A method for evaluating the quality of the surface coating of a galvanized sheet against frictional damage

Abstract

The application discloses a kind of passivation galvanized sheet surface coating anti-friction damage quality evaluation method, respectively carry out "heavy load surface layer damage friction experiment" and "light load sliding friction experiment", from simple passivation layer to set various lubricating conditions, to simulate the friction state under various working conditions, from the above macroscopic experiment to select typical sample and carry out multi-dimensional multi-means analysis on thickness, hardness, bonding force, surface three-dimensional topography etc.Microcosmic level, identify the difference of passivation layer, and make a judgment on the influence of friction system.The purpose of the application is to provide a kind of passivation galvanized sheet surface coating anti-friction damage quality evaluation method, which can quantitatively judge the influence of passivation galvanized sheet surface film quality on stamping process, and provide data support for improving the performance of passivation galvanized sheet.

Description

Technical Field

[0001] This invention relates to the field of metal coating quality technology, and in particular to a method for evaluating the quality of friction damage resistance of passivated galvanized sheet surface coating. Background Technology

[0002] With the continuous development of the automotive industry, automakers are increasingly demanding higher corrosion resistance from car bodies, and galvanized steel sheets are gradually replacing cold-rolled steel sheets as the best choice for automotive body panels. Galvanized steel sheets are most commonly used in passenger cars, with many mid-to-high-end sedans in China using them. As domestically produced cars expand globally, the application of galvanized steel sheets for car bodies is also a trend.

[0003] Galvanized steel sheets are commonly used for TV back panels, air conditioner back panels, and computer back panels. With the upgrading of home appliance products, companies like Xiaomi, Hisense, Skyworth, and TCL are constantly developing higher-end TVs. The pursuit of fashion, aesthetics, and individuality is a common consumer mentality, leading to increasingly complex designs with sharp edges and raised corners. The trend towards larger sizes and lighter weights is also putting greater demands on the performance of galvanized steel sheets.

[0004] Due to increasingly fierce competition in the automotive and home appliance industries, products are becoming thinner, more stylish, of higher quality, and lower in price. This puts pressure on material suppliers, demanding thinner dimensions with smaller tolerances, higher performance limits, less anisotropy, stronger surface lubricity, and superior coating quality. This constantly pushes the limits of sheet metal performance. Therefore, the stamping performance of galvanized steel sheets is influenced by numerous factors, requiring comprehensive evaluation. These factors include: the uniformity and density of the surface galvanized and passivation layers; film adhesion; film damage resistance; oil lubrication; sliding friction characteristics; friction fatigue characteristics; and whether the product simultaneously possesses fingerprint resistance, corrosion resistance, good conductivity, and suitability for various stamping processes. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating the quality of the coating on the surface of passivated galvanized steel sheets to resist friction damage. This method can quantitatively assess the impact of the coating quality on the stamping process and provide data support for improving the performance of passivated galvanized steel sheets.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a method for evaluating the quality of the surface coating of passivated galvanized steel sheet to resist friction damage. It involves conducting "heavy load surface damage friction experiments" and "light load sliding friction experiments," simulating friction states under various working conditions by varying the effects of the passivation layer and setting different lubrication conditions. From these macroscopic experiments to the multi-dimensional and multi-method analysis of typical samples at the microscopic level, including thickness, hardness, adhesion, and surface three-dimensional morphology, the method identifies differences in the passivation layer and assesses its impact on the friction system.

[0008] Furthermore, the specific steps include the following:

[0009] 1) Macroscopic characterization under heavy load

[0010] 1.1) Evaluation of friction and wear

[0011] A face friction and wear tester was used to test the change in the surface friction coefficient before the passivation layer was damaged and the iron substrate was exposed.

[0012] Comparative sample setup: Conduct comparative experiments on different parts within the same plate width to obtain the relationship between the friction coefficient and the plate width distribution; differentiate between the upper and lower surfaces, and use the same surface for experiments to eliminate interference from differences between the upper and lower surfaces, ensuring that the data has comparative value;

[0013] Evaluation: The curve of dynamic friction coefficient change under the experimental conditions was obtained. The inflection point where the dynamic friction coefficient curve rises vertically from 0 to the first slope after the load is applied is regarded as the initial dynamic friction coefficient δ1 under the friction and wear characterization conditions of the sample. The average of the maximum and minimum data of the curve after it rises to a stable value as the experiment progresses is regarded as the stable dynamic friction coefficient δ2 under the friction and wear characterization conditions.

