CN1699957A - Method and apparatus for quantitative determination of hydrogen content in casting aluminum alloy liquation - Google Patents

Abstract

The invention provides a quantitative measuring method for casting aluminum alloy liquid hydrogen content, which comprises the following steps: heating melting pot inside vacuum case to 200DEG C to 550DEG C and insulating; taking-up aluminum liquid from smelting furnace, putting the liquid into melting pot quickly; twitching vacuum case with the speed of 0.5dm<3>/s to 3dm<3>/s; Measuring aluminum liquid's hydrogen pressure when aluminum liquid emerges first air bubbles by pressure sensor to get hydrogen pressure's value PH; measuring aluminum liquid's temperature T by electric thermocouple; computing hydrogen value by formula. The apparatus comprises vacuum case, heating constant temperature device, pressure sensor, vacuum device, electric thermocouple and computer handing system. The invention has high measuring accuracy and simple operation and is suit for interval measuring of aluminum liquid hydrogen content with each measuring time 2-4 minutes and effective measuring range: 0.01-3cm<3>/100gAl, effective measuring accuracy 0.01cm<3>/100gAl, replicated error measuring 0.01(cm<3>/100gAl).

Description

Quantitative detection method and device for hydrogen content of cast aluminum alloy melt

Technical Field

The invention belongs to the technical field of metallurgy and metal material processing, and particularly relates to a molten metal quality control method and molten metal quality control equipment.

Background

The aluminum alloy has the characteristics of light weight, high specific strength, good heat dissipation, good shock absorption, good electromagnetic shielding property, strong recyclability and the like, and along with the development of modern industry, the aluminum and the aluminum alloy thereof are more and more widely applied to industrial departments such as aerospace, aviation, automobile, machinery, building and the like. The aluminum alloy is easy to absorb air when being smelted in the atmosphere, hydrogen is the main gas dissolved in aluminum liquid, and the gas H in the aluminum alloy₂And accounts for the vast majority of the total gas. The content of hydrogen in the aluminum liquid is an important mark for reflecting the metallurgical quality of the aluminum alloy, and has great influence on the internal quality of products in the subsequent procedures. Because the solubility of hydrogen of the solid aluminum alloy is lower than that of hydrogen in a liquid state by tens of times or even tens of times, hydrogen can be separated out from a melt when the aluminum liquid is solidified, so that the aluminum casting is easy to generate casting defects such as pinholes, shrinkage porosity and thelike, and the mechanical property and the air tightness of the casting are reduced; the yield and the productivity of the casting are reduced; increasing the cost of the casting. Hydrogen is a harmful element in aluminum alloy, the stokehole detection of the hydrogen content of the aluminum liquid is an important process link for ensuring the internal quality of the casting, and particularly, the hydrogen measurement of the aluminum liquid becomes indispensable when a large-capacity smelting furnace is adopted for mass production. The aluminum resource of China is very rich, the processing technology of the aluminum alloy is relatively lagged behind, and particularly, the detection technology of the hydrogen content of the aluminum alloy is very immature. The development of a hydrogen content detection technique for aluminum alloys is an urgent necessity for expanding the application of aluminum alloys.

The hydrogen measuring technology of aluminum alloy melt is very important in all countries in the world, and the conventional hydrogen measuring methods are many and can be divided into two types: sampling methods and direct methods. The sampling method is to sample from the aluminum liquid for analysis and determine the hydrogen content, and the direct method is to use a probe to directly carry out quantitative measurement on the aluminum liquid on line. Several common methods and related patent cases are listed below.

(1) Solidification under reduced pressure

The method is to pour tens grams of aluminum liquid to be measured into a pressure reduction container for solidification. Since the external pressure is low, even if the amount of gas is small, the gas is precipitated in the form of bubbles. The quantity of the hydrogen content of the measured melt is qualitatively judged by the surface state and the degree of the bulge formed on the upper surface of the sample due to the hydrogen gas precipitation in the solidification process and the experience of an observer. There are also a method of measuring the amount of pores in a cut surface and a method of measuring specific gravity, but a method of comparing the amount of pores in a longitudinal cut surface with a reference sample is generally employed. Although simple, this method is generally a qualitative judgment.

