Corrosion-resistant aluminum alloy die and processing technology thereof

Abstract

This invention belongs to the field of powder metallurgy technology, specifically relating to a corrosion-resistant aluminum alloy mold and its processing technology. The process steps are as follows: providing aluminum alloy powder containing Mn, Sc, Zr, Y, Er, Mg, and Si; using laser powder bed melting to form a mold blank; during the forming process, after each preset number of layers, performing a laser remelting treatment on the surface layer of the blank, with the remelting power lower than the forming power and the scanning speed higher than the forming scanning speed, to obtain a fine-grained surface layer; then performing a two-stage gradient non-isothermal aging, i.e., first heating to 200~240℃ and holding, then heating to 350~380℃ and holding at a temperature plateau, and finally controlling the cooling. This invention, through the synergistic effect of rare earth microalloying, surface remelting, and two-stage aging, makes the grain boundary precipitates appear as discontinuous islands, blocking corrosion channels, and simultaneously obtaining high strength and high resistance to intergranular corrosion.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically relating to a corrosion-resistant aluminum alloy mold and its processing technology. Background Technology

[0002] Aluminum alloy molds possess advantages such as low density, good thermal conductivity, and short processing cycles. These molds are widely used in plastic molding, die casting, and automotive manufacturing. However, aluminum alloy molds are prone to corrosion during service. Among these, intergranular corrosion is one of the most significant failure modes. Intergranular corrosion can lead to sudden fracture of mold structural components and significantly reduce the material's strength, plasticity, and fatigue properties.

[0003] To improve corrosion resistance, existing technologies typically apply protective coatings to the mold surface. However, the bonding strength between the coating and the mold substrate is limited. Under thermal cycling and the scouring of molten aluminum, the coating is prone to peeling off. Once the coating is damaged, corrosive media can rapidly penetrate along the grain boundaries, accelerating mold failure. Existing laser powder bed fusion (LPBF) additive manufacturing technology offers advantages such as high forming precision, the ability to fabricate complex irregular structures, and excellent microstructure uniformity. The industry typically uses conventional aging treatment for post-processing of LPBF-formed aluminum alloy molds to precipitate strengthening phases, thereby improving the hardness and mechanical properties of the mold substrate to meet the forming requirements of the mold.

[0004] However, conventional aging treatment has significant technical drawbacks: LPBF forming aluminum alloys treated with this process precipitate a large number of strengthening phases at grain boundaries, forming a continuous network structure, which significantly increases the material's susceptibility to intergranular corrosion, making it highly susceptible to severe intergranular corrosion failure. In summary, existing LPBF aluminum alloy mold preparation and post-processing technologies struggle to simultaneously achieve high strength and high resistance to intergranular corrosion; these two aspects present an irreconcilable technical contradiction, severely restricting the large-scale, high-end application of LPBF aluminum alloy molds. Therefore, a corrosion-resistant aluminum alloy mold and its processing technology are needed. Summary of the Invention

[0005] In view of the above-mentioned shortcomings in the prior art, the present invention provides a corrosion-resistant aluminum alloy mold and its processing technology to solve the problems in the background art.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A processing technology for a corrosion-resistant aluminum alloy mold includes the following steps: Step 1: Provide aluminum alloy powder, which, by mass percentage, comprises: Mn: 3.5%~5.5%, Sc: 0.4%~0.7%, Zr: 0.3%~0.5%, Y: 0.05%~0.15%, Er: 0.1%~0.2%, Mg: 1.5%~2.0%, Si: 0.6%~1.0%, with the balance being Al and unavoidable impurities; Step 2: Use laser powder bed melting technology to form aluminum alloy powder into aluminum alloy mold blanks; Step 3: During the laser powder bed melting and forming process, a surface laser remelting treatment is performed after each preset number of printing layers. The remelting treatment uses a remelting laser power lower than that used for forming and a remelting scanning speed higher than that used for forming to obtain an aluminum alloy mold blank with a fine grain layer on the surface. Step 4: Perform a two-stage gradient non-isothermal aging heat treatment on the aluminum alloy mold blank. The two-stage gradient non-isothermal aging heat treatment includes: In the first stage, the room temperature is heated to a first temperature at a first heating rate, and then held at that temperature for 15 to 30 minutes. The first temperature is 200 to 240°C. In the second stage, the heating continues at the second heating rate to the second temperature, which is 350~380℃; and the second heating rate is lower than the first heating rate, and the temperature is held for a total of 10~30 minutes in the range of 320~350℃. Then, it is cooled to room temperature at a controlled rate of 0.5~2.0℃ / min.

