Figure 1.
As shown in Figure 1, for the Ti/TiC composite coating material laser clad on the aluminum alloy surface with different TiC powder contents, the microhardness is basically stable at a distance of 0.0~1.5 mm from the coating surface, without significant changes. However, when the distance from the coating surface exceeds 1.5 mm, the microhardness of each sample decreases rapidly. When the distance from the coating surface is 3.0 mm, the microhardness of each sample is basically around 130 HV. It can also be seen from Figure 1 that the laser cladding Ti/TiC composite coating materials on the aluminum alloy surface prepared in this experiment with different TiC powder contents have high microhardness values, especially at 0.5 mm close to the coating surface, the microhardness value of each material is the largest.
Comprehensive analysis shows that when the distance is 0.0~1.5 mm close to the coating surface, the microhardness value increases with the increase of TiC powder content. When the mass fraction of TiC powder in the composite coating material is 12%, its microhardness value at 0.0~1.5 mm close to the coating surface is about 685 HV, which is about 7 times that of the ZL101 aluminum alloy matrix material (102 HV) and about 2 times that when the TiC powder content is 0%. Compared with the ZL101 aluminum alloy substrate material, the microhardness value of the laser cladding Ti/TiC composite coating material increases, and its microhardness value is positively correlated with the TiC powder content.
2.2 Corrosion resistance analysis
According to the test method in 1.3.2, electrochemical corrosion tests were carried out on Ti/TiC composite coating materials with different TiC powder contents and aluminum alloy substrate materials. Figure 2 shows the polarization curves of the electrochemical corrosion test of each material sample; Table 3 shows the electrochemical corrosion test data of each sample obtained by the Tafal curve extrapolation method.
As shown in Figure 2, when the TiC powder content in the laser cladding Ti/TiC composite coating material is 0%, the corrosion current density and corrosion potential are both lower than those of the aluminum alloy substrate material. At the same time, when the TiC powder content in the composite coating material increases, the electrochemical corrosion performance of the composite coating material is improved.
It can be seen from Table 3 that when the TiC powder content in the laser cladding Ti/TiC composite coating material is 0%, the corrosion potential and corrosion current density of the material are -1.443V and 7.018E’-0.05 A/cm’2, respectively, which are lower than the aluminum alloy substrate. It can be seen that the corrosion resistance of the coating material with laser cladding T powder alone is lower than that of the aluminum alloy substrate. When the TiC powder content in the composite coating increases from 0% to 12%, the corrosion potential of the material reaches -1.296V, which is higher than the base material aluminum alloy. Moreover, at this time, the corrosion current density of the composite coating material is as high as 3.549e-0.05 A/cm?, which is one order of magnitude higher than the corrosion current density of the aluminum alloy substrate. In addition, in terms of polarization impedance, the polarization impedance of each cladding layer coating material is far higher than the base material aluminum alloy.
In summary, laser cladding Ti/TiC powder composite coating material on the surface of aluminum alloy can improve the corrosion resistance of the material.
2.3 Wear resistance analysis
According to the test method in 1.3.3, the wear resistance test results of the cladding coating materials with different Ti powder contents and the aluminum alloy substrate material are shown in Figure 3.
As shown in Figure 3(a), the average friction coefficient of the aluminum alloy substrate is 0.452, while the average friction coefficient of each laser cladding coating material is less than that of the aluminum alloy substrate. At the same time, when the TiC powder content in the Ti/TiC composite coating material continues to increase, the average friction coefficient of the material shows a continuous decrease. This shows that after laser cladding of T powder and TiC powder, the friction performance of the material is improved. When the mass fraction of TiC powder in the laser cladding Ti/TiC composite coating material reaches 12%, the average friction coefficient of the material is only 0.238. Compared with the base material aluminum alloy, this is reduced by 52.6%, and the wear resistance of the material is enhanced. In addition, as shown in Figure 3(b), after 20 minutes of friction and wear test, the friction and wear amount of the base material aluminum alloy is the highest, which is 9.1 mg. The friction and wear of laser cladding Ti/TiC composite coating materials are lower than that of the base material aluminum alloy, and the friction and wear decreases with the increase of TO powder content in the coating material. When the mass fraction of TiC powder in the composite coating material reaches 12%, the friction and wear of the material is only 3.1 mg, which is 65.9% less than that of the base material aluminum alloy, and the material has good wear resistance.
In summary, with the increase of TiC powder content, the wear resistance of laser cladding Ti/TiC composite coating materials is improved.
3 Conclusion
(1) With the increase of TC powder content in Ti/TiC composite coating materials, the microhardness increases;
(2) The corrosion resistance of the coating material with laser cladding T powder alone is lower than that of the aluminum alloy substrate. And when the TiC powder content in the Ti/TiC composite coating material increases, the corrosion resistance of the material is enhanced;
(3) Laser cladding Ti/TiC composite coating material on the surface of aluminum alloy can reduce the average friction coefficient of the material, reduce the wear loss, and enhance the wear resistance;
(4) In the experiment, when the mass fraction of TiC powder is 12%, the prepared Ti/TiC composite coating material has good comprehensive performance. Its microhardness reaches 685 HV, which is about 7 times that of ZL101 aluminum alloy substrate (102 HV). At the same time, the corrosion current density reaches 3.549e’-0.05 A/em’2, which is one order of magnitude higher than that of aluminum alloy substrate. And the average friction coefficient is only 0.238, which is 52.6% lower than that of aluminum alloy substrate.
