CN115109999B

CN115109999B - Hot dip galvanized aluminum magnesium high-strength steel and manufacturing method thereof

Info

Publication number: CN115109999B
Application number: CN202210728235.7A
Authority: CN
Inventors: 孙伟华; 阎元媛; 陈一鸣; 孟庆格; 胡宽辉; 陈昊
Original assignee: Wuhan Iron and Steel Co Ltd
Current assignee: Wuhan Iron and Steel Co Ltd
Priority date: 2022-06-24
Filing date: 2022-06-24
Publication date: 2023-05-16
Anticipated expiration: 2042-06-24
Also published as: CN115109999A

Abstract

The invention relates to a hot dip galvanized aluminum magnesium high-strength steel and a manufacturing method thereof, wherein the high-strength steel comprises a base material and a plating layer attached to the surface of the base material, and the base material comprises the following chemical components in percentage by mass: 0.18 to 0.22 percent of C, 0.2 to 0.3 percent of Si, 0.5 to 1.0 percent of Mn, 0.02 to 0.05 percent of Als, less than or equal to 0.02 percent of P, less than or equal to 0.008 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and unavoidable impurities; the plating layer comprises the following chemical components in percentage by mass: 4.0 to 8.0 percent of Al, 2.0 to 4.0 percent of Mg, 0 to 0.5 percent of Si, and the balance of Zn and unavoidable impurities. The base material does not contain micro alloying elements such as Nb, ti, V and the like, and adopts a low-alloy and low-cost design; the plating layer contains no rare earth metal and only comprises zinc, aluminum, magnesium and silicon; the preparation method has the advantages that the carefully designed formula is combined with effective regulation and control of coiling temperature, cold rolling annealing temperature, plating solution temperature and the like, so that the thin galvanized aluminum magnesium high-strength steel plate with yield strength of more than 400MPa, tensile strength of more than 500MPa and elongation of more than 10% is successfully prepared, and the high-strength thinning requirements of building plates and the like are met.

Description

Hot dip galvanized aluminum magnesium high-strength steel and manufacturing method thereof

Technical Field

The invention relates to the technical field of steel, in particular to hot-dip galvanized aluminum magnesium high-strength steel and a manufacturing method thereof.

Background

Compared with hot galvanizing, the hot galvanizing aluminum magnesium obviously improves the corrosion resistance of the steel plate. In order to reduce cost and save energy consumption, high-strength thinned plates are increasingly paid attention to in the manufacturing process of buildings, household appliances and the like, and the high-strength galvanized aluminum magnesium thin-specification steel plate is a high-strength thinned plate with high competitiveness.

Because of the limitation of rolling capability, the conventional cold rolling production line has a requirement on the upper limit of the thickness specification of a hot rolling incoming coil when producing a thin high-strength steel plate (such as a steel plate with the yield strength of more than 400Mpa and the thickness specification of 0.5 mm), however, the conventional hot rolling production line is not easy to produce the thin high-strength raw coil. The CSP process of continuous casting and rolling of sheet billet can be used for directly rolling and producing the sheet steel with the thickness of 0.8-2.5 mm, so that the process can be used for providing hot rolled incoming materials with thin specification, and further producing high-strength steel with thin specification in a conventional cold rolling production line. Compared with the conventional hot rolling, the sheet billet continuous casting and rolling process can also effectively shorten the process flow and greatly reduce the energy consumption.

The search finds that Chinese patent CN110777290B discloses a hot dip galvanized aluminum magnesium high-strength steel with yield strength larger than 550Mpa based on CSP flow, wherein the chemical components and weight percentages of the base material are as follows: c: 0.055-0.10%, si is less than or equal to 0.5%, mn:0.55-1.7%, P is less than or equal to 0.0150%, S is less than or equal to 0.030%, als:0.015 to 0.045 percent, ti+Nb is less than or equal to 0.1 percent, and the balance is iron and unavoidable impurities; the zinc-aluminum-magnesium alloy coating comprises the following chemical components in percentage by weight: al:9.0-13.0%, mg:2.0-4.0%, si:0.02-0.1%, ni:0.01-0.05%, RE (Ce or La): 0.01-0.2%, and the balance Zn and unavoidable impurity elements. The substrate component of the hot-dip galvanized aluminum magnesium high-strength steel adopts the design thought of low-carbon and Nb-Ti composite microalloying, and rare earth components are introduced into the plating solution to improve the corrosion resistance of the plating layer, but the method of introducing Nb and Ti into the substrate and adding the rare earth components into the plating solution can improve the cost of the material.

