Thin-walled aluminum alloys component low-pressure casting method
Technical field
The present invention relates to aluminum casting foundry method, particularly relate to thin-walled aluminum alloys component low-pressure casting method.
Background technology
Modern space flight, aviation field get more and more to the demand of complex thin-wall lighting structural member, and particularly the aspect demand such as airplane intake lip, aircraft vertical fin is given prominence to.The method of usual employing has casting metallurgy method, casting metallurgy method is divided into again compression casting and low pressure casting, compression casting is by liquid state or semi-liquid metal under high pressure, be filled at a relatively high speed in mold cavity, and solidify under pressure and obtain required foundry goods, nearly the aluminum alloy spare part of about 90% is die-casting at present, die-casting is first because liquid Metal Filling die cavity speed is high, fluidised form is unstable, therefore adopt general casting die, foundry goods easily produces pore, can not heat-treat; Secondly the foundry goods of concave complexity, die casting is comparatively difficult; Finally also there is the shortcomings such as die-casting die manufacturing cost is high, and die casting machine production efficiency is high, and small lot batch manufacture is uneconomical, it is very unreasonable for causing and will accomplishing that small lot diversification is produced from the angle of economy.
Low pressure casting is by introducing molten metal from cavity bottom, allowing molten metal filling die cavity from bottom to top, to form foundry goods.Low pressure casting is not owing to having rising head and running channel, and cast gate is less, therefore significantly reduce fee of material and machining period casting utilization rate high; Easy formation directional solidification, internal flaw is few; By changing pressing speed, molten soup carries out filling by laminar flow.
Although the mechanical performance of foundry goods can be made to increase in the process adopting low pressure casting, be still difficult to the tension meeting environment meeting thin-walled aluminum component complicated and changeable in air transportation process, the mechanical performance of resistance to deformation.
Summary of the invention
Order of the present invention is to solve current thin-walled aluminium alloy castings and adopts traditional compression casting mode can there is gate and rising head so stock utilization is low, simultaneously because the temperature difference of the melt temperature in smelting furnace and mold cavity is large, cause melt crystallization speed fast, crystalline particle is large, and tensile strength is low.
The present invention proposes a kind of thin-walled aluminum alloys component low-pressure casting method, comprise the following steps: the first step coats heat conduction slip coating on the inwall of mold cavity and stalk, heat-conductive coating is first sprayed at the inwall of mold cavity and stalk, spray lubricant again, mold cavity is communicated with smelting furnace by stalk; The preheating of second step mold cavity and smelting aluminium alloy: mould is heated, and the temperature controlling mold cavity is in 250 ~ 350 DEG C, first smelting furnace is utilized to add hot smelting 7A55 aluminium alloy, after alloy all melts, secondly temperature is risen to 680 ~ 700 DEG C, the slag on removing surface, finally rises to 710 ~ 720 DEG C and carries out refining to aluminium alloy melt by melt temperature; Gas displacement in 3rd step smelting furnace: passing into pressure by the draught damper of smelting furnace in smelting furnace is 0.01MPa helium 1 ~ 2 minute; 4th step adds strontium salt: in smelting furnace, pass into by draught damper the helium that pressure is 0.05 ~ 0.075MPa, melt temperature is heated to 730 ~ 740 DEG C, adds alterant strontium salt by 0.02% ~ 0.06% of molten alloy gross mass in smelting furnace; 5th step goes bad removal of impurities: to the melt removal of impurities after rotten; 6th step is at low-pressure casting: in smelting furnace, pass into inert gas at 700 ~ 725 DEG C, regulates aluminium alloy liquid level pressure reduction in admission pressure and mold cavity at 0.02 ~ 0.04MPa, to pour into a mould mold cavity by regulator simultaneously; 7th step pressurize after having built, cooling: pressurize duration 2 ~ 4 minutes, stops the heating to mold cavity; 9th step cooling die sinking pickup, mould opened by rear cooling thin-section casting to be heated, takes out foundry goods.
