A low-hydrogen-content high-strength cast aluminum alloy and a method for producing the same

Abstract

The application relates to a low-hydrogen-content high-strength cast aluminum alloy and a preparation method thereof, and belongs to the technical field of metal alloys. The chemical composition of the aluminum alloy is as follows in terms of mass percentage: Si: 7.0-7.3%, Cu: 0.38-0.48%, Ce+La: 0.2-0.3%, Sr: 0.05-0.2%, Mg: 0.45-0.55%, Sb: 0.1-0.2%, Ti: 0.05-0.1%, Fe: <0.2%, the balance being Al and inevitable impurities, total impurities being <=0.3%, and single impurity being <=0.08%. The aluminum alloy obtained by optimizing the component composition of the aluminum alloy and stage-by-stage alloy melting has low gas content and high strength; compared with the aluminum alloy prepared by a conventional method, the strength reduction of the weld seam part is small, and there are no or fewer weld seam pores when the vacuum electron beam welding is carried out.

Description

Technical Field

[0001] This invention relates to the field of metal alloy technology, and in particular to a low-hydrogen-content, high-strength cast aluminum alloy and its preparation method. Background Technology

[0002] Cast aluminum alloys are commonly used alloy materials in the field of lightweight equipment. They are mainly used to manufacture shell, frame, box and cabin parts through casting process. They have the characteristics of excellent formability, strong adaptability to complex structures, good welding performance and good matching of comprehensive mechanical properties. They are widely used in the manufacture of important load-bearing key components in the fields of sea, land, air, space, fire and electricity.

[0003] Currently, cast aluminum alloys widely employ a combination of methods for slag and gas removal, including composite chloride salt slag and gas removal, argon gas blowing, vacuum methods, and ceramic filtration. Mature technologies both domestically and internationally can effectively reduce the gas content in cast aluminum alloys to a certain level, enabling the castings to be strengthened through heat treatment and achieving optimal internal quality standards such as HB963 and GB9438. However, with the increasing application of aluminum alloy castings in land, sea, air, space, and electronic fields, the joining technology for complex aluminum alloy castings has gradually upgraded from conventional riveting, bolting, resistance spot welding, and argon arc welding to vacuum electron beam welding, which offers less deformation, lower welding performance loss, and a higher degree of automation. Currently, when aluminum alloys are welded using vacuum electron beam welding, the strength loss rate at the weld is around 20%, and precipitated pores with a diameter of 0.2–0.5 mm appear at the weld. The welding quality is difficult to meet the development needs of future important equipment. Therefore, there is an urgent need for a casting aluminum alloy preparation method that can have a good hydrogen absorption effect and produce casting aluminum alloys with low gas content. When vacuum electron beam welding is performed, it can avoid the problems of excessive strength loss at the weld and excessive porosity in the weld. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a method for preparing a low-hydrogen-content, high-strength cast aluminum alloy to solve the problems of large strength reduction and excessive porosity in the weld seam when performing vacuum electron beam welding on existing aluminum alloy castings.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] On one hand, the present invention provides a low-hydrogen-content, high-strength cast aluminum alloy, the chemical composition of which, by mass percentage, is: Si: 7.0–7.3%, Cu: 0.38–0.48%, Ce+La: 0.2–0.3%, Sr: 0.05–0.2%, Mg: 0.45–0.55%, Sb: 0.1–0.2%, Ti: 0.05–0.1%, Fe: <0.2%, with the balance being Al and unavoidable impurities, total impurities ≤0.3%, and individual impurities ≤0.08%.

[0007] On the other hand, the present invention also provides a method for preparing a low-hydrogen-content high-strength cast aluminum alloy, which is used to prepare the above-mentioned low-hydrogen-content high-strength cast aluminum alloy, the preparation method comprising the following steps:

[0008] Step 1: Weigh and select pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, Al-Si20 master alloy, Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy as raw materials according to the mass percentage of each element.

[0009] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid, and then transfer it to the liquid.

[0010] Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid;

[0011] Step 4: Mix the first and second molten liquids, refine, heat-hold, cool, and pour to obtain aluminum alloy molten liquid. Pour the molten liquid into castings, and then perform solution treatment and aging treatment on the castings to obtain aluminum alloy.

[0012] Further, in step 2, the smelting process is as follows: after melting the pure Al ingot, Al-Cu50 master alloy, Al-Ti10 master alloy, Al-Si20 master alloy and granular refining agent are added in sequence, and the mixture is allowed to stand. Then, a covering agent is added, and a first smelting is carried out to obtain the first molten liquid, which is then transferred to the lower medium-frequency crucible of the vacuum pressure casting machine.

[0013] Furthermore, the pure Al ingot is melted at a temperature of 690–710°C, and the Al-Ti10 master alloy is preheated at a temperature of 400–450°C.

[0014] Furthermore, the amount of the granular refining agent used is 0.6 to 0.65% of the weight of the first molten liquid.

[0015] Furthermore, the covering agent is a mixed salt of KCl and NaCl, which is baked at 300-310°C for ≥2 hours before use.

[0016] Further, in step 3, the smelting process specifically involves: adding Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy into the upper intermediate frequency furnace of the vacuum pressure casting machine, sealing the vacuum tank, evacuating to -0.09MPa to -0.095MPa, starting the upper intermediate frequency furnace for smelting at a smelting temperature of 740 to 750℃, and obtaining the second molten liquid.

[0017] Further, the refining process in step 4 is as follows: mix the first molten liquid and the second molten liquid, introduce high-purity argon gas into the mixture at a pressure of 0.02-0.04 MPa and a flow rate of 0.1-0.2 m3 / h, rotate and refine for 30-35 min, and refine at a temperature of 720-730℃.

