阅读说明：本技术 一种镁合金薄板带温轧-超低温冷轧生产工艺 (Warm rolling-ultralow temperature cold rolling production process for magnesium alloy sheet ) 是由 马立峰 支晨琛 霍晓娇 贾伟涛 马自勇 朱艳春 黄志权 于 2019-09-27 设计创作，主要内容包括：本发明提供一种镁合金超薄板带温轧—超低温冷轧连续轧制生产方法,初始镁合金板带在300~400℃保温进行均匀化处理,随后在300~400℃下进行多道次可逆等温轧制,得到厚度为1~2mm的中间轧板；将热轧得到的中间轧板经液氮控冷装置送入轧机一侧的卷取装置；随后对镁合金薄板进行可逆低温冷轧,冷轧完成后,板材进入轧机出口侧冷却器中冷却,由卷板机卷曲、保温,最终得镁合金细晶超薄板带。本发明中冷却器和卷板机在轧机两侧对称布置,通过改变轧机和卷板机的转向就可以实现镁合金板材后续多道次超低温冷轧,液氮控制冷却镁合金板材晶粒细化明显,晶粒细小且均匀,可有效提高镁合金板材综合力学性能,改善其后续加工性能。(The invention provides a warm rolling-ultralow temperature cold rolling continuous rolling production method of a magnesium alloy ultrathin plate strip, which comprises the steps of carrying out homogenization treatment on an initial magnesium alloy plate strip at the temperature of 300-400 ℃, and then carrying out multi-pass reversible isothermal rolling at the temperature of 300-400 ℃ to obtain an intermediate rolled plate with the thickness of 1-2 mm; feeding the intermediate rolled plate obtained by hot rolling into a coiling device at one side of a rolling mill through a liquid nitrogen controlled cooling device; and then carrying out reversible low-temperature cold rolling on the magnesium alloy sheet, after the cold rolling is finished, cooling the sheet in a cooler at the outlet side of a rolling mill, curling and preserving heat by a plate rolling machine, and finally obtaining the magnesium alloy fine-crystal ultrathin sheet strip. The cooler and the plate bending machine are symmetrically arranged on two sides of the rolling mill, the subsequent multi-pass ultralow temperature cold rolling of the magnesium alloy plate can be realized by changing the steering of the rolling mill and the plate bending machine, the crystal grains of the magnesium alloy plate cooled by liquid nitrogen control are obviously refined, and the crystal grains are fine and uniform, so that the comprehensive mechanical property of the magnesium alloy plate can be effectively improved, and the subsequent processing property of the magnesium alloy plate can be improved.)

1. A magnesium alloy ultrathin plate warm rolling-ultralow temperature cold rolling production process comprises the following process routes: the method comprises the following steps of heating a plate strip → reversible isothermal hot rolling → liquid nitrogen spraying and cold control → reversible low-temperature cold rolling → low-temperature aging, and is characterized by comprising the following steps:

(1) heating the plate belt: heating the initial magnesium alloy plate strip in a heatable coiling furnace, wherein the heating temperature is 300-400 ℃, the heat preservation time is 0.5-2 h, carrying out annealing treatment to obtain a uniform equiaxial crystal structure, and preparing for isothermal hot rolling;

(2) reversible isothermal hot rolling of the plate strip: carrying out reversible reciprocating rolling on the heated plate strip between the heatable curling furnaces on the two sides to obtain a thin plate with the thickness of less than 2.0 mm;

(3) liquid nitrogen spraying and cooling control: opening a liquid nitrogen cooling control device, cooling the thin plate strip with the thickness to minus 196 to minus 100 ℃ through the liquid nitrogen cooling control device at a cooling speed of 70-100 ℃/s, and then sending the thin plate strip into a crimping device with heat preservation and cold insulation functions;

(4) reversible low-temperature cold rolling of the plate strip: reversible rolling is carried out on the magnesium alloy plate with small deformation by utilizing a liquid nitrogen controlled cooling device and a bilateral cold insulation curling device, and finally an ultrathin strip with the thickness of less than 0.5mm is obtained;

(5) low-temperature aging: and (4) the plate after the liquid nitrogen controlled cold rolling enters a coiling machine with heat preservation and cold insulation functions for low-temperature aging, and the rolling is finished.