[0007] Furthermore, in step 2, the laser power of the laser powder bed melting process is 250~400W, the scanning speed is 0.8~1.5m / s, the scanning spacing is 0.08~0.12mm, the layer thickness is 20~50μm, and the substrate preheating temperature is 100~200℃.

[0008] Furthermore, the controlled cooling process in step 4 is set in an argon protective atmosphere.

[0009] Furthermore, the median particle size of the aluminum alloy powder is 15μm to 53μm, the powder sphericity is ≥90%, and the oxygen content is ≤0.1%.

[0010] Furthermore, the laser powder bed melting process in step 2 is carried out in an argon protective atmosphere with an oxygen content ≤0.1%.

[0011] Furthermore, in step 2, the scanning between adjacent layers in the laser powder bed melting process is a rotational scanning.

[0012] Furthermore, in step 3, the preset number of layers is to perform a surface laser remelting after every 5 to 8 layers of printing.

[0013] Furthermore, in step 3, the remelting laser power, the remelting scanning speed, and the second heating rate satisfy the following relationship: in, It is a cooperating factor and , For remelting laser power, For remelting scan speed, This represents the heating rate in the second stage.

[0014] Furthermore, in step 4, the first heating rate in the first stage is 2~4℃ / min, and the second heating rate in the second stage is 0.5~2℃ / min, with the second heating rate being lower than the first heating rate.

[0015] A corrosion-resistant aluminum alloy mold, wherein the mold has a yield strength ≥590MPa, an elongation ≥13%, and a maximum intergranular corrosion depth ≤11μm in 3.5% NaCl solution.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. By employing microalloyed aluminum alloy powder containing rare earth elements Y and Er, a microstructure with grain boundary purification and dispersed composite precipitates was obtained. Y and Er preferentially react with impurities, reducing the electrochemical activity of grain boundaries; Sc, Zr, Y, and Er synergistically form composite nano-precipitates, resulting in a discontinuous distribution of precipitates at grain boundaries. This effectively blocks the rapid penetration channels of corrosive media along grain boundaries, addressing the intergranular corrosion problem caused by conventional aging treatments from the material's bulk. 2. By periodically performing surface laser remelting during the laser powder bed melting process, and controlling the remelting power to be lower than the forming power and the remelting speed to be higher than the forming speed, a continuous fine-grained layer is obtained on the surface of the mold. This fine-grained layer forms dense discontinuous precipitates during subsequent aging, constituting a corrosion barrier layer that does not require a coating, thereby avoiding the defects of limited bonding strength between the surface coating and the substrate and easy peeling failure under thermal cycling in the prior art; 3. Through a two-stage gradient non-isothermal aging heat treatment, namely, the first stage of rapid heating to the medium temperature zone and holding at that temperature, the second stage of slow heating to the high temperature zone and holding at that temperature within the range of 320~350℃, and then slow-speed programmed temperature cooling, and controlling the heating rate and temperature difference between the two stages, a microstructure in which the grain boundary precipitates are distributed in an isolated island-like pattern is obtained. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the processing technology of a corrosion-resistant aluminum alloy mold according to the present invention. Detailed Implementation To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0018] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0019] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0020] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] The specific process steps are as follows: like Figure 1 As shown, the processing technology of a corrosion-resistant aluminum alloy mold of the present invention includes the following steps: Step 1: Provide aluminum alloy powder, which, by mass percentage, consists of: Mn: 3.5%~5.5%, Sc: 0.4%~0.7%, Zr: 0.3%~0.5%, Y: 0.05%~0.15%, Er: 0.1%~0.2%, Mg: 1.5%~2.0%, Si: 0.6%~1.0%, with the balance being Al and unavoidable impurities; The median particle size of aluminum alloy powder is 15μm to 53μm, with a sphericity ≥90% and an oxygen content ≤0.1%. Specifically, 15μm to 53μm is a typical particle size range suitable for laser powder bed melting (fine powder has good spreading properties, and coarse powder has good flowability). Particles smaller than 15μm are prone to agglomeration, while those larger than 53μm lead to uneven layer thickness and poor fusion. High sphericity ensures powder flowability and spreading density, which are basic requirements for laser powder bed melting. Aluminum alloys are sensitive to oxygen; excessively high oxygen content can lead to oxide films, porosity, and brittle phases. 0.1% is the industry-standard upper limit.