[0018] Furthermore, in step 4, the heat preservation time is 30-40 minutes.

[0019] Furthermore, in step 4, the solution temperature is 500–540°C, the solution time is 8–12 h, the aging temperature is 150–180°C, and the aging time is 6–12 h.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The preparation method of this invention controls the composition ratio of aluminum alloy by adding mixed rare earth elements and optimizing the content of high-strength alloying elements; combined with multi-element modification treatment and staged alloy melting, it realizes the preparation of high-strength aluminum alloy by vacuum casting. The aluminum alloy prepared by this invention has a low hydrogen content while ensuring high strength. Compared with aluminum alloys prepared by conventional methods, the strength drop of the weld is small and there is no weld porosity or the porosity is small when vacuum electron beam welding is performed.

[0022] 2. The preparation method of the present invention reduces the exposure time of easily oxidized and easily hydrogen-absorbing elements in the atmospheric environment by melting the alloy in stages, directly and effectively controlling the hydrogen absorption of the melt and reducing the gas content of the aluminum alloy.

[0023] 3. The preparation method of the present invention achieves multi-stage and multi-dimensional hydrogen removal by slag removal treatment in the first stage of smelting process, mixed chloride salt covering to prevent hydrogen absorption, vacuum treatment in the second stage, rare earth hydrogen removal and low-pressure argon gas hydrogen removal blowing treatment, which effectively reduces the hydrogen content of aluminum alloy.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 This is a diagram of the weld area of ​​aluminum alloy subjected to vacuum electron beam welding in Embodiment 1 of the present invention;

[0027] Figure 2 This is a diagram of the weld area of ​​aluminum alloy in Comparative Example 2 of the present invention, obtained by vacuum electron beam welding. Detailed Implementation

[0028] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0029] This invention provides a low-hydrogen-content, high-strength cast aluminum alloy. The chemical composition of the aluminum alloy, by mass percentage, is as follows: Si: 7.0–7.3%, Cu: 0.38–0.48%, Ce+La: 0.2–0.3%, Sr: 0.05–0.2%, Mg: 0.45–0.55%, Sb: 0.1–0.2%, Ti: 0.05–0.1%, Fe: <0.2%, with the balance being Al and unavoidable impurities, total impurities ≤0.3%, and individual impurities ≤0.08%.

[0030] The reasons for limiting the alloy composition of the cast billet in the low-hydrogen-content high-strength cast aluminum alloy and its preparation method in this invention are explained below. The following uses only % to represent the mass percentage of the composition:

[0031] Si: Improves casting performance, forms a reinforcing phase Mg2Si with Mg, and enhances material strength through heat treatment. The Si content of the low-hydrogen-content, high-strength cast aluminum alloy provided by this invention is selected in the range of 7.0% to 7.3%.

[0032] Cu has a solid solution strengthening effect. CuAl2 can be precipitated through aging treatment, and the aging strengthening effect is obvious. The solubility of Cu in Al is 5.6%. If the Cu content is too high, the excess Cu atoms will combine with Fe atoms in the alloy to form a coarse Al7Cu2Fe precipitate. This phase is a brittle phase, which will significantly reduce the fracture toughness of the alloy. It is also prone to overheating during solid solution treatment, reducing the mechanical properties and corrosion resistance of the alloy. If the Cu content is too low, the strengthening effect is insufficient and the alloy performance is not high. The Cu content of the low hydrogen content high strength cast aluminum alloy provided by this invention is selected in the range of 0.38% to 0.48%.

[0033] Ce+La: Increases compositional supercooling during the solidification process of aluminum alloys, refines grains, reduces secondary grain spacing, reduces gases and inclusions in the alloy, and spheroidizes heterogeneous phases; reduces the surface tension of the aluminum alloy melt, increases fluidity, and is beneficial for casting and molding, but is prone to oxidation and burn-off during the melting process; the Ce+La content of the low-hydrogen-content high-strength cast aluminum alloy provided by this invention is selected in the range of 0.2-0.3%.

[0034] Sr: A long-lasting modifier for silicon-containing aluminum alloys, which can reduce the size of primary silicon particles and significantly improve strength and elongation after fracture. However, aluminum alloys modified with Sr have a greater tendency to absorb gas, resulting in more pinhole defects in aluminum castings and a higher probability of defects. The Sr content of the low-hydrogen-content high-strength cast aluminum alloy provided by this invention is selected in the range of 0.05% to 0.2%.

[0035] Mg: It forms a strengthening phase with silicon, which can improve strength and yield strength and improve the machinability of the alloy. However, it is prone to oxidation and burn-off during the smelting process. If the Mg content is too high, undissolved phases will form. If the Mg content is too low, the strengthening effect is insufficient and the alloy performance is not high. The Mg content of the low hydrogen content high strength cast aluminum alloy provided by this invention is selected in the range of 0.45% to 0.55%.

[0036] Sb: Antimony can perform atypical modification treatment on Al-Si cast aluminum alloys, with good modification long-term effect, improving the mechanical properties of castings, and can also suppress gas absorption of aluminum alloys and reduce the tendency to produce pinholes; the Sb content of the low hydrogen content high strength cast aluminum alloy provided by this invention is selected in the range of 0.1% to 0.2%.

[0037] Ti: Titanium forms the TiAl2 phase with aluminum, which becomes a non-spontaneous nucleus during crystallization and plays a role in refining the casting structure and weld structure; the Ti content of the low hydrogen content high strength cast aluminum alloy provided by this invention is selected in the range of 0.05 to 0.1%.