(2) Method according to the first bubble principle

The measuring principle is that several tens grams of molten liquid is taken and solidified under the decompression state, and according to the principle that the temperature and the pressure when the first bubble is emitted from the surface of the molten body are different, the hydrogen content of the measured molten aluminum is obtained by measuring the two parameters and converting through a special formula. Using this principle, some foreign companies have developed some quantitative hydrogen meters. The utility model of our country 'first bubble amplification method furnace front rapid hydrogen detector' (application number: 99256124.8) mainly designs a magnifying glass which is beneficial to observation and is easy to observe the appearance of the first bubble.

(3) Inert gas circulation method (Tele-gas method)

The method is a direct hydrogen measuring method, developed by Ransley et al in the middle of 1950 s, and uses a small amount of argon or nitrogen to continuously and circularly pass through the aluminum liquid, when the hydrogen partial pressure in the inert gas bubble and the hydrogen content of the melt are balanced, the hydrogen partial pressure is measured by a heat-conducting gas-separating meter, and simultaneously the temperature of the melt is measured by a thermocouple, and the hydrogen content of the measured melt is obtained by conversion of a special formula. The method has the disadvantages of complicated equipment and instruments, high cost, complicated operation, short service life of the probe and high use cost. The hydrogen measurement rate is relatively slow, generally requiring at least 5 minutes.

(4) Proton conductive ceramic method

This method is a sensor measurement method developed by TYK, a university of Industrial science in Minkou, Japan. The principle is a method of directly measuring the amount of hydrogen gas by using a proton conductive ceramic, and generating a voltage change by a hydrogen sensor from a concentration difference between the hydrogen concentration in the melt and a predetermined hydrogen concentration to be compared. The present approach is made possible by the development of hydrogen sensors.

(5) Other methods

There are also a concentration cell method, a direct extraction method and the like. In addition, the Chinese invention patent "method and apparatus for rapidly measuring hydrogen content in aluminum alloy melt" (patent No. 95113756.5) invented a method for measuring hydrogen content by measuring the expansion caused by hydrogen evolution when a sample is solidified in a sand mold. The invention relates to a Chinese utility model patent, a high-speed and high-stability hydrogen measuring probe for aluminum melt and aluminum alloy melt (application number: 02244622.2), and discloses a probe design and a material for continuous hydrogen measurement.

In summary, the research and development of hydrogen measuring devices in China are relatively lagged behind at present, and most quantitative hydrogen measuring devices are imported. However, there are two problems with the use of foreign instruments: firstly, the purchase cost is too high, and the popularization and the use are difficult; secondly, after-sale service is not guaranteed, and particularly after an instrument fails, the instrument is difficult to recover to use in time. Therefore, it is very important to independently develop a quantitative hydrogen measurement technology for aluminum liquid with excellent performance and low price.

Object of the Invention

The invention aims to provide a quantitative detection method and a device for hydrogen content of cast aluminum alloy melt, which can be used for the stokehole rapid quantitative detection of the hydrogen content of aluminum alloy, so as to control the hydrogen content of aluminum liquid, improve the quality of the aluminum liquid and reduce the casting defects of pinholes, shrinkage porosity and the like of aluminum castings.

The invention provides a quantitative determination method for hydrogen content of casting aluminum alloy melt, which comprises the following steps:

(1) heating the crucible in the vacuum chamber to 200-550 ℃ and then preserving heat;

(2) taking out the aluminum liquid from the smelting furnace, and quickly placing the aluminum liquid into a crucible;

(3) the vacuum chamber is vacuumized at the air exhaust speed of 0.5dm³/s～3dm³/s；

(4) Measuring the hydrogen pressure of the aluminum liquid when the first batch of bubbles appear in the aluminum liquid by adopting a pressure sensor, and acquiring a hydrogen pressure value P_H；

(5) Measuring the temperature T of the aluminum liquid when the first batch of bubbles appear in the aluminum liquid by adopting a thermocouple;

(6) calculating the hydrogen content C of the aluminum liquid by using the following formula_H：

$\lg C_H=0.51{\mathrm{gP}}_H-\frac{A}{T}+B$

Wherein A, B is a correction coefficient of alloy composition.

