Chemical composition of ingots

【China Aluminum Network】 The chemical composition of aluminum alloy ingots is determined by chemical analysis and spectral chemical analysis. The chemical analysis method has the advantages of high accuracy of analysis, unaffected by the condition of the sample, and simple comparison of the equipment. It is a fundamental analysis method of aluminum alloys, but the experimental operation is rather messy and the experiment time is long, and it is not suitable for the analysis of the furnace at the production line. .

Spectroscopic chemical analysis is based on the analysis of the spectroscopy of the composition of the components of its analytical methods, referred to as spectral analysis, the commonly used analysis instrument is a spectrometer. Its characteristics are: analysis speed, analysis process is simple. Can analyze a variety of elements together, as well as dissect trace elements with content below 0.01%.

First, chemical analysis

Chemical analysis is the first method to use chemical analysis to determine the chemical composition of the alloy. The sample disposal, separation skills, and masking methods that are touched are also attributed to the scale of chemical analysis. GB/T6987-2001 "Aluminum and aluminum alloy chemical analysis methods" a total of 22 elements were measured, there are 32 analysis methods, during which some elements are analyzed using two or more methods. The main methods of chemical analysis used in this specification include: heavy (mass) method, volumetric method, photometric method, ion selective electrode method, complexation method, redox method, atomic absorption spectrometry, and the like. Each analysis method makes rules for the use of scale, method summary, profiling process, and analysis of the results of analysis. It also clearly clarifies the reagents, equipment, and sample disposal required for the experiment. The chemical analysis method is an adjudication experiment method for checking the chemical composition of ingots.

Second, the instrument analysis

Instrument analysis method is to use more messy or special equipment, determine the material's chemical composition, component content and chemical structure by measuring the physical and physical chemical properties of the material and its changes. With the development of scientific skills, the proportion of instrumental analysis in analytical chemistry is increasing, and it has become an important pillar of modern analytical chemistry. Instrumental analysis is more intelligent, more efficient, and more versatile. However, the analysis of the composition of the aluminum alloy using the instrument analysis method still has certain limitations. The first is that the accuracy of the inspection is not high. Although the analysis of low-content components has satisfied the demand, the accuracy of the inspections such as titration analysis and heavy (mass) measurement cannot be reached for the analysis of the constant components. Therefore, the selection of inspection methods should fully consider the need to analyze accuracy. In addition, before the analysis of the instrument, the chemical sample is generally used to pretreat the sample (such as enrichment, removal of disturbing impurities, etc.); together, instrument analysis generally requires the calibration of the specification, and many specifications require the use of chemical Analytical method to calibrate.

The instrument analysis method widely used in the analysis of the chemical composition of aluminum alloys is the optical analysis method. The spectral analysis method among them is an optical analysis method that is widely used. Spectral analysis is based on the characteristics of the material spectrum to study the chemical composition, structure and existence of the material, touch the various electromagnetic spectrum, can be subdivided into atomic emission spectroscopy, atomic absorption spectroscopy, infrared and Raman spectroscopy and other analysis Method.

1 Atomic Emission Spectroscopic Analysis

1) Principle

Atomic emission spectroscopy can analyze more than 70 elements. This method is often used for qualitative, semi-quantitative and quantitative analysis. In general, the detection limit for components with a content of 1% or less can be up to lx 10-6 (ppm) with an accuracy of ±10% and the linear scale can be about 2 orders of magnitude, but if an inductively coupled plasma is used As the light source, the detection limit of certain elements can be reduced to (10-3 to 10-4)×10-6, with an accuracy of ±1% or less, and the linear scale can be extended to 7 orders of magnitude.

Atomic emission spectrometry determines the chemical composition of a substance based on the spectrum emitted by the atom. Different substances are made up of atoms of different elements, and atoms contain a closely-constructed atomic nucleus surrounded by constantly moving electrons. Each electron is at a certain energy level and has a certain amount of energy. Under normal circumstances, the atom is in a stable state, its energy is lower, and this condition is called the ground state. But when the atom is affected by external energy (such as heat energy, electric energy, etc.), the atom gains energy by colliding with the adjustment of the gaseous particles and electrons, causing the electrons in the outer layer of the atom to jump from the ground state to a higher energy level. Above, the atom in this condition is called aroused state. One of the outer electrons in the atom is transitioned from the ground state to infinity, ie, the binding force from the nucleus causes the atom to become an ion. This process is called ionization. The energy required for an atom to lose an outer electron to become an ion is called the first ionization potential. When the applied energy is greater, the ions can further ionize into secondary ions (losing two electrons) or tertiary ions (losing three outer electrons), and have corresponding ionization potentials. The outer electrons in these ions can also be excited, and the required energy is the evoked potential of the corresponding ion.

