A method for quantitatively evaluating the coverage of zinc phosphate coating on cold-rolled automobile steel

Abstract

The invention discloses a method for quantitatively evaluating the coverage of zinc phosphate film of cold-rolled automobile steel, which comprises the following steps: (1) using the phase quantitative function of an X-ray diffractometer to determine the phase composition of the phosphate film on the surface of the cold-rolled automobile steel sample; and (2) according to the detection result of step (1), calculating the coverage of the phosphate film, the phosphate film coverage=(percentage of three-generation zinc phosphate Zn3(PO4)2·4H2O+ferrous zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of three-generation zinc phosphate Zn3(PO4)2·4H2O+ferrous zinc phosphate Fe2Zn(PO4)2·4H2O+Fe). The invention can directly calculate the coverage of the phosphate film in the target phosphated area without measuring with a ruler or comparing with a graph, and the calculation method is simple and fast.

Description

Technical Field

[0001] The invention belongs to the technical field of measuring and evaluating the compactness and coverage of phosphate films, and in particular relates to a method for quantitatively evaluating the coverage of zinc-based phosphate films of cold-rolled automobile steel. Background Art

[0002] At present, cold-rolled automobile sheets enter the paint shop after stamping and welding, and undergo processes such as phosphating and electrophoresis. The quality of phosphating of automobile sheets directly affects the performance and corrosion resistance of subsequent processes such as electrophoresis. The so-called phosphating is a process in which metal parts are chemically treated in a solution containing phosphate to form a phosphate protective film (phosphating film) that is difficult to dissolve in water on the metal surface. Phosphating treatment is an important method to prevent metal corrosion.

[0003] Painting is like building a wall. The quality of the previous layer will have a significant impact on the next layer. The surface of the cold-rolled plate affects the quality of the phosphate film, and the quality of the phosphate film affects the electrophoretic plate. The corrosion resistance of the steel surface after phosphating is about 12 times higher than that of direct painting without phosphating. The phosphate film can increase the bonding strength between the electrophoretic paint and the plate. The steel plant produces cold-rolled automobile and home appliance plates, galvanized plates, and hot stamping steel quenched bare plates. Phosphate film quality evaluation is required during customer use and third-party coating process adaptability evaluation.

[0004] The industry standard for evaluating the quality of phosphate film after phosphating of automobile plates includes appearance inspection, and the implementation standards are GB / T11376 "Phosphate conversion film of metal" and GB / T "Technical conditions for phosphating treatment of steel workpieces before painting", which require the phosphating appearance to be uniform in color, free of metal bright spots, white ash and rust, etc. The weight of the phosphating film is determined according to GB / T 9792 "Weight method for determining the mass per unit area of ​​conversion film on metal materials". The size of phosphating crystals is detected by scanning electron microscopy, the physical phase of phosphating film is measured by X-ray diffractometer, and the thickness of phosphating film is measured by magnetic thickness gauge. Whether the phosphating film is uniform and dense, technicians will also pay attention to the crystal morphology of phosphating and some other data, but they cannot directly determine quantitatively.

[0005] The density of the phosphate film directly affects the adhesion and corrosion resistance of the electrophoretic paint. Generally, the denser the better. Traditionally, the evaluation of the density of the phosphate film is generally done by technicians based on the apparent morphology and SEM electron microscope photos. The density of the phosphate film is judged based on experience. If the density of the phosphate crystal is further refined, some chemical methods can be used for quantitative evaluation, such as P ratio detection. If the P ratio detection value is high, it is generally believed that the generated phosphate crystal is small, uniform and dense. Patent document CN112595736A discloses a method for quantitatively evaluating the density of the phosphate film, which uses AdobePhotoshop CS6 special software to quantitatively evaluate the density of the phosphate film. The operation method is complicated and difficult for non-professionals to complete. None of the above detection methods can quickly and quantitatively evaluate the density and coverage of the phosphate crystal. Summary of the invention

[0006] In view of one or more problems existing in the prior art, the present invention provides a method for quantitatively evaluating the coverage of zinc phosphating film of cold-rolled automobile steel, which comprises the following steps:

[0007] (1) The phase quantitative function of the X-ray diffractometer was used to determine the phase composition of the phosphating film on the surface of the cold-rolled automotive steel sample. The working conditions were Cu target, voltage 40 kV, current 40 mA, continuous scanning, each step dwelling 20.4 s, and step length 0.026° / step;

[0008] (2) According to the test results of step (1), the coverage of the phosphate film is calculated, and the coverage of the phosphate film = (percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O + Fe).