The device for realizing the method is characterized in that: the vacuum chamber consists of a body and an upper cover, the upper cover is provided with an observation window, the crucible is positioned in the vacuum chamber, a heating constant temperature device is arranged outside the vacuum chamber and used for preheating and heat preservation, a gap between the body and the crucible is filled with a heat insulation material, the vacuum device is used for vacuumizing the vacuum chamber, the pressure sensor is connected with an air exhaust pipeline of the vacuum device, and the thermocouple is arranged in the crucible and used for measuring the temperature of the aluminum liquid; the computer processing system is connected with the thermocouple and the pressure sensor and used for collecting temperature and pressure signals.

The invention directly utilizes the measured values of the hydrogen pressure and the aluminum liquid temperature in the aluminum liquid and the components of the aluminum alloy to determine the hydrogen content of the aluminum liquid, thereby having higher measurement precision and simple, convenient and quick operation. The method is suitable for the interval measurement of the hydrogen content of the aluminum liquid, and the measurement time is only 2-4 minutes each time. The hydrogen content measuring range of the aluminum liquid of the device can reach 0.01-3 cm³100gAl, the hydrogen content measuring precision can reach 0.01cm³100gAl, the repeated measurement error can reach 0.01 (cm)³Per 100 gAl). In the actual production process, aluminum smelting is usually carried out on the basis of prescribing the hydrogen content of the aluminum liquid to the maximum extent in advance, and whether the hydrogen content in the aluminum liquid is in an allowable range can be easily judged by adopting the method. Considering the low hydrogen content range (0.05-0.07 cm) of the aviation parts with the highest requirement³100gAl) of the inventionThe device can perform the measurement.

In a word, the invention is beneficial to improving the mechanical property and the air tightness of the aluminum casting, improving the yield and the labor productivity of the aluminum casting and reducing the cost of the aluminum casting.

Drawings

FIG. 1 is a schematic diagram of the apparatus of the present invention;

FIG. 2 is a flow chart of the detection of hydrogen content in the molten aluminum alloy.

Detailed Description

The working principle of the invention is as follows: when melting, the liquid aluminum reacts with water molecules in the air, so that the hydrogen is melted into the aluminum liquid. Hydrogen is present in aluminium melts mainly in several forms: in the atomic state, i.e. [ H]]Dissolving in molten aluminum; molecular state, i.e. H and H₂Present in Al₂O₃Hydrogen bubbles with negative curvature radius are formed in the included cracks; in the compound state, hydrogen atoms and certain elements in the aluminum liquid form hydrides. The air suction mechanism of the aluminum alloy is as follows:

solubility C of hydrogen in molten aluminum_HThe temperature T of the aluminum liquid and the pressure P of hydrogen in the aluminum liquid_HIn connection with this, their relationship can be expressed by the following formula:

$C_H=K\sqrt{P_H\&CenterDot;e^{\frac{\mathrm{Es}}{2\mathrm{RT}}}}---\left(3\right)$

in the formula E_sMolar heat of solution of Hydrogen, J/mol

K-constant

T-temperature of molten aluminum, K

R-gas constant, K.mol/J

C_HSolubility of Hydrogen in molten aluminum, cm³/100gAl

P_H-hydrogen pressure in the aluminium liquid, Pa

Equation (3) can also be expressed by Sievert's Law as follows:

$\lg C_H=0.51g{P}_H-\frac{A}{T}+B---\left(4\right)$

wherein A, B- -constant dependent on alloy composition

In formula (4), A, B, T is easily determined, only P_HIt is difficult to determine. Therefore, it is required to obtain the hydrogen content C_HThe key point is to find P_HThe value is obtained.

