An online waste heat quenching system for magnesium alloy extrusions

Abstract

The present invention discloses an online waste heat quenching system for magnesium alloy extrusions, belonging to the field of metal plastic processing auxiliary forming technology. The online waste heat quenching system includes a pre-compression processing device, a multi-stage cooling device, and a traction device; wherein the pre-compression processing device includes segmented rollers arranged in sequence along the extrusion direction of the extrusion material, which are divided into a heating roller, a temperature-maintaining roller, and a cooling roller. The temperature of the heating roller is 20-50°C higher than the temperature of the extrusion material, the temperature of the temperature-maintaining roller is the extrusion temperature of the extrusion material, and the temperature of the cooling roller is room temperature; the multi-stage cooling device is divided into two layers, the inner layer is a nozzle composed of a spiral tube body, and the outer layer is a shell for fixing; the nozzle and the shell are connected by welding, and the nozzle sprays two types of cooling media onto the surface of the extrusion material, and the temperature difference between the cooling media is 40-80°C; the extrusion material is pulled by the traction device, and a gas injection device is provided on one side of the extrusion material pulled out of the multi-stage cooling device.

Description

Technical Field

[0001] The invention relates to an online residual heat quenching system for magnesium alloy extrusion materials, which is used for increasing the quenching depth of extrusion materials and reducing quenching residual stress, and belongs to the technical field of metal plastic processing auxiliary forming. Background Art

[0002] After high-temperature plastic processing, the inherent temperature and stress of alloy materials will increase the activity of the internal structure of the alloy body, which means that the driving force for grain size growth or precipitation of strengthening phases is enhanced. For some alloys, this increase in internal activity may not have much impact. For example, some grades of aluminum alloys will undergo solution treatment in the later stage, so the need for cooling and precipitation control of strengthening phases is not very strong. However, for some types of aluminum alloys or magnesium alloys, if they are not quenched in time after deformation, the precipitation of strengthening phases or changes in structure will have a catastrophic impact on the alloy. For example, some aluminum alloys will have uneven structure due to dimensional issues if they are not cooled in time after hot working. If static recrystallization occurs due to thermal factors, the performance fluctuations caused by this uneven structure are extremely dangerous to the subsequent service of the alloy. In addition, for magnesium alloys, due to their low stacking fault energy, the degree of dislocation accumulation during deformation is extremely high. Dynamic recrystallization is its most important grain refinement mechanism. If it is not cooled in time, the grain boundary diffusion capacity under high temperature conditions is extremely large, and the resulting recrystallization growth or even abnormal growth will affect the subsequent service of the alloy. Therefore, timely cooling of the extruded material after hot extrusion deformation plays an extremely important role in improving the stability of the material's organizational properties.

[0003] Although online residual heat quenching has many advantages, its disadvantages are also obvious. The most important of these is the substantial increase in quenching stress caused by excessively fast cooling, which ultimately leads to processing deformation and even cracking. Therefore, matching the process device with a suitable cooling rate is a key issue that needs to be urgently addressed. Patent document CN104073608A proposes an online residual heat quenching device, which includes a guide with a spraying function placed in front of the extruder outlet. The guide is composed of an air jet guide and a water spray guide in sequence, or an air jet guide, a spray guide and a water spray guide in sequence. This invention application, while ensuring the aging strengthening effect, weakens the quenching residual stress of the extruded profile, avoids core cracking, reduces the difficulty of pre-stretching, and achieves shape and dimensional stability of the final product. Patent document CN105714049A discloses an online waste heat quenching device, including a guide with a spraying function placed in front of the extruder outlet, which is composed of an air jet guide, a water spray guide and a low-temperature cold water spray guide in sequence, or is composed of an air jet guide, a spray guide, a water spray guide and a low-temperature cold water spray guide in sequence. The above two invention patents are essentially the same. Mai Hongjie once published an article in aluminum processing, introducing the online precision quenching technology and device for extruded aluminum profiles, which is the technical prototype of the above two invention applications. Patent document CN201605294U introduces an improved structure of a spray-type extruded profile water quenching cooling device, which divides the cooling tank into an aerosol zone, a spray zone and a water column cooling zone, and sets an atomizing nozzle and a spray nozzle to form a mist spray under the action of high-pressure water and compressed air. Combined with the cooling of the spray and water column, the heat exchange is good, the profile is evenly cooled, the cooling effect is good, and the purpose of the heat treatment process is achieved.