[0022] Step 2: Use laser powder bed melting technology to form aluminum alloy powder into aluminum alloy mold blanks; Aluminum alloy powder is formed into an aluminum alloy mold blank using a laser powder bed melting process. The laser powder bed melting process parameters are: laser power 250~400W, scanning speed 0.8~1.5m / s, scanning spacing 0.08~0.12mm, layer thickness 20~50μm, and substrate preheating temperature 100~200℃.

[0023] Specifically, aluminum alloys have high laser reflectivity, requiring high power for complete melting. Below 250W, incomplete fusion defects are likely to occur, while above 400W, spattering and vaporization are likely. A scanning speed of 0.8~1.5m / s is used to balance production efficiency and molten pool stability; too low a speed leads to overheating / spheroidization, while too high a speed results in incomplete fusion. This range is a typical window for aluminum alloy LPBF (Liquid-to-Boiler) melting. To ensure sufficient overlap between adjacent melt channels (typically 30%~50%), the scanning spacing is 0.08~0.12mm; too small a spacing reduces efficiency, while too large a spacing creates grooves. A layer thickness of 20~50μm is a commonly used range balancing accuracy and speed; thinner layers improve accuracy, while thicker layers improve efficiency. Aluminum alloys are commonly preheated to 100~200℃; temperatures above 200℃ may cause powder oxidation. Preheating reduces thermal stress and inhibits cracking.

[0024] The laser powder bed melting process is carried out in an argon protective atmosphere with an oxygen content ≤0.1%. The scanning strategy for adjacent layers is rotational scanning. Specifically, the rotation angle is usually 67° or 90°. Changing the scanning direction can reduce anisotropy and residual stress.

[0025] Step 3: During the laser powder bed melting and forming process, a surface laser remelting treatment is performed after each preset number of printing layers. The remelting treatment uses a remelting laser power lower than that used for forming and a remelting scanning speed higher than that used for forming to obtain an aluminum alloy mold blank with a fine grain layer on the surface. After each preset number of layers is printed, a surface laser remelting process is performed. This remelting process is conducted with a remelting laser power lower than that used for forming and a remelting scanning speed higher than that used for forming. Specifically, the laser power for the remelting process is set to 50% to 70% of the forming power, and the scanning speed is set to 1.2 to 1.8 times the forming scanning speed. This process forms a fine-grained layer with a thickness of 50 to 100 μm on the surface of the mold. The preset number of layers is one remelting process after every 5 to 8 layers are printed.

[0026] The remelting laser power is lower than the forming power, remelting only the surface layer without causing excessive penetration. Too low a power will prevent remelting, while too high a power will damage the already formed layer. The remelting scanning speed is higher than the forming scanning speed, achieving rapid remelting and solidification to obtain a fine-grained layer. Too low a speed will cause the heat-affected zone to expand, while too high a speed will result in insufficient remelting.

[0027] Remelting every 5-8 layers is the optimal interval for balancing strengthening effect and efficiency. Too frequent remelting reduces efficiency, while too infrequent remelting results in discontinuous fine-grained layers. An interval of 5-8 layers is the most effective. From the perspective of heat-affected zone (HAZ), the energy input of a single laser remelting can penetrate approximately 3-5 layers and trigger localized remelting and heat conduction. If the remelting interval is less than 5 layers, the HAZ of two adjacent remeltings will overlap, causing localized areas of the surface to undergo multiple thermal cycles, leading to abnormal grain growth or thermal stress accumulation, which is detrimental to the uniform formation of fine-grained layers. If the remelting interval is greater than 8 layers, too many layers will remain unremelted, and the original coarse-grained structure of these layers will be retained in the final product, resulting in "discontinuities" or uneven thickness in the surface fine-grained layer, preventing the formation of a continuous and complete corrosion barrier layer.