It can be considered that when the first batch of bubbles is separated out, the hydrogen partial pressure in the aluminum liquid is approximately equal to the pressure above the aluminum liquid. If the alloy liquid is decompressed (vacuumized), when the first batch of bubbles appear on the liquid surface, the pressure in the decompression chamber (namely the pressure of hydrogen in the alloy) and the temperature of the alloy are recorded, and the hydrogen content C in the aluminum alloy can be calculated according to the Sievert's law_H。

As shown in fig. 1, the steps of the present invention are:

(1) and heating the crucible in the vacuum chamber to 200-550 ℃, preserving heat, and determining the specific temperature according to the type of the aluminum alloy.

(2) And taking out the aluminum liquid from the smelting furnace and quickly placing the aluminum liquid into a crucible.

(3) When a vacuum pump is used for pumping vacuum, a certain pumping speed is required to be kept, and the pumping speed is 0.5dm³/s～3dm³And the limiting vacuum degree is 0.06Pa to 10 Pa.

(4) And adopting a pressure sensor to measure absolute pressure when the first batch of bubbles appear in the aluminum liquid, and acquiring a hydrogen pressure value P_H(ii) a The pressure measurement accuracy was 0.1%.

(5) And measuring the temperature T of the aluminum liquid when the first batch of bubbles appear in the aluminum liquid by using a K-type thermocouple, wherein the temperature measurement precision is +/-0.5 ℃.

(6) Calculating the hydrogen content of the aluminum liquid by using the following formula:

$\lg C_H=0.51g{P}_H-\frac{A}{T}+B$

for standard-grade aluminum alloy, the correction coefficients A and B are obtained by looking up a table. For aluminum alloy with non-standard grade or aluminum alloy without corresponding components in the table, the correction coefficients A and B are determined by extracting certain aluminum alloy solution and water quenching to obtain a sample. The sample is measured for hydrogen content in a high temperature gas chromatograph, so that correction coefficients A and B are obtained by a regression analysis method.

The device for realizing the method is shown in figure 2, the vacuum chamber is composed of a body 1 and an upper cover 2, the upper cover 2 is provided with an observation window, and a seal is arranged between the upper cover 2 and the body 1The ring is sealed to keep airtight. The crucible 3 is positioned in the vacuum chamber, and a heating constant temperature device 4 is arranged outside the crucible for preheating and heat preservation, so that the heat preservation temperature of the crucible is 200-550 ℃. The gap between the body 1 and the crucible 3 is filled with heat insulation materials. The vacuum device 5 is used for vacuumizing the vacuum chamber, and the air suction speed is 0.5dm³/s～3dm³And s. The pressure sensor 6 is connected with an air exhaust pipeline of the vacuum device 5 and is used for measuring the hydrogen pressure value P of the aluminum liquid_H. And the thermocouple 7 is arranged in the crucible and used for measuring the temperature of the aluminum liquid. The computer processing system 8 is connected with the thermocouple 7 and the pressure sensor 6, collects temperature and pressure signals, and obtains a temperature value T and a hydrogen pressure value P_H. And calculating the hydrogen content C of the obtained aluminum liquid by using the calculation formula_H。

The computer processing system stores the correction coefficient of the common aluminum alloy so as to accelerate the detection speed.

The operation process of the device comprises the following steps: about 100g of measured aluminum liquid is taken from the aluminum alloy melting furnace and poured into a crucible 3 in a vacuum chamber, an upper cover 2 of the vacuum chamber is covered, a vacuum device is started to extract vacuum, and the condition of bubbles on the aluminum liquid surface in the crucible is observed through an observation window. When the first batch of bubbles appear on the aluminum liquid surface, the computer processing system 8 collects the temperature signal and the pressure signal to obtain the temperature value T and the hydrogen pressure value P at the time_HAnd calculating the hydrogen content of the aluminum liquid and displaying the calculation result. After the measurement is finished, the vacuum device stops working, air is filled in the vacuum chamber, the upper cover 2 is opened, and the sample is taken out. The above process is repeated to make multiple measurements.