[0004] Analysis shows that the technical principles of the quenching devices described in the above literature are similar, and all can achieve the effect of online quenching. By combining multiple devices, the cooling intensity can be changed to achieve quenching. Existing equipment has many advantages, but the biggest difference is that the cooling medium is mostly in liquid or gaseous form. After contact with the extruded material, the cooling intensity is poorly controllable. Therefore, further improvement or development of new quenching devices is needed. Summary of the Invention

[0005] The purpose of the present invention is to provide an online residual heat quenching system for magnesium alloy extrusions, which can more effectively improve the cooling intensity, regulate the stress state of the extrusions, and thus coordinately regulate the quenching effect.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An online waste heat quenching system for magnesium alloy extrusions comprises a pre-compression treatment device, a multi-stage cooling device and a traction device; wherein,

[0008] The pre-compression treatment device includes segmented rollers arranged in sequence along the extrusion direction of the extruded material, which are divided into heating rollers, isothermal rollers and cooling rollers. The temperature of the heating rollers is 20-50°C higher than the temperature of the extruded material, the temperature of the isothermal rollers is the extrusion temperature of the extruded material, and the temperature of the cooling rollers is room temperature.

[0009] The multi-stage cooling device is divided into two layers: the inner layer is a nozzle composed of a spiral tube body, and the outer layer is a fixed shell. The inner nozzle and the outer shell are connected by welding. The nozzle can spray two types of cooling media, and the temperature difference between the two types of cooling media is 40 to 80 degrees Celsius.

[0010] The extruded material output from the multi-stage cooling device is pulled by a pulling device. A gas injection device is provided on one side of the pulled extruded material to inject gas onto the surface of the extruded material to remove the cooling medium.

[0011] Preferably, the number of rollers in each section along the extrusion direction is odd, and the number of rollers in the cross-sectional direction is even; the linear length of each section of rollers in contact with the extruded material is greater than or equal to 50% of the circumference of the cross-sectional area of the extruded material, thereby achieving symmetrical stress elimination.

[0012] Preferably, the ratio of the distance between the heating roller and the isothermal roller to the distance between the isothermal roller and the cooling roller is 1:2 to 1:3. Adjustment of this distance ratio is dependent on the initial extrusion temperature. When the extrusion temperature is above 450°C, the ratio is 1:2; when the extrusion temperature is below 350°C, the ratio is 1:3; and within the temperature range of 350°C to 450°C, the ratio is adjustable within the set range. The distance ratio is primarily designed to balance stress release and deformation, and the choice of different distance ratios is primarily based on temperature.

[0013] Preferably, the stress applied by each roller section to the extruded material mainly corresponds to the yield stress of the material. Specifically, the stress applied by the heating roller is 10-15% of the compressive yield strength of the extruded material under the extrusion temperature conditions, the stress applied by the isothermal roller is 5-10% of the compressive yield strength of the extruded material under the extrusion temperature conditions, and the stress applied by the cooling roller is 0-5% of the compressive yield strength of the extruded material under the extrusion temperature conditions.

[0014] Preferably, the nozzle is a seamless steel tube with a diameter of 25 mm. A plurality of holes with a diameter of 1.5 mm are provided on the surface facing the extruded material. The distance between two adjacent holes along the extrusion direction is 5 mm. The cooling medium is gas or liquid. The multiple holes can be sprayed simultaneously or in a combined manner. The combined spraying method mainly refers to the simultaneous spraying of gas and liquid cooling media.

[0015] The advantages of the present invention are:

[0016] 1. Using segmented rollers to preload the extruded material can not only achieve stress balance on the surface of the extruded material, but also take into account the straightening effect, minimize the fluidity defects of the extruded material caused by uneven initial temperature, and avoid edge waves or bending problems.

[0017] 2. The temperature gradient of the segmented roller can make up for certain extrusion process defects during the preloading process. At the same time, the use of the roller can more directly correct the stress after extrusion.

[0018] 3. The multi-stage cooling device used is an integrated quenching device. In addition to the advantages of other quenching devices, its spiral structure allows the cooling medium to pass through the quenching device from beginning to end, so that the cooling intensity can be gradient and continuous, and the cooling effect can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the positional relationship between the roller and the extruded material along the extrusion direction in the pre-compression processing device.