The progress of atomic emission spectroscopy can be briefly described as the outer electrons of the sample transformed into gaseous atoms under the effect of external energy are excited to high energy states, when transitioning from higher energy levels to lower energy levels. The atoms will release the remaining energy and emit characteristic lines. Dispersion is performed on the radiation generated by the spectrograph apparatus and recorded on the photosensitive plate in the order of wavelengths, and a spectroscopic line, ie, a spectrogram, can be presented, and qualitative or quantitative analysis can be performed based on the obtained spectrum.

The atomic emission spectrometer generally consists of three parts: the light source, the spectroscopic system, and the observation system.

The primary effect of the light source is to supply energy to the sample, to evaporate the components in the sample to gaseous atoms, and then to excite these gaseous atoms, causing the characteristic spectrum to occur. The light source used for spectrum analysis is an important factor in determining the sensitivity and accuracy of spectrum analysis. The commonly used light sources include DC arc, arc communication, electric spark, and inductive coupled high frequency plasma (ICP).

The spectroscopic system is used to investigate the spectrum of the light source and decompose the electromagnetic waves of the light source into spectra in a certain order. Commonly used spectral elements are: prisms and gratings.

The observation system is used to measure the intensity of the spectral line and then determine the element's content. In atomic emission spectroscopy, the commonly used observation methods are: visual, spectroscopic, and optoelectronic methods. The method of investigating the intensity of the line with both eyes is called visual inspection. This method is used for semi-quantitative analysis of steel and non-ferrous metals. Spectrophotometry is the use of photographic plate to record the spectrum, the spectral plate is placed on the focal plane of the spectrograph, and subjected to the effect of the profile of the sample to be sensitized. After the development, fixation and other processes, a spectral film is prepared. There are many spectral lines with different degrees of darkness, and then the spectrometer is used to investigate the azimuth and approximate intensity of the spectral lines, and qualitative spectroscopic analysis, semi-quantitative analysis or quantitative analysis is performed. The photoelectron method uses a photomultiplier to measure the spectral line intensity. The photomultiplier tube not only plays a role in photoelectric conversion, but also plays a role in current expansion.

The atomic emission spectrometer can be used for qualitative analysis and quantitative analysis. The advantage of quantification of emission spectroscopy is that in many cases, the elements to be analyzed do not have to be separated from the matrix before profiling. Second, an analysis can measure the contents of multiple elements together in one sample. In addition, the amount of sample consumed during profiling is small and the analytical sensitivity is high. Spectrometric quantitative analysis can measure the mass fraction from a few thousand to a few tens of percent, but when the mass fraction exceeds 10%, it is difficult to select a traditional spectral method for the analysis to have satisfactory accuracy. The analysis is suitable for the analysis of low and trace elements.

Atomic emission spectroscopy cannot dissect organic matter and most non-metallic elements. When performing spectrophotometric quantitative analysis, the specifications of the sample, the photosensitive plate, the development conditions, etc. should meet the requirements of the specification rules, otherwise it will affect the accuracy of the analysis. In particular, there is a high demand for the specification sample, and a set of specification samples is required for analysis.

2) Optoelectronic emission spectrum analysis method

Photoelectric emission spectroscopy (photometric method) is a commonly used one in atomic emission spectroscopy, and is widely used in pre-decomposition and alloy composition manipulation of aluminum profile production companies. For the determination method, please refer to GB/T7999-2000 (Aluminum and Aluminum Alloy Optoelectronics (Photometric Method Emission Spectroscopic Analysis Method). Photoelectron Emission Spectrometry Analysing Method is to stimulate the processed sample to excite and emit light through the spectroscopic system. Dispersion into a spectrum, the selected internal reference line and analysis line are photoelectrically converted and measured by a photoelectric conversion system and a measurement system, and the content of each element determined in the analysis sample is calculated according to an analysis curve produced by a corresponding specification material (normative sample). Optoelectronic Emission Spectrometry Analysis Methods For the determination of alloying elements and impurity elements in aluminum and aluminum alloys, see Table 6-1-1.