In such scheme: the first step first sprays heat-conductive coating in mold cavity and stalk, heat-conductive coating can accelerate the heat exchange of melt and mould and stalk, the lubricant sprayed again can effectively reduce the resistance that melt flows in stalk and mold cavity, reduce the speed causing the local stress of thin-walled aluminium alloy castings and distortion because flowing velocity is slow and affect filling melt mold cavity, stalk is communicated with mold cavity and smelting furnace conducting, and stalk can realize the water conservancy diversion to the melt in smelting furnace, second step, the preheating of mold cavity and smelting aluminium alloy, thermocouple is adopted to heat mould, and the temperature controlling mold cavity is in 250 ~ 350 DEG C, when melt enters mold cavity, because mould type cavity temperature is in 250 ~ 350 DEG C, effectively can slow down the speed of melt cooling crystallization, avoid because mold cavity temperature is positioned at room temperature, and accelerate the speed of melt cooling crystallization, cause crystalline particle large, foundry goods deforms because of local stress, smelting furnace melting 7A55 aluminium alloy, 680 ~ 700 DEG C are risen in its temperature, the slag on removing surface, remove surperficial slag, can prevent slag in the low pressure casting process below from entering mold cavity from stalk, the slag entering mold cavity becomes a part for foundry goods, and affect the quality of foundry goods, finally melt temperature is risen to 710 ~ 720 DEG C and refining is carried out to aluminium alloy melt, to go out slag further, reduce slag to the compositional effect of foundry goods, gas displacement in 3rd step smelting furnace: pass into the helium 1 ~ 2 minute that pressure is 0.01MPa by the draught damper of smelting furnace in smelting furnace, the helium passed into tentatively can be got rid of the air in smelting furnace, 4th step passes into by draught damper the helium that pressure is 0.05 ~ 0.075MPa in smelting furnace, melt temperature is heated to 730 ~ 740 DEG C, in smelting furnace, strontium salt is added by 0.02% ~ 0.06% of molten alloy gross mass, strontium salt can make to touch when making melt recrystallization and form more how tiny casting crystal grain, improves the mechanical performance of foundry goods, 5th step, to the melt removal of impurities after rotten, reduce slag to the impact of foundry goods, 6th step, at low-pressure casting: pass into inert gas at 700 ~ 725 DEG C in smelting furnace, by inert gas, the melt liquid level in smelting furnace is exerted pressure, melt is injected in mold cavity by stalk, by aluminium alloy liquid level pressure reduction in regulator adjustment admission pressure and mold cavity at 0.02 ~ 0.04MPa, melt can be effectively reduced and entering the speed of mould cavity, reduce melt and be splashed to mould cavity inwall under large pressure condition, melt after causing expense to subtract cools in mould cavity, the material skewness and the local stress that affect single-casting are below excessive, cause local deformation, 7th step pressurize duration can make melt fully can be filled with mold cavity for 2 ~ 4 minutes, stops effectively starting to carry out annealing cooling to melt to the heating energy of mold cavity simultaneously, the bipolar Homogenization Treatments of 8th step, 450 DEG C/60h+470 DEG C two-step homogenization process is adopted to thin-section casting, in in crystallization process, the phase structure of alloy is the thick non-equilibrium eutecticum in nonequilibrium supersaturated solid solution and interdendritic, because matrix degree of super saturation is high, add the existence of non-equilibrium eutecticum and residual stress, cause alloy rigidity higher, after Homogenization Treatments, non-equilibrium eutecticum fully dissolves, and residual stress is eliminated, and supersaturated solid solution decomposes, and separates out in a large number without the balance second-phase of strengthening effect, alloy rigidity is declined in cooling procedure, 9th step cooling die sinking pickup, mould opened by rear cooling thin-section casting to be heated, and take out foundry goods, foundry goods cools rear taking-up in a mold, can reduce it because local temperature changes large and occur that stress is concentrated, causing local deformation, heating in above-mentioned second step utilizes in second step to heat the heat of smelting furnace in melting 7A55 process, heat in the insulation crystallization process of the bipolar Homogenization Treatments medium casting in the 8th step is mainly heated by smelting furnace master, but because literary composition in smelting furnace is higher than insulation crystallization temperature, so the mould residing for foundry goods is positioned at outside smelting furnace, utilize the waste heat of smelting furnace, in bipolar Homogenization Treatments process, temperature regulates the electric current of the thermocouple resistance silk be positioned at outside mould to realize temperature constant by sensor, reach the effect of isothermal holding, in this method, the casting of thin-walled aluminium alloy castings and heat treatment are merged, the efficiency of casting can be ensured, also can heat-treat thin-section casting simultaneously, it is made to meet the mechanical performance of aviation use, heating and thermal insulation origin of heat simultaneously in heat treatment process is in smelting furnace temperature, the effective economize energy of energy, reduce energy resource consumption.
Further optimization, be preferable temperature to the control temperature of mould at 300 ~ 320 DEG C in described second step, this temperature effectively can improve and effectively slow down the crystallization rate of melt in mold cavity, basis can be provided for the heat treatment insulation of the bipolar Homogenization Treatments of the 8th step is modified simultaneously, reduce because stress is concentrated in mold temperature low melt crystallization process, heat treatment is below difficult to improve thin-section casting crystal structure, improves the flowing speed of melt simultaneously, causes the casting thin foundry goods time period.
Further optimization, it is good that described 6th step regulates aluminium alloy liquid level pressure reduction in admission pressure and mold cavity to be full of the mechanical integrated performance after mold cavity in the pressure reduction melt of 0.035MPa, 0.035MPa by regulator.