[0014] 1.2) Microhardness Comparison

[0015] The samples after the above friction and wear test were subjected to passivation layer microhardness test to identify the difference in passivation layer hardness of the sample. Microhardness measurement was performed on the unworn part of the sample, and three points were measured on each test surface.

[0016] Comparative sample setup: Conduct comparative experiments on different parts within the same plate width to obtain the relationship between microhardness and plate width distribution; differentiate between upper and lower surfaces, and use the same surface for experiments to eliminate interference from differences between upper and lower surfaces, ensuring that the data has comparative value;

[0017] Evaluation: Microhardness was measured on the unworn areas of the sample. Ten points were measured on each test surface, and the average of three points was taken as Y.

[0018] 1.3) Three-dimensional morphological comparison analysis

[0019] The differences between the friction marks and the substrate morphology after macroscopic friction experiments were analyzed to identify the surface morphology factors that affect friction and wear.

[0020] Control sample setup: After the surface friction experiment, observe the matrix morphology and friction mark morphology of the samples respectively;

[0021] Evaluation: Observe the wear morphology at the wear area to determine the part with the most severe damage seen macroscopically. Is it the surface peaks that are pressed into the substrate or only the troughs are filled without damaging the substrate? Combine δ1 and δ2 and microhardness Y to determine the cause of the damage. If the values ​​of δ1 and δ2 are stable and lower than those of similar materials, while the value of Y is higher than that of similar materials, it indicates that the damage is caused by excessive hardness of the surface coating. If the values ​​of δ1 and δ2 are stable and lower than those of similar materials, and the value of Y is also lower than that of similar materials, then the next step of micro-load characterization should be carried out to evaluate the passivation film layer on the coating surface.

[0022] 2) Microscopic characterization under microload

[0023] 2.1) Evaluation of sliding friction

[0024] A multi-functional friction and wear testing machine was used to set a slight load force and repeat the loading 30 times to obtain the change of dynamic friction coefficient during this period, thus characterizing the state of the passivation layer surface friction system under micro-load conditions.

[0025] Comparative sample setup: Comparative experiments were conducted on different parts within the same plate width to obtain the relationship between the friction coefficient and the plate width distribution; the upper and lower surfaces were distinguished, and the same surface was used for experiments to eliminate interference caused by differences between the upper and lower surfaces, ensuring that the data has comparative value; the transverse and longitudinal directions were distinguished to obtain the difference in friction coefficient caused by the processing direction; comparative experiments were conducted on the oil on the surface of cleaned and uncleaned samples. The cleaned samples showed the various properties of the passivation layer itself, and the uncleaned samples could represent the dynamic friction state under the condition of finished product delivery and use, provided that the original oil film was not damaged by sample stacking and processing.

[0026] Evaluation: The average dynamic friction coefficient within 10 seconds of each sliding test is taken as a data point. Connecting the data points of 30 loading tests forms a curve, which shows the trend of friction coefficient change. The starting point of the curve and the vertical axis is the initial dynamic friction coefficient under this condition. The level of the initial dynamic friction coefficient can characterize the resistance state of the surface passivation film to a single stamping friction process. The dynamic friction coefficient curve of the last 29 tests is observed to see if there are obvious fluctuations, which can characterize the lubrication stability of the film layer. Combining the presence, quantity, and composition of the oil film in the experimental sample can evaluate the comprehensive effect of the oil and the surface film layer.

[0027] 2.2) Evaluation of Nanoindentation

[0028] Microscopic surface hardness tests were conducted using a nanoindenter. Based on the results of the above dynamic friction experiments, the relationship between the surface hardness of the passivation layer and the increase in the coefficient of dynamic friction and the degree of surface friction damage with the increase of the number of reciprocating cycles was analyzed.