As previously mentioned, conventional hot rolling lines are not easily adapted to provide thin gauge hot rolled feedstock rolls required for the production of high strength thin gauge cold rolled products. In addition, the cold-rolled material with the yield strength above 350MPa grade usually adopts a precipitation strengthening or phase transformation strengthening route (such as CN 110777290B), the precipitation strengthening route needs to add micro alloying elements such as Nb, ti, V and the like into the material, and the phase transformation strengthening route has requirements on the capacity of a cold mill unit, such as quick cooling rate and the like. The plating layer components are introduced with other elements except Al, mg and Si, so that the plating layer cost is increased, and the surface quality in production is not easy to control. These all present challenges to the development and production of hot dip galvanized aluminum magnesium high strength steels.

Disclosure of Invention

One of the objects of the present invention is to provide a hot dip galvanized aluminum magnesium high strength steel comprising a substrate and a plating layer attached to the surface of the substrate; the chemical composition of the base material in mass percent is as follows: 0.18 to 0.22 percent of C, 0.2 to 0.3 percent of Si, 0.5 to 1.0 percent of Mn, 0.02 to 0.05 percent of Als, less than or equal to 0.02 percent of P, less than or equal to 0.008 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and unavoidable impurities; the chemical composition of the coating in mass percent is as follows: 4.0 to 8.0 percent of Al, 2.0 to 4.0 percent of Mg, 0 to 0.5 percent of Si, and the balance of Zn and unavoidable impurities.

Further, the metallographic structure of the base material includes ferrite and pearlite, wherein the ferrite grain size is 8-20 μm.

Further, the structure of the plating layer comprises a bulk (Al) phase, a bulk (Zn) phase and a bulk MgZn phase ₂ Phase, eutectic Al/Zn/MgZn ₂ Organization.

Further, the thickness of the hot dip galvanized aluminum magnesium high strength steel is 0.4-1.0 mm, the yield strength is 420-570 Mpa, the tensile strength is 520-630 Mpa, and the elongation is more than or equal to 10%.

The second object of the present invention is to provide a method for producing the hot dip galvanized aluminum magnesium high strength steel, comprising the steps of: firstly, adopting a thin slab continuous casting and rolling CSP process to produce a thin specification cold-rolled raw material roll, then cold-rolling the raw material roll and plating zinc-aluminum-magnesium alloy on the surface of the raw material roll.

Further, the CSP process comprises the steps of smelting, refining, continuous casting of thin slabs, soaking of casting blanks, rolling, laminar cooling, coiling, leveling and the like.

Further, smelting is carried out in the smelting and refining process according to the designed base material formula.

Further, the superheat degree of the ladle molten steel is 15-30 ℃ in the control of the thin slab continuous casting process, the thickness of a casting blank is 70-75 mm, and the pulling speed is 4.0-4.8 m/s.

Further, the casting blank needs to be subjected to descaling treatment before being fed into the furnace in the casting blank soaking process, and the descaling pressure is 15-30 bar; the casting blank is charged at 820-1050 deg.c and discharged at 1150-1190 deg.c.

Further, the rolling pass reduction distribution in the rolling step is as follows: the first pass is 50-60%, the second pass is 40-50%, the last pass is 8-12%, the rolling speed is controlled to be 7-12 m/s, and the final rolling temperature is 840-880 ℃; the descaling process in the rolling process is to adopt high-pressure water to carry out descaling before entering a rolling mill, wherein the descaling water pressure is 200-380 bar.

Further, in the coiling process, the coiling temperature is controlled to be 520-650 ℃, and the coil is flattened after the temperature of the coil is reduced to be below 50 ℃.

Further, the thickness of the raw material roll is controlled to be 2.0-2.5 mm.

Further, the raw material coil is pickled and then is rolled again, the temperature of acid liquor in pickling is controlled to be 70-90 ℃, the total rolling reduction rate of cold rolling is 65-80%, and the thickness of the strip steel after cold rolling is controlled to be 0.4-1.0 mm.

