Method for rapidly improving surface organization structure and roughness of cast aluminum alloy part

Abstract

The invention provides a method for rapidly improving the surface organization structure and roughness of a cast aluminum alloy part, and relates to the technical field of laser beam machining. The method comprises the following steps that the cast aluminum alloy part is fixed to a carrying platform capable of conducting multi-axis movement; continuous laser beams are adopted for scanning the initial surface layer of the cast aluminum alloy part, and the laser power and the scanning speed are controlled to enable the adjacent molten pools to be continuously overlapped to form a uniform molten layer; when the thickness of the uniform melting layer reaches a first preset thickness required by surface structure reconstruction, laser scanning is stopped; the uniform melting layer is self-cooled and solidified in a room temperature environment to form a solidified surface layer; wherein the solidified surface layer forms a submicron equiaxed crystal structure, and the roughness of the solidified surface layer is smaller than that of the initial surface layer. According to the method, by accurately controlling the overlapping and cooling rate of the molten pool, the submicron equiaxed crystal structure is directly generated under the room-temperature self-solidification condition, and the purpose of rapidly modifying the surface layer of the cast aluminum alloy part is achieved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of laser beam processing, in particular to a method for rapidly improving the surface structure and roughness of a cast aluminum alloy part. BACKGROUND

[0002] Cast aluminum alloys are widely used in the fields of aerospace, automobile manufacturing and high-end decoration, and the surface quality of the cast aluminum alloy directly determines the fatigue strength, corrosion resistance and assembly precision of the part. Currently, shot blasting technology is generally used to improve the surface performance, but this technology has the following defects: Severe work hardening: high-speed impact of the shot causes lattice distortion in the surface layer, resulting in a residual stress concentration area and accelerating stress corrosion cracking; Surface integrity is damaged: the concave and convex formed after shot blasting deteriorate the surface roughness, and subsequent polishing is required, increasing the processing cost; In order to overcome the above problems, the prior art adopts secondary processing such as surface heat treatment or mechanical polishing, but this will prolong the processing cycle. Especially for precision castings such as turbocharger housings and engine manifolds containing curved surfaces / angles, it is difficult to quickly and uniformly modify the full surface by using the traditional method. SUMMARY

[0003] In view of the above defects or deficiencies in the prior art, the application aims to provide a method for rapidly improving the surface structure and roughness of a cast aluminum alloy part, comprising the following steps: Fixing the cast aluminum alloy part on a multi-axis movable object platform; Scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam, and controlling the laser power and scanning speed to make adjacent molten pools continuously overlap to form a uniform molten layer; Stopping the laser scanning when the thickness of the uniform molten layer reaches a first preset thickness required for surface structure reconstruction; The uniform molten layer is self-cooled and solidified at room temperature to form a solidified surface layer; wherein the solidified surface layer forms a sub-micron equiaxed crystal structure, and the roughness of the solidified surface layer is less than that of the initial surface layer.

[0004] According to the technical solution provided by the application, the spot shape of the continuous laser beam is single ring, double ring or a combination of ring and circle; Before scanning the initial surface layer of the cast aluminum alloy part with the continuous laser beam, the following steps are further included: Retrieving the three-dimensional topographic data of the initial surface layer of the cast aluminum alloy part to obtain the distribution of the angle region, curved surface region and plane region in the initial surface layer; The scanning of the initial surface layer of the cast aluminum alloy part by the continuous laser beam comprises the following steps: According to the area distribution of the initial surface layer, the corresponding spot shape is matched for scanning, wherein the included angle area is matched with the double ring shape, the curved surface area is matched with the composite shape, and the plane area is matched with the single ring shape.

[0005] According to the technical scheme provided in the present application, during the process of scanning the initial surface layer of the cast aluminum alloy part by the continuous laser beam, the pose of the cast aluminum alloy part is adjusted by controlling the multi-axis movement of the object platform, so that the continuous laser beam is perpendicular to the surface in the included angle area and / or the curved surface area.