[0029] Comparative sample setup: Samples from the same location were selected, and the tests were conducted under identical conditions for other samples. Evaluation: The measured nano-hardness value can characterize the surface hardness of the passivation film. Whether the force trajectory shown by the measured hardness force curve gradually increases or decreases can characterize the hardness difference between the surface layer and the passivation film substrate. If the surface hardness is higher than the substrate, it indicates that the damage is mainly caused by shallow indentation. In this case, the optimal friction state is that the force on the surface should be less than the critical force for surface damage. If the surface hardness is lower than the hardness of the passivation film substrate, the optimal friction should only require that the overall passivation film not be damaged.

[0030] 2.3) Evaluation of Nanoscale Scratch

[0031] Nanoscale scratch testing was performed using a nano-scratch analyzer, and the differences in the adhesion force of the passivation layer were analyzed through multiple signals including mechanical, acoustic, and morphological analysis.

[0032] Comparative sample setup: Select samples from the same location and conduct the test under identical conditions for other samples;

[0033] Evaluation: The adhesion value of the passivation layer was determined based on the morphology of the scratch damage of the film layer combined with mechanical and acoustic signals. The influence of the surface hardness of the film layer on the final friction damage was judged based on the adhesion. If the surface hardness of the film layer corresponding to strong adhesion is greater than or less than that of the substrate, the sample can withstand a higher optimal friction critical force, and vice versa.

[0034] Furthermore, in step 1.1), when a heavier load is set using an end-face friction and wear testing machine, the appropriate friction load, rotation speed, and duration for the current sample type are determined through experiments.

[0035] Furthermore, in step 2.1), the American Rtec multi-functional friction and wear testing machine is used.

[0036] Furthermore, in step 2.1), when a slight load is set using a multi-functional friction and wear testing machine, the appropriate friction load, rotation speed, and duration for the current sample type are determined through experiments.

[0037] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0038] This method is based on extensive practical analysis experience and tribological theory. It can achieve efficient and standardized evaluation of the surface friction characteristics of passivated galvanized steel sheets, effectively guide optimization and improvement, and can also be extended to the judgment and optimization of friction damage characteristics of multi-layer coatings / films. Attached Figure Description

[0039] The present invention will be further described below with reference to the accompanying drawings.

[0040] Figure 1 The friction coefficient of sample B;

[0041] Figure 2 Let S be the coefficient of friction of sample S.

[0042] Figure 3 The macroscopic morphology of different samples after the experiment (top row is sample B, bottom row is sample S).

[0043] Figure 4 Microscopic and 3D morphology of surface B;

[0044] Figure 5 The surface microstructure and 3D morphology of S;

[0045] Figure 6 For sample B before cleaning, compare the horizontal and vertical sides.

[0046] Figure 7 Comparison of sample B after cleaning (horizontal and longitudinal directions)

[0047] Figure 8 For sample S before cleaning, compare the horizontal and vertical sides;

[0048] Figure 9 For sample S after cleaning, compare the horizontal and vertical sides;

[0049] Figure 10 The hardness curve of sample B(B-4-L) after nano-gradient compressive testing;

[0050] Figure 11 The hardness curve of sample S(S-4-L) after nano-gradient compressive testing. Detailed Implementation

[0051] Example

[0052] This is a comparative experiment to evaluate the frictional damage state of the surface films of samples B and S.

[0053] 1. Friction and Wear Test

[0054] (1) Test Method. Each sample number contains two test samples. One sample is cleaned (using anhydrous ethanol for ultrasonic cleaning), and the other is tested on its original surface. Sampling should be done on the same areas from both manufacturers. Note: During the experiment, ensure that the "top surface" of each sample is used to guarantee the comparative value of data from the same sample plate.

[0055] (2) Experimental conditions. After actual experimentation, the conditions for determining the friction coefficient of the passivation layer were set as follows: pressure 100N, rotation speed 50r / min, and experimental time 10s.

[0056] (3) Experimental data analysis:

[0057] from Figure 1 and 2 As can be seen from the 10-second experiment, the friction coefficient of most samples fluctuates within a small range after reaching a certain value in 2 seconds, showing a linear trend. The friction coefficient at 1 second is taken as the linear part state and used as the initial friction coefficient. The friction coefficient at 10 seconds is taken as the friction coefficient of the sample in this experiment. The values ​​are shown in the table below.

