Coating protection method for high-aluminum-equivalent titanium alloy hot-rolled plate blank

Abstract

The invention provides a coating protection method for a high-aluminum-equivalent titanium alloy hot-rolled slab, and relates to the technical field of laser additive manufacturing, the coating protection method comprises the following steps: S1, chamfering the slab; s2, pure titanium powder is deposited on the upper surface of the plate blank through laser melting; s3, pure titanium powder is subjected to laser melting and deposited on the lower surface of the plate blank, and the plate blank with the pure titanium protective layers deposited on the upper surface and the lower surface is obtained; s4, the plate blank is subjected to one-fire cogging rolling, straightening and air cooling coping; and S5, the plate blank is subjected to secondary heating rolling and is straightened, and the plate is obtained. Pure titanium protection layers with good metallurgical bonding are deposited on the planes and the inclined planes of the upper surface and the lower surface of the plate blank, meanwhile, due to the characteristics of rapid heating and rapid cooling in laser additive manufacturing, crystal grains often cannot grow in time when melt is solidified, the pure titanium protection layers can be net basket structures with extremely small crystal grains, high plasticity is achieved, and the service life of the plate blank is prolonged. Therefore, a good protection effect is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of laser additive manufacturing, and specifically relates to a coating protection method for a high aluminum equivalent titanium alloy hot-rolled slab. Background Art

[0002] Titanium has a very strong affinity for oxygen. When titanium alloys are heated at high temperatures, severe oxygen diffusion will form a hard and brittle α layer on the surface of the titanium alloy billet. The presence of the α layer reduces the maximum strain that the titanium alloy surface can withstand before deformation and cracking, and is prone to cracking during the subsequent rolling process; especially high aluminum equivalent titanium alloys such as TA15, Ti60, TC11 and TC6, the surface of the plate often cracks severely during the hot rolling process, which not only reduces the yield rate, but also poses uncontrollable risks to the quality of the plate. Therefore, the surface of the slab needs to be properly protected before heating.

[0003] At present, there are usually two surface protection schemes for high aluminum equivalent titanium alloy hot-rolled slabs. One is to spray / brush BN, Al2O3+SiO2 and other inorganic antioxidant coatings on the slab surface; the other is to explosively composite high-plasticity TA1 or TA2 pure titanium layers on the upper and lower surfaces of the slab.

[0004] There are still certain technical bottlenecks in the application of inorganic antioxidant coatings in slab protection. First, the protective effect of antioxidant coatings is limited. After heating, there is still a hard and brittle α layer of several millimeters on the surface of the slab, which will still cause the alloy plate under the coating to crack during the subsequent rolling process; in addition, the bonding force between the existing inorganic antioxidant coating and the titanium alloy substrate is limited at room temperature, and it is easy to fall off locally during overhead crane lifting or roller transmission; when the slab is opened and heated in a walking beam or walking bottom heating furnace, there is a large friction between the moving mechanism and the slab surface, which often leads to local shedding of the coating. The two make the protective effect of the slab surface uneven, and the plate will eventually crack locally. Furthermore, the coating will form a secondary film during the heating process, which will greatly improve the adhesion between the coating and the slab surface. As rolling progresses, the coating will be partially broken and partially embedded in the surface of the plate, which will increase the loss of subsequent milling or water grinding tools, extend the processing cycle, and cause waste of resources.

[0005] Explosive composite pure titanium layer can make the surface of the slab have good protection effect during hot rolling, but the effective protection area is limited, and the processing method is not friendly to the environment and resources; on the one hand, in order to facilitate the biting of the rolling mill, it is usually necessary to chamfer the upper surface of the thick titanium alloy slab along the length direction (the chamfer bevel angle is 15~25°), and explosive composite cannot make the chamfer bevel composite with a pure titanium layer. There is stress concentration at the upper edge of the bevel, and it has a large degree of deformation freedom. Therefore, during the rolling process of the plate, cracks will first crack on the bevel of the uncompounded pure titanium and gradually expand in the horizontal and vertical directions. Subsequent cutting, surface milling and water grinding will cause high raw material loss and resource waste; on the other hand, the explosives used in explosive composite are dangerous goods strictly controlled by the state. The site is outdoors and is greatly affected by the weather, making it difficult to achieve continuous and automated production; the solid waste, harmful gases and shock waves generated during the explosion will cause great damage to the surrounding environment, so Western countries have expressly banned the use of this process. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a coating protection method for high aluminum equivalent titanium alloy hot-rolled slabs. Through laser melting deposition technology and a unique scanning strategy, a 0.8-1.5 mm thick pure titanium protective layer is deposited on the upper surface plane, chamfered bevel and lower surface plane of the titanium alloy hot-rolled thick slab.

