Thick-coating cold-rolled hot-dip aluminum-zinc steel plate with yield strength of 160MPa

Abstract

The invention discloses a thick-coating cold-rolled hot-dip aluminum-zinc steel plate with yield strength of 160MPa. The thick-coating cold-rolled hot-dip aluminum-zinc steel plate mainly solves the technical problem of poor binding force between a coating and a steel substrate of an existing cold-rolled hot-dip aluminum-zinc steel plate with yield strength of 160MPa, thickness of 1.2-1.6 mm and single-side coating weight of 70-90g / m < 2 >. The invention discloses a thick-coating cold-rolled hot-dip aluminum-zinc steel plate with yield strength of 160MPa. A substrate of the thick-coating cold-rolled hot-dip aluminum-zinc steel plate comprises the following chemical components in percentage by weight: 0.0010%-0.0040% of C, 0.001%-0.034% of Si, 0.05%-0.15% of Mn, less than or equal to 0.020% of P, less than or equal to 0.015% of S, 0.015%-0.050% of Alt, 0.020%-0.050% of Ti and the balance of Fe and inevitable impurity elements. And the weight of a single-sided coating of the cold-rolled hot-dipped aluminum-zinc steel plate is 70-90g / m

Description

Technical Field

[0001] The present invention relates to a cold-rolled hot-dip aluminum-zinc steel sheet, in particular to a cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 160 MPa and a thick coating and a manufacturing method thereof, specifically to a cold-rolled hot-dip aluminum-zinc steel sheet with a thickness of 1.2 to 1.6 mm and a single-sided coating weight of 70 to 90 g / m 2 The invention relates to a hot-dip aluminum-zinc steel sheet and a manufacturing method thereof, belonging to the technical field of iron-based alloys. Background Art

[0002] Steel used in household appliances generally uses cold-rolled hot-dip galvanized steel plates or cold-rolled hot-dip aluminum-zinc steel plates. Actual use results show that the corrosion resistance of cold-rolled hot-dip aluminum-zinc steel plates is 2 to 6 times that of cold-rolled hot-dip galvanized steel plates under the same conditions. Steel used in household appliances outdoors gradually adopts cold-rolled hot-dip aluminum-zinc products to replace cold-rolled hot-dip galvanized products to meet high corrosion resistance requirements.

[0003] Usually, the steel used in household appliances has complex forming requirements, and the cold-rolled galvanized coating will crack during the forming process, and in severe cases, it will fall off. Especially for outdoor uses such as the chassis and bottom corners of air conditioner outdoor units, the thickness of the load-bearing plate is usually 1.2-1.6mm, and the single-sided coating thickness is generally 60g / m 2 Above, some require single-sided coating weight of 70-90g / m 2 During the production of this type of thick-coated cold-rolled hot-dip galvanized steel sheet, the adhesion of the coating is more difficult to control. The finished product is prone to poor bonding between the coating and the substrate, and cracking or falling off of the coating after forming. The coating bonding strength of this thick-coated cold-rolled galvanized steel sheet is tested by V-bend test, and the product is eventually downgraded due to failure to meet the requirements, resulting in quality loss.

[0004] The Chinese patent document with application publication number CN101376956A discloses a method for controlling the phase structure of the alloyed hot-dip galvanized steel sheet coating and a method for producing the alloyed hot-dip galvanized steel sheet. The production method adopts a steel plate stabilizing device arranged between the air knife and the top roller and controls the hot-dip plating process parameters and the air knife parameters to obtain a steel plate with uniform coating thickness; selects an inclined alloy coating heat treatment annealing curve with high temperature first and low temperature later in the soaking section, and uniformly alloys the steel plate to improve the uniformity of the alloying process and alloying degree of the strip coating; the technical solution disclosed cannot solve the problem of poor bonding between the thick-coated cold-rolled hot-dip aluminum-zinc steel sheet and the steel substrate.