[0058] Initial friction coefficient δ1 for different samples; friction coefficient δ2 after stabilization for different samples

[0059]

[0060] summary:

[0061] ① The initial friction coefficient and the minimum friction coefficient after stabilization are both for sample S. The average initial friction coefficient and the average dynamic friction coefficient after stabilization are both higher for sample B than for sample S.

[0062] ②The macroscopic morphology of the sample after the test is as follows Figure 3 As shown, from Figure 3 It can be clearly seen that despite the same experimental conditions, the surface wear marks of sample B are very significant, while the wear marks of sample S are slight and almost invisible under the same conditions. The above results indicate that the passivation layer of sample B was significantly damaged during the experiment, and the damage to the passivation layer may further increase the friction coefficient.

[0063] 2. Microhardness Comparison

[0064] (1) Test method. The hardness test was performed using a microhardness tester. The sample was ultrasonically cleaned with petroleum ether for 15 minutes, dried, and then the Vickers hardness test was performed directly.

[0065] (2) Experimental conditions. Based on the hardness value of the sample, the loading force selected during the test was 50g, and the holding time was 10s. To ensure the accuracy of the experimental data as much as possible, 10 points were randomly selected for each sample and the average value was taken.

[0066] (3) Analysis of experimental results. The results of the microhardness experiment are as follows: Figure 1 As shown, the horizontal axis represents the sample number, and the vertical axis represents the Vickers hardness.

[0067] Microhardness test results

[0068] B S Y value 66.2 69.4

[0069] Summary: The Vickers hardness of sample S (number S) is slightly higher than that of sample B, but the difference in Vickers hardness values ​​between the two manufacturers is not significant.

[0070] 3. Three-dimensional morphological comparison analysis

[0071] (1) Test methods

[0072] The Olympus 4000 laser confocal microscope was used for observation. Samples used in the friction and wear test were taken for observation and surface microscopic data collection. The data collection sites were the matrix and damaged areas of each sample.

[0073] (2) Analysis of experimental results

[0074] file name SQ[μm] Ssk Sku Sp[μm] Sv[μμm] Sz[μm] Sa[μm] Sk[μm] Spk[μm] Svk[μm] SMr1[%] SMr2 [%] Sxp[μm] <![CDATA[Vvv[μm 3 / ]]> <![CDATA[Vvc[μm 3 / ]]> <![CDATA[Vmp[μm 3 / ]]> <![CDATA[Vmc([μm 3 / ]]> Sa1[μm] Str S1-1 1.763 0.537 11.092 29.583 26.202 55.784 1.21 3.023 2.688 2.366 14.386 87.213 2.924 0.234 1.771 0.144 1.153 12.737 0.806 S2-1 2.091 0.218 13.751 45.107 33.109 78.216 1.431 3.469 3.024 2.765 15.385 86.314 3.501 0.282 2.126 0.161 1.375 14.567 0.922 S4-1 2.207 0.052 10.5 28.848 28.205 57.053 1.537 3.963 3.056 2.943 13.586 86.513 3.733 0.303 2.217 0.162 1.516 14.243 0.901 S6-1 2.108 0.832 14.887 54.494 27.626 82.121 1.448 3.498 3.177 2.838 15.584 86.913 3.524 0.282 2.161 0.171 1.364 13.964 0.86 S7-1 1.66 0.535 13.869 34.016 35.536 69.552 1.195 3.099 2.383 1.861 16.184 89.311 3.099 0.185 1.91 0.12 1.189 13.512 0.863 S8-1 1.961 0.608 10.491 31.517 31926 63.444 1.438 4.239 2.872 1.844 12.088 90.709 3.725 0.195 2202 0.148 1.523 14.241 0.934 average value 1.965 0.463667 12.43167 37.26083 30.434 67.695 1.3765 3.5485 2.866667 2.436167 14.5355 87.82883 3.417667 0.246833 2.0645 0.151 1.353333 13.87733 0.881 B1-1 1.95 0.447 8.052 31.31 22.436 53.746 1.403 3.88 2.846 2.257 12.288 87.912 3.531 0.231 2.067 0.148 1.463 16.808 0.952 B2-1 1.855 0.624 8.814 22.806 21.921 44.727 1.325 3.65 2.8 2.067 12.887 88.711 3.348 0.209 1.985 0.147 1.362 11.855 0.859 B4-1 1.836 0.325 9.168 22.409 24.095 46.504 1.308 3.558 2.633 2.178 13.087 88.212 3.294 0.219 1.952 0.137 1.342 15.039 0.923 B6-1 1.908 0.689 7.96 20.883 20.755 41.638 1.372 3.748 2.945 2.05 13.786 89.61 3.523 0.203 2.123 0.153 1.401 15.998 0.846 B7-1 1.599 0.237 6.739 22.276 13.274 35.55 1.174 3.357 2.186 1.856 11.289 87.912 2.952 0.195 1.705 0.112 1.246 19.025 0.845 B8-1 2.329 0.34 7.012 28.571 23.371 51.942 1.678 4.434 3.364 2.717 12.887 85.814 4.213 0.294 2.454 0.176 1.759 18.573 0.927 average value 2.319813 0.904313 10.30894 34.04669 27.02781 61.07438 1.65275 4.4705 3.720188 2.390438 13.0745 88.34288 4.179563 0.250938 2.485625 0.196813 1.69375 29.52975 0.525063