[0007] The microstructure of the pure titanium protective layer is an extremely fine basketweave structure with good plasticity and good metallurgical bonding with the slab surface. It can inhibit the diffusion of oxygen and the formation of hard and brittle α layer in the titanium alloy slab during heating, reduce the degree of surface cracking during the plate rolling process, and avoid local uneven cracking on the plate surface, thereby improving the plate quality and material utilization.

[0008] The technical solution adopted by the present invention is: A coating protection method for a high aluminum equivalent titanium alloy hot-rolled slab, comprising the following steps: Step S1. Chamfering both sides of one surface of the slab, then transporting the slab with the chamfered side facing upward to an effective working area in a laser melting deposition chamber, and then evacuating the chamber; Step S2. laser melting and depositing pure titanium powder on the upper surface of the slab under a protective atmosphere; Step S3. The slab is transported out of the chamber and the upper and lower surfaces are turned over, and then the lower surface of the slab is turned upward and transported to the effective working area in the laser melting deposition chamber, and then vacuumed, and pure titanium powder is laser melted and deposited on the lower surface of the slab under a protective atmosphere to obtain a slab with pure titanium protective layers deposited on both the upper and lower surfaces; Step S4. The slab processed in step S3 is placed in a heating furnace for heating, then rolled in one heat, and then straightened, air-cooled and ground; Step S5. Place the product processed in step S4 in a heating furnace for heating, then perform secondary rolling, and then perform straightening to obtain a plate.

[0009] Preferably, in the coating protection method for high aluminum equivalent titanium alloy hot-rolled slab, in step S1, the slab thickness is 150-500 mm, the chamfered slab has a chamfer height of 10-15 mm, a chamfer length of 25-35 mm, and an inclination angle of 15-25°.

[0010] Preferably, in the coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent, the process of laser melting and depositing pure titanium powder on the upper surface of the slab in step S2 specifically comprises the following steps: Step S21. Perform laser scanning on the two upper edges of the chamfered bevel; Step S22. Determine the planar position scanning strategy of the two chamfered surfaces and the upper surface of the slab; Step S23. Depositing the first to third layers of pure titanium layers on the two chamfered surfaces on the upper surface of the slab according to the scanning strategy; then depositing the first to second layers of pure titanium layers on the plane position on the upper surface of the slab according to the scanning strategy.

[0011] Preferably, in the coating protection method for high aluminum equivalent titanium alloy hot-rolled slab, the specific conditions of the laser scanning in step S21 are: the laser power is 600~1000W, and the scanning rate is 240~480mm / min.

[0012] Preferably, in the coating protection method for the hot-rolled titanium alloy slab with high aluminum equivalent, the scanning strategy of the two chamfered inclined surfaces of the slab in step S22 is specifically as follows: taking the projection surface facing the inclined surface as the coordinate, the first deposition layer of the inclined surface is deposited from Y positive to Y negative, and overlapped from X negative to X positive, the second deposition layer is deposited from X negative to X positive, and overlapped from Y negative to Y positive, and the third deposition layer is deposited from X positive to X negative, and overlapped from Y negative to Y positive.

[0013] Preferably, in the coating protection method for high aluminum equivalent titanium alloy hot-rolled slab, the planar position scanning strategy of the upper surface in step S22 is specifically: performing serpentine reciprocating scanning at the planar position of the upper surface of the slab.

[0014] Preferably, in the coating protection method for high aluminum equivalent titanium alloy hot-rolled slab, the specific conditions for depositing the pure titanium layer in step S22 are: laser power of 1000~1400W, scanning rate of 300~600mm / min, powder feeding amount of 2.4~5.4g / min, overlap rate of 25~35%, and single layer lifting amount of 0.3~0.6mm.

[0015] Preferably, in the coating protection method for high aluminum equivalent titanium alloy hot-rolled slab, in step S22, the powder feeding amount of the inclined first deposition layer is 1.1 to 1.3 times that of the second deposition layer and the third deposition layer, and the powder feeding amount and powder feeding gas flow rate of the inclined second deposition layer and the third deposition layer are the same as those of the flat first deposition layer and the second deposition layer.

[0016] Preferably, in the coating protection method for high aluminum equivalent titanium alloy hot-rolled slab, in step S1 and step S3, the slab is transported to the effective working area in the laser melting deposition chamber by a powered roller, the roller spacing of the powered roller is 400~450mm, and the material transfer speed is 500~2000mm / min.

[0017] Preferably, in the coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent, the process of laser melting and depositing pure titanium powder on the lower surface of the slab in step S3 specifically comprises the following steps: Step S31. Determine the plane position scanning strategy of the lower surface of the slab; Step S32: Depositing a first layer of pure titanium to a second layer of pure titanium at the planar position of the lower surface of the slab according to the scanning strategy; The specific scanning strategy of the plane position of the lower surface in step S32 is: performing serpentine reciprocating scanning on the plane position of the lower surface of the slab.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The coating protection method of the high aluminum equivalent titanium alloy hot-rolled slab of the present invention is based on the large design and forming freedom of laser additive manufacturing, and can achieve the deposition of a pure titanium protective layer on the chamfered inclined surface and the flat surface of the upper and lower surfaces of the slab. At the same time, the thickness of the deposited pure titanium layer can also be flexibly adjusted according to the thickness of the different slabs and the type of slabs (forged slabs or EB furnace cast ingots), so as to achieve comprehensive protection of the upper and lower surfaces of the slab.