Further, the heating rate of the strip steel obtained by cold rolling in the hot galvanizing aluminum magnesium working procedure is 5-40 ℃/s, the annealing temperature is 680-800 ℃ and heat preservation is not needed, then the strip steel is directly cooled to 400-450 ℃ or 10-15 ℃ higher than the plating solution temperature at the cooling rate of 5-15 ℃/s, then the strip steel enters a zinc pot filled with the plating solution for hot dip galvanizing of zinc aluminum magnesium, and the strip steel is cooled by air and then cooled by water after being discharged from the zinc pot.

Further, the temperature of the plating solution is 40-50 ℃ higher than the melting point of the plating solution.

The invention optimally designs the base material, the plating layer components and the whole manufacturing process of the high-strength steel, and is specifically characterized in the following aspects:

(1) And (3) designing the components of a base material: adopts low alloy and low cost design, does not contain micro alloying elements such as Nb, ti, V and the like, and mainly comprises the following components in percentage by weight:

c: carbon is the most basic strengthening element in steel. The higher the C content, the higher the yield strength and tensile strength of the steel, but the plasticity and toughness are lowered, and the higher C content lowers the weldability of the steel. Since the peritectic region is to be avoided in the CSP process, the C content is required to be higher than 0.17% or lower than 0.07%. In order to ensure the strength and the welding performance, the invention strictly controls the C content within the interval range of 0.18 to 0.22 percent.

Si: silicon is a commonly used deoxidizer in steelmaking. Si does not form carbide in steel, but exists in ferrite or austenite in the form of a solid solution, and further increases the strength of the solid solution. During low-temperature tempering, si can reduce the diffusion rate of carbon and increase the tempering stability and strength of steel. However, too high a Si content will significantly reduce the plasticity, toughness and weldability of the steel. In addition, too high a Si content reduces the adhesion of the coating. Therefore, the Si content is strictly controlled within the range of 0.20-0.30 percent.

Mn: manganese is an excellent deoxidizer and desulfurizing agent in steelmaking. Mn and S are easy to form high-melting-point MnS, and thermal embrittlement caused by FeS is prevented. Mn can improve the strength of steel, but too high Mn content can reduce the adhesion of the coating. Therefore, the Mn content is strictly controlled within the range of 0.5-1.0%.

(2) Coating composition design: the plating layer mainly comprises zinc, aluminum, magnesium and silicon, and does not contain other components such as rare earth metals.

Al: the Al in the coating can obviously improve the corrosion resistance of the steel plate, and the Al content is more than 3.0 percent generally can better exert the improvement effect on the corrosion resistance; when the Al content is high, the brittle Fe-Al compound grows remarkably on the interface between the molten plating solution and the substrate, so that the bonding property between the plating layer and the substrate is poor. In order to ensure the adhesion of the coating, the invention strictly controls the Al content in the coating to be 4.0-8.0%.

Mg: the Mg in the coating can uniformly generate corrosion products with certain fluidity on the surface of the coating, and the existence of the corrosion products enables the notch processed by the steel plate to have self-healing capacity and mechanism. In order to fully exert this effect of Mg, it is necessary to ensure a content of > 2.0%. When the Mg content is more than 4.0%When the coating is used, massive brittle MgZn is easy to appear in the coating ₂ The phase itself is extremely liable to crack, and the formability of the plating layer is seriously affected. Therefore, in order to obtain a high-quality plating layer with both corrosion resistance and formability, the present invention strictly controls the Mg content in the plating layer to be 2.0 to 4.0%.

Si: the growth of the Fe-Al compound can be effectively inhibited by adding a small amount of Si into the plating solution, which is beneficial to improving the combination property of the plating layer and the steel plate. In addition, the addition of a small amount of Si can also suppress blackening of the Zn-Al-Mg-based plating. However, too high Si content is detrimental to the Fe-Al reaction on the substrate and also generates a lot of dross in the zinc pot. Therefore, the Si content in the plating layer is strictly controlled to be 0-0.5%.

(3) In the aspect of manufacturing process, the product performance is improved mainly by regulating and controlling coiling temperature, cold rolling annealing temperature, plating solution temperature and the like.

Coiling temperature: when the CSP rolling coiling temperature is too high, the crystal grains of the cold-rolled raw material coil are coarse, the strength is lower, and the strength of a final cold-rolled product is reduced; when the coiling temperature of CSP rolling is too low, the requirement on the laminar cooling capacity of the production line is high, and the coiling is not facilitated because the plate head is easy to tilt before coiling, so that the coiling temperature is controlled to be 520-650 ℃ finally.