[0075] The experimental data in the table above show that the mean roughness (Sa) in the passivation layer domain is greater in sample B than in sample S, the mean peak height (SPk) in the surface domain is greater in sample B than in sample S, the mean valley depth (SVk) in the surface domain is slightly less in sample B than in sample S, and the mean maximum height (Sz) of the profile is less in sample B than in sample S. This indicates that sample B has more obvious fluctuations and a greater number of fluctuations.

[0076] Conclusion: The δ1 and δ2 values ​​of sample B are stable and lower than those of similar materials, and the Y value is also lower than that of similar materials, but the damage is greater than that of sample S. Further micro-load characterization and evaluation of the passivation film on the coating surface are required.

[0077] (II) Microscopic Characterization Experiments under Microload

[0078] Sample preparation: Wear gloves during sample processing to avoid contaminating the original surface. During the packaging process, strictly distinguish the rolling direction and upper and lower surfaces of the sample, and use a film to protect the original surface state of the sample to ensure that the variables in the experimental process are controllable. Take sample B and sample S under the condition of a downlight.

[0079] 1. Sliding friction experiment

[0080] (1) Test methods

[0081] Each sample number contains two test samples. One sample is cleaned (using anhydrous ethanol for ultrasonic cleaning), and the other is tested on its original surface. The sample along the rolling direction is designated L, and the sample perpendicular to the rolling direction is designated T. Note: During the experiment, each sample is tested using its "top surface" to ensure that the data from the same plate are comparable.

[0082] (2) Experimental conditions

[0083] After several attempts, the experimental conditions were determined to be: a loading force of 10N, a speed of 4mm / s, a single uniform sliding motion over 10 seconds, and a displacement of 40mm. A 6mm diameter GCr15 steel ball was used. The single sliding motion was repeated 30 times.

[0084] (3) Experimental data processing

[0085] The average value of the dynamic friction coefficient within 10 seconds of each sliding experiment is taken as a data point. The data points of 30 loading cycles are connected to form a curve, which shows the trend of friction coefficient change.

[0086] (4) Experimental data analysis. (The colors of the labels below should be consistent with the sample numbers.)

[0087] refer to Figure 6-9 :

[0088] Summary: ① Regardless of manufacturer or cleaning condition, the longitudinal friction coefficient is consistently lower than the transverse friction coefficient. ② Although the friction coefficient curves differ across locations, there is no clear correlation between the locations. ③ After cleaning (in a pure passivation layer state), compared to before cleaning, the longitudinal and transverse friction curves of sample B show the same trend, shifting forward, while the trends of the longitudinal and transverse friction curves of sample S change significantly, with the curves remaining stable before cleaning. This indicates that the rust-preventive oil in sample B does not significantly contribute to the friction system under these experimental conditions.

[0089] 2. Nanoindentation experiment

[0090] (1) Sample selection: B-4-L, S-4-L

[0091] (2) Test conditions: Berkovich diamond indenter was used, the test cycle was controlled by load, the maximum load was 10mN, and the holding time was 10s.

[0092] (3) Experimental data analysis:

[0093] The following are the results of indentation stress and indentation depth. Data were collected from three test points for each sample, and the test was conducted in a flat area.