[0020] Figure 2 Schematic diagram of the positional relationship between the roller and the cross-sectional direction of the extruded material in the pre-compression processing device.

[0021] Figure 3 It is a schematic diagram of the longitudinal section (along the extrusion direction) of the multi-stage cooling device.

[0022] Figure 4 Schematic diagram of the cross section of a multi-stage cooling device.

[0023] Figure 5 This is a schematic diagram of a single-sided gas injection device provided on the side of the traction device. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments, but these are not intended to limit the scope of protection of the present invention.

[0025] The online residual heat quenching system of the present invention is mainly used for quenching treatment of magnesium alloy extrusion materials, and comprises a pre-compression treatment device, a multi-stage cooling device and a traction device.

[0026] like Figure 1 、 2As shown, the pre-compression treatment device includes segmented rollers arranged sequentially along the extrusion direction of the extruded material. These rollers are divided into a heating roller 1, a temperature-maintaining roller 2, and a cooling roller 3. The temperature of the heating roller 1 is 20-50°C higher than that of the extruded material, the temperature of the temperature-maintaining roller 2 is the extrusion temperature of the extruded material, and the temperature of the cooling roller 3 is room temperature. Each segment of rollers has an odd number of rollers along the extrusion direction (i.e., 2n+1), while the number of rollers along the cross-sectional direction is an even number. The linear length of each roller segment in contact with the extruded material is greater than or equal to 50% of the circumference of the extruded material's cross section.

[0027] like Figure 1 As shown, the distance between the last heating roller and the first isothermal roller is L1, and the distance between the last isothermal roller and the first cooling roller is L2. The ratio L1:L2 is considered to be the ratio of the distance between the heating roller and the isothermal roller to the distance between the isothermal roller and the cooling roller. This distance ratio is preferably controlled within a range of 1:2 to 1:3. The adjustment requirement of this distance ratio is related to the initial extrusion temperature. When the extrusion material temperature is higher than 450°C, the distance ratio is 1:2. When the extrusion material temperature is lower than 350°C, the distance ratio is 1:3. When the extrusion material temperature is between 350°C and 450°C, the distance ratio is adjusted within the set range.

[0028] The stress applied by each roller section to the extruded material is as follows: the stress applied by the heating roller is 10-15% of the compressive yield strength of the extruded material under the extrusion temperature conditions; the stress applied by the isothermal roller is 5-10% of the compressive yield strength of the extruded material under the extrusion temperature conditions; the stress applied by the cooling roller is 0-5% of the compressive yield strength of the extruded material under the extrusion temperature conditions.

[0029] like Figure 3 、 4 As shown, the multi-stage cooling device consists of two layers: an inner layer comprising a nozzle 5 formed from a spiral seamless steel tube 6, and an outer layer comprising a fixed housing 4. The inner nozzle and the outer housing are welded together and can spray either gas or liquid cooling media, with a temperature difference between the two media of 40°C to 80°C. The nozzle is a 25mm diameter seamless steel tube with multiple 1.5mm diameter holes on the surface facing the extruded material. The distance between adjacent holes along the extrusion direction is 5mm.

[0030] like Figure 5 As shown, the extruded material output from the multi-stage cooling device is pulled by a pulling device 10, and a gas injection device is provided on one side of the pulled extruded material. The gas injection device injects gas to one side of the extruded material through a gas nozzle 9 provided on a gas pipe 8. Air can be selected as the gas, and the temperature is room temperature.

[0031] The process of treating magnesium alloy extrusions using the in-line residual heat quenching system of the present invention involves pre-compressing the cross-sectionally symmetrical extruded profile using rollers as it continues to be extruded. After being preloaded by the segmented rollers, the extruded profile undergoes cooling and quenching in an integrated quenching device, and then continues under traction by a traction machine until extrusion is complete.

[0032] In the following examples, the conventional quenching method used for comparison is direct water cooling.

