[China Aluminum Industry Network] First, check the low magnification of the ingot
Low magnification inspection is an inspection method to investigate the microscopic arrangement and defects of etched surfaces and fractures of aluminum and aluminum alloys with the naked eye or with a magnifying glass (8 to 10 times or less). The equipment required for low-level inspections is simple, simple and agile, and the results are intuitive and easy to grasp. It is an important method to determine the quality of the finished product. It is also a technique used to discuss the forging and processing skills of aluminum and aluminum alloys and the quality analysis of finished products. Aluminum alloy ingot low magnification inspection can refer to the national standard GB/T3246.2 "deformation of aluminum and aluminum alloy products low-frequency arrangements for inspection methods" for inspection.
1.1 Specimen cutting and processing
In the production inspection, the low-exposure etched test specimens are taken from the parts where the finished products have various shortcomings. The low-exposure etched specimens used in the study should be selected from the representative parts of the requirements study. The number of test strips should be determined based on inspection intentions and requirements. Inspection of the test piece of the semi-continuous ingot shall be performed by cutting the two ends of the ingot after the head and tail. The thickness of the test piece is usually l5 to 30 mm. The test piece is usually cut and cut.
The finish of the test strip inspection surface should be based on inspection intentions, skills, and aggressive etching of the etchant. The test strips of the ingot can be used, and if necessary, they can be polished with fine sandpaper. The surface appearance roughness of the test piece inspection surface should reach Ra l.6μm. To ensure the inspection surface of the test piece is clean, there should be no oil, dirt and mechanical scratches.
1.2 Test piece etching
The uneven arrangement and arrangement of defects in aluminum and aluminum alloys can be flashed by etch because they act at different speeds with the etchant to cause relief on the investigation surface of the test piece and then flash. Such as coarse-grained areas, optical crystal areas, white spots, metal compounds and other shortcomings. Some shortcomings, such as stomata and looseness before erosion, are simply connected with others, and some defects have very small dimensions. They are difficult to discriminate with the naked eye, and the need to etch them makes them correspondingly larger in scale. To the extent visible to the naked eye, it will be clearly flashed. The arrangement of test strips and the degree of flashover of defects are primarily determined by the composition of the etchants, the temperature, the etch time, and the finish of the inspection surface.
The requirements for low-rate inspections of etchants are: clear and accurate flash arrangements and shortcomings; simple composition and ease of manufacture; low cost; safe composition during operation; operation with less gas and no harm. The commonly used etchant for aluminum and aluminum alloy ingots is 8% to l2% sodium hydroxide solution. When flashing the grain size of the soft alloy finished product, the etching solution used was a mixed solution of 5 mL hydrofluoric acid, 75 mL hydrochloric acid, and 25 mL nitric acid. The composition, usage and applicable scale of commonly used aluminum and aluminum alloy etchants are shown in Table 6-1-6.
Table 6-1-6 Aluminum and aluminum alloy commonly used low magnification
Ingredients/mL
Use method
Customary scale
10% to 20% sodium hydroxide solution
Greenhouse or heated to 40 °C, etching time is not based on the alloy
Same as different
Microscopic arrangement of aluminum and aluminum alloys
flash
Hydrofluoric acid
hydrochloric acid
Nitric acid
water
10
5
5
380
When etched, immersion method can be used, or test rubbing method can be used to generate
Black film is cleaned and cleaned with a cleaning solution
Flash of hard alloy grain size
Hydrofluoric acid
hydrochloric acid
water
10
L5
90
Flashing grain size, exceptionally suitable
Pure Aluminum
Hydrofluoric acid
hydrochloric acid
Nitric acid
water
L5
42
L6
27
The etching time is about 6 min. When the nitric acid content is added,
Etched contrast can also be added. After eroding with clear water
Wash the test piece and neutralize with sodium carbonate solution
Micro-etching of pure aluminum
(1) Ferric chloride
water
(2) Hydrofluoric acid
water
Solutions (1) and (2) are mixed equally
10
100
0.5
100
Micro-etching of pure aluminum
16% sodium sulfate solution
10% chromic acid solution
hydrochloric acid
water
50
3
L5
30
The chromic acid content in the solution can still be improved, chromic acid should be used
Before joining
Pure aluminum and high purity aluminum grain
flash
Hydrofluoric acid
hydrochloric acid
Nitric acid
14
43
43
Etching temperature 20 °C, etching time. 1 min, repeated
Etching to prevent the sample from heating and eroding
Microscopic view of aluminum, titanium alloy and pot
Etching
Ferric chloride
hydrochloric acid
Hydrofluoric acid
glycerin
9
75
1.5
L8
Heat treatment does not strengthen the aluminum alloy
Ferric chloride
Nitric acid
hydrochloric acid
5
25
75
Heat treatment does not strengthen the aluminum alloy
sulfuric acid
Hydrofluoric acid
water
L0
L0
80
Etching time does not exceed 30 min
Micro-etching of aluminum and aluminum alloys,
Especially large specimens
Phosphoric acid
Hydrofluoric acid
water
(hydrofluoric acid can be replaced by equivalent amount of hydrochloric acid)
L0
5
85
Etching time does not exceed 30 min
Micro-etching of aluminum and aluminum alloys
Continued Table 6-1-6
Ingredients/mL
Use method
Customary scale
25%～30% nitric acid solution
Remove the etched black film
Potassium dichromate
sulfuric acid
water
25
60
500
Remove the etched black film
The concentration, temperature, and time of the etchant all affect the flashing of the test surface. As the concentration of the etchants decreases, the etch time will extend. The temperature of the etchant increases, the reaction is intense, and the etching speed is accelerated. At this time, if the etching time is slightly longer, the test piece can be over-etched, and the authenticity of the arrangement and the disadvantages are lost. Conversely, the temperature of the etchant is too low, the etching speed is slow, and the etching time will be extended. For ease of experimentation, etching is preferably performed in a greenhouse. In the etching process, when the etched test piece is large, the temperature of the etched agent increases simply because of the effect of the test piece etchant. It should be noted that the concentration of the etchant may decrease due to repeated use of the etchant during the etching process, and therefore, the etching time may be appropriately extended when its arrangement and disadvantages are not clearly understood. Inspection of welds and oxide film test specimens, the etching time than the usual arrangements and shortcomings of the etching time added 1 to 2 times. If the test piece is etched and transited, it is required to be re-worked. The appearance of more than 1 mm must be milled and then etched.
After the test pieces of aluminum and aluminum alloy ingots are etched, they should be quickly moved into the water tank for cleaning. Then use 20% to 30% nitric acid solution to wash away the black film, then rinse it in the sink. When the grain size of the finished product of the soft alloy is flashed, etching is preferably performed in segments. After dipping for a while, remove and rinse. According to the etching degree, etch again, and then clean until the grains are thoroughly cleaned and flashed. Since the etchant and the cleaning liquid all have vaporized gas during operation, the etching needs to be performed under ventilation. Aluminum and aluminum alloy etching equipment is simple, usually porcelain, glass tank or wooden slot, etc., can also use acid and alkali resistant plastic plate welding tank.
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