[0028] The interval of 5-8 layers corresponds precisely to a suitable thermal cycling cycle. During this cycle, the printed layers are sufficiently cooled to reduce heat accumulation, while retaining some residual heat to improve interlayer bonding. During remelting, the laser not only refines the current surface grains but also induces a tempering effect on the underlying layers through heat conduction, alleviating residual stress and promoting uniform diffusion of elements at the interface, thereby enhancing the bonding strength between the fine-grained layer and the core substrate. Remelting every 5-8 layers ensures the integrity of the fine-grained layer while avoiding the significant loss in forming efficiency caused by overly frequent remelting operations (such as remelting every layer or every 2 layers). Experimental data shows that using a remelting frequency of 5-8 layers can form a continuous fine-grained layer with a thickness of approximately 50-100 μm on the mold surface. This fine-grained layer can induce a denser and more uniform discontinuous precipitate distribution during subsequent two-stage gradient non-isothermal aging, thereby effectively improving corrosion resistance.

[0029] Step 4: Perform a two-stage gradient non-isothermal aging heat treatment on the aluminum alloy mold blank. The two-stage gradient non-isothermal aging heat treatment includes: In the first stage, the room temperature is heated to the first temperature at a first heating rate of 2~4℃ / min, and then held at the first temperature for 15~30min. The first temperature is 200~240℃. Specifically, the temperature range of 200–240℃ is chosen because this temperature range falls precisely within the optimal nucleation temperature range for the Al3(Sc,Zr,Y,Er) composite precipitate (a metal compound with an L12 ordered structure, where Sc, Zr, Y, and Er atoms collectively occupy the X position in the Al3X structure). Below 200℃, atomic diffusion is insufficient, resulting in a low nucleation rate and uneven distribution of the precipitate, making it difficult to form the particle clusters required for subsequent grain boundary pinning. Above 240℃, once the precipitate nucleates, it grows rapidly, failing to achieve a fine and dispersed strengthening precipitate morphology, leading to a decrease in grain boundary pinning effect and loss of mechanical properties. Therefore, controlling the heating endpoint of the first stage at 200–240℃, along with an appropriate holding time, ensures that the composite rare earth precipitate achieves a high-density, fine-particle, and uniformly distributed nucleation state, laying the microstructural foundation for the high-temperature pinning in the second stage.

[0030] Then, a relatively fast heating rate of 2~4℃ / min is used to allow the billet to quickly pass through the low-temperature zone, suppressing the premature precipitation of continuous network phases at grain boundaries, while ensuring a sufficiently high nucleation drive within the grains. When the first heating rate is below 2℃ / min, the nucleation efficiency is low, and the microstructure coarsens; when it is above 4℃ / min, excessive thermal stress may induce cracks. Holding for 15~30 minutes ensures that the precipitated phases fully nucleate and are evenly distributed. Too short a time results in incomplete nucleation, while too long a time leads to grain coarsening.

[0031] In the second stage, the temperature is further increased to a second temperature of 350-380℃ at a second heating rate of 0.5-2.0℃ / min, and the second heating rate is lower than the first heating rate; the temperature is held for a total of 10-30 minutes within the range of 320-350℃ (the holding can be continuous or segmented); then the temperature is controlled to cool to room temperature at a rate of 0.5-2.0℃ / min.

[0032] Specifically, in the second stage, the temperature is increased to 350-380℃ using a slow heating rate of 0.5-2℃ / min. The purpose is to allow the precipitates already formed at the grain boundaries to partially dissolve and redefine at higher temperatures. This slow heating provides sufficient rearrangement time for the grain boundary atoms, thereby breaking the continuous network into isolated islands. Within the 320-350℃ range, a cumulative holding time of 10-30 minutes (continuous or segmented holding) is applied to ensure that the precipitated particles within this temperature range fully pinnate the grain boundaries, further enhancing the discontinuous effect. The 320-350℃ temperature range is the optimal pinning temperature range for the Al3(Sc,Zr,Y,Er) composite precipitate. This precipitate is an L12 structure intermetallic compound precipitated from the α-Al matrix, where Sc, Zr, Y, and Er atoms collectively occupy the X positions in the Al3X structure. Within this temperature range, the precipitate can exist stably in a fine, dispersed morphology and effectively pinnate grain boundaries through coherent interfaces. Below 320℃, the nucleation driving force of the precipitated phase is insufficient, making it difficult to form enough pinning sites; above 350℃, the precipitated phase coarsens, the coherent relationship is disrupted, and the pinning effect decreases significantly. When the second heating rate is below 0.5℃ / min, the production efficiency is too low and the intragranular precipitated phase grows; above 2.0℃ / min, grain boundary pinning may be insufficient, in which case the cumulative holding time can be appropriately extended to compensate.