[0006] According to the technical scheme provided in the present application, before the scanning of the initial surface layer of the cast aluminum alloy part by the continuous laser beam, the following steps are further included: Obtaining the initial surface roughness of the initial surface layer; Retrieving and traversing a process database to obtain initial laser parameters corresponding to the initial surface roughness, the process database including multiple processing modes, surface roughness intervals corresponding to each processing mode, and processing parameters corresponding to each processing mode, the processing parameters including power intervals, scanning speeds, and melting depth requirements; the initial laser parameters are the processing parameters corresponding to the processing mode corresponding to the surface roughness interval into which the initial surface roughness falls; The scanning of the initial surface layer of the cast aluminum alloy part by the continuous laser beam comprises the following steps: Based on the power interval and the scanning speed in the initial laser parameters, the continuous laser beam is started to scan the initial surface layer of the cast aluminum alloy part.

[0007] According to the technical scheme provided in the present application, the laser power and the scanning speed are controlled to make adjacent molten pools continuously overlap to form a uniform molten layer, comprising the following steps: Real-time monitoring of the molten pool width and the solidification front state; Dynamically adjusting the laser power and / or the scanning speed to simultaneously maintain: the ratio of the line spacing to the molten pool width is maintained in a critical interval that induces the nucleation of dendritic fragments, and the adjacent molten pool overlap rate is greater than or equal to a first preset threshold value, the critical interval needs to satisfy that the melt in front of the next molten pool penetrates the solidification microzone of the previous molten pool, and induces the dendritic fragments as heterogeneous nucleation points; the line spacing is the center distance of adjacent laser scanning paths; Repeat the above steps until the thickness of the uniform molten layer reaches the first preset thickness, the first preset thickness being the melting depth requirement in the initial laser parameters.

[0008] According to the technical scheme provided in the application, the method further comprises judging whether the thickness of the uniform molten layer reaches a first preset thickness; The step of judging whether the thickness of the uniform molten layer reaches a first preset thickness comprises the following steps: If the thickness of each detected unit of the uniform molten layer reaches the first preset thickness, it is determined that the thickness of the uniform molten layer reaches the first preset thickness; all the detected units constitute the entire uniform molten layer.

[0009] According to the technical scheme provided in the application, the method further comprises the following steps: During the laser scanning process, the theoretical penetration depth of each detected unit is calculated in real time according to the laser power, the scanning speed and material characteristics; the material characteristics are the material thermal diffusivity of the cast aluminum alloy part; The displacement amount of each axis of the object platform and the rotation angle are obtained, and the theoretical penetration depth is converted into a vertical penetration depth in a part coordinate system through a coordinate transformation matrix; the vertical penetration depth is the thickness of the detected unit.

[0010] According to the technical scheme provided in the application, the detected unit is set by the following method: During the laser scanning process, a continuous scanning path segment with constant laser power and scanning speed is defined as one detected unit; Wherein, the length of the detected unit is dynamically adjusted according to the machining path, and the lengths of adjacent detected units are allowed to be unequal.

[0011] According to the technical scheme provided in the application, the theoretical penetration depth of the detected unit is calculated through a penetration depth calculation model, and the penetration depth calculation model represents the relationship between the theoretical penetration depth and the laser power, the scanning speed, the material thermal diffusivity and the heat input coefficient; After the step of calculating the theoretical penetration depth of each detected unit in real time according to the laser power, the scanning speed and material characteristics during the laser scanning process, the method further comprises the following steps: The verification information of the detected unit is retrieved, and the verification information is the acoustic emission signal of the detected unit in the laser scanning process collected in real time through an acoustic emission sensor; The characteristic value of the acoustic emission signal in the frequency band of 20-200 kHz is extracted, and the characteristic value includes the main frequency peak value, the signal energy integral value and the kurtosis coefficient; According to the characteristic value, the measured penetration depth deviation rate of the detected unit is obtained; If the measured penetration deviation rate is less than or equal to a second preset threshold, a theoretical penetration of a next detected unit is calculated using the penetration calculation model.

[0012] According to the technical scheme provided in the application, after the measured penetration deviation rate of the detected unit is obtained according to the characteristic value, the following steps are further included: If the absolute value of the measured penetration deviation rate is greater than the second preset threshold, the heat input coefficient is corrected based on the measured penetration deviation rate to obtain a corrected penetration calculation model. The theoretical penetration of a next detected unit is calculated using the corrected penetration calculation model.