[0019] (2) In the coating protection method of the high aluminum equivalent titanium alloy hot-rolled slab of the present invention, laser additive manufacturing has the characteristics of rapid heating and rapid cooling. When the melt solidifies, the grains often do not have time to grow. The pure titanium protective layer can be a basket structure with extremely fine grains and high plasticity, thereby ensuring a good protective effect.

[0020] (3) In the coating protection method for hot-rolled titanium alloy slabs with high aluminum equivalent of the present invention, laser scanning of the upper edge of the chamfered bevel surface can alleviate stress concentration at the edge and promote smooth transition of the pure titanium deposition layer between the plane and the bevel, which is beneficial to delaying deformation and cracking of the chamfered bevel surface; the first deposition layer of the bevel surface adopts a scanning strategy from Y positive to Y negative deposition, which can realize that the subsequent deposition molten pool replenishes the melt for the first deposition molten pool under the combined action of gravity and laser beam; the higher powder feeding amount of the first deposition layer can offset the powder loss caused by the smooth bevel surface of the slab, thereby obtaining a pure titanium layer with high density, good metallurgical bonding and high flatness; the chamfered bevel surface has a smaller single-layer lifting amount than the flat surface, and a slightly thicker pure titanium protective layer is deposited, which can suppress the severe deformation and cracking of the chamfered bevel surface due to its large deformation freedom.

[0021] (4) The coating protection method for high aluminum equivalent titanium alloy hot-rolled slab of the present invention does not involve dangerous goods such as explosives, does not generate solid waste or harmful gases, has high material utilization rate, is environmentally and resource-friendly, and at the same time, the production process is not affected by the environment and climate, and can achieve continuous and automated production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the cladding protection device for the hot-rolled titanium alloy slab with high aluminum equivalent in Example 1.

[0023] Figure 2 Schematic diagram of chamfering of hot-rolled titanium alloy slab.

[0024] Figure 3 This is the metallographic phase diagram of the pure titanium protective layer in Example 2.

[0025] Figure 4 This is the appearance of the hot-rolled plate after the protective layer is deposited on the slab in Example 5.

[0026] Figure 5 This is the appearance of the hot-rolled plate of the slab without protective layer in Comparative Example 1.

[0027] Figure 6 This is the appearance of the coating-protected titanium alloy in Comparative Example 2 and the metallographic image from the surface to the core after the alloy is heated.

[0028] Figure 7 These are the appearance pictures of the coated protective titanium alloy plate in Comparative Example 3 before and after hot rolling.

[0029] Figure 8 This is the appearance of the coated titanium alloy hot-rolled plate in Comparative Example 3 during water grinding.

[0030] Fig. 9 This is the appearance of the hot-rolled plate after the slab in Comparative Example 4 is explosively composited with a pure titanium protective layer.

[0031] Fig.10This is the appearance of the hot-rolled plate during water grinding after the slab in Comparative Example 4 was explosively composited with a pure titanium protective layer. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific embodiments.

[0033] Example 1 like Figure 1 The coating protection device for hot-rolled slab of high aluminum equivalent titanium alloy includes a first powered roller 1 outside a sealed cabin, a sealed cabin 2, a second powered roller 3 inside a sealed cabin, a slab 4, pure titanium powder 5, a pure titanium deposition layer on a chamfered bevel 6, a laser beam 7, a powder delivery pipe 8, an out-of-cabin laser system 9, an out-of-cabin powder delivery system 10, and 11 is a deposition scanning strategy for the chamfered bevel.

[0034] A powered roller 1 is arranged outside the sealed cabin 2, a second powered roller 3 is arranged inside the sealed cabin 2, a slab 4 is arranged on the second powered roller 3, a powder delivery pipe 8 is arranged inside the sealed cabin 2, the powder delivery pipe 8 transports pure titanium powder 5 to the slab 4 for laser melting deposition through a laser beam 7, the laser beam 7 is connected to an outside laser system 9, the powder delivery pipe 8 is connected to an outside powder delivery system 10, and the two chamfered bevels on the upper surface of the slab 4 are deposited with the first to third layers of pure titanium layers, thereby forming a chamfered bevel pure titanium deposition layer 6 on the slab 4.