The instrument commonly used for photometry is an opto-electronic spectrometer. When selecting an opto-electronic spectrometer, the required accuracy required to analyze the mission should be selected. Table 6-1-2 shows the skill parameters of a commonly used photoelectric spectrometer.

Table 6—1 Measurement scales of each element in photometry

element

Measurement scale/%

Si

Fe

Cu

Mg

Mn

Zn

Ti

Cr

Ga

Ni

Pb

V

Sn

Be

Zr

Sr

Ce

Sb

Ca

P

Bi

0.00010 to 15.00

0.O0010 to 5.00

0.00010 to 11.00

0.00010 to 11.00

0.00050~2.00

0.00050 to 13.00

0.00050 to 0.50

0.0010 to 0.50

0.0010 to 0.050

0.0050 to 3.00

0.0010 to 0.80

0.0010 to 0.20

0.0010 to 0.50

0.00050 to 0.20

0.0010 to O.50

0.0010 to 0.50

0.050 to 0.60

0.0050 to 0.50

0.00050 to 0.0050

0. O0050~O.0050

0.0050 to O.80

Table 6—1—2 Optoelectronic Spectrometer's Skill Parameters Table

Performance

Technical Parameters

Curvature radius/m

1 or 75

Density/line·mm-1

1080

1667

2160

Decimal dispersion (once)/nm·mm-1

0.93

0.60

0.47

Wavelength scale (once)/nm

400~820

220~528

170~407

The need for assisted equipment, materials, and the environment when using optoelectronic emission spectrum analysis methods:

1 establish the profile of the normative substances (normative samples) using important or recognized prestige normative substances (normative samples). In principle, the normative substance (normative sample) should be consistent with the chemical composition of the analytical sample and the metallurgical forging process.

2 Use high-purity argon gas as an inter-maintenance gas (or use of an opto-electronic spectrometer for clarification);

3 The environment of the photoelectric spectrometer room should be controlled against electromagnetic interference, shock and gas corrosion control, temperature and humidity should be consistent

Photoelectric spectrometer needs.

Photoelectric spectrometer analysis process:

1 Optoelectronics Spectrometer working condition control and calibration: Make full use of the status of the instrument to diagnose the function, punctuality (per shift or daily) for status diagnosis, if any abnormal timely disposal; timing noise, dark current, lamp intensity experiment, and initial and Comparing the collected data, and then admitting that the system is not normal; regular use of one or more aluminum alloy samples with uniform chemical composition for strength determination (more than 10 times) and mathematical statistics disposal;

2 According to the species and chemical composition of the sample, select the appropriate normative substance (specification sample);

3 According to the variety and chemical composition of the sample, according to the experimental or elucidation book to select the appropriate conditions to stimulate and analyze the line pairs. See Table 6-1-3 for the commonly used excitation conditions of an opto-electronic spectrometer. See Table 6-1-4 for common internal reference lines and analysis lines.

Table 6-1-3 Examples of Exciting Conditions of Photoelectric Spectrometer

parameter

species

Voltage/V

Frequency/Hz

Resistance/Ω

Capacitance/mF

Inductance/mH

Pre-spark condition

Integral spark condition

Analyze the gap distance/mm

300

400

3 to 5

400

400

0.5

8

3

2

20

20

Table 6-1-4 common internal markings and analysis lines

element

Wavelength/nm

Measurement scale/%

Internal Marking Line (Al)