Detailed description of the invention
Embodiments of the present invention are as follows:
The first step coats heat conduction slip coating on the inwall of mold cavity and stalk,
First spray heat-conductive coating colloid at the inwall of mold cavity and stalk, then spray zinc oxide,
Mold cavity is communicated with smelting furnace by stalk;
The preheating of second step mold cavity and smelting aluminium alloy:
Adopt thermocouple to heat mould, and the temperature controlling mold cavity is in 250 ~ 350 DEG C,
First utilize smelting furnace to add hot smelting 7A55 aluminium alloy, after alloy all melts, secondly temperature is risen to 680 ~ 700 DEG C, the slag on removing surface, finally rises to 710 ~ 720 DEG C and carries out refining to aluminium alloy melt by melt temperature;
Gas displacement in 3rd step smelting furnace:
In smelting furnace, passing into pressure by the draught damper of smelting furnace is 0.01MPa helium 1 ~ 2 minute;
4th step adds strontium salt:
In smelting furnace, passing into pressure by draught damper is 0.05 ~ 0.075MPa, melt temperature is heated to 730 ~ 740 DEG C, adds strontium salt by 0.02% ~ 0.06% of molten alloy gross mass in smelting furnace;
5th step goes bad removal of impurities:
To the melt removal of impurities after rotten;
6th step is at low-pressure casting:
In smelting furnace, pass into inert gas at 700 ~ 725 DEG C, regulate aluminium alloy liquid level pressure reduction in admission pressure and mold cavity at 0.02 ~ 0.04MPa, to pour into a mould mold cavity by regulator simultaneously;
7th step pressurize after having built, cooling:
Pressurize duration 2 ~ 4 minutes, stops the heating to mold cavity;
The bipolar Homogenization Treatments of 8th step the 8th step, adopts 450 DEG C/60h+470 DEG C two-step homogenization process to thin-section casting, adopts thermocouple resistance silk and sensor to regulate the temperature difference of bipolar Homogenization Treatments.
9th step is opened mould and is taken out thin-wall part.
Embodiment 1 controls at 255 DEG C for second step mold cavity temperature in above-mentioned embodiment, and the mechanical performance that the cast pressure reduction in the 6th step controls the thin-walled aluminium alloy castings drawn at 0.025MPa is as follows:
Sequence number |
Tensile strength δ b/%MPa |
Yield strength δ s/%MPa |
Percentage elongation δ/%MPa |
End face shrinks ψ/%MPa |
Embodiment 1 |
158 |
93 |
3.7 |
3.24 |
Embodiment 2 controls at 298 DEG C for second step mold cavity temperature in above-mentioned embodiment, and the mechanical performance that the cast pressure reduction in the 6th step controls the thin-walled aluminium alloy castings drawn at 0.03MPa is as follows:
Sequence number |
Tensile strength δ b/%MPa |
Yield strength δ s/%MPa |
Percentage elongation δ/%MPa |
End face shrinks ψ/%MPa |
Embodiment 1 |
156 |
94 |
3.9 |
3.28 |
Embodiment 3 controls at 327 DEG C for second step mold cavity temperature in above-mentioned embodiment, and the mechanical performance that the cast pressure reduction in the 6th step controls the thin-walled aluminium alloy castings drawn at 0.04MPa is as follows:
Sequence number |
Tensile strength δ b/%MPa |
Yield strength δ s/%MPa |
Percentage elongation δ/%MPa |
End face shrinks ψ/%MPa |
Embodiment 1 |
163 |
98 |
4.1 |
3.54 |
Embodiment 4 controls at 348 DEG C for second step mold cavity temperature in above-mentioned embodiment, and the mechanical performance that the cast pressure reduction in the 6th step controls the thin-walled aluminium alloy castings drawn at 0.035MPa is as follows:
Sequence number |
Tensile strength δ b/%MPa |
Yield strength δ s/%MPa |
Percentage elongation δ/%MPa |
End face shrinks ψ/%MPa |
Embodiment 1 |
165 |
97 |
4.1 |
3.61 |
Embodiment 5 controls at 350 DEG C for second step mold cavity temperature in above-mentioned embodiment, and the mechanical performance that the cast pressure reduction in the 6th step controls the thin-walled aluminium alloy castings drawn at 0.03MPa is as follows:
Sequence number |
Tensile strength δ b/%MPa |
Yield strength δ s/%MPa |
Percentage elongation δ/%MPa |
End face shrinks ψ/%MPa |
Embodiment 1 |
164 |
98 |
4.2 |
3.85 |
Above-described is only the preferred embodiment of the present invention; should be understood that; for a person skilled in the art; without departing from the inventive concept of the premise; some distortion and improvement can also be made; these also should be considered as protection scope of the present invention, and these all can not affect effect of the invention process and practical applicability.