[0094]

[0095] refer to Figure 10-11 :

[0096] Summary: The surface hardness of the passivation layer in sample S < the base hardness of the passivation layer in sample S ≈ the base hardness of the passivation layer in sample B < the base hardness of the passivation layer in sample B. The combined results of the nanohardness and nano-gradient indentation experiments with the micro-Vickers hardness indicate that the hardness change of the passivation layer in sample B from the surface to the core is "from hard to soft," while that in sample S is "from soft to hard." Since the base hardness of the passivation layer is roughly the same, sample B, which suffers more severe surface damage, is damaged because the surface hardness is greater than the substrate hardness, leading to indentation damage and thus reducing the sample's friction and wear limit.

[0097] 2. Nanoscale scratch test

[0098] (1) Sample selection: B-4-L, S-4-L

[0099] (2) Test conditions: The test used a diamond ball-cone indenter (apex angle of 120°±1.0°, tip radius R of 100μm±10%).

[0100] Experimental data analysis:

[0101] The data mainly presents the adhesion values ​​of the film layer, as shown in the LC1 values ​​in the table below.

[0102] Testing Item Lc1[mN] Lc1[mN] Sample No. S-4-L B-4-L Measurement 1 1677.025 1309.989

[0103] Conclusion: The critical adhesion value of the surface layer was obtained by combining the changes in light signal and force signal, indicating that the adhesion of sample S is stronger than that of sample B.