[0035] Example 2 A coating protection method for a high aluminum equivalent titanium alloy hot-rolled slab comprises the following steps: Step S1. Remove foreign matter such as oil and dust from the surface of a TC11 alloy slab with a size of 200mm×850mm×1300mm after six face milling and dry it at room temperature; hoist the slab onto the first powered roller table 1 with the chamfered bevel facing upward, open the hatch of the sealed cabin 2, transport the slab to the effective working area of ​​the cabin at a speed of 1000mm / min, close the hatch, and evacuate the slab to below 500ppm; After chamfering, the height of the bevel of the slab is 10~15mm, the length of the bevel is 25~35mm, and the inclination angle of the bevel is 15~25°; Figure 2 , 12 is the height of the chamfered surface, 13 is the length of the chamfered surface; Step S2. Select dry TA1 pure titanium powder with a particle size of 45-150 μm and an oxygen content of ≤1000 ppm, feed the pure titanium powder through a powder feeder, and laser melt and deposit the pure titanium powder on the upper surface of the slab under a protective atmosphere; Step S2: The process of laser melting and depositing pure titanium powder on the upper surface of the slab specifically includes the following steps: Step S21. The two upper edges of the chamfered bevel are laser scanned at a laser power of 800 W and a scanning speed of 300 mm / min. Step S22. Determine the planar position scanning strategy of the two chamfered surfaces and the upper surface of the slab; The scanning strategy of the two chamfered inclined surfaces of the slab is specifically as follows: with the projection surface facing the inclined surface as the coordinate, the first deposition layer of the inclined surface is deposited from Y positive to Y negative, and overlapped from X negative to X positive, the second deposition layer is deposited from X negative to X positive, and overlapped from Y negative to Y positive, and the third deposition layer is deposited from X positive to X negative, and overlapped from Y negative to Y positive; the scanning strategy of the plane position of the upper surface in step S22 is specifically as follows: a serpentine reciprocating scan is performed at the plane position of the upper surface of the slab; Step S23. The deposition of the first pure titanium layer on the chamfered bevel is completed with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 4.2 g / min, an overlap rate of 30%, a single layer lifting amount of 0.4 mm, a powder feeding gas flow rate of 6.5 L / min, and a scanning strategy of 11; the deposition of the second and third pure titanium layers on the chamfered bevel is completed with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 3.5 g / min, an overlap rate of 30%, a single layer lifting amount of 0.4 mm, a powder feeding gas flow rate of 6.5 L / min, and a scanning strategy of 11; Step S24. Repeat step S23 to complete the deposition of the first, second and third pure titanium layers on another chamfered surface; Step S25. The deposition of the first and second pure titanium layers on the plane was completed by a serpentine reciprocating scanning strategy with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 3.5 g / min, an overlap rate of 30%, a single layer lift of 0.5 mm, a powder feeding gas flow rate of 6.5 L / min, and a laser power of 1250 W. Step S3. The slab is transported out of the chamber at a speed of 1000 mm / min and the upper and lower surfaces are turned over. Then, the lower surface of the slab is turned upward with the chamfered surface for depositing the pure titanium layer facing downward, and the slab is placed stably on the powered roller 1. The slab is transported to the effective working area in the laser melting deposition chamber at a speed of 1000 mm / min and evacuated. Pure titanium powder is fed through a powder feeder, and the pure titanium powder is laser melted and deposited on the lower surface of the slab under a protective atmosphere to obtain a slab with pure titanium protective layers deposited on both the upper and lower surfaces.

[0036] In step S1 and step S3, the slab is transported to the effective working area in the laser melting deposition chamber by the power rollers, the roller spacing of the power rollers is 400 mm, and the material transfer speed is 1200 mm / min.

[0037] Step S3: The process of laser melting and depositing pure titanium powder on the lower surface of the slab specifically includes the following steps: Step S31. Determine the plane position scanning strategy of the lower surface of the slab; Step S32. According to the scanning strategy, the first layer to the second layer of pure titanium layer is deposited on the planar position of the lower surface of the slab; the laser power is 1250W, the scanning speed is 360mm / min, the powder feeding amount is 3.5g / min, the overlap rate is 30%, the single layer lifting amount is 0.5mm, and the powder feeding gas flow rate is 6.5L / min. The scanning strategy for the planar position of the lower surface in step S32 is specifically: serpentine reciprocating scanning is performed at the planar position of the lower surface of the slab.

[0038] Step S4. The slab is placed in a walking beam gas heating furnace, heated at 1050°C for 200 min, and rolled from 200 mm to 100 mm in one heat, and then straightened, air-cooled and ground; Step S5. Place the slab in a roller-type electric heating furnace, heat at 990° C. for 100 min, perform secondary rolling from 100 mm to 50 mm, and then straighten to obtain a plate.