[0013] Compared with the prior art, the application has the beneficial effects that: the application directly generates sub-micron equiaxed crystal organization (0.2-2 microns) under the room temperature self-solidification condition by accurately controlling the molten pool overlap and the cooling rate, which is more than 10 times finer than the micron broken grain (5-10 microns) after the shot blasting treatment, and significantly improves the fatigue resistance; at the same time, the surface roughness is reduced by the melting layer flow spreading effect, and the typical roughness can be reduced by 3-4 levels, so that the subsequent polishing process is omitted, the purpose of rapid modification is achieved, and the composition of the cast aluminum alloy is not changed. In addition, the application also has high-speed processing capability, which accelerates the progress of surface modification from another dimension: the multi-axis platform cooperates with laser scanning to realize full coverage of complex curved surfaces, the single-piece processing time is shortened, the self-adaptive penetration control and real-time verification system avoids manual parameter adjustment, the qualified rate is improved, the object platform is rotated in real time to ensure that the laser is always perpendicular to the incident in the included angle / curved surface area, and the uniform processing problem of dead angles such as deep cavities and narrow grooves is solved, a uniform equiaxed crystal layer is formed on the whole surface, the edge effect and thermal affected zone gradient of the traditional process are eliminated, and the surface layer structure of the part is rapidly improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The step flow chart of the method for rapidly improving the surface organization structure and roughness of the cast aluminum alloy part provided in the application. DETAILED DESCRIPTION

[0015] The application will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0016] It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other without conflict. The application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0017] Embodiment 1 As mentioned in the background, in view of the problems in the prior art, the present application proposes a method for quickly improving the surface structure and roughness of cast aluminum alloy parts, as shown in Figure 1 The method comprises the following steps: S1, fixing the cast aluminum alloy part on a multi-axis movable object platform; specifically, the cast aluminum alloy part (such as a hub, an engine shell) is fixed on a six-degree-of-freedom object platform through a customized clamp, and the platform needs to have X / Y / Z translation and rotation functions (±180°) around three axes.

[0018] S2, scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam, and controlling the laser power and scanning speed to make adjacent molten pools continuously overlap to form a uniform molten layer; Further, in the process of scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam, the pose of the cast aluminum alloy part is adjusted by controlling the multi-axis movement of the object platform, so that the continuous laser beam is perpendicular to the surface in the included angle region and / or the curved surface region.

[0019] Further, before the step of scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam, the following steps are further included: Obtaining the initial surface roughness of the initial surface layer; Accessing and traversing a process database to obtain initial laser parameters corresponding to the initial surface roughness, the process database including a plurality of processing modes, a surface roughness interval corresponding to each processing mode, and processing parameters corresponding to each processing mode, the processing parameters including a power interval, a scanning speed, and a melting depth requirement; the initial laser parameters are the processing parameters corresponding to the processing mode corresponding to the surface roughness interval in which the initial surface roughness falls; The step of scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam comprises the following steps: Based on the power interval and the scanning speed in the initial laser parameters, the continuous laser beam is started to scan the initial surface layer of the cast aluminum alloy part.

[0020] Specifically, considering the surface state classification, the initial roughness (Ra) directly reflects the depth of surface defects (such as pores and cracks), and a higher Ra value requires a deeper molten layer for reconstruction. According to the Ra value, the laser power and scanning speed are dynamically allocated to ensure that the molten depth accurately covers the defect layer. Therefore, the initial surface roughness is first obtained by using a white light interferometer or a laser profilometer: 5x5 grid points are selected on the surface of the part, avoiding the edge 10mm, each point is measured 3 times to take the average value, and the final Ra value is the average value of all grid points. The process database is shown in Table 1 as follows: Table 1

[0021] Furthermore, controlling the laser power and scanning speed so that adjacent molten pools continuously overlap to form a uniform molten layer comprises the following steps: Real-time monitoring of the molten pool width and solidification front state; specifically, the solidification front state is the solid-liquid coexistence zone at the edge of the molten pool, characterized by a temperature gradient (>100 K / mm) and dendrite growth morphology (cellular / columnar). The position and morphology of the semi-solid zone are identified by a two-color infrared thermometer. Temperature signal processing: the temperature distribution from the solidus line (Ts=577℃) to the liquidus line (Tl=660℃) is extracted, and the formula is used to calculate the temperature distribution of the semi-solid zone. Calculate the transverse temperature gradient of the molten pool dT / dx, where W represents the width of the molten pool and T 凝固前沿 represents the liquidus-solidus boundary temperature, T pool center represents the maximum temperature at the center of the pool, and the solidification front is determined by the lateral temperature gradient dT / dx across the pool. A dT / dx range (K / mm) greater than 150 indicates a planar interface, 50-150 indicates cellular dendrites, and <50 indicates coarse columnar dendrites. The pool width is monitored using a high-speed CMOS camera.