Annealing temperature: the annealing temperature is a key factor for determining the mechanical property of the steel plate, and the strength and the elongation of the material can be adjusted by adjusting the temperature so as to meet different material requirements. When the temperature is 680-730 ℃, the material is in an incomplete annealing state, the yield and tensile strength are higher, and the elongation is lower; when the temperature is above 740 ℃, the material is completely recrystallized, while yield and tensile strength decrease, elongation increases. For the high-strength steel plate with the elongation requirement higher than 14%, a process with higher Mn component and higher annealing temperature can be adopted; for high strength steel sheets with elongation less than 14% and high strength, an incomplete annealing process may be used, and lower alloy compositions and lower annealing temperatures may achieve this effect. After the temperature reaches the target annealing temperature, the steel plate is directly cooled to the temperature before plating without heat preservation, and then hot dip plating is carried out.

Plating solution temperature: the melting point of the coating system is related to the components, and the melting point of the components is lower when the components are close to the ternary eutectic point of the system. The excessive plating solution temperature will cause zinc slag to increase and the surface defects of the plating layer to increase, and the invention sets the plating solution temperature to be 40-50 ℃ higher than the melting point of the plating layer based on the principle.

Compared with the prior art, the invention has the main advantages that:

(1) The product has excellent performance and low production and manufacturing cost. The yield strength of the hot-dip galvanized aluminum magnesium high-strength steel product provided by the invention is 420-570 Mpa, the tensile strength is 520-630 Mpa, the elongation is more than or equal to 10%, and the high-strength thinning requirements of manufacturing industries such as buildings are met.

(2) The technology of combining CSP hot rolling and cold rolling zinc-plated aluminum magnesium is adopted, so that the method is simpler and more feasible. Compared with the conventional hot rolling, the CSP process not only can provide thin-specification raw material rolls, but also has short manufacturing flow and reduced production cost.

(3) The cold rolling annealing process adopts rapid heating, and heat preservation is not needed after the target annealing temperature is reached, so that energy sources are effectively saved, and the production cost is reduced.

(4) The plating layer contains no rare earth elements, so that the composition is simple, the cost is low, the simple plating layer formula is easy to coat, the quality of the plating layer is ensured, and the corrosion resistance is better than that of a pure zinc plating layer.

(5) The process is flexible, and the product performance is controllable. The strength of the final product can be properly regulated and controlled by regulating the coiling temperature, and the full annealing or incomplete annealing can be realized by regulating the annealing temperature, so that the strength and the elongation of the final product can be regulated and controlled to meet different material requirements.

Drawings

FIG. 1 is a photograph showing a metallographic microstructure of a substrate of a steel sample obtained in example 1;

FIG. 2 is a photograph showing a metallographic microstructure of a substrate of a steel sample obtained in example 4;

FIG. 3 is a photograph showing a metallographic microstructure of a steel sample obtained in comparative example 16.

Detailed Description

In order to make the technical scheme and the beneficial effects of the present invention fully understood by those skilled in the art, the following description is further made with reference to specific embodiments and drawings.

The hot dip galvanized aluminum magnesium high strength steel comprises the following chemical components in percentage by mass: 0.18 to 0.22 percent of C, 0.2 to 0.3 percent of Si, 0.5 to 1.0 percent of Mn, 0.02 to 0.05 percent of Als, less than or equal to 0.020 percent of P, less than or equal to 0.008 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and other unavoidable impurities; the zinc-aluminum-magnesium alloy plating layer comprises the following chemical components in percentage by mass: al:4.0 to 8.0 percent, mg:2.0 to 4.0 percent, si:0 to 0.5 percent, and the balance of Zn and other unavoidable impurities. The analysis and test results show that the metallographic structure of the high-strength steel plate comprises ferrite and pearlite, wherein the size of ferrite grains is 8-20 mu m, the yield strength is 420-570 Mpa, the tensile strength is 520-630 Mpa, and the elongation is more than or equal to 10%.

The manufacturing process of the high-strength steel plate is divided into two stages: the CSP process mainly comprises the steps of smelting, refining, continuous casting of thin slabs, soaking of casting blanks, rolling, laminar cooling, coiling, leveling and the like, and the cold rolling process mainly comprises the steps of pickling, rolling, hot galvanizing of aluminum magnesium and the like.

