Online dehydrogenation method and device in magnesium-aluminum alloy die-casting process

Abstract

The invention relates to the technical field of aluminum alloy machining, in particular to an online hydrogen removal method and device in the magnesium-aluminum alloy die-casting process. The method comprises the steps that smelted magnesium-aluminum alloy melt is guided into a closed launder system, multi-stage deep hydrogen removal is achieved through first-stage ultrasonic cavitation hydrogen removal, second-stage cyclone bubble flotation hydrogen removal and third-stage composite adsorption medium gradient adsorption hydrogen removal in sequence under the protective atmosphere, and finally the hydrogen content is stably reduced to be smaller than or equal to 0.10 ml / 100 g. The corresponding device comprises a first-stage hydrogen removal zone box body, a second-stage hydrogen removal zone box body and a third-stage hydrogen removal zone box body which are sequentially connected, and the first-stage hydrogen removal zone box body, the second-stage hydrogen removal zone box body and the third-stage hydrogen removal zone box body are respectively provided with an ultrasonic probe, an air brick, a graphite rotor, an adsorption bed The device can continuously remove hydrogen on line, effectively prevents secondary hydrogen absorption of the melt, improves the hydrogen removal efficiency and the die casting quality, and is suitable for the magnesium-aluminum alloy die-casting forming process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy processing, in particular to a magnesium-aluminum alloy die casting process online hydrogen removal method and device. BACKGROUND

[0002] Magnesium-aluminum alloy is widely used in the fields of automobile parts, electronic device housings, aerospace structural parts, etc. due to its low density, high specific strength, good die casting formability, etc. In the die casting production process, magnesium-aluminum alloy melt is prone to absorb hydrogen from the smelting environment, raw materials and process medium. Hydrogen precipitates due to the sharp decrease in solubility when the melt solidifies, forming internal defects such as pores, pinholes and porosity, which seriously reduces the mechanical properties, air tightness and corrosion resistance of the castings, and even leads to the rejection of the castings, restricting the application expansion of magnesium-aluminum alloy in high-precision and high-reliability scenarios.

[0003] Existing magnesium-aluminum alloy hydrogen removal technologies mainly include offline static hydrogen removal and online dynamic hydrogen removal. Offline methods such as vacuum degassing and inert gas purging have low efficiency, cannot be operated continuously, and the melt temperature is prone to fluctuation, etc., making it difficult to adapt to the rhythm of modern continuous die casting production lines. Online hydrogen removal technology realizes the synchronization with the die casting process, but it mainly uses a single hydrogen removal mechanism, which has limited removal depth of residual hydrogen, and is prone to secondary oxidation and hydrogen absorption during melt flow. At the same time, the activity and selectivity of the adsorption medium are insufficient, making it difficult to stably control the melt hydrogen content at a low level, and unable to meet the stringent requirements of high-end castings on material purity. Therefore, developing an efficient, continuous and deep online hydrogen removal technology and supporting device has become the key to solving the pain points of the magnesium-aluminum alloy die casting industry. SUMMARY

[0004] To make up for the above shortcomings, the present application provides a magnesium-aluminum alloy die casting process online hydrogen removal method and device, which realizes online, continuous and deep hydrogen removal of the melt by adopting a three-stage hydrogen removal process combining ultrasonic cavitation, cyclone bubble flotation and gradient adsorption of composite adsorption medium, and supporting the corresponding device, effectively reducing the hydrogen content to below 0.10 ml / 100g, thereby significantly improving the internal quality and mechanical properties of the die castings.

[0005] To achieve the above objectives, the technical solutions adopted by the present application are as follows:

[0006] The magnesium-aluminum alloy die casting process online hydrogen removal method comprises the following steps:

[0007] 1. The molten magnesium-aluminum alloy is introduced into a closed flow channel system with heating and insulation functions. A protective gas hood is applied over the entire flow channel, and inert gas is introduced to form a local atmosphere protection, preventing secondary oxidation and hydrogen absorption during the melt flow. Magnesium-aluminum alloy melt is highly reactive at high temperatures, readily reacting with oxygen and water vapor in the air and absorbing hydrogen. The closed flow channel and inert gas protection isolate it from external reactive media, while the heating and insulation functions maintain a stable melt temperature, preventing temperature fluctuations from causing changes in hydrogen solubility. This blocks the secondary hydrogen absorption path at the source, ensuring the initial stability of the melt and providing a good foundation for subsequent multi-stage hydrogen removal.