[0033] Example 1

[0034] A homogenized Mg-8Gd-4Y-1Zn-0.5Zr (wt.%) magnesium alloy was extruded at 460°C into a rod-shaped extrusion with a radius of 5 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 16 cm length. The heating rollers were set at 485°C and applied a stress of 29 MPa; the isothermal rollers were set at 460°C and applied a stress of 15 MPa; and the cooling rollers were set at room temperature (25°C) and applied a stress of 10 MPa. The distance between the last heating roller and the first isothermal roller was 0.5 m, and the distance between the last isothermal roller and the first cooling roller was 1 m.

[0035] The pre-compression extrudates are fed into a multi-stage cooling system, where they are first cooled by a gas jet using argon at 75°C, followed by a liquid jet using water at 25°C. After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas jet using room-temperature air. The resulting Mg-8Gd-4Y-1Zn-0.5Zr extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 10% and residual stress is reduced by 28%.

[0036] Example 2

[0037] A homogenized Mg-5Zn-1Mn (wt.%) magnesium alloy was extruded at 350°C into a rod-shaped extrusion with a radius of 7 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 23 cm length. The heating rollers were set at 380°C and applied a stress of 21 MPa; the isothermal rollers were set at 350°C and applied a stress of 10 MPa; and the cooling rollers were set at room temperature (25°C) and applied a stress of 5 MPa. The distance between the last heating roller and the first isothermal roller was 0.5 m, and the distance between the last isothermal roller and the first cooling roller was 1.4 m.

[0038] The pre-compression extrudates are fed into a multi-stage cooling system, where they are first cooled by a gas jet using argon at 70°C, followed by a liquid jet using water at 20°C. After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas jet using room-temperature air. The resulting Mg-5Zn-1Mn extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 15% and residual stress is reduced by 22%.

[0039] Example 3

[0040] A homogenized Mg-7Gd-5Y-1Nd-1Zn-0.5Zr (wt.%) magnesium alloy was extruded at 480°C into a rod-shaped extrusion with a radius of 6.5 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 22 cm length. The heating rollers were heated to 505°C and applied a stress of 32 MPa; the isothermal rollers were heated to 480°C and applied a stress of 24 MPa; and the cooling rollers were heated to room temperature (24°C) and applied a stress of 10 MPa. The distance between the last heating roller and the first isothermal roller was 0.6 m, and the distance between the last isothermal roller and the first cooling roller was 1.2 m.

[0041] The pre-compression extrudates are fed into a multi-stage cooling system, where they are first cooled by a gas injection process using argon at 80°C. This is followed by a simultaneous gas and liquid injection process using water as the liquid and air as the gas at 20°C. After the multi-stage cooling process, the extrudates are then pulled by a traction device while undergoing a single-sided gas injection process using air at room temperature. The resulting Mg-7Gd-5Y-1Nd-1Zn-0.5Zr extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 13% and residual stress is reduced by 16%.

[0042] Example 4

[0043] At 340°C, a homogenized Mg-2Mn-2Zn (wt.%) magnesium alloy was extruded into a rod-shaped extrusion with a radius of 5.5 cm. The extrusion was first preloaded by a segmented roller system, with each roller contacting the extrusion for an 18 cm line length. The heating rollers were set at 362°C and applied a stress of 35 MPa; the isothermal rollers at 340°C and applied a stress of 23 MPa; and the cooling rollers at room temperature (25°C) and applied a stress of 9 MPa. The distance between the last heating roller and the first isothermal roller was 0.6 m, and the distance between the last isothermal roller and the first cooling roller was 1.8 m.

[0044] The pre-compression extrudates are fed into a multi-stage cooling system, where liquid cooling is performed using water at 75°C. This is followed by simultaneous gas and liquid cooling using water and air at 23°C. After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas injection of room-temperature air. The resulting Mg-2Mn-2Zn extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 11% and residual stress is reduced by 17%.

[0045] Example 5

[0046] A homogenized Mg-9Y-1MM-1Zn-0.6Zr (wt.%) magnesium alloy was extruded at 510°C into a rod-shaped extrusion with a radius of 5 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 17 cm length. The heating rollers were set at 540°C and applied a stress of 38 MPa; the isothermal rollers were set at 510°C and applied a stress of 25 MPa; and the cooling rollers were set at room temperature (25°C) and applied a stress of 10 MPa. The distance between the last heating roller and the first isothermal roller was 0.5 m, and the distance between the last isothermal roller and the first cooling roller was 1 m.