[0033] The material was then cooled to room temperature at a controlled rate of 0.5~2.0℃ / min, with the cooling process taking place under an argon protective atmosphere.

[0034] Specifically, slow cooling at 0.5~2.0℃ / min can avoid thermal stress and quenching cracks caused by rapid cooling, while allowing residual supersaturated atoms to continue to precipitate in a gentle manner, thus stabilizing the microstructure.

[0035] Furthermore, the remelting laser power, the remelting scanning speed, and the second heating rate in step 4 satisfy the following relationship: in, It is a cooperating factor and , For remelting laser power, For remelting scan speed, The heating rate in the second stage determines the grain size and grain boundary nucleation site density of the remelted layer, while the aging heating rate controls the degree of isolation of the grain boundary precipitates. Only when the two are matched can discontinuous island-like precipitates be obtained.

[0036] To achieve an intergranular corrosion depth ≤11μm, the following must be met: Greater than or equal to the critical value of the synergy factor ,Right now Based on the Rosenthal heat conduction model and precipitation phase kinetics, the critical value can be expressed as: in, This is the critical value of the synergy factor; The superheat of the molten pool is taken as 800 K. This value is a well-known parameter in the field of laser remelting of aluminum alloys. It is derived from the standard thermophysical assumptions of the Rosenthal moving point heat source model and is used to characterize the excess amount by which laser heating raises the alloy temperature above the melting point. The density of aluminum alloy is taken as 2700 kg / m³. For specific heat capacity, take 900 J / (kg·K). , These are the macroscopic physical property constants of aluminum alloy materials, which belong to existing technology; The grain size of the remelted layer was determined by scanning electron microscopy observation based on the examples. Take the median value of 1.0 μm; The critical grain boundary precipitate coverage rate is defined as the ratio of the grain boundary precipitate coverage area to the total grain boundary area, and is taken as approximately 0.5. It is determined through image analysis and fitting. When the coverage rate is ≤0.5, the precipitate is in the form of isolated islands, and the intergranular corrosion depth can be controlled below 11μm; otherwise, it is easy to form a continuous network, and the corrosion depth increases significantly. Let be the diffusion constant, taken as 1×10⁻⁶. -5 m 2 / s. This value is the frequency factor of atomic diffusion in the Al3(Sc,Zr) composite precipitate phase, and is cited from the aging precipitation kinetics of aluminum alloys, which is existing technology. To determine the activation energy for precipitation, we take 1.5 × 10⁻⁶. 5 J / mol; This value is between the activation energy of Al3Sc phase precipitation (about 80 kJ / mol) and the activation energy of Zr diffusion (about 189 kJ / mol), and is the average performance of Sc, Zr, Y and Er synergistic precipitation, which belongs to the existing technology of aluminum alloy aging precipitation kinetics research; The gas constant is 8.314 J / (mol·K), which is a current technical parameter. This refers to the absolute temperature for the second stage of aging.

[0037] Since the second stage temperature range of this invention is 350~380℃ (i.e., absolute temperature 623~653 K), the conditions are met within this temperature range. The most unfavorable temperature, i.e., the lower limit temperature of 350℃ (623 K), is taken for calculation because atomic diffusion is slowest and precipitated phase formation is most difficult at this temperature. Substituting the above parameters, the calculation yields... In Example 1 The corrosion depth is 10 μm; in Example 1 The corrosion depth is 11 μm; therefore, it can be seen that when It can achieve a corrosion depth of ≤11 μm in a short time.

[0038] The second stage temperature range is 350~380℃. Within this range, temperature fluctuations have a relatively small impact on the morphology of the precipitated phase, while the synergistic factor plays a dominant role. If the temperature deviates from this window (e.g., below 350℃ or above 380℃), even... It is also possible that due to the mismatch of precipitation kinetics, the ideal isolated island-shaped grain boundary precipitates cannot be obtained, which leads to an increase in the depth of intergranular corrosion.

[0039] To further elucidate the coupling mechanism between temperature and the synergistic factor, an empirical correlation including a temperature term is introduced: in, This represents the depth of intergranular corrosion, indicating the depth of intergranular corrosion. It is related to both the synergistic factor and absolute temperature. When the temperature is in the range of 350~380℃, The variation range is small (approximately ±20%), at which point the co-factor... This can guarantee that μm.