[0038] Fe: In AlSi alloys, it forms needle-like β-AlSiFe phase, which has a severe cutting effect on the matrix and significantly reduces the overall mechanical properties of the alloy. Therefore, its content must be strictly controlled. The low hydrogen content high strength cast aluminum alloy provided by this invention has an Fe content of <0.2%.

[0039] This invention also provides a method for preparing a low-hydrogen-content, high-strength cast aluminum alloy, comprising the following steps:

[0040] Step 1: Based on the mass percentage of each element in the aluminum alloy, weigh and select pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, Al-Si20 master alloy, Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy as raw materials.

[0041] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid;

[0042] Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid;

[0043] Step 4: Mix the first and second molten liquids and refine them to obtain aluminum alloy molten liquid. Cast the molten liquid into a casting. The casting is then subjected to solution treatment and aging treatment to obtain aluminum alloy.

[0044] Specifically, in step 2, after melting pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, Al-Si20 master alloy and granular refining agent are added in sequence, allowed to stand, and then a covering agent is added for a first melting process to obtain the first melt.

[0045] It should be noted that the melting temperature of pure Al ingots is 690–710℃. The Al-Ti10 master alloy is preheated at 400–450℃ to improve the Ti element yield. A granular refining agent is added, with the amount being 0.6–0.65% of the weight of the first molten aluminum. This refining agent is mainly used to remove hydrogen and floating oxide inclusions from the aluminum molten aluminum, making it purer, and also acts as a slag remover. In existing casting processes, the amount of refining agent used is generally 0.3% of the weight of the aluminum molten aluminum. The refining agent of this invention… The dosage is much greater than 0.3% because the refining agent is mainly used for slag removal and degassing. However, when the alloy contains surface-active elements (Sr, RE) or easily oxidized elements such as Mg, a large amount of refining agent will cause severe burn-off. This invention performs alloy melting in stages. In step 2, during the melting of pure aluminum ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid, there are no easily oxidized elements, so the proportion of refining agent can be appropriately increased to achieve better preliminary slag removal and degassing effects. Afterward, the molten liquid is allowed to stand at 695-700℃ for 30-40 minutes for slag removal and purification. Then, a mixed salt of KCl and NaCl, baked at 300–310℃ for more than 2 hours, is used as a covering agent. KCl and NaCl are mixed in a 1:1 mass ratio. The covering agent is applied to the surface of the first molten liquid at a concentration of 0.2–0.25% of the liquid's weight. After the covering agent melts, the temperature is raised to 730–740℃ and held for 2–2.5 hours. The first molten liquid is then transferred to the lower induction crucible within the vacuum pressure casting machine. The crucible is preheated to 700–720℃ before the transfer. The vacuum pressure casting machine includes an upper induction furnace, a lower induction furnace, a graphite stopper rod, a graphite refining rod, a vacuum vessel, and a mold.

[0046] It should be noted that the present invention uses a mixed salt of potassium chloride and sodium chloride as a covering agent, which is applied to the surface of the first molten liquid in a liquid form. The coverage area is large, and it only serves to isolate the melt from the air. It does not have a refining and degassing effect. The mixed salt has strong dispersion and forms a dense and thin molten salt layer on the surface of the first molten liquid. The volume of the molten salt layer is significantly different from that of the first molten liquid. It not only has an isolation effect, but also does not contaminate the first molten liquid due to the density difference and mutual repulsion between the two.

[0047] Specifically, in step 3, Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy are added to the upper intermediate frequency furnace. The upper and lower intermediate frequency furnaces are connected by a single cover. The cover is then placed on the furnace, the vacuum tank is sealed, and a vacuum is drawn. During the vacuuming process, the lower intermediate frequency furnace is kept at 720-750℃ to preheat the furnace body. When the vacuum reaches -0.09MPa to -0.095MPa, the upper intermediate frequency furnace is started until the furnace charge is melted to 740-750℃ to obtain the second molten liquid.

[0048] Start the graphite plug rod at the bottom of the upper intermediate frequency furnace, and all the second molten liquid falls into the lower intermediate frequency furnace. The first molten liquid and the second molten liquid are mixed. The mixture is kept at 720-730℃ for 10-20 minutes in the lower intermediate frequency furnace.

[0049] Specifically, in step 4, at this point, the first and second molten liquids have been mixed. The graphite stopper rod is rotated, and the graphite refining rod on the outer side of the upper intermediate frequency furnace is started. The graphite refining rod rotates along the circular track on the outer side of the upper intermediate frequency furnace, and high-purity argon gas is introduced into the lower intermediate frequency furnace through the middle of the graphite refining rod at a pressure of 0.02-0.04 MPa and a flow rate of 0.1-0.2 m³ / s. 3 Rotary refining for 30-35 minutes at a refining temperature of 720-730℃. After refining, continue to hold at 720-730℃ for 30-40 minutes, then furnace cooling. When the temperature drops to 705-710℃, tilt and pour to obtain the casting.

[0050] The obtained castings were subjected to solution treatment and aging treatment in sequence. The solution treatment temperature was 500-540℃ and the solution treatment time was 8-12h. The aging temperature was 150-180℃ and the aging time was 6-12h to obtain the low hydrogen content high strength aluminum alloy.

[0051] The cast aluminum alloy prepared by the method of this invention has a gas content of 0.056-0.062 ml / 100gAl. After heat treatment, the tensile strength of the sand mold specimen is 365-375 MPa, and the elongation after fracture is 6-8.5%. After heat treatment, the tensile strength of the gypsum mold specimen is 345-358 MPa, and the elongation after fracture is 4.5-5.5%. Vacuum electron beam welding of the cast aluminum alloy of this invention, compared with conventional melting methods, results in a weld area with no or very small pores.