In the continuous casting step of the sheet billet in the CSP process stage, the superheat degree of the ladle molten steel is 15-30 ℃, the thickness of a casting blank is 70-75 mm, and the pulling speed is 4.0-4.8 m/s. The descaling treatment is needed before the casting blank is fed into the furnace during the continuous casting of the sheet billet, the descaling pressure is 15-30 bar, the feeding temperature of the casting blank is 820-1050 ℃, and the discharging temperature is 1150-1190 ℃. The rolling pass reduction distribution is as follows: the first pass is 50-60%, the second pass is 40-50%, the last pass is 8-12%, the rolling speed is controlled to be 7-12 m/s, and the final rolling temperature is 840-880 ℃. The descaling process in the rolling process adopts high-pressure water for descaling before entering the rolling mill, and the descaling water pressure (high pressure) is 200-380 bar. The coiling temperature is 520-650 ℃. After the temperature of the steel coil is reduced to below 50 ℃, flattening is carried out, and the thickness of the raw material coil prepared by the process is 2.0-2.5 mm.

The temperature of the acid liquor during the acid washing of the strip steel in the cold rolling process stage is 70-90 ℃, the total rolling reduction is 65-80%, and the thickness of the strip steel after cold rolling is controlled to be 0.4-1.0 mm. The heating rate in hot dip coating is 5-40 ℃/s, the annealing target temperature is 680-800 ℃ and heat preservation is not needed, the strip steel is directly cooled to 400-450 ℃ or 10-15 ℃ higher than the temperature of the plating solution at the rate of 5-15 ℃/s, then the strip steel enters a zinc pot for hot dip galvanizing aluminum magnesium, and the strip steel is cooled by air cooling and then water cooling after being discharged from the zinc pot. The temperature of the plating solution in the zinc pot is 40-50 ℃ higher than the melting point of the plating solution.

With reference to the above substrate, plating formulation and manufacturing process, a batch of steel sheets were prepared according to the conditions described in tables 1 to 3 below (examples are numbered 1 to 3 and comparative examples are numbered 4).

Table 1 differently numbered substrate chemistry composition table (wt.%)

Table 2 chemical composition of plating solution of different numbers is tabulated (wt.%)

TABLE 3 Main Process parameter Table for examples and comparative examples

The steel sheets obtained in examples 1 to 15 and comparative examples 16 to 20 were subjected to various tests according to the relevant standards, and the results are shown in Table 4.

TABLE 4 comparison of Performance test results for different Steel sheet products

Note that: v indicates good surface after plating; the x represents the surface difference after plating, and there was significant missing plating.

From table 4, the following conclusions can be drawn:

(1) the tensile properties of the samples obtained in examples 1-6 and comparative example 16 showed that the material was not recrystallized at all at an annealing temperature of 660℃or less and the rolled hard structure was evident as shown in FIG. 3. When the annealing temperature is between 680 ℃ and 720 ℃, the strength of the material is higher but the elongation is lower, the material is in an incompletely annealed state, and the partially rolled hard state structure is reserved, as shown in fig. 1. When the soaking temperature is equal to or higher than 740 ℃, the strength of the material is reduced but the elongation is increased, and at this time, the material is completely annealed, recrystallized completely and the structure is shown in fig. 2. Then as the temperature increases, the strength decreases slightly due to the slow growth of the grains.

(2) The tensile properties of the test pieces obtained in examples 4 and 7 showed that the strength of the final product was decreased but the elongation was increased as the winding temperature was increased.

(3) Examples 8-9 used different cold rolled stock thicknesses and reduction ratios, with slightly different tensile properties of the product, indicating that when the reduction ratio was already high, further increases in reduction had no significant improvement in tensile properties.

(4) Examples 4, 10, 11 and comparative example 18 used different plating bath compositions, and when the Al and Mg contents in the plating bath were increased, the corrosion resistance of the product was increased; when the Mg content in the plating solution is lower than 2.0%, the corrosion resistance of the product is obviously reduced.

(5) Examples 12-15 employed different substrate compositions, with increasing strength of the product as the Si, mn content in the substrate increased.

(6) The comparative examples 19 to 20 have Si content of more than 0.3% and the hot dip plated product has poor surface quality and plating leakage, which means that the Si content in the substrate should be controlled within 0.3%.