[0008] 2. The melt enters the primary hydrogen removal zone for ultrasonic cavitation hydrogen removal. This zone is equipped with a high-power ultrasonic probe with an adjustable power range. When the ultrasonic generator is activated, the probe applies ultrasonic waves of a specific frequency and power to the melt. The cavitation effect generated by the ultrasonic waves creates localized instantaneous high pressure, causing hydrogen atoms to diffuse and aggregate into hydrogen microbubbles that escape. The hydrogen escape flux... Synergistic contribution from diffusion and cavitation:

[0009]

[0010] in, : Diffusion coefficient of hydrogen in magnesium-aluminum melt; , : Hydrogen concentration at the interface between the melt bulk and cavitation; Boundary layer thickness; : Cavitation effect coefficient; Ultrasonic power :frequency.

[0011] Utilizing the cavitation effect generated by ultrasound propagation in the melt, countless tiny cavitation bubbles are formed. As these bubbles oscillate, grow, and collapse, they release localized instantaneous high pressure, disrupting the stable state of hydrogen atoms in the melt. This causes hydrogen atoms to rapidly diffuse and aggregate, forming hydrogen microbubbles. This achieves rapid initial hydrogen removal. The ultrasonic power and frequency are adjustable, adaptable to melts with different initial hydrogen contents. The hydrogen removal process is gentle and does not damage the homogeneity of the melt composition, reducing the burden on subsequent deeper hydrogen removal processes.

[0012] 3. The melt, after ultrasonic pretreatment, flows into the secondary dehydrogenation zone for deep dehydrogenation via cyclone bubble flotation. The bottom of the secondary dehydrogenation zone is equipped with special permeable bricks, through which high-purity inert gas is introduced. Simultaneously, a high-speed rotating graphite rotor disperses the rising inert bubbles into a dispersed stream of inert microbubbles. At this point, residual hydrogen atoms in the melt rapidly diffuse into these microbubbles and rise to the surface to escape. The rate of hydrogen diffusion from the melt to the inert microbubbles is as follows:

[0013]

[0014] The integral of the hydrogen removal efficiency is:

[0015]

[0016] Wherein: : current hydrogen concentration; : hydrogen equilibrium concentration in the bubble, approximately 0, due to inert gas dilution; : liquid phase mass transfer coefficient; : specific surface area of unit volume of bubble, ; : gas volume fraction; : average bubble diameter, which can reach 50-200 μm after being dispersed by a graphite rotor; : secondary zone residence time.

[0017] The special gas permeable brick uniformly releases high-purity inert gas, and the high-speed rotating graphite rotor disperses the gas into 50-200 μm dispersed micro-bubbles, increases the contact specific surface area of the gas and the melt, and the residual hydrogen atoms in the melt diffuse into the micro-bubbles due to the concentration difference, and escape with the bubbles rising to the liquid surface. The high specific surface area of the micro-bubbles improves the hydrogen mass transfer efficiency, the cyclone state prolongs the contact time of the melt and the bubbles, and the hydrogen removal efficiency is significantly improved, which can quickly reduce most of the residual hydrogen, and adapt to the high-speed production rhythm of continuous die casting.

[0018] 4, the melt flowed by the bubble flotation flows into the third hydrogen removal zone, and is subjected to gradient adsorption hydrogen removal by the adsorption bed containing composite adsorption medium; the third hydrogen removal zone is divided into a "high-temperature adsorption zone" and a "low-temperature adsorption zone" along the melt flow direction;

[0019] High temperature zone: Mo element in the composite medium preferentially combines with high concentration of residual hydrogen to generate MoH2, rapidly reducing the hydrogen content to 0.15-0.17 ml / 100g; high temperature zone adsorption capacity:

[0020]

[0021] Low temperature zone: rare earth elements Ce / La in the composite medium capture trace hydrogen to generate CeH2 / LaH2 through chemical adsorption, and Ti element removes tiny hydrogen bubbles through physical adsorption, and finally the hydrogen content is stabilized to ≤0.10 ml / 100g; low temperature zone adsorption capacity:

[0022]

[0023] In the above two formulas, : high-temperature zone hydrogen adsorption amount; : low-temperature zone hydrogen adsorption amount; : Mo hydrogen adsorption rate constant; : rare earth chemical adsorption constant; : Ti physical adsorption constant; : Mass fraction of the corresponding element in the composite medium; Specific surface area of ​​the medium; : Porosity of the medium; Adsorption threshold in the high-temperature zone; Hydrogen content at the outlet of the high-temperature zone; Contact time between the melt and the adsorption medium;

[0024] A ceramic screen with a 0.5mm aperture is installed at the bottom of the adsorption bed to intercept tiny particles generated by media abrasion and prevent impurities from being introduced into the casting.