[0052] The advantages of precise control of the elemental chemical composition, content, and preparation process parameters of the present invention will be demonstrated below with specific examples.

[0053] Example 1

[0054] This embodiment is a sand casting.

[0055] A low-hydrogen-content, high-strength cast aluminum alloy has the following chemical composition by mass percentage: Si: 7.0%, Cu: 0.38%, Ce+La: 0.2%, Sr: 0.05%, Mg: 0.45%, Sb: 0.2%, Ti: 0.1%, Fe: 0.1%, with the balance being Al and unavoidable impurities, total impurities 0.12%, and individual impurities 0.04%.

[0056] In this embodiment, the preparation method of low-hydrogen-content high-strength cast aluminum alloy is as follows:

[0057] Step 1: Based on the mass percentage of each element in the aluminum alloy, weigh and select 104.48 kg of pure Al ingot, 1.52 kg of Al-Cu50 master alloy, 2 kg of Al-Ti10 master alloy, 70 kg of Al-Si20 master alloy, 8 kg of Al-Sb5 master alloy, 9 kg of Al-Mg10 master alloy, 1 kg of Al-Sr10 master alloy, and 4 kg of Al-(Ce+La)10 master alloy as raw materials;

[0058] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid;

[0059] Among them, pure Al ingots are melted at 710℃, and Al-Ti10 master alloy is preheated at 400℃.

[0060] Add granular refining agent at a rate of 0.6% of the weight of the first molten liquid, settling at 695°C for 30 minutes.

[0061] A mixture of potassium chloride and sodium chloride, baked at 300°C for more than 2 hours, is used as a covering agent to cover the surface of the first molten liquid. The amount of the mixed salt is 0.2% of the weight of the first molten liquid. After the mixed salt melts, the temperature is raised to 730°C and held for 2 hours. Then, the first molten liquid is transferred to the lower medium-frequency crucible in the vacuum pressure casting machine. The crucible is preheated to 700°C before the liquid is transferred.

[0062] Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid;

[0063] Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy are added to the upper intermediate frequency furnace. The upper and lower intermediate frequency furnaces have integrated covers. The cover is closed, and the vacuum tank is sealed. The lower intermediate frequency furnace is evacuated and maintained at 720℃ throughout the evacuation process. When the vacuum reaches -0.09MPa to -0.095MPa, the upper intermediate frequency furnace is started until the charge is melted to 740℃, obtaining the second molten liquid. The graphite stopper at the bottom of the upper intermediate frequency furnace is activated, and the second molten liquid falls entirely into the lower intermediate frequency furnace. It is held at 720℃ for 10 minutes, and then the power is turned off.

[0064] Step 4: Mix the first and second molten liquids and refine them to obtain aluminum alloy molten liquid, which is then cast into a casting.

[0065] The first and second molten metals have been mixed. The graphite stopper rod is rotated, and the graphite refining rod on the outer side of the upper intermediate frequency furnace is started. The graphite refining rod rotates along the circular track on the outer side of the upper intermediate frequency furnace, and high-purity argon gas is introduced into the lower intermediate frequency furnace through the middle of the graphite refining rod at a pressure of 0.04 MPa and a flow rate of 0.1 m³ / s. 3 / h, rotary refining for 30min, refining temperature 720℃, holding temperature 720℃, holding time 30min, wait for the temperature to drop to 705℃, tilt and pour to obtain the casting.

[0066] The obtained castings were subjected to solution treatment and aging treatment sequentially. The solution treatment temperature was 500℃ and the solution treatment time was 12 hours. The aging temperature was 180℃ and the aging time was 8 hours. The low-hydrogen-content high-strength aluminum alloy was obtained.

[0067] Example 2

[0068] This embodiment is a sand casting.

[0069] A low-hydrogen-content, high-strength cast aluminum alloy has the following chemical composition by mass percentage: Si: 7.16%, Cu: 0.42%, Ce+La: 0.27%, Sr: 0.11%, Mg: 0.51%, Sb: 0.12%, Ti: 0.07%, Fe: 0.10%, with the balance being Al and unavoidable impurities, total impurities 0.16%, and individual impurities 0.05%.

[0070] In this embodiment, the preparation method of low-hydrogen-content high-strength cast aluminum alloy is as follows:

[0071] Step 1: Weigh and select the following raw materials according to the mass percentage of each element: 205.44 kg of pure Al ingot, 3.36 kg of Al-Cu50 master alloy, 2.8 kg of Al-Ti10 master alloy, 143.2 kg of Al-Si20 master alloy, 9.6 kg of Al-Sb5 master alloy, 20.4 kg of Al-Mg10 master alloy, 4.4 kg of Al-Sr10 master alloy, and 10.8 kg of Al-(Ce+La)10 master alloy.

[0072] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid;

[0073] Pure Al ingots were melted at 710℃, and the Al-Ti10 master alloy was preheated at 400℃. Granular refining agent was added at a rate of 0.62% of the weight of the first melt. The settling temperature was 700℃ and the settling time was 40 minutes.

[0074] A mixture of potassium chloride and sodium chloride salt, baked at 300°C for more than 2 hours, is used as a covering agent to cover the surface of the first molten liquid. The amount of the mixed salt is 0.25% of the weight of the first molten liquid. After the mixed salt melts, the temperature is raised to 740°C and held for 2.5 hours. Then, the first molten liquid is transferred to the lower medium-frequency crucible in the vacuum pressure casting machine. The crucible is preheated to 700°C before the liquid is transferred.