[0005] The Chinese patent document with application publication number CN103849828A discloses a production method for hot-dip aluminum-zinc-silicon substrate, which comprises sequentially annealing the substrate base material by using an annealing furnace and hot-dip coating the substrate base material with aluminum-zinc-silicon alloy in a zinc pot, wherein the temperature of the substrate base material in the outlet section is 590-595°C, and the temperature of the alloy liquid in the zinc pot is 595-605°C. It mainly provides a process method for producing thin specifications, and the technical solution disclosed in it cannot solve the problem of poor bonding between thick-coated cold-rolled hot-dip aluminum-zinc steel sheets and steel substrates.

[0006] The Chinese patent document with application publication number CN103966537A discloses a method for controlling zinc flow lines of thick material and thick coating hot-dip galvanized products. It discloses that the temperature of the spraying medium is adjusted to improve the cooling capacity of the spraying medium on the steel plate in view of the cause of the zinc flow line defect, and the process parameters of the air knife are optimized at the same time to achieve the purpose of controlling the zinc flow line. The specific parameter selections are as follows: 1) before production, the temperature in the fan room is controlled within the range of 0 to 10°C; 2) the air knife parameters are optimized: the distance between the air knife lip and the liquid surface is 600 to 1000mm; the distance between the air knife lip and the steel plate is 15-30mm; according to the unit speed and the coating thickness, the air knife pressure is 100 to 300mbar; the patent application discloses a method for controlling thick material (≥2.0mm) and thick coating (≥220g / m 2 ) A method for removing the surface zinc flow defects of hot-dip galvanized products, the disclosed technical solution cannot solve the problem of poor bonding between thick-coated cold-rolled hot-dip aluminum-zinc steel sheets and steel substrates.

[0007] The existing technology cannot solve the problem of yield strength of 160MPa, thickness of 1.2-1.6mm, single-sided coating weight of 70-90g / m 2 The technical problem of poor bonding between the coating of cold-rolled hot-dip aluminum-zinc steel sheet and the steel substrate. Summary of the invention

[0008] The purpose of the present invention is to provide a cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 160 MPa and a thick coating and a manufacturing method thereof, which mainly solves the problem of the existing yield strength of 160 MPa, a thickness of 1.2 to 1.6 mm, and a single-sided coating weight of 70 to 90 g / m 2 The technical problem of poor bonding between the coating of cold-rolled hot-dip aluminum-zinc steel sheet and the steel substrate.

[0009] The technical idea of ​​the present invention is that the steel substrate is designed with the composition of ultra-low carbon steel, and the surface morphology and surface state of the substrate, the uniformity of the coating thickness, and the degree and thickness of the fusion between the alloy layer and the substrate are controlled through a combination of cold rolling, annealing, hot dip plating and post-plating cooling process parameters, so as to achieve the purpose of improving the bonding strength between the coating of the cold-rolled hot-dip aluminum-zinc steel plate and the steel substrate.

[0010] The technical solution adopted by the present invention is a thick-coated cold-rolled hot-dip aluminum-zinc steel plate with a yield strength of 160MPa, wherein the chemical composition weight percentage of the substrate is: C: 0.0010% to 0.0040%, Si: 0.001% to 0.034%, Mn: 0.05% to 0.15%, P≤0.020%, S≤0.015%, Alt: 0.015% to 0.050%, Ti: 0.020% to 0.050%, and the balance is Fe and unavoidable impurity elements.

[0011] Yield strength R of 1.2~1.6mm thick cold-rolled hot-dip galvanized steel sheet P0.2 140~180MPa, tensile strength R m 235~320MPa, elongation after fracture A 80 mm The coating weight on one side is 70-90g / m 2 The cold-rolled hot-dip aluminum-zinc steel sheet passed the V-bending test and the coating did not fall off.