[0025] Based on the different adsorption characteristics and temperature adaptability of hydrogen for various elements, a gradient adsorption design is adopted. High-concentration hydrogen is preferentially removed in the high-temperature zone, while trace amounts of hydrogen are precisely captured in the low-temperature zone. A ceramic screen at the bottom of the adsorption bed intercepts particles worn by the adsorption medium. This achieves precise and deep removal of hydrogen, avoiding the adsorption saturation problem of low-concentration hydrogen by a single adsorption medium, while preventing impurities from being introduced into the melt, thus ensuring the purity of the casting.

[0026] The composite adsorption medium in the adsorption bed needs to be pretreated and activated: Ti-Mo-RE composite honeycomb particles with a particle size of 3-5 mm and a porous structure with a porosity of 50%-60% are selected and prepared according to the mass ratio of Mo 1.0%, Ce 0.3%, La 0.2%, and the balance Ti; after filling the adsorption bed with the medium, argon gas with a purity ≥99.999% is introduced at a flow rate of 5-8 L / min; at the same time, it is heated to 700±10℃ by electromagnetic induction and held for 30 min to remove water vapor and impurities adsorbed on the surface of the medium; after activation, it is cooled to 680℃ and maintained at a constant temperature to form active adsorption sites on the surface of the medium.

[0027] High-purity argon gas prevents oxidation of the medium during heating, and the high temperature of 700±10℃ completely desorbs impurities such as water vapor and oil from the medium surface. The isothermal treatment promotes the formation of unsaturated active sites on the medium surface, enhancing its adsorption affinity for hydrogen. The pretreated medium exhibits significantly improved adsorption activity and selectivity; a 50%-60% porosity increases the adsorption contact area; a 3-5mm particle size ensures smooth melt flow; the activated medium has an extended service life; and the adsorption effect remains stable over a long period, reducing production and maintenance costs.

[0028] 5. The low-hydrogen melt, after undergoing three stages of hydrogen removal, is discharged from the unit outlet and supplied to the die-casting machine for molding. The three-stage hydrogen removal process forms a complete chain of "preliminary removal - deep removal - precise purification." Once the hydrogen content is stably reduced to a low level, defects caused by hydrogen precipitation will not occur during melt solidification. The output low-hydrogen melt can be directly adapted for die casting, significantly reducing the incidence of defects such as porosity, pinholes, and looseness in castings, and improving the mechanical properties, airtightness, and corrosion resistance of castings.

[0029] The magnesium-aluminum alloy die casting process on-line hydrogen removal device comprises a plurality of aluminum melt pipelines and matched valves, one end of one of the aluminum melt pipelines is connected with a first-stage hydrogen removal zone box, the other side of the first-stage hydrogen removal zone box is connected with a second-stage hydrogen removal zone box through an aluminum melt pipeline, the other side of the second-stage hydrogen removal zone box is connected with the top of a third-stage hydrogen removal zone box through an aluminum melt pipeline, and the other side bottom of the third-stage hydrogen removal zone box is connected with an aluminum melt pipeline.

[0030] The "tandem" box layout is adopted, the melt flows continuously in the order of "first stage→second stage→third stage", the pipe diameter and length of the aluminum melt pipeline are matched with the melt flow rate, the residence time of each hydrogen removal zone is ensured to meet the hydrogen removal requirement, the hydrogen removal process is realized to be on-line synchronized with the die casting production, the melt does not need to be transported offline, the temperature loss and secondary hydrogen absorption in the transportation process are avoided, the production efficiency is greatly improved, and the modern continuous die casting production line is adapted.

[0031] An ultrasonic probe is arranged in the first-stage hydrogen removal zone box.

[0032] A gas conveying pipe is fixedly connected to the bottom of the second-stage hydrogen removal zone box, a gas permeable brick is arranged in the second-stage hydrogen removal zone box, the gas conveying pipe extends into the second-stage hydrogen removal zone box and is connected with the gas permeable brick, a motor is arranged on the top of the second-stage hydrogen removal zone box, and the output end of the motor extends into the second-stage hydrogen removal zone box and is fixedly connected with a graphite rotor.

[0033] The gas conveying pipe conveys high-purity inert gas to the gas permeable brick, the microporous structure of the gas permeable brick uniformly releases the gas, the motor drives the graphite rotor to rotate at high speed, and the gas bubbles are broken into micro-bubbles by the shearing force. The gas bubbles are well dispersed and distributed, fully contact with the melt, the graphite rotor is resistant to high temperature and corrosion, and is suitable for the high-temperature melt environment.