[0075] Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid;

[0076] Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy are added to the upper intermediate frequency furnace. The upper and lower intermediate frequency furnaces have integrated covers. The cover is closed, and the vacuum tank is sealed. The lower intermediate frequency furnace is evacuated and maintained at 736℃ throughout the evacuation process. When the vacuum reaches -0.09MPa to -0.095MPa, the upper intermediate frequency furnace is started until the charge is melted to 750℃, obtaining the second molten liquid. The graphite stopper at the bottom of the upper intermediate frequency furnace is activated, and the second molten liquid falls entirely into the lower intermediate frequency furnace. It is held at 730℃ for 20 minutes, and then the power is turned off.

[0077] Step 4: Mix the first and second molten liquids and refine them to obtain aluminum alloy molten liquid, which is then cast into a casting.

[0078] The first and second molten metals have been mixed. The graphite stopper rod is rotated, and the graphite refining rod on the outer side of the upper intermediate frequency furnace is started. The graphite refining rod rotates along the circular track on the outer side of the upper intermediate frequency furnace, and high-purity argon gas is introduced into the lower intermediate frequency furnace through the middle of the graphite refining rod at a pressure of 0.032 MPa and a flow rate of 0.14 m³ / s. 3 The process involves rotating the refining vessel for 35 minutes at a refining temperature of 725℃ and a holding temperature of 725℃ for 34 minutes. Once the temperature drops to 706℃, the vessel is tilted and poured to obtain the casting.

[0079] The obtained castings were subjected to solution treatment and aging treatment in sequence. The solution treatment temperature was 530℃ and the solution treatment time was 10h. The aging temperature was 150℃ and the aging time was 12h to obtain the low hydrogen content high strength aluminum alloy.

[0080] Example 3

[0081] This embodiment is a sand casting.

[0082] A low-hydrogen-content, high-strength cast aluminum alloy has the following chemical composition by mass percentage: Si: 7.0%, Cu: 0.38%, Ce+La: 0.2%, Sr: 0.05%, Mg: 0.45%, Sb: 0.2%, Ti: 0.1%, Fe: 0.1%, with the balance being Al and unavoidable impurities, total impurities 0.12%, and individual impurities 0.04%.

[0083] In this embodiment, the preparation method of low-hydrogen-content high-strength cast aluminum alloy is as follows:

[0084] Step 1: Based on the mass percentage of each element in the aluminum alloy, weigh and select 104.48 kg of pure Al ingot, 1.52 kg of Al-Cu50 master alloy, 2 kg of Al-Ti10 master alloy, 70 kg of Al-Si20 master alloy, 8 kg of Al-Sb5 master alloy, 9 kg of Al-Mg10 master alloy, 1 kg of Al-Sr10 master alloy, and 4 kg of Al-(Ce+La)10 master alloy as raw materials;

[0085] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid;

[0086] Pure Al ingots were melted at 710℃, and the Al-Ti10 master alloy was preheated at 400℃. Granular refining agent was added at a rate of 0.62% of the weight of the first melt. The settling temperature was 700℃ and the settling time was 40 minutes.

[0087] A mixture of potassium chloride and sodium chloride salt, baked at 300°C for more than 2 hours, is used as a covering agent to cover the surface of the first molten liquid. The amount of the mixed salt is 0.25% of the weight of the first molten liquid. After the mixed salt melts, the temperature is raised to 740°C and held for 2.5 hours. Then, the first molten liquid is transferred to the lower medium-frequency crucible in the vacuum pressure casting machine. The crucible is preheated to 700°C before the liquid is transferred.

[0088] Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid;

[0089] Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy are added to the upper intermediate frequency furnace. The upper and lower intermediate frequency furnaces have integrated covers. The cover is closed, and the vacuum tank is sealed. The lower intermediate frequency furnace is evacuated and maintained at 736℃ throughout the evacuation process. When the vacuum reaches -0.09MPa to -0.095MPa, the upper intermediate frequency furnace is started until the charge is melted to 750℃, obtaining the second molten liquid. The graphite stopper at the bottom of the upper intermediate frequency furnace is activated, and the second molten liquid falls entirely into the lower intermediate frequency furnace. It is held at 730℃ for 20 minutes, and then the power is turned off.

[0090] Step 4: Mix the first and second molten liquids and refine them to obtain aluminum alloy molten liquid, which is then cast into a casting.

[0091] The first and second molten metals have been mixed. The graphite stopper rod is rotated, and the graphite refining rod on the outer side of the upper intermediate frequency furnace is started. The graphite refining rod rotates along the circular track on the outer side of the upper intermediate frequency furnace, and high-purity argon gas is introduced into the lower intermediate frequency furnace through the middle of the graphite refining rod at a pressure of 0.032 MPa and a flow rate of 0.14 m³ / s. 3 The process involves rotating the refining vessel for 35 minutes at a refining temperature of 725℃ and a holding temperature of 725℃ for 34 minutes. Once the temperature drops to 706℃, the vessel is tilted and poured to obtain the casting.

[0092] The obtained castings were subjected to solution treatment and aging treatment in sequence. The solution treatment temperature was 530℃ and the solution treatment time was 10h. The aging temperature was 150℃ and the aging time was 12h to obtain the low hydrogen content high strength aluminum alloy.

[0093] Example 4

[0094] This embodiment is a plaster mold casting.

[0095] A low-hydrogen-content, high-strength cast aluminum alloy has the following chemical composition by mass percentage: Si: 7.3%, Cu: 0.48%, Ce+La: 0.3%, Sr: 0.2%, Mg: 0.55%, Sb: 0.1%, Ti: 0.05%, Fe: 0.2%, with the balance being Al and unavoidable impurities, total impurities 0.18%, and individual impurities 0.08%.