Claims

1. A hot dip galvanized aluminum magnesium high strength steel, characterized in that: the high-strength steel comprises a base material and a plating layer attached to the surface of the base material, wherein the base material comprises the following chemical components in percentage by mass: 0.18 to 0.22 percent of C, 0.2 to 0.3 percent of Si, 0.5 to 1.0 percent of Mn, 0.02 to 0.05 percent of Als, less than or equal to 0.02 percent of P, less than or equal to 0.008 percent of S, less than or equal to 0.008 percent of N, and the balance of Fe and unavoidable impurities; the plating layer comprises the following chemical components in percentage by mass: 4.0% -8.0% of Al, 2.0% -4.0% of Mg, 0% -0.5% of Si, and the balance of Zn and unavoidable impurities; the preparation method of the high-strength steel comprises the following steps: firstly, producing a thin gauge cold-rolled raw material roll by adopting a thin slab continuous casting and rolling CSP process, and then cold-rolling the raw material roll and hot-plating zinc-aluminum-magnesium alloy on the surface of the raw material roll, wherein the CSP process comprises smelting, refining, thin slab continuous casting, casting blank soaking, rolling, laminar cooling, coiling and flattening; wherein the descaling treatment is required before the casting blank enters the furnace in the casting blank soaking process, and the descaling pressure is 15-30 bar; the casting blank is charged at the temperature of 820-1050 ℃ and discharged at the temperature of 1150-1190 ℃; the rolling pass reduction distribution in the rolling process is as follows: the first pass is 50-60%, the second pass is 40-50%, the last pass is 8-12%, the rolling speed is controlled to be 7-12 m/s, and the final rolling temperature is 840-880 ℃; the descaling process in the rolling process is to adopt high-pressure water for descaling before entering a rolling mill, wherein the pressure of the descaling water is 200-380 bar; the heating rate of the strip steel obtained by cold rolling in the hot galvanizing aluminum magnesium working procedure is 5-40 ℃/s, the annealing temperature is 680-800 ℃ and heat preservation is not needed, then the strip steel is directly cooled to 400-450 ℃ or 10-15 ℃ higher than the plating solution temperature at the cooling rate of 5-15 ℃/s, then the strip steel enters a zinc pot filled with the plating solution for hot dip galvanizing of zinc aluminum magnesium, and the strip steel is cooled by air and then cooled by water after being discharged from the zinc pot.

2. A hot dip galvanised aluminium magnesium high strength steel according to claim 1, characterised in that: the metallographic structure of the base material comprises ferrite and pearlite, wherein the size of ferrite grains is 8-20 mu m; the structure of the coating comprises a bulk Al phase, a bulk Zn phase and a bulk MgZn phase ₂ Phase, eutectic Al/Zn/MgZn ₂ Organization.

3. A hot dip galvanised aluminium magnesium high strength steel according to claim 1, characterised in that: the thickness of the high-strength steel is 0.4-1.0 mm, the yield strength is 420-570 MPa, the tensile strength is 520-630 MPa, and the elongation is more than or equal to 10%.

4. A hot dip galvanised aluminium magnesium high strength steel according to claim 1, characterised in that: smelting and refining according to the designed base material formula; the superheat degree of the ladle molten steel is controlled to be 15-30 ℃ in the thin slab continuous casting process, the thickness of a casting blank is controlled to be 70-75 mm, and the pulling speed is controlled to be 4.0-4.8 m/s.

5. A hot dip galvanised aluminium magnesium high strength steel according to claim 1, characterised in that: the coiling temperature is controlled to be 520-650 ℃ in the coiling process, and the coil is flattened after the temperature of the coil is reduced to be below 50 ℃, so that the thickness of the prepared raw coil is 2.0-2.5 mm.

6. A hot dip galvanised aluminium magnesium high strength steel according to claim 1, characterised in that: the raw material coil is pickled and then is rolled again, the temperature of acid liquor in pickling is controlled to be 70-90 ℃, the total rolling reduction rate of cold rolling is 65-80%, and the thickness of the strip steel after cold rolling is controlled to be 0.4-1.0 mm.

7. A hot dip galvanised aluminium magnesium high strength steel according to claim 1, characterised in that: the temperature of the plating solution is 40-50 ℃ higher than the melting point of the plating solution.