[0034] The third-stage hydrogen removal zone box is divided into upper and lower parts and connected by an aluminum melt pipeline, a plurality of adsorption beds are fixedly connected to the interiors of the upper and lower third-stage hydrogen removal zone boxes, and screens are arranged in the interiors of the third-stage hydrogen removal zone boxes below the adsorption beds.

[0035] The upper and lower boxes correspond to high-temperature adsorption zones and low-temperature adsorption zones respectively, the plurality of adsorption beds increase the contact area of the melt and the composite medium, and the screens below the adsorption beds can directly intercept the falling wear particles. The function of gradient adsorption is realized, and the hydrogen removal precision is improved.

[0036] Exhaust pipes are arranged on the tops of the first-stage and second-stage hydrogen removal zone boxes. The hydrogen gas escaped from the first-stage and second-stage hydrogen removal zones needs to be discharged in time, so as to avoid the increase of the hydrogen gas concentration in the box, the increase of the partial pressure, the reverse inhibition of the hydrogen escape from the melt, and the rapid discharge of the hydrogen gas by the exhaust pipes.

[0037] Working principle:

[0038] After the melt flows into the first-stage hydrogen removal zone tank, the high-power adjustable ultrasonic probe installed in the tank is started to apply ultrasonic waves of a specific frequency and power to the melt. The ultrasonic waves produce cavitation effect when propagating in the melt, forming countless micro cavitation bubbles. The oscillation and growth of the cavitation bubbles to the collapse stage releases local transient high pressure, breaks the stable state of hydrogen atoms in the melt, and promotes the rapid diffusion and aggregation of hydrogen atoms to form hydrogen micro-bubbles. The micro-bubbles rise with the melt flow or buoyancy and are finally discharged through the exhaust pipe at the top of the tank, completing the preliminary removal of hydrogen.

[0039] After the first-stage hydrogen removal, the melt flows into the second-stage hydrogen removal zone tank through the aluminum melt pipeline. The gas delivery pipe at the bottom of the tank supplies high-purity inert gas to the special gas-permeable brick, and the graphite rotor is driven by the motor at the top to rotate at high speed. The gas-permeable brick releases the inert gas uniformly, and the graphite rotor disperses the rising gas into dispersed micro-bubbles through shear force, greatly increasing the specific surface area of the gas in contact with the melt. The residual hydrogen atoms in the melt rapidly diffuse into the inert micro-bubbles due to the concentration difference. After the micro-bubbles fully contact the melt under the action of the rotational flow, they carry hydrogen gas to the liquid surface and are discharged through the exhaust pipe, achieving deep removal of hydrogen.

[0040] The melt enters the third-stage hydrogen removal zone tank which is divided into upper and lower parts. The upper and lower tanks correspond to the "high-temperature adsorption zone" and "low-temperature adsorption zone", respectively, and both are equipped with adsorption beds filled with Ti-Mo-RE composite honeycomb particles. In the high-temperature zone, the Mo element in the composite medium preferentially combines with high-concentration residual hydrogen to form MoH2, rapidly reducing the hydrogen content. In the low-temperature zone, the rare earth elements Ce / La capture trace hydrogen to form CeH2 / LaH2 through chemical adsorption, and the Ti element removes small hydrogen bubbles through physical adsorption, achieving precise purification of hydrogen. The 0.5mm aperture ceramic screen below the adsorption bed intercepts the small particles generated by the wear of the medium, preventing the introduction of impurities into the melt.

[0041] After the third-stage hydrogen removal zone completes the purification, the low-hydrogen melt with a hydrogen content of ≤0.10ml / 100g is discharged from the device outlet through the aluminum melt pipeline, directly supplying the die casting machine for molding. During the entire process, the first-stage hydrogen removal reduces the load, the second-stage hydrogen removal improves the efficiency, and the third-stage hydrogen removal purifies the hydrogen. The hydrogen removal zones are connected in series through the aluminum melt pipeline, forming a continuous operation link. The exhaust pipe discharges the escaped hydrogen gas in real time, avoiding the increase of hydrogen partial pressure in the tank which may inhibit the hydrogen removal efficiency, and finally achieving the goal of efficient, continuous, and deep hydrogen removal.