[0039] Figure 3 This is a metallographic image of the chamfered surface of the deposited pure titanium layer after step S9 is completed. 14 is the TC11 slab, 15 is the heat-affected zone, and 16 is the pure titanium layer. It can be observed that the slab and the pure titanium layer are well metallurgically bonded. The thickness of the pure titanium layer is about 1.1-1.2 mm, and it is dense without obvious pores. Figure 3 From the right picture, it can be observed that the pure titanium layer is a fine basket structure composed of laths with a width of 1~3μm and a length of 5~15μm, which can ensure good plasticity of the slab surface during rolling.

[0040] Figure 4 For the plate that has been rolled in step S11, there is no obvious cracking in the plate area corresponding to the chamfered bevel of the slab, indicating that the technical solution has a good and comprehensive protective effect. Subsequent machining only needs to remove the pure titanium layer on the surface to meet the customer's size requirements.

[0041] Comparative Example 1 A method for hot rolling a high aluminum equivalent titanium alloy plate with no protection on the surface of a slab, comprising the following steps: Step S1: placing the TC11 alloy slab with a size of 180 mm × 850 mm × 1300 mm after milling in a walking-beam gas-fired heating furnace, heating at 1050° C. for 180 min, rolling the slab from 180 mm to 90 mm in one heat, and then straightening, air cooling and grinding; Step S2: placing the slab in a roller-type electric heating furnace, heating at 990°C for 90 minutes, rolling the slab from 90 mm to 50 mm in thickness, and then straightening the slab to obtain a plate.

[0042] Figure 5This is the appearance of the plate after rolling. The surface cracks are serious and the quality is uncontrollable. At the same time, subsequent surface treatment will also cause great material and energy loss, indicating that the slab needs to be properly protected before hot rolling of high aluminum equivalent titanium alloy plate.

[0043] Comparative Example 2 A coating protection method for a high aluminum equivalent titanium alloy, comprising the following steps: Step S1: Cut three 70 mm × 50 mm × 50 mm specimens from the TC11 ingot, and remove foreign matter such as oil, dust, etc. on the surface of the specimens; Step S2: Stir the imported Al2O3+SiO2 coating (orange-red), the domestic Al2O3+SiO2 coating (green) and the imported BN coating (white) respectively, and then preheat the test block in a 200°C heating furnace for 15 minutes, and then spray the coating evenly on each surface of the test block. After the coating is air-dried at room temperature, the thickness is controlled to be 450±30μm. Figure 4 The actual picture is shown from left to right; Step S3: Preheat the 1#, 2# and 3# samples in a 350°C heating furnace for 30 minutes, then transfer them to a 1050°C natural gas heating furnace for heating for 500 minutes and then air-cool them to obtain the 1#, 2# and 3# samples of the simulated coating-protected TC11 alloy that was blanked and rolled above the phase transformation point.

[0044] The surface coating of the sample prepared in Comparative Example 2 was removed, and the sample was cut along the center line to observe the microstructure of the surface layer of the sample. Figure 6 As shown in Figure 17, 18 and 19, there are obvious brittle α layers in the microstructures, with thicknesses of 3.8 mm, 4.1 mm and 4.7 mm, respectively. The α phase content in the α layer gradually decreases from the surface to the center of the sample. Figure 6 As shown in Figure 20, there are still obvious microcracks in the brittle α layer, which will become the crack source of subsequent plate rolling cracking, indicating that conventional inorganic coatings such as BN, Al2O3+SiO2 have limited antioxidant protection for hot-rolled slabs.

[0045] Comparative Example 3 A coating protection method for a high aluminum equivalent titanium alloy hot-rolled slab, comprising the following steps: Step S1: removing foreign matter such as oil, dust, etc. on the surface of a TC11 alloy slab having a size of 180 mm×850 mm×1300 mm after six face milling; Step S2: The imported BN coating (named 3#, white in color) in Comparative Example 1 was stirred evenly, and then the slab was placed in a 200°C heating furnace for preheating for 30 minutes, and then the coating was evenly sprayed on the 6 surfaces of the slab. After the coating was air-dried at room temperature, the thickness was controlled to be 450±30μm; Step S3: placing the slab in a walking-beam gas-fired heating furnace, heating at 1050° C. for 180 min, rolling the slab from 180 mm to 90 mm in one heat, and then straightening, air cooling and grinding; Step S4: the imported BN coating (named 3#, white in color) in Comparative Example 1 was stirred evenly, and then a slab was placed in a 200°C heating furnace for preheating for 30 minutes, and then the coating was evenly sprayed on the 6 surfaces of the slab. After the coating was air-dried at room temperature, the thickness was controlled to be 450±30μm; Step S5: placing the slab in a roller-type electric heating furnace, heating at 990° C. for 90 min, performing secondary rolling from 90 mm to 50 mm, and then straightening to obtain a plate.