The invention is further illustrated by the following examples.

Example 1

The hydrogen content of ZL102 aluminum alloy melt in two states of no degassing and degassing by adopting a non-toxic degassing agent is compared and tested, and the test results are shown in Table 1. The results show that the stability of the invention in practical use is good, and the maximum error is 0.01cm³Within the range of 100gAl, the requirements of aluminum alloy production and aluminum melt dehydrogenation research can be completely guaranteed.

TABLE 1 ZL102 degassing before and with non-toxic degassing agentHydrogen content after gassing (cm)³/100gAl)

Status of state	Test sequence number	Hydrogen content	Average hydrogen content	Maximum error
					Before degassing	①	0.1759	0.1757	0.0098
②	0.1700
		③	0.1771
④	0.1798
		Degassing for 1 time by using a nontoxic degassing agent	①	0.0881		0.0834	0.0076
②	0.0834
			③	0.0816
④	0.0805

Example 2

The hydrogen content of ZL201 aluminum alloy melt in two states of no degassing and inert gas argon rotary blowing degassing is compared and tested, and the test results are shown in Table 2.

TABLE 2 Hydrogen content (cm) before degassing ZL102 and after degassing by rotation with argon³/100gAl)

Status of state	Test sequence number	Hydrogen content	Average hydrogen content	Maximum error
					Before degassing	①	0.2321	0.2350	0.0061
②	0.2382
		③	0.2362
④	0.2335
		Degassing for 12 minutes using argon And after standing for 5 minutes	①	0.0789		0.0755	0.0083
②	0.0795
			③	0.0722
④	0.0712

Example 3

The hydrogen content of ZL104 aluminum alloy melt in two states of no degassing and degassing by hexachloroethane is compared and tested, and the test results are shown in Table 3.

TABLE 3 Hydrogen content (cm) of ZL102 before degassing and after degassing with hexachloroethane³/100gAl)

Status of state	Test sequence number	Hydrogen content	Average hydrogen content	Maximum error
					Before degassing	①	0.1862	0.1857	0.0055
②	0.1843
		③	0.1889
④	0.1834
		Degassing with hexachloroethane 1 time later	①	0.0893		0.0845	0.0087
②	0.0844
			③	0.0806
④	0.0837

Claims (2)

1. A quantitative determination method for hydrogen content of cast aluminum alloy melt comprises the following steps:

(1) heating the crucible in the vacuum chamber to 200-550 ℃ and then preserving heat;

(2) taking out the aluminum liquid from the smelting furnace, and quickly placing the aluminum liquid into a crucible;

(3) the vacuum chamber is vacuumized at the air exhaust speed of 0.5dm³/s～3dm³/s；

(4) Measuring the hydrogen pressure of the aluminum liquid when the first batch of bubbles appear in the aluminum liquid by adopting a pressure sensor, and acquiring a hydrogen pressure value P_H；

(5) Measuring the temperature T of the aluminum liquid when the first batch of bubbles appear in the aluminum liquid by adopting a thermocouple;

(6) calculating the hydrogen content C of the aluminum liquid by using the following formula_H：

$\lg C_H=0.5\lg P_H-\frac{A}{T}+B$

Wherein A, B is a correction coefficient of alloy composition.

2. An apparatus for implementing the method of claim 1, wherein: the vacuum chamber is composed of a body (1) and an upper cover (2), the upper cover (2) is provided with an observation window, the crucible (3) is positioned in the vacuum chamber, a heating constant temperature device (4) is arranged outside the crucible and used for preheating and heat preservation, a heat insulation material is filled in a gap between the body (1) and the crucible (3), the vacuum device (5) is used for vacuumizing the vacuum chamber, the pressure sensor (6) is connected with an air exhaust pipeline of the vacuum device (5), and the thermocouple (7) is arranged in the crucible and used for measuring the temperature of the aluminum liquid; and the computer processing system (8) is connected with the thermocouple (7) and the pressure sensor (6) and is used for acquiring temperature and pressure signals.

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