305.47*201

266.04*2

256.79*1

Si

288.16*2

251.61*3

390.55*1

0.00010 to 1.00

0.00050 to 5.00

0.020 to 15.00

Fe

239.5*1

371.99*2

273.O7*2

271.44*1

259.93*1

0.040 to 1.20

0.00010 to 1.00

0.10 to 3.00

0.10 to 5.00

0.0010 to 3.00

Cu

324.75*2

510.55*1

0.00010 to 0.50

0.020 to 11.00

Mg

279.08*2

285.2*1

382.93*1

0.00010 to 3.00

0.0040 to 1.00

0.0030 to 11.00

Mn

403.45*2

293.3*2

0.00030 to 3.00

0.0020 to 2.00

Zn

213.8*1

334.5*2

330.26*2

0.0020 to 7.00

0.00050 to 0.50

0.00080~13.00

Ti

337.28*2

374.16*1

0.00050 to 1.00

0.10 to l0.00

Continued Table 6-1-4

element

Wavelength/nm

Measurement scale/%

Cr

425.43*1

267.72*3

0.0010 to 0.30

0.00030 to 3.00

Ga

417.21*1

393.36*1

0.0010 to 0.10

0.O0010 to O.50

Ni

231.6*2

341.47*1

0.0010 to 5.00

0.0010 to 3.00

Pb

405.78*2

283.31*1

0.00050 to 0.10

0.0050 to 1.00

V

311.07*2

0.0050 to 0.50

Sn

317.51*2

0.0050 to 20.00

Be

313.04*2

0.00002 to 0.50

Zr

339.20*2

343.82*2

0.00005 to 0.50

0.0050 to 0.50

Sr

460.73*1

0.00010 to 0.50

Ce

399.92*1

357.75*2

0.0010 to 0.60

0.0010 to 0.50

Sb

259.81*2

0.00080 to 0.50

Ca

396.85*2

0.00050 to 0.50

P

178.29*

30.00010 to 0.10

Bi

306.77*1

0.0010 to 1.00

Note 1: * and the number behind it represent the spectrometer channel, such as +2, which is the second channel of the spectrometer.

4 Profiling Curve Establishment and Curve Drift Calibration Obtaining the initial strength of the sample: The specification material (normative sample) that sets up the profile curve and the drift proofing sample together stimulate measurement. Each sample stimulated 3 ~ 10 times, and its uniform value was stored and used. Use the uniform intensity value of the specification material (normative sample) and the corresponding chemical content (or content ratio) to establish an analysis curve;

5 Analyze the drift calibration of the curve: Before each measurement of the analysis sample, use one or more control samples to analyze, and admit that the used analysis curve is not drifting. If the curve has drifted, use the calibration sample to make the curve drift. Proofreading, and then use the control sample to recognize;

6 When analysing the sample, the sample is less provoked for 2 determinations, and its average value is taken as the analysis result; the percentage of content of the analysis result indicates that the number of repairs is reduced to the number of digits of the commodity specification rule according to the number.

2 atomic absorption spectroscopy analysis

Atomic Absorption Spectrometry (AAS) is a method for determining the elemental content of an atomic absorption spectrometer by converting the measured element into a ground-state free-atom atom. The measurement process is: the sample solution is atomized into a mist bead and fed into the flame. The bead is in the flame. Evaporation becomes solid particles. In the atomization tank (flame, graphite furnace), the vapor molecules are further dissociated into atoms that are ionized as ions. After reaching a certain atomization efficiency, an atomic absorption spectrometer was used to measure the absorption signal of the ground-state atoms on the resonance line of the sharp-line light source.

Atomic Absorption Spectrometer chooses Czery-Turner or Littrow grating spectroscopic system, adjusts the required wavelength by changing the rotation angle of the grating, and the incident slit and the exit slit of the spectroscopic system take the same conjugate width.

Atomic Absorption Spectrometry Atomic Absorption Spectrophotometry (AAS) is based on the measurement of the absorption of the resonance electrons in the outer electrons of gaseous atoms. Atomic Absorption Spectrometry can quantitatively measure more than 70 kinds of metal elements and some non-metal elements. The limit of inspection is up to ng/mL, and the relative standard deviation is 1% to 2%. This method is widely used in low-content elements. Quantitative determination.

Atomic Absorption Spectroscopy analysis of the main features are: the instrument is simple, easy to operate, high sensitivity measurement, good special effects, anti-disturbance ability, good stability, applicable to a wide range, the sensitivity of the elements of the analysis is not the same. Atomic Absorption Spectroscopy has occupied an important position in the field of chemistry and is the preferred quantitative method.

