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GB/T 26492.1-2011 English PDF (GBT26492.1-2011)

GB/T 26492.1-2011 English PDF (GBT26492.1-2011)

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GB/T 26492.1-2011: Defects of wrought aluminium and aluminium alloys ingots and products -- Part 1: Defects for ingots

This Part specifies the definitions and characteristics of common defects in wrought aluminum and aluminum alloy ingots and products. It also analyzes their main causes. This Part is applicable to the analysis and determination of defects in wrought aluminum and aluminum alloy ingots.
GB/T 26492.1-2011
GB
NATIONAL STANDARD OF THE
PEOPLE REPUBLIC OF CHINA
ICS 77.150.10
H 60
Defects for wrought aluminium and aluminium alloys ingots
and products - Part 1: Defects for ingots
ISSUED ON: MAY 12, 2011
IMPLEMENTED ON: FEBRUARY 01, 2012
Issued by: General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Definitions, characteristics and main causes of defects ... 4
Annex A (informative) Index in Chinese Pinyin ... 25
Defects for wrought aluminium and aluminium alloys ingots
and products - Part 1: Defects for ingots
1 Scope
This Part specifies the definitions and characteristics of common defects in wrought aluminum and aluminum alloy ingots and products. It also analyzes their main causes. This Part is applicable to the analysis and determination of defects in wrought aluminum and aluminum alloy ingots.
2 Definitions, characteristics and main causes of defects
2.1 nodule of segregation (segregation knoble)
During the semi-continuous casting process, the nodules produced on the surface of the ingot are called nodule of segregation. The macroscopic structure is characterized by uneven bulges on the surface of the ingot [Figure 1a), Figure 1b)]. Microscopic tissue observation shows that the second part of the segregation knoble is larger than that of the matrix and is densely distributed. The volume fraction of the second phase is also large. Sometimes primary crystals can be found in segregation knobles [Figure 1c)]. Main causes:
a) The casting temperature is high and the casting speed is fast.
b) The crystallizer or core taper is too large.
c) The cooling intensity is low or there is a lack of water inside the crystallizer. d) The funnel is not placed correctly.
2.5 bow
The longitudinal axis of the ingot is not in a straight line.
Main causes:
a) The crystallizer is not installed correctly or is not firmly fixed. There is misalignment during casting.
b) The casting machine is running unstable.
c) The guide rail of the casting machine is not straight or the gap between the guide rails is too large, and the base is unstable.
d) The cover plate is uneven, causing the crystallizer to skew.
e) The crystallizer is deformed, with improper taper or poor smoothness, causing local suspension and bending.
f) Lifting or placement is improper.
2.6 pull crack
When the frictional resistance between the solidified shell formed during casting and the crystallizer wall exceeds the strength of the ingot itself, pull marks will be formed on the surface of the ingot. In severe cases, transverse cracks on the surface of the ingot are called pull cracks [Figure 3a), Figure 3b)]. Sometimes sagging occurs at the crack. This defect destroys the continuity of the ingot structure. In severe cases, it shall be discarded. Only when the depth of pull marks and pull cracks does not exceed the machining allowance of the ingot, milling or lathe processing can be performed. Main causes:
a) The inner surface of the crystallizer is not smooth, with burrs, scratches, and is not well lubricated.
b) The crystallizer or funnel is placed skewed, causing great frictional resistance on one side when the ingot is lowered.
c) During the casting process, the metal melt level fluctuates from high to low, causing the core (hollow ingot) to stick or leak aluminum and hang.
d) The casting speed is fast. The casting temperature is high. The high water pressure in casting can easily cause draw marks and cracks.
e) The crystallizer cooling water is scaled.
f) There is annealing or burnt of crystallizer.
a) The core is not installed correctly. The casting machine is unstable when lowered. b) The casting tool does not meet the requirements.
c) The ingot is bent or bored incorrectly.
2.9 shrinkage cavity
When liquid metal solidifies, when the liquid metal is insufficiently fed due to volume shrinkage, the cavity formed in the center of the tail end of the ingot after solidification is called a shrinkage cavity.
2.10 hot crack
During the solidification process of metal, the crystallization end interval from the online shrinkage start temperature to the solidus point temperature produces tensile stress because the crystallization shrinkage is hindered. And because this interval contains more brittle metal compounds, the tensile stress exceeds the strength of the metal in this area. Cracks produced at the extreme are called hot cracks. The macroscopic structural characteristics of hot cracks are cracks that are tortuous, bifurcated, or reticular or arc-shaped [Figure 5a), Figure 5b)]. The cracks on the fracture surface are mostly yellowish brown. There is oxidation. The cracks are uneven. The microstructure is characterized by cracks along grain boundaries. The cracks are filled with low melting point eutectic material [Figure 5c)].
Main causes:
a) The casting speed, temperature, cooling water pressure are Improper, or cooling is uneven.
b) The crystallizer and cover plate are deformed or the crystallizer and core taper are improper.
c) The melt is overheated or the liquid metal stays for too long.