[0022] Dynamically adjusting the laser power and / or the scanning speed to simultaneously maintain: a ratio of line spacing to the molten pool width maintained within a critical interval for inducing dendrite fragment nucleation, and an overlap rate of adjacent molten pools greater than or equal to a first preset threshold, wherein the critical interval requires that the melt at the leading edge of the subsequent molten pool penetrates the solidification microregion of the previous molten pool, inducing dendrite fragments as heterogeneous nucleation points; and the line spacing is the center distance between adjacent laser scanning paths; Repeat the above steps until the thickness of the uniform molten layer reaches the first preset thickness, where the first preset thickness is the penetration depth requirement in the initial laser parameters.

[0023] Specifically, the adjacent molten pool overlap rate is calculated by the molten pool width and the line spacing, which is generally maintained in the range of 0.3-0.8 mm, which can cooperate with the line spacing to ensure the overlap rate between the molten pools; for example, in the scanning process, W=0.65 mm is detected, the line spacing D=0.15 mm, and the overlap rate η=(0.65-0.15) / 0.65=76.9% is calculated; then the molten pool transverse temperature gradient is obtained by temperature field acquisition to determine the dendrite morphology, and the laser power and / or scanning speed are adjusted in real time to achieve three goals: goal 1: maintain the overlap rate η≥0.6 (first preset threshold); goal 2: control the line spacing ratio D / W=0.4-0.6 (critical interval); goal 3: ensure that the solidification front is cellular dendrite (dT / dx=50-150 K / mm). For example: when η<0.6, the scanning speed is reduced by 10% or the power is increased by 5%, the molten pool width W is increased, and the coverage continuity is improved. When D / W>0.6, the line spacing D is reduced to 0.8W, the scanning spacing is shortened, and the post-molten pool penetration depth is increased. When the columnar dendrite (dT / dx<50), the power is controlled to increase by 5% + the scanning speed is controlled to decrease by 5% to increase the heat input to change the temperature gradient and suppress the growth of columnar crystals, etc.

[0024] Specifically, the present embodiment controls the thermal-mechanical coupling of adjacent molten pools: the high-temperature melt (1600-1800℃) of the post-molten pool impacts the semi-solid zone (solid phase rate 40-60%) of the pre-molten pool, mechanically breaks the un-solidified dendrite network, and generates micron-sized crystal fragments as nucleation cores, so that the melt can trigger equiaxed crystal nucleation at 5-8K below the equilibrium solidification point, realizing microstructure refinement.

[0025] S3, when the thickness of the uniform molten layer reaches a first preset thickness required for surface structure reconstruction, stopping laser scanning; S4, the uniform molten layer is self-cooled and solidified in a room temperature environment to form a solidified surface layer; wherein the solidified surface layer forms a sub-micron equiaxed crystal structure, and the roughness of the solidified surface layer is less than the roughness of the initial surface layer.

[0026] Specifically, the technical principle of the method is explained as follows: surface reconstruction is realized by laser ultrafast melting-ultra-high cooling rate solidification, and the physical mechanism includes three key processes: molten layer flow leveling effect: high-power laser (0.8-6 kW) melts the micron-sized protrusions on the surface into liquid metal, which flows to the pit area under the action of surface tension, directly fills the surface defects (such as pores, shrinkage), and reduces the original roughness. Non-equilibrium solidification mechanism: the molten layer is cooled by forced air cooling (nitrogen flow rate 20-50 L / min) in a room temperature environment to realize >10 4K / s ultra-high cooling rate, inhibits the dendrite growth of aluminum matrix, promotes uniform nucleation, forms sub-micron equiaxed crystal (0.2-2 pm). Precise control of heat affected zone: by limiting the thickness of the molten layer to 50-300 pm (i.e. the first preset thickness), it is ensured that the heat will not be excessively conducted to the matrix, avoiding the degradation of the matrix structure performance.