[0046] like Figure 7 As shown in Figures 21, 22, and 23, the sprayed protective coating itself has poor bonding strength with the slab, and there is obvious local coating shedding during the transportation and flipping of the slab. The part where the protective coating of the plate falls off cracks significantly during subsequent rolling; Figure 8 As shown in Figure 24, the secondary film-formed coating is well bonded to the surface of the plate, and is partially broken and embedded in the plate during the rolling process. It is difficult to ensure the surface quality and dimensional accuracy of the plate in subsequent milling or water grinding processing. The loss of consumables such as tool heads increases by more than 50% compared to uncoated plates, and the processing cycle is extended by more than 80%.

[0047] Comparative Example 4 A method for hot rolling a high aluminum equivalent titanium alloy plate with an explosive composite pure titanium layer on the surface of a slab, comprising the following steps: Step S1: TC11 alloy slab (upper surface chamfered: chamfer length is 25 mm, chamfer height is 10 mm) with a size of 200 mm×850 mm×1300 mm after milling, and the upper plane and the lower plane are explosively composited with a 1.0 mm thick pure titanium layer; Step S2: placing the slab with the surface explosion-composite pure titanium layer in a walking-beam gas-fired heating furnace, heating at 1050° C. for 200 min, rolling the slab from 200 mm to 100 mm in one heat, and then straightening, air cooling and grinding; Step S3: placing the slab in a roller electric heating furnace, heating at 990°C for 100 min, rolling the slab from 10 mm to 50 mm in thickness through a second heat rolling process, and then straightening the slab to obtain a plate.

[0048] Fig. 9 Figure 2 is the plate after rolling. Figure 25 is the area corresponding to the explosively composited pure titanium layer of the slab. The surface is flat and no obvious cracks are seen. Figure 26 is the area corresponding to the non-explosive composited pure titanium layer of the slab chamfered bevel. The chamfered bevel of the slab has greater deformation freedom during the hot rolling process and is not composited with a pure titanium protective layer, so it cracks severely. Fig.10As shown in Figure 27, it is difficult to remove the large deep cracks in this area by subsequent water grinding. If edge trimming is performed, it will cause a material loss of no less than 6%. If the surface cracks are removed as a whole by milling or water grinding surface treatment, the quality and dimensional accuracy of the finished plate are difficult to guarantee, and the material, consumables and resource losses caused by surface treatment are also difficult to measure. This shows that the composite pure titanium layer of the slab has a good protective effect during the hot rolling process. At the same time, the chamfered edges of the thick slab also need to be protected.

[0049] Comparative Example 5 Figure 1 Schematic diagram of the coating protection device, first powered roller 1, sealed cabin 2, second powered roller 3 in the sealed cabin, slab 4, pure titanium powder 5, pure titanium deposition layer on chamfered bevel 6, laser beam 7, powder delivery pipe 8, extracabin laser system 9, extracabin powder delivery system 10. 11 is the deposition scanning strategy for the chamfered bevel.

[0050] A coating protection method for a high aluminum equivalent titanium alloy hot-rolled slab, comprising the following steps: Step S1: removing foreign matters such as oil, dust, etc. on the surface of the TC11 alloy slab with a size of 200 mm×850 mm×1300 mm after six face milling and drying at room temperature; Step S2: hoist the slab onto the first powered roller table 1 with the chamfered surface facing upward, open the hatch between the first powered roller table 1 and the sealed cabin 2, transport the slab to the effective working area of ​​the cabin at a speed of 1000 mm / min, close the hatch, and draw the vacuum to below 500 ppm; Step S3: Select dry TA1 pure titanium powder with a particle size of 45-150 μm and an oxygen content of ≤1000 ppm, and use a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 3.5 g / min, an overlap rate of 30%, a single layer lifting amount of 0.5 mm, a powder feeding gas flow rate of 6.5 L / min (Ar), and a serpentine reciprocating scanning strategy to complete the deposition of the first and second pure titanium layers on the plane; Step S4: Deposition of the first pure titanium layer on a chamfered surface is completed with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 4.2 g / min, an overlap rate of 30%, a single layer lift of 0.4 mm, a powder feeding gas flow rate of 6.5 L / min (Ar), and a scanning strategy of 11; Step S5: Deposition of the second to third pure titanium layers on a chamfered surface is completed with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 3.5 g / min, an overlap rate of 30%, a single layer lift of 0.4 mm, a powder feeding gas flow rate of 6.5 L / min (Ar), and a scanning strategy of 11; Step S6: repeating steps S4 to S5 to complete the deposition of the first to third pure titanium layers on another chamfered surface; Step S7: performing laser scanning on the pure titanium protective layer at the two upper edges of the chamfered bevel with a laser power of 800 W and a scanning speed of 300 mm / min; Step S8: the vacuum of the cabin is broken, the hatch between the first powered roller 1 and the sealed cabin 2 is opened, the slab is transported out of the cabin at a speed of 1000 mm / min, the slab is turned over, the chamfered surface on which the pure titanium layer is deposited faces downward and is stably placed on the first powered roller 1, the hatch between the first powered roller 1 and the sealed cabin 2 is opened, the slab is transported to the effective working area of ​​the cabin at a speed of 1000 mm / min, the hatch is closed, and the vacuum is pumped to below 500 ppm; Step S9: With a laser power of 1250W, a scanning speed of 360mm / min, a powder feeding amount of 3.5g / min, an overlap rate of 30%, a single layer lifting amount of 0.5mm, a powder feeding gas flow rate of 6.5L / min (Ar), and a serpentine reciprocating scanning strategy, the deposition of the first and second pure titanium layers on the plane is completed to obtain a slab with pure titanium protective layers deposited on the upper and lower surfaces.

