A method for improving the coating quality of a galvanized sheet

Abstract

This invention discloses a method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion, comprising: 1) selecting a measurement point every 5cm along the width of the sheet as a group, and measuring a group at the head, middle, and tail of the coil along the length of the sheet; ensuring that the measured height parameters Ssk, Sku, Sa, Sk, Spk, Smr1, Smr2, and spatial parameters all meet the requirements; 2) the zinc ingots used for galvanizing have a Zn content of 99.2%-99.4%; 3) the zinc bath temperature is 450℃±10℃; 4) after galvanizing, the upper surface of the coating consists of a fragmented δ phase connected to a fully covered γ phase at the bottom layer; 5) the coating weight and coating test values ​​should meet the requirements. This invention, based on the existing general hot-dip galvanizing process flow, focuses on the design of key process parameters, which can enhance the zinc layer adhesion in a low-cost and easy-to-operate manner.

Description

Technical Field

[0001] This invention relates to the field of low-carbon and ultra-low-carbon galvanized steel sheet technology, and particularly to a method for controlling the coating quality of galvanized steel sheets to improve the adhesion of the zinc layer. 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] In terms of the performance of galvanized steel sheets, the strength of the galvanized layer's adhesion affects many aspects of the steel sheet's performance, including stamping, forming, coating, and corrosion resistance.

[0004] The patent CN105296907A, entitled "A Method for Improving the Quality of Zinc Layer on Galvanized Automotive Steel Sheets," mainly improves the quality of the zinc layer through methods such as zinc pot temperature control and air knife process, as well as by controlling the Ra and Rpc of the hot-dip galvanized steel strip surface within a certain range to improve the structural uniformity of the surface zinc layer. However, it does not control the original surface parameters of the steel strip before galvanizing, which has certain limitations. This invention focuses on setting control points for the original surface parameters, which are an important factor affecting the adhesion of the zinc layer. Under the dual effect of the original surface morphology and the key zinc pot process, the adhesion is effectively improved.

[0005] The patent CN110965087B, entitled "A Cyanide-Free Zinc Immersion Solution and Its Preparation Method and Application", designs a coating structure with strong adhesion. Its composition and process path are complex, which is different from the process parameter design of this invention based on the existing hot-dip galvanizing process. Moreover, patent 2 is applicable to laser protection, which is different from the scope of application of this patent. Summary of the Invention

[0006] The purpose of this invention is to provide a method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion. Based on the existing general hot-dip galvanizing process, this method involves limiting key process parameters, enabling low-cost and easy-to-operate enhancement of zinc layer adhesion. This results in improved performance of galvanized steel sheets in various applications.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion, comprising:

[0009] 1) Select a measurement point every 5cm along the width of the sheet as a group, and measure one group each at the beginning, middle, and end of the roll along the length of the sheet. Ensure that the measured height parameter Ssk value is controlled within the range of 0-2.0, height parameter Sku value is 3-15, height parameter Sa value is 1.0-2.0μm, functional parameter Sk value is 3.0-7.0μm, functional parameter Spk value is 2.5-6.5μm, functional parameter Smr1 value is 10%-15%, functional parameter Smr2 value is 85%-95%, and spatial parameter Str value is <1;

[0010] Sa: Arithmetic mean height, Ssk: Skewness, Sku: Kurtosis (sharpening), Sk: Horizontal difference of the center, SMr1: Loading area ratio separating the protruding peaks from the center, SMr2: Loading area ratio separating the protruding valleys from the center, Spk: Average height of the protruding peaks, Svk: Average depth of the protruding valleys, Str: Aspect ratio of surface features.

[0011] 2) Zinc ingots selected for galvanizing have a Zn content between 99.2% and 99.4%;

[0012] 3) The temperature of the zinc bath is 450℃±10℃;

[0013] 4) After galvanizing, the upper surface of the coating is composed of fragmented δ phase connected to the fully covered γ phase of the underlying layer, and the ratio of the average thickness of the δ phase to the average thickness of the γ phase is 0.6-0.7.

[0014] 5) The coating weight and coating test values ​​should conform to the following table:

[0015]

[0016]

[0017] Furthermore, in 1), the standard deviation of the data for each parameter Ssk, Sa, Spk, and Svk is less than 0.06, the standard deviation of the data for parameters Smr1 and Smr2 is less than 1.2, and the standard deviation of the data for parameter Sku is less than 3.0.