[0009] The cold-rolled automobile steel sample in the above step (1) is a sample that has been subjected to zinc phosphating treatment, has a length of 20 mm and a width of 15 mm, and the surface of the sample is cleaned with alcohol.

[0010] The method for quantitatively evaluating the coverage of zinc phosphate film of cold-rolled automobile steel provided by the above technical solution utilizes the phase quantitative analysis function of an X-ray diffractometer to detect the proportions of three-generation zinc phosphate Zn3(PO4)2·4H2O, iron zinc phosphate Fe2Zn(PO4)2·4H2O, and α-Fe in the zinc phosphate film of cold-rolled sheet or several of the three phases, wherein the sum of the proportions of three-generation zinc phosphate Zn3(PO4)2·4H2O and iron zinc phosphate Fe2Zn(PO4)2·4H2O is the coverage of the phosphate film. The present invention can directly calculate the coverage of the phosphate film in the target phosphated area without the need for measuring with a ruler or comparing with a map. The calculation method is simple and quick, and is very helpful for improving the performance detection of the electrophoresis plate and the corrosion resistance detection after phosphating. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is the X-ray diffraction phase quantitative analysis diagram in Example 1;

[0012] Figure 2 is the X-ray diffraction phase quantitative analysis diagram in Example 2;

[0013] Figure 3 This is the X-ray diffraction phase quantitative analysis diagram in Example 3;

[0014] Figure 4 is the X-ray diffraction phase quantitative analysis diagram in Example 4;

[0015] Figure 5 This is the X-ray diffraction phase quantitative analysis diagram in Example 5. DETAILED DESCRIPTION

[0016] The purpose of the present invention is to provide a method for quantitatively evaluating the coverage rate of zinc phosphate film of cold-rolled automobile steel. The basic principle of the method is that the zinc phosphate film of cold-rolled sheet is composed of three phases or several phases of tertiary zinc phosphate Zn3(PO4)2·4H2O, iron zinc phosphate Fe2Zn(PO4)2·4H2O and α-Fe, wherein the sum of the proportions of the two phases of tertiary zinc phosphate Zn3(PO4)2·4H2O and iron zinc phosphate Fe2Zn(PO4)2·4H2O is the coverage rate of the phosphate film. Therefore, the present invention can utilize the phase quantitative analysis function of the X-ray diffractometer to detect the three phases or several phases of the tertiary zinc phosphate Zn3(PO4)2·4H2O, iron zinc phosphate Fe2Zn(PO4)2·4H2O, and α-Fe in the zinc-based phosphating film, thereby directly calculating the coverage ratio of the phosphating film in the target phosphating area. Therefore, there is no need to measure with a ruler or compare with the map. The calculation method is simple and fast, which is very helpful for improving the performance detection of the electrophoresis plate and the corrosion resistance detection after phosphating.

[0017] The present invention is described in detail below through specific examples. The examples are intended to help understand the present invention but are not intended to limit the present invention.

[0018] Example 1

[0019] 1. Cut the cold-rolled automobile sheet that has been treated with zinc phosphating into samples with a length of 20 mm and a width of 15 mm, and clean the surface of the sample with alcohol.

[0020] 2. The phase quantitative function of the X-ray diffractometer was used to determine the phase composition of the phosphating film on the surface of the cold-rolled automotive steel sample. The working conditions were Cu target, voltage 40 kV, current 40 mA, continuous scanning, dwell time of 20.4 s per step, and step length of 0.026° / step.

[0021] 3. Phase detection results such as Figure 1 As shown, the phosphate film coverage is calculated, phosphate film coverage = (percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O + Fe), the results are shown in the following Table 1.

[0022] Example 2

[0023] 1. Cut the cold-rolled automobile sheet that has been treated with zinc phosphating into samples with a length of 20 mm and a width of 15 mm, and clean the surface of the sample with alcohol.

[0024] 2. The phase quantitative function of the X-ray diffractometer was used to determine the phase composition of the phosphating film on the surface of the cold-rolled automotive steel sample. The working conditions were Cu target, voltage 40 kV, current 40 mA, continuous scanning, dwell time of 20.4 s per step, and step length of 0.026° / step.