[0027] The following describes the method steps: Step 1, part fixing: surface pretreatment: ultrasonic cleaning of parts with acetone for 5 minutes to remove oil stains and oxide layer, and blow-drying with compressed air to ensure that the surface is free of residues. Clamping and positioning: place the part on a six-axis load platform (such as KUKA KR60HA robot integrated numerical control turntable), and fix it with a vacuum chuck to prevent displacement during machining.

[0028] Step 2, laser scanning: initial parameter setting: measure the initial surface roughness (e.g. white light interferometer measures Ra=6.176 pm). Access the process database and match the "mode C" corresponding to the roughness interval >5.0 pm: laser power: 5.0 kW (range 4.0-6.0 kW), scanning speed: 1.2 m / s (range 0.5-1.5 m / s), target melt depth: 250 pm (range 200-300 pm, i.e. the first preset thickness); molten pool dynamic regulation: real-time monitoring: molten pool width: capture molten pool image through 2000 fps high-speed CMOS camera, edge detection algorithm calculates width W; solidification front: dual-color infrared thermometer monitors temperature gradient, identifies semi-solid zone (solidus-liquidus interval). Dynamic adjustment rule: calculate overlap rate through the following formula: η = (W - D) / W (D is the line spacing, preset 0.15 mm), if η <0.6 (i.e. risk of discontinuous molten pool), reduce scanning speed by 10% (e.g. 1.2 m / s→1.08 m / s) or increase power by 5% (5.0 kW→5.25 kW). Maintain dendrite fragment nucleation conditions: strictly control the line spacing ratio D / W between 0.4-0.6, based on the principle that the rear molten pool invades the front molten pool solidification microzone >20 pm, mechanically peels off dendrite fragments (size 1-5 pm), and the fragments promote fine crystals as heterogeneous nucleation points. Scanning execution: galvanometer performs Zigzag path scanning with 0.15 mm line spacing (covers an area of ≥300 mm×300 mm), laser spot shape defaults single annular (flat area), power density distribution is uniform.

[0029] Step 3: molten layer thickness determination: termination condition: you can choose to monitor the molten pool depth in real time with an infrared thermal imager, turn off the laser when the target melt depth of 250 pm is reached, or control by melt time, or by the following method.

[0030] Step 4: room temperature self-cooling: immediately after the laser is stopped, open the annular nitrogen nozzle (50 mm from the surface), airflow speed 30 m / s, cooling rate > 1.2 x 10 4 K / s. The liquid metal jumps over the dendrite growth zone at ultra-high cooling rate and forms equiaxed grains directly. The grain boundaries are complete and there is no segregation of precipitates (verified by SEM-EDS, taking A356 cast aluminum alloy as an example, the composition is still composed of two phases of α-Al and Si).

[0031] In a preferred embodiment, the spot shape of the continuous laser beam is single ring, double ring or a combination of ring and circle; Before the step of scanning the initial surface layer of the cast aluminum alloy part by using the continuous laser beam, the method further comprises the following steps: Accessing the three-dimensional topography data of the initial surface layer of the cast aluminum alloy part to obtain the distribution of the angle region, curved surface region and plane region in the initial surface layer; Specifically, point cloud data is obtained by a laser scanner, and the angle region, curved surface region and plane region are obtained by curvature analysis. A plane region is determined as a region with a curvature radius greater than 1000 mm, a curved surface region is determined as a region with a curvature radius between 50-1000 mm, and an angle region is determined as a region with an angle between two planes less than 90 degrees.

[0032] The step of scanning the initial surface layer of the cast aluminum alloy part by using the continuous laser beam comprises the following steps: According to the regional distribution of the initial surface layer, the corresponding spot shape is matched for scanning, wherein the angle region is matched with the double ring, the curved surface region is matched with the composite shape, and the plane region is matched with the single ring.