[0018] Furthermore, in step 2), the zinc ingots used for galvanizing are selected with a Zn content between 99.2% and 99.4%, an Al content between 0.500% and 0.800%, an Fe content ≤ 0.002%, and Cu, Pb, Cd, and Sn contents all ≤ 0.0005%, and no other elements.

[0019] Furthermore, in the fourth case, the ratio of the average thickness of the δ phase to the average thickness of the γ phase is 2 / 3.

[0020] Furthermore, the target zinc coating thickness is 75-85 g / m. 2 .

[0021] Furthermore, the target zinc layer thickness is 80 g / m. 2 .

[0022] Furthermore, the zinc bath temperature is 450℃.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0024] The method for controlling the coating quality of galvanized steel sheets with improved zinc layer adhesion of the present invention can produce galvanized steel sheet products with high zinc layer adhesion, which can meet the application conditions that have high requirements for adhesion of new production capacity. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] Figure 1 To test the bonding strength level using nano-scratch testing before using this invention;

[0027] Figure 2 To test the bonding strength level of nano-scratch after using the present invention. Detailed Implementation

[0028] Example

[0029] A method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion includes:

[0030] 0.8mm DCJD1+Z galvanized steel sheet, with a target zinc coating thickness of 80g / m2. The steelmaking process to the annealing process follows the company's own standards.

[0031] 1. Cold-rolled steel sheets before galvanizing are inspected for surface characteristics after passing through the final rolling mill. Measurements are taken at 5cm intervals along the width of the sheet, forming one group. Measurements are also taken at the beginning, middle, and end of the coil along the length of the sheet, forming another group. The measured values ​​are as follows:

[0032]

[0033] 2. The composition of the zinc ingots used for galvanizing is as follows:

[0034]

[0035] 3. The zinc pot galvanizing temperature is 452℃.

[0036] 4. After galvanizing, the upper surface of the coating consists of discontinuous δ phases connected to the fully covered γ phase of the underlying layer, and the ratio of the average thickness of the δ phase to the average thickness of the γ phase is approximately 2 / 3.

[0037] 5. Coating weight and coating test values: Target 80g / m2, actual measured minimum average value of three-point detection on both sides is 80, minimum value of single point on both sides is 76, and minimum value of single point on one side is 38.

[0038] 6. The obtained zinc coating adhesion meets specific requirements in the bending test (the standard is higher than the national standard). Samples were selected from the edge, center, and 1 / 4 section along the width of the steel strip. Under the experimental conditions shown in the table below, there was no obvious phenomenon of zinc coating lifting or peeling.

[0039]

[0040] Using a nano-scratch analyzer for scratch testing, the measured critical value for coating damage was significantly increased, as follows: Figure 1 and Figure 2 As shown.

[0041] 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 controlling the quality of galvanized sheet coating to improve zinc layer adhesion, characterized in that: include: 1) Select a measurement point every 5cm along the width of the sheet as a group, and measure a group at the head, middle and tail of the roll along the length of the sheet; ensure that the height parameter Ssk value is controlled within the range of 0-2.0, the height parameter Sku value is 3-15, the height parameter Sa value is 1.0-2.0μm, the functional parameter Sk value is 3.0-7.0μm, the functional parameter Spk value is 2.5-6.5μm, the functional parameter Smr1 value is 10%-15%, the functional parameter Smr2 value is 85%-95%, and the spatial parameter Str value is <1; 2) The zinc ingots selected for galvanizing have a Zn content between 99.2% and 99.4% by mass. 3) The temperature of the zinc bath is 450℃±10℃; 4) After galvanizing, the upper surface of the coating is composed of fragmented δ phase connected to the fully covered γ phase of the underlying layer, and the ratio of the average thickness of the δ phase to the average thickness of the γ phase is 0.6-0.

7. 5) The coating weight and coating test values ​​should conform to the following table: 。 2. The method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion according to claim 1, characterized in that: In 1), the standard deviation of each parameter Ssk, Sa, Spk, and Svk is less than 0.06, the standard deviation of parameters Smr1 and Smr2 is less than 1.2, and the standard deviation of parameter Sku is less than 3.

0.

3. The method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion according to claim 1, characterized in that: In step 4), the ratio of the average thickness of the δ phase to the average thickness of the γ phase is 2 / 3.

4. The method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion according to claim 1, characterized in that: The target zinc coating thickness is 75-85 g / m. 2 .

5. The method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion according to claim 1, characterized in that: The target zinc coating thickness is 80 g / m 2 .

6. The method for controlling the coating quality of galvanized steel sheets to improve zinc layer adhesion according to claim 1, characterized in that: The temperature of the zinc bath is 450℃.

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