[0051] Step S10: placing the slab in a walking-beam gas-fired heating furnace, heating at 1050° C. for 200 min, rolling the slab from 200 mm to 100 mm, straightening it, air cooling it, and grinding it; Step S11: placing the slab in a roller-type electric heating furnace, heating at 990° C. for 100 min, performing secondary rolling from 100 mm to 50 mm, and then straightening to obtain a plate.

[0052] If the two upper edges of the chamfered surface of the slab are not laser scanned, metallurgical defects and stress concentration will occur in the pure titanium protective layer at the edges of the plane and the slope of the upper surface of the slab. In the subsequent rolling process, the chamfers will still crack. The main reason is that laser additive manufacturing has the characteristics of rapid heating and rapid cooling. When the pure titanium protective layer is deposited near the edge of the upper surface plane, the limited melt width and depth prevent the molten pool from overflowing to the slope. When the pure titanium protective layer is subsequently deposited on the upper surface slope, the pure titanium protective layers at the edges cannot fuse with each other, thus forming metallurgical defects such as holes and unfused surfaces, which cannot be eliminated even if the pure titanium protective layer is subsequently laser scanned.

[0053] Comparative Example 6 A coating protection method for a high aluminum equivalent titanium alloy hot-rolled slab, comprising the following steps: Step S1: removing foreign matters such as oil, dust, etc. on the surface of the TC11 alloy slab with a size of 200 mm×850 mm×1300 mm after six face milling and drying at room temperature; Step S2: hoist the slab onto the first powered roller table 1 with the chamfered surface facing upward, open the hatch between the first powered roller table 1 and the sealed cabin 2, transport the slab to the effective working area of ​​the cabin at a speed of 1000 mm / min, close the hatch, and draw the vacuum to below 500 ppm; Step S3: performing an air scan on the two upper edges of the chamfered bevel surface with a laser power of 800 W and a scanning speed of 300 mm / min; Step S4: Select dry TA1 pure titanium powder with a particle size of 45-150 μm and an oxygen content of ≤1000 ppm, and complete the deposition of the first pure titanium layer on a certain chamfered bevel with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 4.2 g / min, an overlap rate of 30%, a single layer lifting amount of 0.4 mm, a powder feeding gas flow rate of 6.5 L / min (Ar), and a scanning strategy of 11; Step S5: Deposition of the second to third pure titanium layers on a chamfered surface is completed with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 3.5 g / min, an overlap rate of 30%, a single layer lift of 0.4 mm, a powder feeding gas flow rate of 6.5 L / min (Ar), and a scanning strategy of 11; Step S6: repeating steps S4 to S5 to complete the deposition of the first to third pure titanium layers on another chamfered surface; Step S7: with a laser power of 1250 W, a scanning speed of 360 mm / min, a powder feeding amount of 3.5 g / min, an overlap rate of 30%, a single layer lift of 0.5 mm, a powder feeding gas flow rate of 6.5 L / min (Ar), and a serpentine reciprocating scanning strategy, the deposition of the first and second pure titanium layers on the plane is completed; Step S8: performing laser scanning on the pure titanium protective layer at the two upper edges of the chamfered bevel with a laser power of 800 W and a scanning speed of 300 mm / min; Step S9: Break the vacuum in the chamber, open the hatch between the first powered roller conveyor 1 and the sealed chamber 2, and transport the slab out of the chamber at a speed of 1000 mm / min. Turn the slab over, place it on the powered roller conveyor 1 with the chamfered surface where the pure titanium layer is deposited facing downward, open the hatch between the powered roller conveyors 1 and 2, transport the slab to the effective working area of ​​the chamber at a speed of 1000 mm / min, close the hatch, and pump the vacuum to below 500 ppm; Step S10: With a laser power of 1250W, a scanning speed of 360mm / min, a powder feeding amount of 3.5g / min, an overlap rate of 30%, a single layer lifting amount of 0.5mm, a powder feeding gas flow rate of 6.5L / min (Ar), and a serpentine reciprocating scanning strategy, the deposition of the first and second pure titanium layers on the plane is completed to obtain a slab with pure titanium protective layers deposited on the upper and lower surfaces.