[0012] The cold-rolled hot-dip aluminum-zinc steel sheet of the present invention meets the requirements of outdoor use environments such as chassis and bottom corners of air conditioner outdoor units, which have complex molding and high corrosion resistance requirements.

[0013] A method for manufacturing a thick-coated cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 160 MPa, the method comprising:

[0014] The hot-rolled steel sheet with a thickness of 3.5 to 5.0 mm is pickled, cold-rolled, alkali-washed, electrolytically cleaned, annealed in a horizontal continuous annealing furnace, hot-dip galvanized, cooled after plating, and flattened to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.2 to 1.6 mm, wherein:

[0015] The chemical composition weight percentage of the hot-rolled steel plate is: C: 0.0010% to 0.0040%, Si: 0.001% to 0.034%, Mn: 0.05% to 0.15%, P≤0.020%, S≤0.015%, Alt: 0.015% to 0.050%, Ti: 0.020% to 0.050%, the balance is Fe and unavoidable impurity elements, the yield strength is 150 to 190 MPa, the tensile strength is 240 to 330 MPa, and the elongation after fracture is A 80 mm 43% to 49%

[0016] The cold rolling step is five-stand continuous rolling, the total cold rolling reduction rate is 54% to 76%; the surface roughness of the hardened strip after cold rolling is 0.8 to 1.5 μm;

[0017] The annealing step includes annealing the hardened steel strip after cold rolling in a horizontal continuous annealing furnace soaking section at a temperature of 790-830°C for 35-50s; the H2 volume content in the soaking section of the horizontal continuous annealing furnace is 20%-25%; cooling the annealed steel strip to 680°C, the cooling rate of the steel strip from the soaking section of the horizontal continuous annealing furnace to 680°C is 3-7°C / s, the cooling section in the horizontal continuous annealing furnace is air-cooled, and the air volume and pressure of the cooling fans on the upper and lower surfaces are consistent;

[0018] The composition of the hot-dip aluminum-zinc coating in the zinc pot is Al: 52-58%, Si: 1.3-1.8%, and the balance is Zn and inevitable impurity elements; the bath temperature is 600°C-605°C, and the temperature of the hot-dip aluminum-zinc steel plate substrate when entering the zinc pot is 605°C-610°C; the weight of the single-side coating of the hot-dip aluminum-zinc steel plate is controlled to be 70-90g / m 2 , the height of the air knife is 0.3-0.7m from the zinc pot liquid surface;

[0019] The post-plating cooling is a two-stage cooling, both of which use air cooling. The first stage cooling is to cool the hot-dip aluminum-zinc steel plate after passing through the air knife. The distance from the first stage cooler to the air knife is 0.5-0.9m, the first stage cooling rate is 40-60℃ / S, and the first stage cooling end temperature is 550-560℃; the second stage cooling is to air cool the hot-dip aluminum-zinc steel plate from 550-560℃ to 280-300℃.

[0020] The applicant has found through long-term research that the bonding strength of cold-rolled hot-dip aluminum-zinc steel plate coating is mainly affected by two aspects:

[0021] On the one hand, the coating thickness is brittle. The thicker the coating thickness, the easier it is for the cold-rolled galvanized steel sheet to fall off when deformed. During production, the nominal coating thickness is used as the lower limit and controlled according to the positive tolerance. In production practice, the steel plate often has plate shape problems (common warping along the width of the plate, that is, C warping). After the air knife is sprayed, the coating on one side of the steel plate is thicker in the middle and thinner at the edge, while the coating thickness distribution on the other side of the steel plate is the opposite. In order to ensure the nominal value of the coating, the thickness of the coating control must be increased to ensure that the thinnest part meets the nominal value, making the coating locally over-thick, which increases the risk of coating detachment. Therefore, controlling the plate shape of the steel plate before entering the zinc pot is a key technical point.