2. The warm rolling-ultralow temperature cold rolling production process of the magnesium alloy ultrathin strip as claimed in claim 1, is characterized in that: the specific equipment structure related to the production process takes a four-roller finishing mill as a center, and a heatable coiling furnace, two pairs of guide rollers and a liquid nitrogen cooling control device are sequentially distributed on two sides of the four-roller finishing mill from outside to inside; the curling device is arranged between the two pairs of guide rollers; the production process comprises the steps of firstly heating a coiling device, then insulating heat and cold, and then arranging a liquid nitrogen cooling device at the position close to an inlet and an outlet of a rolling mill; and opening the liquid nitrogen controlled cooling device to continue liquid nitrogen cold rolling until the high-strength fine-grain magnesium alloy ultrathin plate with the required thickness is obtained.

3. The warm rolling-ultralow temperature cold rolling production process of the magnesium alloy ultrathin strip as claimed in claim 1, is characterized in that: the thickness of the magnesium alloy plate strip before low-temperature cold rolling is less than or equal to 2 mm.

4. The warm rolling-ultralow temperature cold rolling production process of the magnesium alloy ultrathin strip as claimed in claim 1, is characterized in that: the optimal cooling rates of magnesium alloy sheets with different specifications are different, and the parameters of the liquid nitrogen cooling and controlling device for adjusting the temperature and controlling the cooling speed are as follows: the final cooling temperature range is-196 to-100 ℃, the cooling rate range is 70 to 100 ℃/s, and the method comprises the following steps:

(1) the thickness of the magnesium alloy plate is within the range that d is not less than 1mm and not more than 1.3mm, the final cooling temperature is minus 100 +/-10 ℃, and the cooling rate is 70-80 ℃/s;

(2) the thickness of the magnesium alloy plate is within the range that d is not less than 1.3mm and not more than 1.7mm, the final cooling temperature is-150 +/-10 ℃, and the cooling rate is 80-90 ℃/s;

(3) the thickness of the magnesium alloy plate is within the range that d is not less than 1.7mm and not more than 2mm, the final cooling temperature is the liquid nitrogen temperature of-196 ℃ under normal pressure, and the cooling rate is 90-100 ℃/s.

5. The warm rolling-ultralow temperature cold rolling production process of the magnesium alloy ultrathin strip as claimed in claim 1, is characterized in that: the grain size of the high-strength magnesium alloy is 50% -79% finer than that of the intermediate plate grain size, and the high-strength magnesium alloy is uniform and fine isometric crystal.

Technical Field

The invention relates to the field of metal material processing, in particular to a warm rolling-ultralow temperature cold rolling production process of a magnesium alloy ultrathin plate.

Background

The magnesium alloy has wide application prospect in the fields of aerospace, 3C products, war industry, medicine and the like due to a series of unique advantages. This requires that the magnesium alloy product have good mechanical properties. The rolling deformation is the main deformation mode of magnesium alloy, the deformation temperature of magnesium alloy plates and strips has great influence on the performance and the tissue uniformity of plates in the rolling production process, and the control cooling after rolling also directly influences the quality of finished products.

Because magnesium alloy has poor room temperature formability, a magnesium alloy sheet is usually rolled by a hot rolling process to convert an as-cast or cast-rolled structure into a deformed structure, thereby obtaining a magnesium alloy sheet. However, the microstructure of the magnesium alloy hot rolled product is not uniform enough, and the strength, ductility and structure uniformity need to be further improved.