[0054] Step S11: placing the slab in a walking-beam gas-fired heating furnace, heating at 1050° C. for 200 min, rolling the slab from 200 mm to 100 mm, straightening it, air cooling it, and grinding it; Step S12: placing the slab in a roller-type electric heating furnace, heating at 990° C. for 100 min, performing secondary rolling from 100 mm to 50 mm, and then straightening to obtain a plate.

[0055] After the upper edge of the chamfered surface is air-scanned, a pure titanium protective layer is deposited on the upper surface bevel first, and then a pure titanium protective layer is deposited on the upper surface plane. Due to the lower roughness of the bevel and the gravity of the powder during the deposition of the pure titanium layer, the thickness of the pure titanium protective layer near the upper edge of the bevel is too small, resulting in limited protective effect during the subsequent rolling process, and the plate may still crack at the chamfered edge.

[0056] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A coating protection method for hot-rolled titanium alloy slabs with high aluminum equivalent, characterized in that: The following steps are involved: Step S1. Chamfering both sides of one surface of the slab, then transporting the slab with the chamfered side facing upward to an effective working area in a laser melting deposition chamber, and then evacuating the chamber; Step S2. laser melting and depositing pure titanium powder on the upper surface of the slab under a protective atmosphere; Step S3. The slab is transported out of the chamber and the upper and lower surfaces are turned over, and then the lower surface of the slab is turned upward and transported to the effective working area in the laser melting deposition chamber, and vacuumed, and pure titanium powder is laser melted and deposited on the lower surface of the slab under a protective atmosphere to obtain a slab with pure titanium protective layers deposited on both the upper and lower surfaces; Step S4. The slab processed in step S3 is placed in a heating furnace for heating, then rolled in one heat, and then straightened, air-cooled and ground; Step S5. Place the product processed in step S4 in a heating furnace for heating, then perform secondary rolling, and then perform straightening to obtain a plate.

2. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 1 is characterized in that: In step S1, the thickness of the slab is 150-500 mm, the height of the bevel of the slab after chamfering is 10-15 mm, the length of the bevel is 25-35 mm, and the inclination angle of the bevel is 15-25°.

3. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 1 is characterized in that: Step S2: The process of laser melting and depositing pure titanium powder on the upper surface of the slab specifically includes the following steps: Step S21. Perform laser scanning on the two upper edges of the chamfered bevel; Step S22. Determine the planar position scanning strategy of the two chamfered surfaces and the upper surface of the slab; Step S23. Depositing the first to third layers of pure titanium layers on the two chamfered surfaces on the upper surface of the slab according to the scanning strategy; then depositing the first to second layers of pure titanium layers on the plane position on the upper surface of the slab according to the scanning strategy.

4. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 3 is characterized in that: The specific conditions of the laser scanning in step S21 are: the laser power is 600-1000W, and the scanning rate is 240-480mm / min.

5. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 3 is characterized in that: The scanning strategy of the two chamfered inclined surfaces of the slab in step S22 is specifically as follows: taking the projection surface facing the inclined surface as the coordinate, the first deposition layer of the inclined surface is deposited from Y positive to Y negative, and overlapped from X negative to X positive, the second deposition layer is deposited from X negative to X positive, and overlapped from Y negative to Y positive, and the third deposition layer is deposited from X positive to X negative, and overlapped from Y negative to Y positive.

6. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 3 is characterized in that: The planar position scanning strategy of the upper surface in step S22 is specifically: performing serpentine reciprocating scanning on the planar position of the upper surface of the slab.

7. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 4 is characterized in that: The specific conditions for depositing the pure titanium layer in step S22 are: laser power of 1000-1400 W, scanning rate of 300-600 mm / min, powder feeding amount of 2.4-5.4 g / min, overlap rate of 25-35%, and single layer lifting amount of 0.3-0.6 mm.

8. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 3 is characterized in that: In step S22, the powder feeding amount of the first deposition layer on the inclined surface is 1.1 to 1.3 times that of the second deposition layer and the third deposition layer. The powder feeding amount and powder feeding gas flow rate of the second deposition layer and the third deposition layer on the inclined surface are the same as those of the first deposition layer and the second deposition layer on the plane.

9. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 1, characterized in that: In step S1 and step S3, the slab is transported to the effective working area in the laser melting deposition chamber by the power rollers, the roller spacing of the power rollers is 400-450 mm, and the material transfer speed is 500-2000 mm / min.

10. The coating protection method for hot-rolled titanium alloy slab with high aluminum equivalent according to claim 1, characterized in that: Step S3: The process of laser melting and depositing pure titanium powder on the lower surface of the slab specifically includes the following steps: Step S31. Determine the plane position scanning strategy of the lower surface of the slab; Step S32: Depositing a first layer of pure titanium to a second layer of pure titanium at the planar position of the lower surface of the slab according to the scanning strategy; The specific scanning strategy of the plane position of the lower surface in step S32 is: performing serpentine reciprocating scanning on the plane position of the lower surface of the slab.

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