[0042] The present application has the following advantages:

[0043] Achieve deep stable hydrogen removal: This technology constructs a gradient dehydrogenation link through the series process of "primary ultrasonic cavitation preliminary dehydrogenation, secondary cyclone bubble flotation deep dehydrogenation, and tertiary gradient adsorption precise purification", and finally stabilizes the hydrogen content at a low level of ≤0.10 ml / 100g, far exceeding the effect of traditional single dehydrogenation technology, which can meet the stringent requirements of high-precision automobile parts and other materials on purity.

[0044] Block the secondary hydrogen absorption path: From the melt transmission source, design a sealed flow tank system, and match the heating and insulation function with the inert gas protection hood, which not only avoids the change of hydrogen solubility caused by temperature fluctuation in the flow of melt, but also isolates active media such as air and water vapor that can easily cause hydrogen absorption, fundamentally blocking the possibility of secondary oxidation and hydrogen absorption. At the same time, the exhaust pipe at the top of the primary and secondary dehydrogenation zones can remove the escaped hydrogen in real time, preventing the increase of hydrogen partial pressure in the tank and inhibiting the dehydrogenation efficiency, ensuring that the melt is always in a low-hydrogen environment during the entire dehydrogenation process, avoiding the problem of "dehydrogenation-hydrogen absorption" repeatedly, and ensuring the continuity of the dehydrogenation effect.

[0045] Adapt to continuous die casting production line and improve production efficiency: Compared with traditional offline dehydrogenation technology, which needs to interrupt production and transport the melt, there are problems of low efficiency and large temperature fluctuation. The device uses a "series" tank layout and online continuous operation design. The melt is directly introduced into the device after smelting and can be directly supplied to the die casting machine after three-stage dehydrogenation without offline processing. The entire process is synchronized with the die casting production rhythm, avoiding temperature loss and secondary pollution during melt transportation. The dehydrogenation efficiency of a single production line can be improved by more than 30%, which adapts to the production needs of modern large-scale continuous die casting and helps enterprises improve productivity.

[0046] Composite adsorption medium has strong durability: The Ti-Mo-RE composite honeycomb particles used in the three-stage dehydrogenation zone can remove surface water vapor and impurities after pretreatment and activation, forming unsaturated active adsorption sites, significantly improving adsorption activity and selectivity. The 50%-60% porosity increases the adsorption contact area, and the 3-5mm particle size design ensures smooth melt flow and avoids blockage. The effective adsorption period of the composite medium can be 2-3 times that of traditional adsorption materials, reducing the frequency of medium replacement, and reducing equipment maintenance costs and downtime. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The flow chart of the online dehydrogenation method for magnesium-aluminum alloy die casting process proposed by the present application.

[0048] Figure 2 The overall structure diagram of the online dehydrogenation device for magnesium-aluminum alloy die casting process proposed by the present application.

[0049] Figure 3 The structure diagram of the first-stage dehydrogenation zone of the online dehydrogenation device for magnesium-aluminum alloy die casting process proposed by the present application.

[0050] Figure 4 The structure diagram of the second hydrogen removal area of the on-line hydrogen removal device for the magnesium-aluminum alloy die casting process.

[0051] Figure 5 The structure diagram of the third hydrogen removal area of the on-line hydrogen removal device for the magnesium-aluminum alloy die casting process.

[0052] Legend: 1, aluminum melt pipeline; 2, first-stage hydrogen removal area box; 3, ultrasonic probe; 4, exhaust pipe; 5, second-stage hydrogen removal area box; 6, gas-permeable brick; 7, gas conveying pipe; 8, motor; 9, graphite rotor; 10, third-stage hydrogen removal area box; 11, adsorption bed; 12, screen. DETAILED DESCRIPTION

[0053] The application will be described in further detail below with specific embodiments. It is apparent that the described embodiments are only a part of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0054] This embodiment takes the die casting production of AZ91D magnesium-aluminum alloy automobile gearbox shell as the application scenario. AZ91D is a commonly used magnesium-aluminum alloy for die casting. After smelting, the hydrogen content of AZ91D is easily increased due to the moisture, oil stains contained in raw materials (such as waste aluminum and magnesium ingot), and water vapor in the smelting environment (usually the initial hydrogen content is 0.35-0.45 ml / 100g). Therefore, the device of the application is used to realize deep hydrogen removal, so as to ensure that the castings are free of pores and pinhole defects, and meet the air tightness and mechanical property requirements of the gearbox shell.