[0096] In this embodiment, the preparation method of low-hydrogen-content high-strength cast aluminum alloy is as follows:

[0097] Step 1: Weigh and select the following raw materials according to the mass percentage of each element: 24.77 kg of pure Al ingot, 0.48 kg of Al-Cu50 master alloy, 0.25 kg of Al-Ti10 master alloy, 18.25 kg of Al-Si20 master alloy, 1 kg of Al-Sb5 master alloy, 2.75 kg of Al-Mg10 master alloy, 1 kg of Al-Sr10 master alloy, and 1.5 kg of Al-(Ce+La)10 master alloy.

[0098] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid;

[0099] Pure aluminum ingots were melted at 710℃, and Al-Ti10 master alloy was preheated at 400℃. Granular refining agent was added at a rate of 0.65% of the weight of the first melt. The settling temperature was 698℃ and the settling time was 30 minutes.

[0100] A mixture of potassium chloride and sodium chloride, baked at 300°C for more than 2 hours, is used as a covering agent to cover the surface of the first molten liquid. The amount of the mixed salt is 0.22% of the weight of the first molten liquid. After the mixed salt melts, the temperature is raised to 736°C and held for 2.1 hours. Then, the first molten liquid is transferred to the lower medium-frequency crucible in the vacuum pressure casting machine. The crucible is preheated to 700°C before the transfer.

[0101] Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid;

[0102] Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy are added to the upper intermediate frequency furnace. The upper and lower intermediate frequency furnaces have integrated covers. The cover is closed, and the vacuum tank is sealed. The lower intermediate frequency furnace is evacuated and maintained at 750℃ throughout the evacuation process. When the vacuum reaches -0.09MPa to -0.095MPa, the upper intermediate frequency furnace is started until the charge is melted to 746℃, obtaining the second molten liquid. The graphite stopper at the bottom of the upper intermediate frequency furnace is activated, and the second molten liquid falls entirely into the lower intermediate frequency furnace. It is held at 725℃ for 16 minutes, and then the power is turned off.

[0103] Step 4: Mix the first and second molten liquids and refine them to obtain aluminum alloy molten liquid, which is then cast into a casting.

[0104] The first and second molten metals have been mixed. The graphite stopper rod is rotated, and the graphite refining rod on the outer side of the upper intermediate frequency furnace is started. The graphite refining rod rotates along the circular track on the outer side of the upper intermediate frequency furnace, and high-purity argon gas is introduced into the lower intermediate frequency furnace through the middle of the graphite refining rod at a pressure of 0.02 MPa and a flow rate of 0.2 m³ / s. 3 The process involves rotating the refining vessel for 33 minutes at a refining temperature of 730℃ and a holding temperature of 730℃ for 40 minutes. After the temperature drops to 710℃, the vessel is tilted and poured to obtain the casting.

[0105] The obtained castings were subjected to solution treatment and aging treatment in sequence. The solution treatment temperature was 540℃ and the solution treatment time was 8h. The aging temperature was 165℃ and the aging time was 6h to obtain the low hydrogen content high strength aluminum alloy.

[0106] Comparative Example 1

[0107] This comparative example is a sand casting.

[0108] A low-hydrogen-content, high-strength cast aluminum alloy has the following chemical composition by mass percentage: Si: 7.0%, Cu: 0.1%, Ce+La: 0.05%, Sr: 0.05%, Mg: 0.45%, Sb: 0.04%, Ti: 0.1%, Fe: 0.1%, with the balance being Al and unavoidable impurities, total impurities 0.12%, and individual impurities 0.04%.

[0109] In this embodiment, the preparation method of low-hydrogen-content high-strength cast aluminum alloy is as follows:

[0110] Step 1: Weigh and select the following raw materials based on the mass percentage of each element: 172.5 kg of pure Al ingot, 0.6 kg of Al-Cu50 master alloy, 3 kg of Al-Ti10 master alloy, 105 kg of Al-Si20 master alloy, 2.4 kg of Al-Sb5 master alloy, 13.5 kg of Al-Mg10 master alloy, 1.5 kg of Al-Sr10 master alloy, and 1.5 kg of Al-(Ce+La)10 master alloy.

[0111] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid;

[0112] Pure aluminum ingots were melted at 710℃, Al-Ti10 master alloy was preheated at 400℃, granular refining agent was added at a rate of 0.6% of the weight of the first melt, and the settling temperature was 695℃ for 20 minutes.

[0113] A mixture of potassium chloride and sodium chloride, baked at 300°C for more than 2 hours, is used as a covering agent to cover the surface of the first molten liquid. The amount of the mixed salt is 0.2% of the weight of the first molten liquid. After the mixed salt melts, the temperature is raised to 730°C and held for 2 hours. Then, the first molten liquid is transferred to the lower medium-frequency crucible in the vacuum pressure casting machine. The crucible is preheated to 700°C before the liquid is transferred.

[0114] Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid;

[0115] Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy are added to the upper intermediate frequency furnace. The upper and lower intermediate frequency furnaces have integrated covers. The cover is closed, and the vacuum tank is sealed. The lower intermediate frequency furnace is evacuated and maintained at 720℃ throughout the evacuation process. When the vacuum reaches -0.09MPa to -0.095MPa, the upper intermediate frequency furnace is started until the charge is melted to 740℃, obtaining the second molten liquid. The graphite stopper at the bottom of the upper intermediate frequency furnace is activated, and the second molten liquid falls entirely into the lower intermediate frequency furnace. It is held at 720℃ for 10 minutes, and then the power is turned off.

[0116] Step 4: Mix the first and second molten liquids and refine them to obtain aluminum alloy molten liquid, which is then cast into a casting.