[0022] On the other hand, there is the tightness of the bonding between the coating and the steel plate, including the wetting degree between the steel plate surface and the plating solution. The better the wetting degree, the better the bonding between the coating and the steel plate. The state of the steel plate surface. The surface in a reduced state is conducive to the improvement of the bonding strength of the coating. When the plating solution and the steel substrate are in contact at high temperature, they will quickly diffuse and fuse with each other to form a zinc-aluminum-iron alloy layer. This alloy layer is between the coating and the steel substrate. The more intense the diffusion of the plating solution and the steel substrate, the better the bonding strength of the coating and the steel substrate. At the same time, the alloy layer is a brittle phase and cannot be too thick, so its thickness needs to be controlled.

[0023] The reasons for selecting the key process parameters of the method of the present invention are as follows:

[0024] 1. Setting of cold rolling process

[0025] In addition to ensuring the dimensions of the cold-rolled hardened steel plate, cold rolling must also ensure that its surface has a certain degree of roughness. Studies have shown that the bonding force between the steel substrate and the coating increases with the increase in the surface roughness of the substrate, because the increase in roughness can improve the wettability of the plating solution and the steel substrate, making them more closely bonded. However, the roughness cannot be too high, otherwise, the production of the cold rolling unit will be difficult, and the zinc flowers on the surface of the cold-rolled hot-dip aluminum-zinc steel plate will be too large and unsightly. Comprehensively considered, the total cold rolling reduction rate is 54% to 76%; the surface roughness of the cold-rolled hardened strip is set to 0.8 to 1.5μm.

[0026] 2. Setting of atmosphere in horizontal continuous annealing furnace, annealing temperature of strip steel in soaking section and annealing time

[0027] The cold-rolled hardened steel plate is annealed in a horizontal continuous annealing furnace to keep the steel plate at high temperature for a certain period of time. The purpose is to eliminate its cold rolling deformation stress, obtain a uniform structure in a fully annealed state, and meet the requirements of mechanical properties. Through research, it is found that a higher annealing temperature combined with a higher H2 furnace atmosphere can fully reduce the surface oxide layer of the steel plate, so that the surface of the steel plate is in a reduced state, which is beneficial to the coating bonding during subsequent hot dip plating. However, the annealing temperature is too high and exceeds the unit capacity, and the H2 content is too high and the cost increases. Taking into account the product mechanical properties, coating bonding, unit capacity and cost, the present invention sets the temperature of the hot-dip section strip steel to 790℃~830℃, the annealing time is 35s~50s, and the H2 content is 20~25% when the cold-rolled hardened steel plate is continuously annealed in the horizontal continuous annealing furnace of the continuous hot-dip aluminum-zinc unit.

[0028] 3. Setting of cooling speed of strip steel in horizontal continuous annealing furnace

[0029] After high-temperature annealing, the steel plate is cooled in the furnace to the temperature for entering the zinc pot, and hot-dip plating begins. Rapid cooling of the steel plate at the high temperature stage is prone to C-warping, which will cause excessive thickness of the local coating during subsequent hot-dip plating, which is not conducive to the bonding strength of the coating. Therefore, it is necessary to cool at the lowest possible cooling rate in the high-temperature section, and the cooling air volume and pressure on the upper and lower surfaces should be consistent to prevent the occurrence of C-warping. At the same time, the cooling rate cannot be too small, otherwise the steel plate cannot be cooled to the temperature for entering the zinc pot in the cooling section. Comprehensive consideration is that the cooling rate of the section greater than or equal to 680°C is 3 to 7°C / s.