[0104] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for evaluating the quality of a surface coating of a galvanized sheet against frictional damage, characterized by, Respectively, "heavy load surface layer damage friction experiment" and "light load sliding friction experiment", from the simple passivation layer to set various types of lubrication conditions, to simulate the friction state under various working conditions, from the above macro experiment to select typical samples for thickness, hardness, adhesion, surface three-dimensional morphology of microcosmic level multi-dimensional multi-method analysis, identify the difference of passivation layer, and make a judgment on the influence of friction system; Specifically includes the following steps: (1) Macroscopic characterization under heavy load (1.1) Friction and wear evaluation Use end face friction and wear tester, set heavy load, test the change of surface friction coefficient before the passivation layer is damaged to expose the iron base; Comparison sample setting: distinguish different parts in the same plate width to carry out comparative experiment to obtain the relationship between friction factor and plate width direction distribution; distinguish the upper and lower surfaces, use the same surface to carry out experiment to exclude the interference caused by the difference between the upper and lower surfaces, ensure that the data have comparative value; Evaluation: obtain the dynamic friction coefficient curve under the experimental conditions, the dynamic friction coefficient curve after load application rises vertically from 0 to the inflection point where the first slope begins to change, which is regarded as the initial dynamic friction coefficient δ1 of the sample under the friction and wear characterization condition; Take the average of the maximum and minimum data of the segment data after the curve rises to the stable stage as the stable dynamic friction coefficient δ2 under the friction and wear characterization condition; (1.2) Microhardness comparison Test the microhardness of the sample after the above friction and wear experiment to identify the difference of the hardness of the passivation layer, measure the microhardness at the un-worn part of the sample, 3 points per test surface; Comparison sample setting: distinguish different parts in the same plate width to carry out comparative experiment to obtain the relationship between microhardness and plate width direction distribution; distinguish the upper and lower surfaces, use the same surface to carry out experiment to exclude the interference caused by the difference between the upper and lower surfaces, ensure that the data have comparative value; Evaluation: measure the microhardness at the un-worn part of the sample, take the average of the three points after measuring 10 points per test surface as Y; (1.3) Three-dimensional morphology comparison analysis Analyze the difference between the friction trace and the base morphology after the macro friction experiment to compare and obtain the surface morphology factors affecting friction and wear; Comparison sample setting: observe the base morphology and friction trace morphology of the sample after surface friction experiment; Evaluation: observe the wear morphology at the wear part, judge the part with heavy damage trace observed in macro, whether it is the surface wave peak pressing into the base or only filling into the wave valley without damaging the base, combine δ1 and δ2 and microhardness Y to judge the damage cause; if δ1, δ2 values are stable and lower than those of similar materials and Y value is higher than that of similar materials, it indicates that the damage is caused by the too high hardness of the surface coating, if δ1, δ2 values are stable and lower than those of similar materials and Y value also lower than that of similar materials, then proceed to the next micro load characterization to evaluate the passivation film layer on the surface of the coating; (2) Microscopic characterization under micro load (2.1) Sliding friction evaluation Use multifunctional friction and wear tester, set light load, repeat loading 30 times to obtain the change of dynamic friction coefficient during this period, characterize the passivation layer surface friction system state under micro load condition; Contrast sample setting: distinguish different parts within the same board width to carry out contrast experiment to obtain the relationship between friction factor and board width direction distribution; distinguish upper and lower surfaces, use the same surface to carry out experiment to exclude the interference caused by the difference between upper and lower surfaces, and ensure that the data have comparative value; distinguish horizontal and vertical directions to obtain the difference between processing direction and friction coefficient; distinguish the contrast experiment of cleaning and not cleaning the oil on the surface of the sample, and the performance of the passivation layer itself is exhibited, and under the condition of ensuring that the original oil film is not damaged by sample stacking and processing, the sample without cleaning can express the dynamic friction state under the condition of finished product delivery for use; Evaluation: the average value of the dynamic friction coefficient contained in the experimental data of each sliding is taken as a data point, and the data points of 30 times of loading are connected into a curve, and the change trend of the friction coefficient can be seen; The starting point of the curve and the longitudinal axis is the initial dynamic friction coefficient under this condition, and the high and low of the initial dynamic friction coefficient can represent the resistance state of the surface passivation film layer to the single stamping friction process; whether the dynamic friction coefficient curve of the last 29 times has obvious fluctuation can represent the stability state of the film layer lubrication, and the evaluation of the comprehensive action of the oil and the surface film layer is combined with whether the experimental sample contains oil film, how much oil film, and what composition of the oil film; (2.2) Nanoindentation evaluation In the micro-surface hardness test using a nanoindentation tester, the relationship between the surface hardness of the passivation layer and the increase of the dynamic friction coefficient with the increase of the number of reciprocating times, and the degree of surface friction damage is analyzed according to the above dynamic friction experiment results; Contrast sample setting: select samples at the same position, and carry out experiments under the condition that other sample conditions are consistent; Evaluation: the measured nano-hardness value can represent the surface hardness of the passivation film layer; whether the force trajectory displayed by the measured hardness force curve gradually increases or gradually decreases can represent the hardness difference between the surface layer and the passivation film substrate of the passivation film layer, which hardness is higher and which hardness is lower. If the surface layer hardness is higher than the substrate, it indicates that the damage is mainly caused by the shallow surface layer indentation, and the best friction state is that the surface layer stress should be less than the critical force of the surface layer damage. If the surface layer hardness is lower than the hardness of the passivation film substrate, the best friction at this time only requires not to damage the whole passivation film layer; (2.3) Nano-scratch evaluation The nano-scratch tester is used for nano-scale scratch testing, and the adhesion difference of the passivation layer is analyzed through mechanical, acoustic and topographic multiple signals. Contrast sample setting: select samples at the same position, and carry out experiments under the condition that other sample conditions are consistent; Evaluation: the adhesion value of the passivation layer is determined according to the scratch damage morphology of the film layer combined with mechanical and acoustic signals; the influence of the surface hardness of the film layer on the final friction damage is judged according to the adhesion, and if the film layer adhesion is strong, the surface layer hardness is greater than or less than the substrate, and the best friction critical force is higher, and vice versa.

2. The method of evaluating the quality of the surface coating of a galvannealed sheet against frictional damage according to claim 1, characterized in that, In the step (1.1), a heavy load force is set on the end face friction and wear tester, and the appropriate friction load force, speed and time for the current sample type are obtained through experiments.

3. The method of evaluating the quality of the surface coating of a galvannealed sheet against frictional damage according to claim 1, characterized in that, In the step (2.1), a multifunctional friction and wear tester from the United States Rtec is used.

4. The method of evaluating the quality of the surface coating of a galvanization passivated sheet against frictional damage according to claim 1, characterized in that, In the step (2.1), the multi-functional friction and wear testing machine is used to set a slight load force, and the friction load force, rotation speed and time length suitable for the current sample type are obtained through experiments.

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