[0117] The first and second molten metals have been mixed. The graphite stopper rod is rotated, and the graphite refining rod on the outer side of the upper intermediate frequency furnace is started. The graphite refining rod rotates along the circular track on the outer side of the upper intermediate frequency furnace, and high-purity argon gas is introduced into the lower intermediate frequency furnace through the middle of the graphite refining rod at a pressure of 0.04 MPa and a flow rate of 0.1 m³ / s. 3 / h, rotary refining for 30min, refining temperature 720℃, holding temperature 720℃, holding time 30min, wait for the temperature to drop to 705℃, tilt and pour to obtain the casting.

[0118] The obtained castings were subjected to solution treatment and aging treatment in sequence. The solution treatment temperature was 500℃ and the solution treatment time was 12h. The aging temperature was 180℃ and the aging time was 8h to obtain the low hydrogen content high strength aluminum alloy.

[0119] Comparative Example 2

[0120] This comparative example is a sand casting.

[0121] A low-hydrogen-content, high-strength cast aluminum alloy has the following chemical composition by mass percentage: Si: 7.1%, Cu: 0.4%, Ce+La: 0.21%, Sr: 0.08%, Mg: 0.47%, Sb: 0.13%, Ti: 0.07%, Fe: 0.2%, with the balance being Al and unavoidable impurities, total impurities 0.16%, and individual impurities 0.05%.

[0122] In this embodiment, the preparation method of low-hydrogen-content high-strength cast aluminum alloy is as follows:

[0123] Step 1: Weigh and select the following master alloys according to the mass percentage of each element: 182.26 kg of pure Al ingot, 1.6 kg of Al-Cu50 master alloy, 1.4 kg of Al-Ti10 master alloy, 71 kg of Al-Si20 master alloy, 5.2 kg of Al-Sb5 master alloy, 9.4 kg of Al-Mg10 master alloy, 1.6 kg of Al-Sr10 master alloy, and 4.2 kg of Al-(Ce+La)10 master alloy as raw materials;

[0124] Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, Al-Si20 master alloy, Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy at 780℃.

[0125] Add granular refining agent at a rate of 0.3% of the weight of the molten liquid, set at a standing temperature of 710℃, and set for 20 minutes.

[0126] The melt is transferred to the lower intermediate frequency furnace inside the vacuum furnace. The graphite refining rod on the outer side of the upper intermediate frequency furnace is started. The graphite refining rod rotates along the circular track on the outer side of the upper intermediate frequency furnace, and high-purity argon gas is introduced into the lower intermediate frequency furnace through the middle of the graphite refining rod at a pressure of 0.04 MPa and a flow rate of 0.1 m³ / s. 3 / h, rotary refining for 30min, refining temperature 720℃, holding temperature 720℃, holding time 30min, wait for the temperature to drop to 705℃, tilt and pour to obtain the casting.

[0127] The obtained castings were subjected to solution treatment and aging treatment sequentially. The solution treatment temperature was 500℃ and the solution treatment time was 12 hours. The aging temperature was 180℃ and the aging time was 8 hours. Aluminum alloy castings were obtained.

[0128] The aluminum alloy compositions of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1. The content of some components in the aluminum alloy of Comparative Example 1 does not meet the requirements of this invention. The gas content of the cast aluminum alloys of Examples 1-4 and Comparative Examples 1-2 was tested, and the results are shown in Table 2. The room temperature performance of the cast aluminum alloys of Examples 1-4 and Comparative Examples 1-2 was tested according to GB / T 228.1-2010, and the results are shown in Table 3. The cast aluminum alloys of Examples 1-4 and Comparative Examples 1-2 were subjected to vacuum electron beam welding, and the porosity of the weld area is shown in Table 4. The cast aluminum alloys of Examples 1-4 and Comparative Examples 1-2 were subjected to vacuum electron beam welding, and the weld area strength is shown in Table 5.

[0129] Table 1. Aluminum alloy composition (wt, %) of the examples and comparative examples

[0130] Example 1 7.0 0.38 0.2 0.05 0.45 0.2 0.1 0.1 0.12 0.04 Example 2 7.16 0.42 0.27 0.11 0.51 0.12 0.07 0.1 0.16 0.05 Example 3 7.0 0.38 0.2 0.05 0.45 0.2 0.1 0.1 0.12 0.04 Example 4 7.3 0.48 0.3 0.2 0.55 0.1 0.05 0.2 0.18 0.08 Comparative Example 1 7.0 0.1 0.05 0.05 0.45 0.04 0.1 0.1 0.12 0.04 Comparative Example 2 7.1 0.4 0.21 0.08 0.47 0.13 0.07 0.2 0.16 0.05

[0131] Table 2 Gas content of aluminum alloys in the examples and comparative examples

[0132] Example 1 0.056ml / 100gAl Example 2 0.062ml / 100gAl Example 3 0.057ml / 100gAl Example 4 0.059ml / 100gAl Comparative Example 1 0.062ml / 100gAl Comparative Example 2 0.10ml / 100gAl

[0133] Table 3 Mechanical properties of aluminum alloys in the examples and comparative examples at room temperature

[0134] Example 1 375 300 8.5 Example 2 371 280 7 Example 3 372 293 8.0 Example 4 365 288 6 Comparative Example 1 353 276 6 Comparative Example 2 332 268 4.5

[0135] Table 4. Porosity of weld area after vacuum electron beam welding of aluminum alloys in the examples and comparative examples.

[0136] Example 1 none / / Example 2 have 1 0.05 Example 3 none / / Example 4 none / / Comparative Example 1 none / / Comparative Example 2 have 3 0.13

[0137] Table 5. Weld zone strength after vacuum electron beam welding of aluminum alloys in the examples and comparative cases.