[0040] Furthermore, in step 4, the second heating rate is lower than the first heating rate. The temperature difference between the first-stage holding temperature and the second-stage segmented holding temperature is 90~140℃. Specifically, the first heating rate (2~4℃ / min) is controlled to be higher than the second heating rate (0.5~2.0℃ / min), that is, to achieve a relatively fast nucleation stage and a relatively slow pinning stage, ensuring the process essence of rapid nucleation and slow pinning. If the difference between the first and second heating rates is too small (i.e., the second heating rate is too fast, for example, the second heating rate is close to the first heating rate), the precipitates at the grain boundaries will not have enough time to pin, and will easily form a continuous network distribution, increasing the depth of intergranular corrosion; if the difference between the first and second heating rates is too large (i.e., the second heating rate is too slow, for example, the second heating rate is lower than 0.5℃ / min), the intragranular precipitates may become excessively coarsened, reducing mechanical properties and decreasing production efficiency. The rate range of the present invention (first heating rate 2~4℃ / min, second heating rate 0.5~2.0℃ / min, and the second is lower than the first) can simultaneously avoid the two adverse situations mentioned above.

[0041] The minimum temperature difference between the first-stage insulation temperature and the second-stage platform temperature is designed to be 90~140℃ to ensure effective separation of the two temperature ranges and avoid tissue regression or coarsening caused by temperature overlap.

[0042] A corrosion-resistant aluminum alloy mold has a continuous fine-grained layer on its surface. The mold can be used directly. If surface polishing and dimensional finishing are required, it is recommended to control the removal amount on one side to no more than 1 / 2 of the fine-grained layer thickness (approximately ≤25μm) to avoid damaging the surface fine-grained layer. Precision grinding followed by light polishing is recommended, with the removal amount controlled within 20μm. The mold has a yield strength ≥590MPa, elongation ≥13%, and a maximum intergranular corrosion depth ≤11μm in 3.5% NaCl solution. Based on the intergranular corrosion determination method for aluminum alloys, after immersion in a 3.5% NaCl solution at 35±1℃ for 24h, the maximum corrosion depth was measured to be ≤11μm.

[0043] Example 1 This embodiment provides a processing technology for corrosion-resistant aluminum alloy molds; Step 1: Weigh the aluminum alloy powder raw material according to the mass percentage. The mass percentage of each element is: Mn 4.5%, Sc 0.6%, Zr 0.4%, Y 0.10%, Er 0.15%, Mg 1.8%, Si 0.8%, with the balance being Al and unavoidable impurities. The median particle size of this aluminum alloy powder is 32 μm. The powder sphericity is 95%. The oxygen content is ≤0.1%.

[0044] Step 2: The obtained aluminum alloy powder is formed into an aluminum alloy mold blank using a laser powder bed fusion (LPBF) process. The LPBF process parameters are: laser power 350W, scanning speed 1.2m / s, scanning spacing 0.10mm, layer thickness 30μm, and substrate preheating temperature 150℃. The adjacent layer scanning strategy is rotational scanning. The LPBF process is carried out under an argon protective atmosphere, with the oxygen content controlled below 0.1%.

[0045] Step 3: During the laser powder bed melting process, a surface laser remelting treatment is performed after every 6 layers of printing. The remelting laser power is 150W (lower than the forming laser power of 350W), and the remelting scanning speed is 2m / s (higher than the forming scanning speed of 1.2m / s). This treatment forms a fine-grained layer with a thickness of about 75μm on the surface of the mold, finally obtaining an aluminum alloy mold blank.

[0046] Step 4: Place the aluminum alloy mold blank obtained in step 4 into a heat treatment furnace for two-stage gradient non-isothermal aging treatment.

[0047] The first stage involves heating from room temperature to 220°C at a heating rate of 3°C / min, and holding at that temperature for 20 minutes.

[0048] In the second stage, the temperature is increased to 360℃ at a rate of 1℃ / min, and the temperature is held for a total of 20 minutes in the range of 320~350℃ (for example, holding for 10 minutes at 325℃ and 10 minutes at 345℃).

[0049] Finally, the temperature was controlled to room temperature at a rate of 0.5 °C / min. The controlled cooling process was carried out under an argon protective atmosphere.

[0050] For finishing, it is recommended to control the removal amount on one side to not exceed 1 / 2 of the fine-grained layer thickness (i.e., ≤25μm) to ensure the continuity and integrity of the surface fine-grained layer. Precision grinding followed by light polishing is recommended, with the removal amount controlled within 20μm. The surface roughness Ra after finishing should be ≤0.6μm.