[0033] Specifically, in the plane region, the single ring is matched, and the energy distribution of the single ring is high at the edge and weak at the center. In the plane region, the single ring spot is used to avoid overheating at the center and to uniform the penetration depth. In the angle region, the double ring is matched, and the energy distribution of the double ring is a double-peak energy distribution. In the plane region, the single ring spot is used to offset heat accumulation and prevent overheating at the angle. In the curved surface region, the composite shape is matched, and the energy distribution of the composite shape is adjustable (for example, 70% ring + 30% circle). In the curved surface region, the composite shape is used to adapt to the curvature change and maintain the stability of the molten pool, for example: high curvature area (R < 30 mm): convex surface is easy to dissipate heat, high energy is needed to maintain the penetration depth → ring: circle = 70%:30%; medium curvature area (30 mm ≤ R < 80 mm): balance heat input → ring: circle = 80%:20%; low curvature area (R ≥ 80 mm): approximately plane, weak edge effect → ring: circle = 90%:10%.

[0034] Specifically, the following is another embodiment of the above-mentioned embodiment for judging the depth of the molten pool in real time by using an infrared thermal imager. The above-mentioned embodiment is obtained by direct measurement, and the present embodiment is obtained by calculation. Different adaptive monitoring methods can be used in different scenarios.

[0035] In a preferred embodiment, the method further comprises judging whether the thickness of the uniform molten layer reaches a first preset thickness. The step of judging whether the thickness of the uniform molten layer reaches a first preset thickness comprises the following steps: If the thickness of each detected unit of the uniform molten layer reaches the first preset thickness, it is determined that the thickness of the uniform molten layer reaches the first preset thickness. All the detected units constitute the entire uniform molten layer.

[0036] Further, the method further comprises the following steps: During the laser scanning process, the theoretical penetration depth of each detected unit is calculated in real time according to the laser power, the scanning speed, and the material properties. The material properties are the material thermal diffusivity of the cast aluminum alloy part. The displacement of each axis of the object platform and the rotation angle are obtained, and the theoretical penetration depth is converted into a vertical penetration depth in the part coordinate system through a coordinate transformation matrix. The vertical penetration depth is the thickness of the detected unit.

[0037] Further, the detected unit is set by the following method: During the laser scanning process, a continuous scanning path segment with constant laser power and scanning speed is defined as a detected unit. Wherein, the length of the detected unit is dynamically adjusted according to the processing path, and the lengths of adjacent detected units are allowed to be unequal.

[0038] In a preferred embodiment, the theoretical penetration depth of the detected unit is calculated by a penetration depth calculation model. The penetration depth calculation model represents the relationship between the theoretical penetration depth and the laser power, the scanning speed, the material thermal diffusivity, and the heat input coefficient. After the step of calculating the theoretical penetration depth of each detected unit in real time according to the laser power, the scanning speed, and the material properties during the laser scanning process, the method further comprises the following steps: The verification information of the detected unit is retrieved. The verification information is the acoustic emission signal collected by an acoustic emission sensor in real time during the laser scanning process of the detected unit. Specifically, the sensor arrangement for acoustic emission signal collection is a piezoelectric ceramic sensor (frequency response 20-400 kHz) installed on the object platform clamp.

[0039] extracting characteristic values of the acoustic emission signal in a 20-200 kHz frequency band, the characteristic values including a main frequency peak value, a signal energy integral value, and a kurtosis coefficient; obtaining a measured penetration deviation rate of the detected unit according to the characteristic values; if the measured penetration deviation rate is less than or equal to a second preset threshold value, continuing to use the penetration calculation model to calculate a theoretical penetration of a next detected unit.

[0040] Specifically, the penetration calculation model is: wherein, represents a theoretical penetration, represents a comprehensive correction coefficient, , represents an initial heat input coefficient (default 0.85), ξ (R) represents a curvature compensation coefficient, convex ξ (R) = 1.2-0.2e -0.05R , concave ξ (R) = 0.8+0.2e -0.05R ; P represents laser power, v represents scanning speed, T m represents melting point, T0 represents room temperature, represents material thermal diffusion coefficient, t represents laser residence time.

[0041] Specifically, according to the characteristic values, the measured penetration deviation rate is obtained by the following formula: ; wherein, f1 represents the main frequency peak value, E 1 represents the signal energy integral value, K 1 represents the kurtosis coefficient, 128 kHz represents a main frequency reference value, which is a characteristic frequency of molten pool oscillation, and is related to molten pool size and surface tension, 105 is an energy integral reference value, which is the total energy of the acoustic emission signal, and reflects the intensity of molten pool dynamic behavior, 3.2 is a kurtosis reference value, which is the sharpness of the signal pulse, and reflects the burstiness of dendrite fragmentation, and under ideal penetration, dendrite fragmentation is uniform, and the kurtosis is stable at 3.2.