[0138]

[0139] In Comparative Example 1, the content of some components of the aluminum alloy did not meet the requirements of this invention. The preparation process parameters were the same as in Example 1, and the mechanical properties of the resulting cast aluminum alloy were lower than those in Example 1. In Comparative Example 2, although the component content of the aluminum alloy was within the range required by this invention, the preparation process method differed from that of this invention. Staged alloy melting was not performed, and the gas content of the final aluminum alloy was significantly higher than that of the examples of this invention. After vacuum electron beam welding, the number and size of pores in the weld area were significantly higher than those in the examples of this invention; the weld area strength was lower than that of the examples; and compared to the mechanical properties of the aluminum alloy at room temperature, the decrease in weld area strength was greater than that of the examples.

[0140] The cast aluminum alloy prepared by the method of this invention has a gas content of 0.056–0.062 ml / 100 g Al; its mechanical properties are: tensile strength of 365–375 MPa, yield strength of 288–300 MPa, and elongation after fracture of 6–8.5%. Vacuum electron beam welding of the cast aluminum alloy of this invention, compared with conventional melting methods, results in a weld area with no or very small porosity and a low strength reduction in the weld area.

[0141] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a low-hydrogen-content, high-strength cast aluminum alloy, characterized in that, The preparation method includes the following steps: Step 1: Weigh and select pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, Al-Si20 master alloy, Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy as raw materials according to the mass percentage of each element. Step 2: Melt pure Al ingots, Al-Cu50 master alloy, Al-Ti10 master alloy, and Al-Si20 master alloy to obtain the first molten liquid, and then transfer it to the liquid. Step 3: Melt the Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy to obtain the second molten liquid; Step 4: Mix the first and second molten liquids and refine them to obtain aluminum alloy molten liquid. Keep the aluminum alloy molten liquid at a constant temperature, cool it, and pour it to obtain a casting. The casting is then subjected to solution treatment and aging treatment in sequence to obtain an aluminum alloy. The chemical composition of the aluminum alloy, by mass percentage, is: Si: 7.0~7.3%, Cu: 0.38~0.48%, Ce+La: 0.2~0.3%, Sr: 0.05~0.2%, Mg: 0.45~0.55%, Sb: 0.1~0.2%, Ti: 0.05~0.1%, Fe: <0.2%, balance is Al and unavoidable impurities, total impurities ≤0.3%, individual impurities ≤0.08%.

2. The method for preparing low-hydrogen-content high-strength cast aluminum alloy according to claim 1, characterized in that, In step 2, the smelting process is as follows: after melting the pure Al ingot, Al-Cu50 master alloy, Al-Ti10 master alloy, Al-Si20 master alloy and granular refining agent are added in sequence, and the mixture is allowed to stand. Then, a covering agent is added, and a first smelting is carried out to obtain the first molten liquid. The molten liquid is then transferred to the lower medium-frequency crucible of the vacuum pressure casting machine.

3. The method for preparing low-hydrogen-content high-strength cast aluminum alloy according to claim 2, characterized in that, The pure Al ingot is melted at 690~710℃, and the Al-Ti10 master alloy is preheated at 400~450℃.

4. The method for preparing low-hydrogen-content high-strength cast aluminum alloy according to claim 2, characterized in that, The amount of the granular refining agent used is 0.6 to 0.65% of the weight of the first molten liquid.

5. The method for preparing low-hydrogen-content high-strength cast aluminum alloy according to claim 2, characterized in that, The covering agent is a mixed salt of KCl and NaCl, which is baked at 300~310℃ for ≥2h before use.

6. The method for preparing low-hydrogen-content high-strength cast aluminum alloy according to claim 1, characterized in that, In step 3, the smelting process is as follows: Al-Sb5 master alloy, Al-Mg10 master alloy, Al-Sr10 master alloy, and Al-(Ce+La)10 master alloy are added to the upper intermediate frequency furnace of the vacuum pressure casting machine, the vacuum tank is sealed, and when the vacuum is evacuated to -0.09MPa to -0.095 MPa, the upper intermediate frequency furnace is started for smelting at a temperature of 740 to 750℃ to obtain the second molten liquid.

7. The method for preparing low-hydrogen-content high-strength cast aluminum alloy according to claim 1, characterized in that, The refining process in step 4 is as follows: The first molten liquid and the second molten liquid are mixed, and high-purity argon gas is introduced into the mixture at a pressure of 0.02~0.04 MPa and a flow rate of 0.1~0.2 m³ / s. 3 / h, rotary refining time 30~35min, refining temperature 720~730℃.

8. The method for preparing low-hydrogen-content high-strength cast aluminum alloy according to claim 7, characterized in that, In step 4, the heat preservation time is 30-40 minutes.

9. The method for preparing a low-hydrogen-content, high-strength cast aluminum alloy according to claim 2, characterized in that, In step 4, the solution temperature is 500~540℃, the solution time is 8~12h, the aging temperature is 150~180℃, and the aging time is 6~12h.

10. A low-hydrogen-content, high-strength cast aluminum alloy, characterized in that, The aluminum alloy is prepared by the preparation method according to any one of claims 1-9, and the chemical composition of the aluminum alloy, by mass percentage, is: Si: 7.0~7.3%, Cu: 0.38~0.48%, Ce+La: 0.2~0.3%, Sr: 0.05~0.2%, Mg: 0.45~0.55%, Sb: 0.1~0.2%, Ti: 0.05~0.1%, Fe: <0.2%, balance being Al and unavoidable impurities, total impurities ≤0.3%, individual impurities ≤0.08%; The aluminum alloy has a gas content of 0.056-0.062 ml / 100gAl.

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