[0055] Preparation before implementation

[0056] 1. Raw material and equipment inspection

[0057] Raw materials: magnesium ingot with a purity of 99.95%, aluminum ingot with a purity of 99.8%, and Zn and Mn alloy additives are selected, and are smelted according to the AZ91D component proportioning (Mg: 91%, Al: 9%, Zn: 0.7%, Mn: 0.3%). The smelting furnace temperature is controlled at 680±10℃, and the initial hydrogen content of the melt after smelting is detected by a hydrogen analyzer to be 0.42 ml / 100g.

[0058] Equipment calibration: check the closed launder heating system to ensure that the holding temperature can be stabilized at 670±5℃; calibrate the ultrasonic generator in the first-stage hydrogen removal zone (power range 1000-3000W, frequency 20-30kHz), the motor speed in the second-stage hydrogen removal zone (0-2000r / min), and the electromagnetic heating system in the third-stage hydrogen removal zone (temperature control accuracy ±5℃); detect the purity of inert gas (argon) to ensure that it is ≥99.999%, and the flow valve can be stably adjusted to 5-8L / min.

[0059] 2. Pretreatment and activation of composite adsorption medium

[0060] Medium preparation: Ti-Mo-RE composite honeycomb particles with a particle size of 3-5mm are prepared according to a mass ratio of Mo 1.0%, Ce 0.3%, La 0.2%, and the balance Ti, and the porosity of the particles is 55% (measured by a mercury porosimeter, which meets the requirement of 50%-60%).

[0061] Activation operation: fill the composite particles into the upper and lower adsorption beds in the third-stage hydrogen removal zone (the upper bed is a high-temperature adsorption zone, and the lower bed is a low-temperature adsorption zone), and close the inlet and outlet valves of the adsorption beds; introduce argon with a purity of 99.999% at a flow rate of 6L / min, and simultaneously start electromagnetic induction heating to raise the temperature to 705℃ (700±10℃) and maintain the temperature for 30min to remove water vapor and oil stains on the surface of the medium; then lower the temperature to 680℃ and maintain the temperature to form unsaturated active adsorption sites on the surface of the medium, and maintain a slight positive pressure of argon (0.02MPa) after the activation is completed to prevent air from entering.

[0062] Specific steps for online hydrogen removal

[0063] Step 1: melt introduction and atmosphere protection

[0064] Start the closed launder heating system, and after the launder temperature is stabilized to 670℃, open the outlet valve of the smelting furnace to introduce the AZ91D melt into the closed launder at a flow rate of 80kg / h;

[0065] Introduce argon into the protective gas cover above the launder at a flow rate of 2.5L / min to form a local inert atmosphere, and monitor the oxygen content in the launder in real time by an oxygen content analyzer to ensure that it is ≤0.01% to avoid secondary oxidation and hydrogen absorption of the melt;

[0066] The melt stays in the launder for about 20s, during which the temperature fluctuation is controlled within ±3℃, and the hydrogen content of the melt before entering the first-stage hydrogen removal zone is still stable at 0.42ml / 100g (without secondary hydrogen absorption).

[0067] Step 2: first-stage ultrasonic cavitation hydrogen removal

[0068] The melt flows into the first-stage hydrogen removal zone box, and the ultrasonic probe is started with a power of 1800W and a frequency of 22kHz;

[0069] Ultrasonic waves generate cavitation effect in the melt, and the collapse of cavitation bubbles releases transient high pressure, which promotes the diffusion and aggregation of hydrogen atoms into hydrogen microbubbles with a diameter of 5-10 μm;

[0070] The melt stays in the primary hydrogen removal zone for 35 s, and the microbubbles rise with the melt flow and are discharged through the exhaust pipe at the top of the box (the exhaust pipe has a negative pressure of 0.01 MPa to ensure that the hydrogen gas is quickly discharged);

[0071] After hydrogen removal, the sample is detected by a hydrogen analyzer, and the hydrogen content of the melt is reduced to 0.28 ml / 100 g, completing the preliminary removal.

[0072] Step 3: Secondary cyclone bubble flotation hydrogen removal

[0073] The melt after primary hydrogen removal flows into the secondary hydrogen removal zone box through the aluminum melt pipeline;

[0074] Open the gas pipeline valve and introduce high-purity argon gas into the special gas-permeable brick at the bottom, with a flow rate of 1.8 L / min. The micro-pores (pore size 5-10 μm) of the gas-permeable brick uniformly release the argon gas into fine bubbles;

[0075] Start the top motor to drive the graphite rotor to rotate at a high speed of 1400 r / min, which disperses the argon bubbles into dispersed microbubbles with a diameter of 80-150 μm through shear force;

[0076] The melt stays in the secondary hydrogen removal zone for 45 s, and the cyclone effect allows the microbubbles to fully contact the melt. Hydrogen atoms diffuse to the microbubbles due to the concentration difference, and the hydrogen-carrying microbubbles rise to the liquid surface and are discharged through the exhaust pipe;

[0077] Sampling detection shows that the hydrogen content of the melt is reduced to 0.16 ml / 100 g (which meets the inlet requirement of 0.15-0.17 ml / 100 g for the high-temperature adsorption zone).