d) The chemical composition and impurity content of the alloy are improperly controlled.
e) The liquid flow is unevenly distributed during casting.
f) The handling of the beginning or end of casting is improper.
Figure 8 -- Non-metallic inclusion
2.16 metallic inclusion
Due to improper casting process or foreign metal falling into the liquid metal, foreign metal objects exist in the structure of the ingot after crystallization. Foreign metal objects present in the organization are called metal inclusions. Its macrostructure and microstructure are characterized by angular metal objects. The color is obviously different from the base metal. There are clear dividing lines. After the ingot is deformed, cracks are likely to occur between the metal inclusions and the base metal. Main causes:
a) Improper operation causes foreign metal to fall into the liquid metal and enter the ingot.
b) Foreign unmelted metal remains in the ingot.
2.17 oxide film
Due to improper operation and melt contamination during melt casting, the oxides and unremoved gases (mainly hydrogen) formed by non-metallic inclusions in the ingot are called oxide films. Due to the small size of the oxide film, it is difficult to find it in the macrostructure of the ingot. The ingot sample used for inspecting the oxide film shall be deformed and then inspected for fracture. The oxide film is characterized by small platforms of yellow-brown or gray strips or flakes, symmetrically distributed on the two fracture surfaces (Figure 9). The oxide film on the microstructure is characterized by black linear inclusions or closed cavities. Black one is the oxide film. White color is aluminum base. Inclusions are often pit-like.
Main causes:
a) The raw and auxiliary materials are not clean, containing oil, moisture, moisture, corrosion, dust, sediment, etc.
b) During the smelting process, repeated feeding, dilution, and improper stirring methods destroy the surface oxide film and cause it to fall into pieces into the melt.
c) Refining and degassing are not complete. The flux and casting tools are wet and not fully dried. The air humidity is high, which can easily produce oxide films. d) During the melt transfer process, the metal melt does not flow throughout the tube. The impact is too great or the drop point is not closed, causing fragments of the oxide film to fall into the melt.
e) The standing time is not enough. There is too much slag accumulation in the smelting furnace and standing furnace.
Figure 10 -- White spot
2.19 porosity
When the melt crystallizes, due to insufficient replenishment of liquid metal between the matrix dendrites or the presence of undrained gas (mainly hydrogen), the micropores formed in the dendrites after crystallization are called porosity. Micropores formed by insufficient feeding are called shrinkage porosity. Porosity formed by gas is called gas porosity. The porosity macrostructure tissue is characterized by irregularly shaped and scattered black pinholes [as shown in Figure 11a)]. The fracture structure is characterized by rough, gray-white dot-like pits, which are not dense. When the porosity is serious, there will be small white spots on the fracture surface. The microstructure features are angular black holes distributed along the dendrites; the porosity is serious; the number of black holes is large; and the size is also larger [as shown in Figure 11b)].
Main causes:
a) There is a big difference between the alloy's starting solidification temperature and the solidification end temperature, that is, the transition bandwidth, which makes feeding and gas escape difficult.
b) The melt is too hot. Long stay. High magnesium alloy is not covered or poorly covered, etc. It absorbs large amounts of gas.
c) The tools are wet. The flux and the refining gas have high moisture content. d) Casting temperature is low. Casting speed is fast. The cooling intensity is small. It is difficult for the gas in the melt to escape.
e) Resting time is insufficient. Refining and degassing are not complete. f) The air humidity is high.
g) Gas and fuel have high moisture content.
h) The raw materials are wet, oily, and watery.
a) Macrostructure of white spot b) Microstructure of white spot
Figure 12 -- Gas porosity
2.21 white freckles
The fracture surface is white, with uneven borders, irregular shapes, and non-selective flocs to light (Figure 13). The microstructure consists of several coarse shrinkage cavities connected in a series along the dendrite boundaries. White freckles are usually distributed at the bottom of the ingot, the gate and the edges of the cross section. Main causes:
a) The starting solidification temperature and the final solidification temperature of the alloy are very different, that is, the transition bandwidth, which makes feeding and gas escape difficult.
b) The melt is overheated, with long stay. The melt is not covered or poorly covered, etc. It absorbs large amounts of gas.
c) The gas content of the melt is high. Tools are wet. The flux and refining gas have high moisture content. Refining and degassing are not complete.
d) Casting temperature is low. Casting speed is fast. The cooling intensity is small. It is difficult for the gas in the melt to escape.
e) Resting time is insufficient.
f) The air humidity is high.
g) The water content of gas and fuel oil is high.
h) The raw materials are wet, oily, and watery.
i) The oven is dry after overhaul, intermediate repair, or long-term shutdown. The oven baking is not thorough.
a) Macrostructure of gas porosity b) Microstructure of gas porosity

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