[0051] The mold's yield strength was tested to be 602 MPa. Its elongation was 14.2%. In a 3.5% NaCl solution, the maximum intergranular corrosion depth was 10 μm. In thermal cycling tests, each cycle consisted of holding at 300°C for 30 min followed by air cooling to 25°C. After multiple cycles, no peeling occurred on the mold surface, and the increase in corrosion depth was minimal.

[0052] Example 2 The differences between this embodiment and Embodiment 1 are as follows.

[0053] Step 1: The composition of the aluminum alloy powder is: Mn 4.0%, Sc 0.55%, Zr 0.35%, Y 0.08%, Er 0.12%, Mg 1.6%, Si 0.7%, with the balance being Al and unavoidable impurities.

[0054] Step 2: The obtained aluminum alloy powder is formed into an aluminum alloy mold blank through laser powder bed melting process. The laser powder bed melting process parameters are: laser power 320W, scanning speed 1.1m / s, scanning spacing 0.10mm, layer thickness 30μm, and substrate preheating temperature 140℃.

[0055] Step 3: After every 5 layers of printing, remelting is performed once. The remelting laser power is 130W (lower than 320W), and the remelting scanning speed is 2.2m / s (higher than 1.1m / s).

[0056] Step 4: First stage: heating rate 2.5℃ / min to 215℃, hold for 25min; Second stage: heating rate 1.2℃ / min to 355℃, hold at 322℃ for 12min, hold at 342℃ for 12min; Cooling rate 0.6℃ / min to control cooling to room temperature.

[0057] The mold was tested and found to have a yield strength of 592 MPa, an elongation of 13.8%, and a maximum intergranular corrosion depth of 11 μm.

[0058] Example 3 The differences between this embodiment and Embodiment 1 are as follows.

[0059] Step 1: The composition of the aluminum alloy powder is: Mn 4.8%, Sc 0.65%, Zr 0.45%, Y 0.12%, Er 0.18%, Mg 1.9%, Si 0.9%, with the balance being Al and unavoidable impurities.

[0060] Step 2: The obtained aluminum alloy powder is formed into an aluminum alloy mold blank using a laser powder bed melting process. The laser powder bed melting process parameters are: laser power 380W, scanning speed 1m / s, scanning spacing 0.11mm, layer thickness 35μm, and substrate preheating temperature 160℃.

[0061] Step 3: After every 8 layers of printing, remelting is performed once. The remelting laser power is 180W (lower than 380W), and the remelting scanning speed is 1.8m / s (higher than 1m / s).

[0062] Step 4: First stage: heating rate 3.5℃ / min to 225℃, hold for 18min; Second stage: heating rate 0.8℃ / min to 365℃, hold at 328℃ for 8min, hold at 348℃ for 8min; Cooling rate 0.8℃ / min to control cooling to room temperature.

[0063] The mold was tested and found to have a yield strength of 608 MPa, an elongation of 13.5%, and a maximum intergranular corrosion depth of 9 μm.

[0064] Comparative Example 1 This comparative example uses the exact same aluminum alloy powder composition and laser powder bed melting process conditions as Example 1. The difference lies in the aging treatment method: the mold blank is placed at 300°C for 5 hours and then naturally cooled in air.

[0065] Tests showed that the mold had a yield strength of 595 MPa, an elongation of 11.2%, and a maximum intergranular corrosion depth of 165 μm.

[0066] Comparative Example 2 This comparative example uses the exact same aluminum alloy powder composition and laser powder bed melting process conditions as Example 1. The difference lies in the aging treatment method: the mold is heated from room temperature to 350°C at a heating rate of 2°C / min, and heating is stopped immediately after reaching the final temperature, allowing the mold to cool naturally in air.

[0067] The mold was tested and found to have a yield strength of 590 MPa, an elongation of 14.5%, and a maximum intergranular corrosion depth of 21 μm.

[0068] Comparative Example 3 This comparative example uses an aluminum alloy with the same chemical composition as Example 1 (Mn 4.5%, Sc 0.6%, Zr 0.4%, Y 0.10%, Er 0.15%, Mg 1.8%, Si 0.8%, balance Al), and prepares a mold blank of the same shape using a conventional metal mold casting method. The blank is then subjected to conventional solution treatment and aging: solution treatment at 540℃ for 2 hours, water quenching, followed by aging at 300℃ for 5 hours, and air cooling.