[0042] Further, after the step of obtaining the measured penetration deviation rate of the detected unit according to the characteristic values, the method further comprises the following steps: if the absolute value of the measured penetration deviation rate is greater than the second preset threshold value, correcting the heat input coefficient based on the measured penetration deviation rate to obtain a corrected penetration calculation model; using the corrected penetration calculation model to calculate a theoretical penetration of a next detected unit.

[0043] Specifically, the first preset threshold can be selected as 5%, and when the measured penetration deviation rate is less than or equal to 5%, it indicates that the penetration calculation model is reliable, and the model is continued to be used to calculate the theoretical penetration. When the measured penetration deviation rate is greater than 5%, it indicates that the penetration calculation model is unreliable, and the heat input coefficient is reduced to compensate for over-melting. When the measured penetration deviation rate is less than -5%, it indicates that the penetration calculation model is unreliable, and the heat input coefficient is increased to compensate for under-melting.

[0044] The embodiment is used in a scene where the thickness of the molten pool is limited and monitored by an infrared thermal imager, for example, for a high-reflective surface, a scene where optical shielding cannot be measured, the penetration is monitored by the acoustic emission feature penetration inversion model, and the surface refinement goal is achieved.

[0045] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method and core idea of the present application. The above description is only the preferred implementation manner of the present application, and it should be pointed out that, due to the limitation of the expression, there are infinite specific structures, and for ordinary skilled persons in the technical field, some improvements, decorations or changes can be made without departing from the principles of the present application, and the above technical features can be combined in an appropriate manner; the improvements, decorations, changes or combinations, or the direct application of the inventive concept and technical solution to other occasions without improvement, should be regarded as the protection scope of the present application.

Claims

1. A method for rapidly improving the surface structure and roughness of cast aluminum alloy parts, characterized in that: The following steps are involved: Fix the cast aluminum alloy parts on a multi-axis movable loading platform; Scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam, and controlling the laser power and scanning speed so that adjacent molten pools continuously overlap to form a uniform molten layer; When the thickness of the uniform melt layer reaches a first preset thickness required for surface tissue reconstruction, stopping laser scanning; The uniform molten layer is self-cooled and solidified in a room temperature environment to form a solidified surface layer; wherein the solidified surface layer forms a submicron equiaxed crystal structure, and the roughness of the solidified surface layer is less than the roughness of the initial surface layer.

2. The method for rapidly improving the surface structure and roughness of cast aluminum alloy parts according to claim 1, characterized in that: The spot shape of the continuous laser beam is a single ring, a double ring, or a combination of a ring and a circle; Before scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam, the method further includes the following steps: Retrieving three-dimensional topographic data of the initial surface layer of the cast aluminum alloy part to obtain distribution of angle areas, curved surface areas, and flat surface areas in the initial surface layer; Scanning the initial surface layer of the cast aluminum alloy part using a continuous laser beam comprises the following steps: According to the regional distribution of the initial surface layer, the corresponding spot shape is matched for scanning, wherein the angle area matches the double ring shape, the curved surface area matches the composite shape, and the plane area matches the single ring shape.

3. The method for rapidly improving the surface structure and roughness of cast aluminum alloy parts according to claim 2, characterized in that: During the process of scanning the initial surface layer of the cast aluminum alloy part using a continuous laser beam, the posture of the cast aluminum alloy part is adjusted by controlling the multi-axis movement of the carrier platform so that the continuous laser beam is perpendicular to the incident surface in the angle area and / or the curved surface area.

4. The method for rapidly improving the surface structure and roughness of cast aluminum alloy parts according to claim 1, characterized in that: Before scanning the initial surface layer of the cast aluminum alloy part with a continuous laser beam, the method further includes the following steps: obtaining an initial surface roughness of the initial surface layer; Retrieving and traversing a process database to obtain initial laser parameters corresponding to the initial surface roughness, the process database including multiple processing modes, a surface roughness interval corresponding to each processing mode, and processing parameters corresponding to each processing mode, the processing parameters including a power interval, a scanning speed, and a penetration depth requirement; the initial laser parameters are processing parameters corresponding to the processing mode corresponding to the surface roughness interval within which the initial surface roughness falls; Scanning the initial surface layer of the cast aluminum alloy part using a continuous laser beam comprises the following steps: The continuous laser beam is started to scan the initial surface layer of the cast aluminum alloy part based on the power range and the scanning speed in the initial laser parameters.