[0030] 4. Setting of the plating solution temperature in the zinc pot, the substrate temperature of the hot-dip aluminum-zinc steel plate entering the zinc pot, the air knife height and the cooling speed of the strip after plating

[0031] After annealing in a horizontal annealing furnace and cooling in the furnace, the cold-rolled hard strip passes through a zinc pot at a certain temperature, and is continuously hot-dip plated in a plating solution at a certain temperature. After the strip exits the zinc pot, it is sprayed by an air knife, and then cooled after plating to a certain temperature to solidify the coating. Since the air knife spraying will cause the unsolidified zinc liquid on the surface of the steel plate to flow downward to the zinc pot, there is a certain distance between the air knife and the zinc pot liquid level, which is called the air knife height. Due to the space limitations of the air knife and the first stage post-plating cooler equipment installation, a small gap will be left between the air knife and the first stage post-plating cooler, and this section is natural air cooling. During the hot-dip plating process, the cold-rolled substrate reacts with the plating bath to form a zinc-aluminum-iron alloy layer. The zinc-aluminum-iron alloy layer is between the plating layer and the cold-rolled substrate. The alloy layer structure is the main factor affecting the poor bonding of the product. The method of the present invention is based on the following research findings. The shedding of the coating of the cold-rolled hot-dip aluminum-zinc steel sheet mostly occurs between the alloy layer and the cold-rolled substrate. When the steel sheet enters the zinc pot at a higher temperature and the plating solution temperature for hot dipping, the reaction between the steel sheet and the plating solution will be violent. At this time, the interface between the alloy layer and the cold-rolled substrate is serrated. The better the alloy layer is combined with the cold-rolled substrate, the better the bonding strength of the coating. At the same time, the alloy layer is a brittle phase. If the thickness is too thick, it is easy to crack or peel off during molding, resulting in poor bonding strength between the coating and the substrate. In order to inhibit the thickening of the alloy layer, it is necessary to cool the steel sheet to below 550-560°C in the high temperature section as soon as possible after contacting the plating solution. At this time, the alloy layer has completed fusion and growth. In terms of technology, multiple parameters such as the height of the air knife, the distance from the first stage cooler to the air knife, and the cooling rate after plating need to be coordinated to achieve. The lower the height of the air knife, the closer the distance from the first stage cooler to the air knife, and the greater the cooling rate of the first stage, the thinner the alloy layer and the better the bonding strength of the coating. Taking into account the control of coating bonding strength and equipment capabilities, the present invention sets the temperature of the aluminum-zinc liquid in the zinc pot to 600-605°C, the temperature of the steel plate entering the zinc pot to 605-610°C, the height of the air knife to 0.3m-0.7m from the zinc pot liquid level, the distance from the first-stage cooler to the air knife to 0.5-0.9m, the first-stage cooling rate to 40-60°C / S, and the first-stage cooling end temperature to 550-560°C; the second-stage cooling is to air cool the hot-dip aluminum-zinc steel plate from 550-560°C to 280-300°C.

[0032] The yield strength R of the cold-rolled hot-dip aluminum-zinc steel sheet with a thickness of 1.2 to 1.6 mm produced by the method of the present invention is P0.2 140~180MPa, tensile strength R m 235~320MPa, elongation after fracture A 80mm The coating weight on one side is 70-90g / m 2 The cold-rolled hot-dip aluminum-zinc steel sheet passed the V-bending test and the coating did not fall off.

[0033] Compared with the prior art, the present invention has the following positive effects: 1. The present invention solves the problem of poor coating bonding of thick-coated cold-rolled hot-dip aluminum-zinc steel plates by controlling the wettability of the cold-rolled hard steel plate with the plating solution, the fusion of the alloy layer with the steel substrate, the thickness of the alloy layer, and preventing the local excessive thickness of the coating of the cold-rolled hot-dip aluminum-zinc steel plate, thereby achieving stable production of thick-coated cold-rolled hot-dip aluminum-zinc steel plates in similar hot-dip aluminum-zinc units, improving the finished product rate of steel plates, and reducing manufacturing costs. 2. The method of the present invention can be achieved by adjusting the key processes of cold rolling, annealing, hot-dip plating and cooling after plating, without changing the existing process path, and has low implementation costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a scanning electron microscope photograph of the coating cross section of the cold-rolled hot-dip aluminum-zinc steel plate in Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with Examples 1 to 6, as shown in Tables 1 to 5.