[0078] Step 4: Three-stage gradient adsorption hydrogen removal

[0079] The melt flows into the upper box of the three-stage hydrogen removal zone (high-temperature adsorption zone) through the pipeline and flows through the adsorption bed filled with activated Ti-Mo-RE composite medium;

[0080] In the high-temperature zone, the Mo element in the medium rapidly reacts with the residual hydrogen in the melt to form MoH2. The melt stays in the high-temperature zone for 28 s, and the hydrogen content is reduced to 0.15 ml / 100 g through sampling detection;

[0081] The melt then flows into the lower box of the three-stage hydrogen removal zone (low-temperature adsorption zone), and the Ce and La elements in the medium form CeH2 and LaH2 through chemical adsorption, and the Ti element removes micro hydrogen bubbles with a diameter of ≤1 μm through physical adsorption (pore capture);

[0082] The melt stays in the low temperature zone for 32 s, and the 0.5 mm aperture ceramic screen at the bottom of the adsorption bed intercepts the small particles generated by the medium abrasion, so as to avoid the impurities from being introduced into the melt.

[0083] After hydrogen removal, sampling detection is performed, and the hydrogen content of the melt is stably reduced to 0.09 ml / 100 g (≤0.10 ml / 100 g, reaching the target requirement).

[0084] Step 5: Melt output

[0085] The low-hydrogen melt after completing three-stage hydrogen removal is delivered to the die casting machine through the aluminum melt pipeline.

[0086] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements to some technical features, as long as they are within the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made shall be included in the protection scope of the present application.

Claims

1. A method for on-line hydrogen removal in magnesium-aluminum alloy die casting processes, characterized by: The method comprises the following steps: S1: The smelted magnesium-aluminum alloy melt is introduced into a closed runner system with heating and holding functions, a protective gas cover is applied on the whole runner, inert gas is introduced to form a local atmosphere protection, and secondary oxidation and hydrogen absorption during melt flow are prevented; S2: The melt enters a first-stage hydrogen removal zone for ultrasonic cavitation hydrogen removal; S3: The melt after ultrasonic pretreatment flows into a second-stage hydrogen removal zone for cyclone bubble flotation deep hydrogen removal; S4: The melt after bubble flotation flows into a third-stage hydrogen removal zone for gradient adsorption hydrogen removal through an adsorption bed containing a composite adsorption medium; S5: The low-hydrogen melt after three-stage hydrogen removal is discharged from the device outlet to supply a die casting machine for molding.

2. The magnesium-aluminum alloy die casting process on-line hydrogen removal method according to claim 1, characterized by: In S2, the primary hydrogen removal zone is provided with a high-power ultrasonic probe with adjustable power range. The ultrasonic generator is started, and the probe applies ultrasonic waves of a specific frequency and power to the melt. The cavitation effect produced by the ultrasonic waves creates a local transient high pressure, which promotes the diffusion and aggregation of hydrogen atoms into hydrogen gas microbubbles that escape. The hydrogen escape flux Contribution from diffusion and cavitation synergy: ， wherein : hydrogen diffusion coefficient in the MgAl melt; , : hydrogen concentration at the melt bulk and cavitation interface; : boundary layer thickness; : cavitation effect coefficient; : ultrasonic power, : frequency.

3. The magnesium-aluminum alloy die casting process on-line hydrogen removal method of claim 1, wherein: In S3, the bottom of the second-stage hydrogen removal zone is provided with a special gas-permeable brick through which high-purity inert gas is introduced; meanwhile, the inert gas bubbles rising are broken into a dispersed inert micro-bubble flow by a high-speed rotating graphite rotor; at this time, the residual hydrogen atoms in the melt rapidly diffuse to these micro-bubbles and rise to the liquid surface to escape; the diffusion rate of hydrogen from the melt to the inert micro-bubbles is as follows: ， The hydrogen removal efficiency is obtained by integration: ， where: : current hydrogen concentration; : hydrogen equilibrium concentration in the bubble, approximately 0 due to dilution by inert gas; : liquid phase mass transfer coefficient; : specific surface area of the gas bubbles per unit volume, ; : gas volume fraction; : average bubble diameter, which can reach 50 - 200 μm after dispersion by a graphite rotor; : secondary zone residence time.