Third, ingot chemical composition inspection sampling

The inspection of chemical composition of ingots is divided into sampling from the molten state and sampling from the ingot processing parts. At present, the vast majority of aluminum alloy production plants use photoelectric emission spectroscopy to analyze the chemical composition of the aluminum alloy, and the condition of the sample has a great influence on the accuracy of the analysis. How to accurately sample is an important part of analyzing the chemical composition of the ingot.

3.1 sample size

For rod specimens, diameter φ6 to φ10 mm, length not less than 60 mm; block specimen, length 38 to 42 mm, width 33 to 37 mm, height 20 to 30 mm, or diameter φ35 to φ60 mm, height 20 ~30 mm.

3.2 Sampling

Sample from the molten state:

1) When sampling in smelting furnace or static furnace, it is necessary to fully mix the melt and then sample it to ensure that the melt composition in the furnace is uniform;

2) Before sampling, the sampling spoon and iron mold (or steel mold) should be filled with dry preheat (can be heated with open flame or placed in aluminum melt

The preheating in the pool prevents the sample from having defects such as pores and looseness, which affects the accuracy of the analysis of the components;

3) It should ensure that the sample composition is uniform, and the sample has no defects such as porosity, looseness, slag inclusion, and cracks;

4) The sample should be representative. Samples of the chemical composition of ingots are shown in Table 6-1-5.

Table 6-1-5 Sampling Methods for Chemical Composition of Ingots

Sampling site

Sampling method

Sample quantity/piece

Check the type

Melting furnace

After all the alloy components are added, the melt is well-mixed.

Sampling at the center of the smelting furnace and half the depth of the melt

sampling

Take 1-2 for each melt

For process inspection

Melting furnace

All alloy composition adjustment is completed and ready to stand still

In front of the furnace, in the center of the smelting furnace, half the melt depth

sampling

Take 1-2 for each melt

For process inspection

Static furnace

The melt is transferred from the smelting furnace to the static furnace and mixed well

Sampling, in the center of the static furnace, half the melt depth

sampling

Take 1-2 for each melt

For process inspection

Static furnace

Sampling after the end of melt refining, in the center of the static furnace, melting

Sampling at half depth

Take 1-2 for each melt

For process inspection

Flow or flow disk

About round ingots, after forging 0.5 m long, from the flow

Slot or flow tray

Take 1-2 for each melt

For final inspection (adjudication inspection)

3.3 sample processing

1) Sample preparation for chemical analysis should meet the requirements

(1) The sample should be clean and free of oxide scale (film), no bleed, no grease, etc. When necessary, the sample can be washed with acetone, washed with dry ethanol and dried, and then prepare samples. Oxide and dirt on the sample can be removed by proper mechanical or chemical methods. When cleaning with chemical methods, the appearance of the sample must not be altered;

(2) When samples are prepared from samples that do not segregate, samples can be taken by drilling, milling, etc. depending on the shape and specifications of the sample. When samples are taken from segregated samples, drills are required to drill through all samples, such as milling, in all sections;

(3) Drills, knives, or other things used for sample preparation should be completely clean and clean before use. The speed and depth of sample preparation should be adjusted to not overheat the sample and cause the sample to oxidize. It is recommended to use cemented carbides. When using steels, remove the adsorbed iron beforehand.

(4) In the preparation of detritus samples, no cooling is required in principle. If high-purity aluminum or more viscous alloy samples are sampled, absolute ethanol may be used as a smoothing agent;

(5) Drill cuttings and milling chips are carefully handled with strong magnets, removing all the iron chips brought in during sample preparation. Prevent the mixing of such impurities as much as possible.

2) Matters needing attention for sample processing for photoemission spectroscopy analysis

(1) The profile of the sample is machined into a smooth surface by a lathe or milling machine;

(2) The tip of the rod specimen should be cut off by 5 to 20 mm, and the bulk specimen by 5 to 10 mm. For alloys with high alloying and segregation, the removal amount of the specimen can be appropriately increased (cut off L0~15 mm);

(3) The industrial pure aluminum sample is selected to analyze ethanol for cooling and smoothness during turning; pure aluminum and aluminum alloy samples can be cooled and smoothed with industrial pure ethanol, and other smoothing agents are not allowed.

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