[0036] Table 1 shows the chemical composition (by weight percentage) of the hot-rolled steel sheets according to the embodiments of the present invention, with the remainder being Fe and unavoidable impurities.

[0037] Table 1 Chemical composition of hot-rolled steel sheets according to the present invention, unit: weight percentage

[0038]

[0039] For the above thickness of 3.5-5.0mm, yield strength of 150-190MPa, tensile strength of 240-330MPa, elongation after fracture A 80mm The hot-rolled steel sheet with a thickness of 43% to 49% is pickled, cold rolled, alkali washed, electrolytically cleaned, annealed in a horizontal continuous annealing furnace, hot-dip galvanized, cooled and leveled after plating, and the finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.2 to 1.6 mm is obtained by coiling.

[0040] Among them, the total reduction rate of cold rolling is 54% to 76%, and the surface roughness of the hardened strip is 0.8-1.5μm; the temperature of the soaking section of the horizontal continuous annealing furnace is 790℃ to 830℃, the annealing time is 35s to 50s, and the volume content of H2 in the soaking section of the annealing furnace is 20% to 25%; the cooling rate of the cooling section greater than or equal to 680℃ in the annealing furnace is 3 to 7℃ / s; the plating liquid temperature in the zinc pot during hot dip galvanizing is 600℃ to 605℃, and the temperature of the steel plate entering the zinc pot is 605℃ to 610℃; the height of the air knife is 0.3 to 0.7m from the zinc pot liquid surface; the distance from the first stage cooler to the air knife in the post-galvanizing cooling is 0.5 to 0.9m, the first stage cooling rate is 40 to 60℃ / S, and the first stage cooling end temperature is 550 to 560℃. The control parameters of the cold rolling, annealing, hot dip galvanizing and post-galvanizing cooling steps are shown in Tables 2, 3 and 4.

[0041] Table 2 Control parameters of cold rolling step in the embodiment of the present invention

[0042]

[0043] Table 3 Annealing step control parameters of the present invention

[0044]

[0045] Table 4 Control parameters of hot dip plating step and post-plating cooling step in the embodiment of the present invention

[0046]

[0047] The metallographic structure of the hot-dip aluminum-zinc-silicon steel plate coating produced by the method of the present invention is shown in Figure 1 The alloy layer connected to the steel plate substrate and the aluminum-zinc coating are Figure 1 It is clearly visible that the coating thickness is uniform and the alloy layer is tightly bonded to the steel substrate.

[0048] Yield strength R of 1.2~1.6mm thick cold-rolled hot-dip galvanized steel sheet P0.2 140~180MPa, tensile strength R m 235~320MPa, elongation after fracture A 80 mm The coating weight on one side is 70-90g / m 2 The cold-rolled hot-dip aluminum-zinc steel sheet passed the V-bending test and the coating did not fall off.

[0049] The cold-rolled hot-dip aluminum-zinc steel sheet obtained by the present invention was subjected to a tensile test according to "GB / T228.1-2010 Tensile test of metal materials Part 1: Room temperature test method"; a V-bending test was carried out according to "GB / T 39130-2020 Test method for adhesion of coating on galvanized products" to test the coating peeling on the test surface, and the adhesion of the coating was evaluated according to the tape method; the mechanical properties and coating weight of the cold-rolled hot-dip aluminum-zinc steel sheet are shown in Table 5.

[0050] Table 5 Mechanical properties and coating weight of cold-rolled hot-dip aluminum-zinc steel sheets according to the present invention

[0051]

[0052] The V-bending test results of the cold-rolled hot-dip aluminum-zinc steel sheets obtained in Examples 1-6 of the present invention are all qualified, and no coating falls off.