[0047] The pre-compression extrudates are fed into a multi-stage cooling system, where they are first cooled by a gas jet using argon at 85°C, followed by a liquid jet using water at 15°C. After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas jet using air at room temperature. The resulting Mg-9Y-1MM-1Zn-0.6Zr extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 9% and residual stress is reduced by 14%.

[0048] Example 6

[0049] A homogenized Mg-7Gd-5Y-1Nd-0.5Zr (wt.%) magnesium alloy was extruded at 520°C into a rod-shaped extrusion with a radius of 6 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 20 cm length. The heating rollers were set at 550°C and applied a stress of 42 MPa; the isothermal rollers at 520°C and applied a stress of 27 MPa; and the cooling rollers at room temperature (25°C) and applied a stress of 11 MPa. The distance between the last heating roller and the first isothermal roller was 0.4 m, and the distance between the last isothermal roller and the first cooling roller was 0.8 m.

[0050] The pre-compression extrudates are fed into a multi-stage cooling system, where liquid cooling spraying (water at 85°C) is performed. This is followed by simultaneous gas and liquid cooling spraying (water at 25°C). After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas spraying (room temperature air). The resulting Mg-7Gd-5Y-1Nd-0.5Zr extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 11% and residual stress is reduced by 19%.

[0051] Example 7

[0052] A homogenized Mg-3Zn-1Ca-0.5Sr (wt.%) magnesium alloy was extruded at 380°C into a rod-shaped extrusion with a radius of 3 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 10 cm length. The heating rollers were set at 410°C and applied a stress of 25 MPa; the isothermal rollers were set at 380°C and applied a stress of 17 MPa; and the cooling rollers were set at room temperature (25°C) and applied a stress of 8 MPa. The distance between the last heating roller and the first isothermal roller was 0.8 m, and the distance between the last isothermal roller and the first cooling roller was 2 m.

[0053] The pre-compression extrudates are fed into a multi-stage cooling system, where they are first subjected to a gas cooling spray using argon at 78°C, followed by a liquid cooling spray using water at 28°C. After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas injection using air at room temperature. The resulting Mg-3Zn-1Ca-0.5Sr extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 22% and residual stress is reduced by 43%.

[0054] Example 8

[0055] A homogenized Mg-6Zn-3Sn-1Cu (wt.%) magnesium alloy was extruded at 380°C into a rod-shaped extrusion with a radius of 4 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 14 cm length. The heating rollers were set at 405°C and applied a stress of 32 MPa; the isothermal rollers were set at 380°C and applied a stress of 25 MPa; and the cooling rollers were set at room temperature (25°C) and applied a stress of 11 MPa. The distance between the last heating roller and the first isothermal roller was 1 m, and the distance between the last isothermal roller and the first cooling roller was 2.8 m.

[0056] The pre-compression extrudates are fed into a multi-stage cooling system, where liquid cooling is performed using water at 83°C. This is followed by simultaneous gas and liquid cooling using water and air at 23°C. After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas injection of room-temperature air. The resulting Mg-6Zn-3Sn-1Cu extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 18% and residual stress is reduced by 33%.

[0057] Example 9

[0058] At 515°C, a homogenized Mg-10Gd-8Y-2Si-1Zn (wt.%) magnesium alloy was extruded into a rod-shaped extrusion with a radius of 2.5 cm. The extrusion was first preloaded by a segmented roller system, with each roller contacting the extrusion for a 9 cm length. The heating rollers were set at 540°C and applied a stress of 34 MPa; the isothermal rollers at 515°C and applied a stress of 22 MPa; and the cooling rollers at room temperature (23°C) and applied a stress of 10 MPa. The distance between the last heating roller and the first isothermal roller was 0.5 m, and the distance between the last isothermal roller and the first cooling roller was 1 m.

[0059] The pre-compression extrudates are fed into a multi-stage cooling system, where they are first subjected to a gas cooling spray using argon at 80°C, followed by a liquid cooling spray using water at 25°C. After the multi-stage cooling system, the extrudates are pulled by a traction device while simultaneously receiving a single-sided gas spray using air at room temperature. The resulting Mg-10Gd-8Y-2Si-1Zn extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 8% and residual stress is reduced by 18%.