Grain refinement is an effective method that can improve both the strength and the plasticity of the material. At present, research methods can be used for realizing grain refinement of metal surfaces, such as shot blasting, surface mechanical grinding and the like, but the grain refinement effect of the methods is only reflected in the surface layer of the alloy, the structure refinement effect of the methods on the inner part of the alloy is not large, the production efficiency is low, the cost is higher, and the methods are not beneficial to large-scale industrial production and application. Through experiments, the invention provides a rolling method for grain refinement of a magnesium alloy plate by combining controlled rolling and controlled cooling technologies, and the method has important significance for improving the grain refinement efficiency and improving the uniformity of the plate.

At present, the cooling process of the magnesium alloy plate hot rolling production line after rolling is generally carried out by air cooling, and the magnesium alloy plate is cooled to room temperature and then is curled by a curling machine. However, the performance of the magnesium alloy sheet is inhibited by air cooling after rolling, and the difference of the cooling speed between the edge part and the center of the sheet causes uneven structure of the sheet, thereby affecting the quality of the sheet. By controlling the cooling process after the magnesium alloy hot rolled plate is rolled, crystal grains are refined, and the structural uniformity of the plate is improved, so that the performance of the plate is improved.

Disclosure of Invention

Aiming at the situation, the invention aims to provide a warm rolling-ultralow temperature cold rolling production process for magnesium alloy ultrathin plates with different thicknesses for subsequent controlled rolling of the magnesium alloy ultrathin plates, improve the comprehensive mechanical property of the magnesium alloy plates and widen the application range of the magnesium alloy plates on the premise of keeping the chemical components of the materials unchanged.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: the production process of the magnesium alloy ultrathin plate with warm rolling-ultralow temperature cold rolling is provided, and the equipment arrangement scheme when the magnesium alloy plates with different thicknesses are subjected to low temperature cold rolling is as follows: a four-roller rolling mill is taken as a center, liquid nitrogen coolers and plate bending machines are symmetrically arranged on two sides of the rolling mill, and the multi-pass cold rolling process of the magnesium alloy plate is realized by changing the steering of the rolling mill and the plate bending machines.

The process route of the method for improving the comprehensive mechanical property of the magnesium alloy sheet by low-temperature cold rolling comprises the following steps: initial plate → homogenization treatment → hot rolling → air cooling → intermediate plate → homogenization treatment → ultrafast cooling → low temperature cold rolling → ultrafast cooling → curling, the specific steps are as follows:

(1) heating the plate belt: heating the initial magnesium alloy plate strip in a heatable coiling furnace, wherein the heating temperature is 300-400 ℃, the heat preservation time is 0.5-2 h, carrying out annealing treatment to obtain a uniform equiaxial crystal structure, and preparing for isothermal hot rolling;

(2) reversible isothermal hot rolling of the plate strip: carrying out reversible reciprocating rolling on the heated plate strip between the heatable curling furnaces on the two sides to obtain a thin plate with the thickness of less than 2.0 mm;

(3) liquid nitrogen spraying and cooling control: opening a liquid nitrogen cooling control device, cooling the thin plate strip with the thickness to minus 196 to minus 100 ℃ through the liquid nitrogen cooling control device at a cooling speed of 70-100 ℃/s, and then sending the thin plate strip into a crimping device with heat preservation and cold insulation functions;

(4) reversible low-temperature cold rolling of the plate strip: and (3) carrying out small-deformation reversible rolling on the magnesium alloy plate by using a liquid nitrogen controlled cooling device and a bilateral cold insulation curling device to finally obtain the ultrathin strip with the thickness of less than 0.5 mm.

(5) Low-temperature aging: and (4) the plate after the liquid nitrogen controlled cold rolling enters a coiling machine with heat preservation and cold insulation functions for low-temperature aging, and the rolling is finished.

The grain size of the high-strength magnesium alloy is 50% -79% finer than that of the intermediate plate grain size, and the high-strength magnesium alloy is uniform and fine isometric crystal.