[0053] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 160 MPa, wherein the chemical composition of the substrate is as follows: C: 0.0010% to 0.0040%, Si: 0.001% to 0.034%, Mn: 0.05% to 0.15%, P≤0.020%, S≤0.015%, Alt: 0.015% to 0.050%, Ti: 0.020% to 0.050%, and the balance is Fe and unavoidable impurity elements; the weight of the single-side coating of the cold-rolled hot-dip aluminum-zinc steel sheet with a thickness of 1.2 to 1.6 mm is 70 to 90 g / m 2 The cold-rolled hot-dip aluminum-zinc steel sheet passed the V-bending test and the coating did not fall off.

2. The yield strength 160MPa grade thick-coated cold-rolled hot-dip aluminum-zinc steel sheet according to claim 1, characterized in that: Yield strength R of 1.2~1.6mm thick cold-rolled hot-dip galvanized steel sheet P0.2 140~180MPa, tensile strength R m 235~320MPa, elongation after fracture A 80mm It is 42% to 47%.

3. The method for manufacturing a thick-coated cold-rolled hot-dip aluminum-zinc steel sheet with a yield strength of 160 MPa as claimed in claim 1, characterized in that: The method includes: The hot-rolled steel sheet with a thickness of 3.5 to 5.0 mm is pickled, cold-rolled, alkali-washed, electrolytically cleaned, annealed in a horizontal continuous annealing furnace, hot-dip galvanized, cooled after plating, and flattened to obtain a finished cold-rolled hot-dip galvanized steel sheet with a thickness of 1.2 to 1.6 mm, wherein: The chemical composition weight percentage of the hot-rolled steel plate is: C: 0.0010% to 0.0040%, Si: 0.001% to 0.034%, Mn: 0.05% to 0.15%, P≤0.020%, S≤0.015%, Alt: 0.015% to 0.050%, Ti: 0.020% to 0.050%, the balance is Fe and unavoidable impurity elements, the yield strength is 150 to 190 MPa, the tensile strength is 240 to 330 MPa, and the elongation after fracture is A 80mm 43% to 49% The cold rolling step is five-stand continuous rolling, the total cold rolling reduction rate is 54% to 76%; the surface roughness of the hardened strip after cold rolling is 0.8 to 1.5 μm; The annealing step includes annealing the hardened steel strip after cold rolling in a horizontal continuous annealing furnace soaking section at a temperature of 790-830°C for 35-50s; the H2 volume content in the soaking section of the horizontal continuous annealing furnace is 20%-25%; cooling the annealed steel strip to 680°C, the cooling rate of the steel strip from the soaking section of the horizontal continuous annealing furnace to 680°C is 3-7°C / s, the cooling section in the horizontal continuous annealing furnace is air-cooled, and the air volume and pressure of the cooling fans on the upper and lower surfaces are consistent; The composition of the hot-dip aluminum-zinc coating in the zinc pot is Al: 52-58%, Si: 1.3-1.8%, and the balance is Zn and inevitable impurity elements; the bath temperature is 600°C-605°C, and the temperature of the hot-dip aluminum-zinc steel plate substrate when entering the zinc pot is 605°C-610°C; the weight of the single-side coating of the hot-dip aluminum-zinc steel plate is controlled to be 70-90g / m 2 , the height of the air knife is 0.3-0.7m from the zinc pot liquid surface; The post-plating cooling is a two-stage cooling, both of which use air cooling. The first stage cooling is to cool the hot-dip aluminum-zinc steel plate after passing through the air knife. The distance from the first stage cooler to the air knife is 0.5-0.9m, the first stage cooling rate is 40-60℃ / S, and the first stage cooling end temperature is 550-560℃; the second stage cooling is to air cool the hot-dip aluminum-zinc steel plate from 550-560℃ to 280-300℃.

4. The manufacturing method according to claim 3, characterized in that: Yield strength R of 1.2~1.6mm thick cold-rolled hot-dip galvanized steel sheet P0.2 140~180MPa, tensile strength R m 235~320MPa, elongation after fracture A 80mm It is 42% to 47%.

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