[0025] 3. Phase detection results such as Figure 2 As shown, the phosphate film coverage is calculated, and the phosphate film coverage = (percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O + Fe) , and the results are shown in the following Table 1.

[0026] Embodiment 3:

[0027] 1. Cut the cold-rolled automobile sheet that has been treated with zinc phosphating into samples with a length of 20 mm and a width of 15 mm, and clean the surface of the sample with alcohol.

[0028] 2. The phase quantitative function of the X-ray diffractometer was used to determine the phase composition of the phosphating film on the surface of the cold-rolled automotive steel sample. The working conditions were Cu target, voltage 40 kV, current 40 mA, continuous scanning, dwell time of 20.4 s per step, and step length of 0.026° / step.

[0029] 3. Phase detection results such as Figure 3 As shown, the phosphate film coverage is calculated, and the phosphate film coverage = (percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O + Fe) , and the results are shown in the following Table 1.

[0030] Embodiment 4:

[0031] 1. Cut the cold-rolled automobile sheet that has been treated with zinc phosphating into samples with a length of 20 mm and a width of 15 mm, and clean the surface of the sample with alcohol.

[0032] 2. The phase quantitative function of the X-ray diffractometer was used to determine the phase composition of the phosphating film on the surface of the cold-rolled automotive steel sample. The working conditions were Cu target, voltage 40 kV, current 40 mA, continuous scanning, dwell time of 20.4 s per step, and step length of 0.026° / step.

[0033] 3. Phase detection results such as Figure 4 As shown, the phosphate film coverage is calculated, and the phosphate film coverage = (percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O + Fe) , and the results are shown in the following Table 1.

[0034] Embodiment 5:

[0035] 1. Cut the cold-rolled automobile sheet that has been treated with zinc phosphating into samples with a length of 20 mm and a width of 15 mm, and clean the surface of the sample with alcohol.

[0036] 2. The phase quantitative function of the X-ray diffractometer was used to determine the phase composition of the phosphating film on the surface of the cold-rolled automotive steel sample. The working conditions were Cu target, voltage 40 kV, current 40 mA, continuous scanning, dwell time of 20.4 s per step, and step length of 0.026° / step.

[0037] 3. Phase detection results such as Figure 5As shown, the phosphate film coverage is calculated, and the phosphate film coverage = (percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O + Fe) , and the results are shown in the following Table 1.

[0038] Table 1: Percentage of each phase of phosphate film on the surface of samples of Examples 1-5

[0039]

[0040] It can be seen from the results of the above embodiments 1-5 that the method provided by the present invention for quantitatively evaluating the coverage rate of the zinc phosphate film of cold-rolled automotive steel can directly utilize the phase quantitative analysis function of the X-ray diffractometer to detect the three phases or several phases of the three-generation zinc phosphate Zn3(PO4)2·4H2O, iron zinc phosphate Fe2Zn(PO4)2·4H2O, and α-Fe in the zinc phosphate film, thereby directly calculating the coverage ratio of the phosphate film in the target phosphating area. Therefore, there is no need to measure with a ruler or compare with the map. The calculation method is simple and quick, which is very helpful for improving the performance detection of the electrophoresis plate and the corrosion resistance detection after phosphating.

[0041] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for quantitatively evaluating the coverage of zinc phosphating film on cold-rolled automotive steel, comprising the following steps: (1) The phase quantitative function of the X-ray diffractometer was used to determine the phase composition of the phosphating film on the surface of the cold-rolled automotive steel sample. The working conditions were Cu target, voltage 40 kV, current 40 mA, continuous scanning, each step dwelling 20.4 s, and step length 0.026° / step; (2) According to the test results of step (1), the coverage of the phosphate film is calculated, and the coverage of the phosphate film = (percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O) / percentage of trigeneration zinc phosphate Zn3(PO4)2·4H2O + iron zinc phosphate Fe2Zn(PO4)2·4H2O + Fe).

2. The method according to claim 1, wherein: The cold-rolled automobile steel sample in step (1) is a sample that has been subjected to zinc phosphating treatment, has a length of 20 mm and a width of 15 mm, and the surface of the sample is cleaned with alcohol.

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