Experiments prove that the magnesium alloy sheets with different thicknesses have different optimal cooling rates, and the cold rolling temperature can be controlled by adjusting the temperature of the liquid nitrogen cooling and controlling device. Wherein the thickness of the magnesium alloy plate is within the range that d is more than or equal to 0.3mm and less than 0.7mm, the final cooling temperature is minus 100 +/-10 ℃, and the cooling rate is 70-80 ℃/s; the thickness of the magnesium alloy plate is within the range that d is more than or equal to 0.7mm and less than 1.0mm, the final cooling temperature is minus 150 +/-10 ℃, and the cooling rate is 80-90 ℃/s; the thickness of the magnesium alloy plate is within the range that d is more than or equal to 1.0mm and less than 1.2mm, the final cooling temperature is the liquid nitrogen temperature of-196 ℃ under normal pressure, and the cooling rate is 90-100 ℃/s. In the above method, the cooling rate is calculated as an average value of the temperature decrease amounts of the sample per unit time.

According to the process method provided by the invention, the coiling machine and the heat-preservation and cold-preservation coiling device are symmetrically arranged on two sides of the rolling mill, equipment does not need to be replaced after multi-pass reversible hot rolling is carried out, and liquid nitrogen cold rolling can be continuously carried out by opening the liquid nitrogen cold control device until a high-strength fine-grain magnesium alloy ultrathin plate with the required thickness is obtained, so that the working efficiency is greatly improved.

The liquid nitrogen is used as a cooling medium, so that the cooling speed is high, the length of a cooling area can be effectively shortened, the temperature gradient in the thickness direction of the plate is weakened, and the cooling is more uniform. In addition, a large amount of dislocation is accumulated in the magnesium alloy plate in the multi-pass isothermal rolling process, liquid nitrogen is sprayed for cooling for many times in the cold rolling process, the rolling deformation and chilling action are repeatedly born, and great stress is accumulated on the surface and the inside of the plate, so that the critical stress of dynamic recrystallization is reduced, and the crystal grains are more easily subjected to dynamic recrystallization.

When the magnesium alloy intermediate plate obtained after multi-pass rolling is subjected to heat preservation within the recrystallization temperature range of 250-300 ℃, the crystal grains are subjected to dynamic recovery and dynamic recrystallization, and uniform equiaxial crystal grains are formed. During low-temperature cold rolling, by controlling the cooling rate and the final cold rolling temperature, large stress is accumulated on the surface and inside of the plate, so that the critical stress of dynamic recrystallization is reduced, the dynamic recrystallization is easier to occur, and the uniform and consistent tissue of the plate is ensured. After rolling, the plate keeps a low-temperature state in a plate rolling machine, so that the growth of crystal grains is inhibited, and the size of the crystal grains is reduced.

The invention has the beneficial effects that: on the premise of not changing the chemical components of the magnesium alloy plate, the comprehensive mechanical property and the toughness of the plate are obviously improved by controlling the cooling and ultralow temperature rolling methods, the plate surface of the plate is flat, the comprehensive property is good, and the low-cost, high-efficiency and pollution-free production of the magnesium alloy plate can be realized.

Drawings

FIG. 1 is a production process diagram of warm rolling-ultra low temperature cold rolling of magnesium alloy of the present invention;

FIG. 2 is a schematic view of the microstructure of the original structure of AZ31 magnesium alloy plate strip with the thickness of 6 mm;

FIG. 3 is a schematic view showing a microstructure of a 6mm thick AZ31 magnesium alloy sheet obtained by a conventional back and forth rolling process at 0.5 mm;

FIG. 4 is a schematic diagram of a microstructure of AZ31 magnesium alloy with a thickness of 6mm when the alloy is subjected to liquid nitrogen controlled cooling controlled rolling to 0.5 mm;

in the figure: 1. the coiler furnace can be heated; 2. a guide roller; 3. a crimping device; 4. a liquid nitrogen controlled cooling device; 5. a four high finishing mill; 6. magnesium alloy plate strip.

Detailed Description

The present invention will be further illustrated by the following examples, but the present invention is not limited to the following examples

The embodiment of the invention is based on the process mentioned in the invention and aims at the warm rolling-ultra-low temperature control cold rolling of three magnesium alloy plates with different specifications.