[0060] Example 10

[0061] A homogenized Mg-7Y-1Nd-0.5Zr (wt.%) magnesium alloy was extruded at 480°C into a rod-shaped extrusion with a radius of 6.5 cm. The extrusion was preloaded by passing it through a series of segmented rollers, with each roller contacting the extrusion for a 22 cm length. The heating rollers were set at 505°C and applied a stress of 24 MPa; the isothermal rollers were set at 480°C and applied a stress of 16 MPa; and the cooling rollers were set at room temperature (20°C) and applied a stress of 7 MPa. The distance between the last heating roller and the first isothermal roller was 0.6 m, and the distance between the last isothermal roller and the first cooling roller was 1.2 m.

[0062] The pre-compression extrudates are fed into a multi-stage cooling system, where they are first cooled by a gas injection process using argon at 78°C. This is followed by a simultaneous gas and liquid injection process using water as the liquid and air at 22°C as the gas. After the multi-stage cooling process, the extrudates are then pulled by a traction device while undergoing a single-sided gas injection process using air at room temperature. The resulting Mg-7Y-1Nd-0.5Zr extrudates avoid bending and exhibit significant cooling efficiency. Compared to conventional quenching methods, cooling intensity is increased by 9% and residual stress is reduced by 11%.

Claims

1. An online waste heat quenching system for magnesium alloy extrusions, characterized in that: It includes a pre-compression processing device, a multi-stage cooling device and a traction device; wherein, The pre-compression treatment device is equipped with segmented rollers arranged in sequence along the extrusion direction of the extruded material. These rollers are divided into heating rollers, isothermal rollers, and cooling rollers. The temperature of the heating rollers is 20-50°C higher than the temperature of the extruded material. The temperature of the isothermal rollers is the extrusion temperature of the extruded material, and the temperature of the cooling rollers is room temperature. The stress applied by the heating rollers is 10-15% of the compressive yield strength of the extruded material at the extrusion temperature. The stress applied by the isothermal rollers is 5-10% of the compressive yield strength of the extruded material at the extrusion temperature. The stress applied by the cooling rollers is 0-5% of the compressive yield strength of the extruded material at the extrusion temperature. The multi-stage cooling device is divided into two layers: the inner layer is a nozzle composed of a spiral tube body, and the outer layer is a shell. The inner nozzle and the outer shell are connected by welding. The nozzle sprays two types of cooling media onto the surface of the extruded material. The temperature difference between the two types of cooling media is 40~80℃. The extruded material output from the multi-stage cooling device is pulled by a pulling device, and a gas injection device is provided on one side of the pulled extruded material.

2. The online residual heat quenching system for magnesium alloy extrusions according to claim 1, characterized in that: The number of rollers in each section along the extrusion direction is an odd number, and the number of rollers in the cross-sectional direction is an even number.

3. The online residual heat quenching system for magnesium alloy extrusions according to claim 1 or 2, characterized in that: The linear length of each roller contact with the extruded material is greater than or equal to 50% of the circumference of the cross section of the extruded material.

4. The online residual heat quenching system for magnesium alloy extrusions according to claim 1 or 2, characterized in that: The ratio of the distance between the heating roller and the isothermal roller to the distance between the isothermal roller and the cooling roller is 1:2~1:

3.

5. The online residual heat quenching system for magnesium alloy extrusions according to claim 4, characterized in that: When the extrusion material temperature is higher than 450°C, the distance ratio is 1:2; when the extrusion material temperature is lower than 350°C, the distance ratio is 1:3; when the extrusion material temperature is in the temperature range of 350~450°C, the distance ratio is adjusted within the set range.

6. The online residual heat quenching system for magnesium alloy extrusions according to claim 1 or 2, characterized in that: The nozzle is a seamless steel pipe with a diameter of 25 mm, and is provided with a plurality of holes with a diameter of 1.5 mm on the surface facing the extruded material.

7. The online residual heat quenching system for magnesium alloy extrusions according to claim 6, characterized in that: The distance between two adjacent holes along the extrusion direction is 5 mm.

8. The online residual heat quenching system for magnesium alloy extrusions according to claim 1 or 2, characterized in that: The cooling medium in the nozzle is gas or liquid, and multiple holes spray simultaneously or in a combined manner.

9. The online residual heat quenching system for magnesium alloy extrusions according to claim 1 or 2, characterized in that: The extruded material is a profile with symmetrical cross section.

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