[0069] Tests showed that the casting mold had a yield strength of 520 MPa, an elongation of 8.5%, and a maximum intergranular corrosion depth of 85 μm.

[0070] The comparison between the examples and the comparative examples is as follows: The above are merely embodiments of the present invention. The circuits, electronic components, and modules involved are all prior art, fully achievable by those skilled in the art, and require no further explanation. The content protected by this application does not involve improvements to the software and methods. Commonly known structures and characteristics in the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all prior art in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A process for machining corrosion resistant aluminum alloy molds, characterized by: Includes the following steps: Step 1: Provide aluminum alloy powder, which, by mass percentage, consists of: Mn: 3.5%~5.5%, Sc: 0.4%~0.7%, Zr: 0.3%~0.5%, Y: 0.05%~0.15%, Er: 0.1%~0.2%, Mg: 1.5%~2.0%, Si: 0.6%~1.0%, with the balance being Al and unavoidable impurities; Step 2: Use laser powder bed melting technology to form aluminum alloy powder into aluminum alloy mold blanks; Step 3: During the laser powder bed melting and forming process, a surface laser remelting treatment is performed after each preset number of printing layers. The remelting laser power is less than the forming laser power, and the remelting scanning speed is greater than the forming scanning speed, to obtain an aluminum alloy mold blank with a fine grain layer on the surface. Step 4: Perform a two-stage gradient non-isothermal aging heat treatment on the aluminum alloy mold blank. The two-stage gradient non-isothermal aging heat treatment includes: The first stage involves heating from room temperature to a first temperature at a first heating rate, and holding at the first temperature for 15 to 30 minutes. The first temperature is 200 to 240°C. The second stage continues heating at a second heating rate to a second temperature, and the second heating rate is lower than the first heating rate. The second temperature is 350~380℃; and the temperature is held for a total of 10~30 minutes within the range of 320~350℃. Then, it is cooled to room temperature at a controlled rate of 0.5~2.0℃ / min.

2. A process for machining a corrosion resistant aluminum alloy mold as recited in claim 1 wherein: The laser power of the laser powder bed melting process in step 2 is 250~400W, the scanning speed is 0.8~1.5m / s, the scanning spacing is 0.08~0.12mm, the layer thickness is 20~50μm, and the substrate preheating temperature is 100~200℃.

3. The processing technology of a corrosion-resistant aluminum alloy mold as described in claim 1, characterized in that: The controlled cooling process in step 4 is set up in an argon protective atmosphere.

4. The processing technology of a corrosion-resistant aluminum alloy mold as described in claim 1, characterized in that: The aluminum alloy powder in step 1 has a median particle size of 15μm to 53μm, a powder sphericity of ≥90%, and an oxygen content of ≤0.1%.

5. The processing technology of a corrosion-resistant aluminum alloy mold as described in claim 1, characterized in that: The laser powder bed melting process in step 2 is carried out in an argon protective atmosphere with an oxygen content ≤0.1%.

6. The processing technology of a corrosion-resistant aluminum alloy mold as described in claim 1, characterized in that: The scanning between adjacent layers in the laser powder bed melting process in step 2 is a rotational scan.

7. The processing technology of a corrosion-resistant aluminum alloy mold as described in claim 1, characterized in that: The preset number of layers in step 3 is to perform a surface laser remelting after every 5 to 8 layers of printing.

8. The processing technology of a corrosion-resistant aluminum alloy mold as described in claim 1, characterized in that: The remelting laser power and remelting scanning speed in step 3 and the second heating rate in step 4 satisfy the following relationship: in, As a cooperating factor, For remelting laser power, For remelting scan speed, This represents the heating rate in the second stage.

9. The processing technology of a corrosion-resistant aluminum alloy mold as described in claim 1, characterized in that: In step 4, the first heating rate in the first stage is 2~4℃ / min, and the second heating rate in the second stage is 0.5~2℃ / min.

10. A corrosion-resistant aluminum alloy mold, characterized in that, The mold is prepared by the processing technology of any one of claims 1 to 9, wherein the mold has a yield strength ≥ 590 MPa, an elongation ≥ 13%, and a maximum intergranular corrosion depth ≤ 11 μm in 3.5% NaCl solution.

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