5. The method for rapidly improving the surface structure and roughness of cast aluminum alloy parts according to claim 4, characterized in that: The method of controlling the laser power and scanning speed so that adjacent molten pools overlap continuously to form a uniform molten layer comprises the following steps: Real-time monitoring of molten pool width and solidification front status; Dynamically adjusting the laser power and / or the scanning speed to simultaneously maintain: a ratio of line spacing to the molten pool width maintained within a critical interval for inducing dendrite fragment nucleation, and an overlap rate of adjacent molten pools greater than or equal to a first preset threshold, wherein the critical interval requires that the melt at the leading edge of the subsequent molten pool penetrates the solidification microregion of the previous molten pool, inducing dendrite fragments as heterogeneous nucleation points; and the line spacing is the center distance between adjacent laser scanning paths; Repeat the above steps until the thickness of the uniform molten layer reaches the first preset thickness, where the first preset thickness is the penetration depth requirement in the initial laser parameters.

6. The method for rapidly improving the surface structure and roughness of cast aluminum alloy parts according to claim 1, characterized in that: The method further includes determining whether the thickness of the uniform molten layer reaches a first preset thickness; The step of determining whether the thickness of the uniform molten layer reaches a first preset thickness comprises the following steps: If the thickness of each detected unit of the uniform melting layer reaches the first preset thickness, it is determined that the thickness of the uniform melting layer reaches the first preset thickness; all the detected units constitute the entire uniform melting layer.

7. The method for rapidly improving the surface structure and roughness of a cast aluminum alloy part according to claim 6, characterized in that: The method further comprises the following steps: During the laser scanning process, the theoretical penetration depth of each detected unit is calculated in real time based on the laser power, the scanning speed and the material properties; the material properties are the thermal diffusion coefficient of the cast aluminum alloy part; The displacement of each axis and the rotation angle of the loading platform are obtained, and the theoretical penetration depth is converted into the vertical penetration depth in the part coordinate system through a coordinate transformation matrix, and the vertical penetration depth is the thickness of the detected unit.

8. The method for rapidly improving the surface structure and roughness of a cast aluminum alloy part according to claim 6, characterized in that: The detected unit is set in the following manner: During the laser scanning process, a continuous scanning path segment in which the laser power and the scanning speed are kept constant is defined as a detected unit; The length of the detected unit is dynamically adjusted according to the processing path, and the lengths of adjacent detected units are allowed to be unequal.

9. The method for rapidly improving the surface structure and roughness of a cast aluminum alloy part according to claim 7, characterized in that: The theoretical penetration depth of the detected unit is obtained by calculating a penetration depth calculation model, wherein the penetration depth calculation model represents a relationship between the theoretical penetration depth and the laser power, the scanning speed, the thermal diffusion coefficient of the material, and the heat input coefficient; During the laser scanning process, after the theoretical penetration depth of each detected unit is calculated in real time according to the laser power, the scanning speed and the material properties, the following steps are also included: Retrieving verification information of the detected unit, wherein the verification information is an acoustic emission signal of the detected unit collected in real time by an acoustic emission sensor during a laser scanning process; Extracting characteristic values ​​of the acoustic emission signal in the 20-200 kHz frequency band, wherein the characteristic values ​​include the main frequency peak, the signal energy integral value and the kurtosis coefficient; Obtaining a measured penetration deviation rate of the detected unit according to the characteristic value; If the measured penetration depth deviation rate is less than or equal to a second preset threshold, the penetration depth calculation model is continuously used to calculate the theoretical penetration depth of the next detected unit.

10. The method for rapidly improving the surface structure and roughness of a cast aluminum alloy part according to claim 9, characterized in that: After obtaining the measured penetration deviation rate of the detected unit according to the characteristic value, the following steps are also included: If the absolute value of the measured penetration deviation rate is greater than the second preset threshold, the heat input coefficient is corrected based on the measured penetration deviation rate to obtain a corrected penetration calculation model; The corrected penetration depth calculation model is used to calculate the theoretical penetration depth of the next detected unit.

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