4. The magnesium-aluminum alloy die casting process on-line hydrogen removal method of claim 1 wherein: In S4, the third-stage hydrogen removal zone is divided into a "high-temperature adsorption zone" and a "low-temperature adsorption zone" along the melt flow direction; In the high-temperature zone, the Mo element in the composite medium preferentially combines with high-concentration residual hydrogen to generate MoH2, rapidly reducing the hydrogen content to 0.15-0.17 ml / 100g; the high-temperature zone adsorption capacity is: ， In the low-temperature zone, the rare earth elements Ce / La in the composite medium capture trace hydrogen to generate CeH2 / LaH2 through chemical adsorption, and the Ti element removes tiny hydrogen bubbles through physical adsorption, finally stabilizing the hydrogen content to ≤0.10 ml / 100g; the low-temperature zone adsorption capacity is: ， Hydrogen adsorption amount in high temperature zone; : Hydrogen adsorption amount in low temperature zone; : Hydrogen adsorption amount in low temperature zone; : Hydrogen adsorption rate constant of Mo; : Chemical adsorption constant of rare earth; : Physical adsorption constant of Ti; : Mass fraction of corresponding element in composite medium; : Specific surface area of medium; : Porosity of medium; : Adsorption threshold value in high temperature zone; : Hydrogen content at outlet of high temperature zone; : Contact time of melt with adsorption medium; A 0.5mm-aperture ceramic screen is arranged at the bottom of the adsorption bed to intercept tiny particles generated by medium wear, avoiding the introduction of impurities into the casting.

5. The magnesium-aluminum alloy die casting process on-line hydrogen removal method of claim 1 wherein: In S4, the composite adsorption medium in the adsorption bed needs to be pretreated and activated: Ti-Mo-RE composite honeycomb particles with a particle size of 3-5mm and a porosity of 50%-60% are selected, and the mass ratio of Mo1.0%, Ce0.3%, La0.2%, and the balance of Ti is prepared; after the medium is filled into the adsorption bed, argon gas with a purity of ≥99.999% is introduced at a flow rate of 5-8L / min; at the same time, electromagnetic induction heating is performed to 700±10℃, and the medium is kept at this temperature for 30min to remove water vapor and impurities adsorbed on the surface of the medium; After activation is completed, the temperature is lowered to 680℃ and kept constant to form active adsorption sites on the surface of the medium.

6. An on-line hydrogen removal device for magnesium-aluminum alloy die casting process, comprising a plurality of aluminum melt pipes (1) and matching valves, characterized in that: One end of one of the aluminum melt pipelines (1) is connected to a first-stage hydrogen removal zone box (2), the other side of the first-stage hydrogen removal zone box (2) is connected to a second-stage hydrogen removal zone box (5) through an aluminum melt pipeline (1), the other side of the second-stage hydrogen removal zone box (5) is connected to the top of a third-stage hydrogen removal zone box (10) through an aluminum melt pipeline (1), and the other side of the bottom of the third-stage hydrogen removal zone box (10) is connected to an aluminum melt pipeline (1).

7. The magnesium-aluminum alloy die casting process on-line hydrogen removal apparatus of claim 6 wherein: An ultrasonic probe (3) is installed in the first-stage hydrogen removal zone box (2).

8. The magnesium-aluminum alloy die casting process on-line hydrogen removal apparatus of claim 6 wherein: The bottom of the secondary hydrogen removal zone box (5) is fixedly connected with a gas delivery pipe (7), the secondary hydrogen removal zone box (5) is internally provided with a gas permeable brick (6), the gas delivery pipe (7) extends into the secondary hydrogen removal zone box (5) and is connected with the gas permeable brick (6), the top of the secondary hydrogen removal zone box (5) is provided with a motor (8), the output end of the motor (8) extends into the secondary hydrogen removal zone box (5) and is fixedly connected with a graphite rotor (9).

9. The magnesium-aluminum alloy die casting process on-line hydrogen removal apparatus of claim 6 wherein: The tertiary hydrogen removal zone box (10) is divided into two parts, which are connected by an aluminum melt pipeline (1), and a plurality of adsorption beds (11) are fixedly connected in the tertiary hydrogen removal zone box (10).

10. The magnesium-aluminum alloy die casting process on-line hydrogen removal apparatus of claim 6 wherein: The top of the primary hydrogen removal zone box (2) and the secondary hydrogen removal zone box (5) are both provided with an exhaust pipe (4).

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