铝合金铸棒缺陷的产生原因(Causes of defects in Aluminum Alloy Casting Bars)

铝合金铸棒缺陷的产生原因（Causes of defects in Aluminum Alloy Casting Bars）

Classification of defects in aluminium and aluminium alloy ingots

Name, fatal defect, serious defect, general defect, minor defect

The chemical composition does not agree with *

Tissue burn *

Slag inclusion * *

Porosity and porosity * * *

Crack *

Size discrepancy * * *

Metal compound *

Laminated *

Bright grain *

Coarse grains * *

Name

Leukoplakia *

Bending *

White dot *

1. the chemical composition does not agree with each other

Where the range of chemical composition of aluminum and aluminum alloy exceeds the national standard

(GB/T3190-1996) provides that impurities higher than the ceiling, and affect the final performance of substandard products, are called chemical composition does not match, is an absolute waste.

Causes

1- the chemical composition of the ingot in the factory does not meet the technical requirements or has no technical qualification certificate.

The estimated percentage of waste and mixture weight in 2- blending is inaccurate.

The 3- ingredient accurately matches the alloying elements of the alloy.

The composition of 4- intermediate alloy is not qualified or fluctuates greatly.

5- rapid analysis of specimens without representation, laboratory, error analysis, or error analysis report.

6- alloy transfer group does not wash furnace or washing furnace is not thorough.

When the 7- is smelted, the burning is too large or the amount of burning loss is not accurate.

8- metal melt in the furnace for a long time and burning, mixing components uneven sampling.

2. layered defects:

In the process of casting liquid metal melt, open mold has been solidified on the surface near the mold wall, the ingot surface formed on the two layer, called a layer (or cold isolation).

This defect seriously damaged the continuity of the whole ingot structure, and should generally be waste products. If the car can be allowed to use completely disappear.

Forming reason:

1- casting speed is slow, the metal melt flow is insufficient, the edge is easy to solidify, the melt that continues to supply does not add up to solidify ahead of time;

The casting temperature of 2- is low, the fluidity of molten metal is not good, and it is easy to solidify near the mould wall;

The casting funnel of 3- is not placed properly, and the metal melt flows unevenly into the funnel;

4- the funnel is blocked, the cooling in the condensate tank is uneven, and the metal is quickly solidified in the place where the cooling rate is great;

5- lubrication uneven or partial oiling too much;

6- casting stops halfway, suspension or metal melt flow, high and low;

The taper in the 7- condenser tank does not meet the requirements.

3. crack and stretch mark

As the friction between the outer surface of the ingot and the mould exceeds the strength of the ingot itself, a tensile mark is formed on the surface of the ingot, and the ingot is broken or broken in severe cases.

This kind of defect seriously damaged the continuity of the whole ingot

structure, and should be waste in serious condition. If the car can be allowed to use completely disappear.

Forming reason:

1- mold internal surface is not smooth, burr, scratches, lubrication is not good;

The 2- mould is produced by tilting and causing great resistance when the ingot is lowered;

In the process of 3- casting, the metal body is high and low and causes suspension of the core (hollow ingot) or aluminum leakage;

4- casting speed, casting temperature is high, casting water pressure is big, easy to cause crack or stretch mark

4. slag inclusion

Metal slag is customarily referred to as copper, iron and other metal fragments that occasionally fall into pieces;

The non-metallic slag inclusion mainly refers to the slag inclusion on the low test piece, such as slag inclusion, slag and flux, asbestos plate and so on.

Slag inclusion is divided into surface slag inclusion and internal slag inclusion.

Slag inclusion damages the continuity of ingot structure and seriously affects the quality of the products.

Causes:

1- raw and auxiliary materials are not clean, such as oil, dirt, dust, moisture and so on;

In the process of 2- smelting, the surface oxide film has been destroyed many times because of repeated feeding, dilution and agitation;

In the process of converting to 3- impact too much, not full of molten metal flow or gap is too large due to oxidation slag;

4- refining improper operation, refining is not sufficient, so that the refining effect is not good;

5- in the casting process, the metal level fluctuates greatly, each falls nearly to seal off, and the beginning and ending are improper;

6- is affected by the nature of alloy. If some alloys are poor in fluidity, it is difficult to float slag;

7- casting temperature is too low, slag is difficult to float

5. oxide film

Fragments of complex oxides consisting of metal aluminum and AI2O3 in oxidation in air and other oxides in alloy elements (such as MgO) exist in the ingot and form an oxide film in the ingot.

It destroys the continuity and compactness of the internal structure of the alloy and reduces the various properties of the alloy.

Causes:

1- raw and auxiliary materials are not clean: if there is oil, moisture, moisture, corrosion, dust, sediment and so on;

In the process of 2- smelting, repeated feeding, diluting and mixing methods are improper, which destroy the surface oxide film and become fragments and fall into the melt.

3- humidity season, easy to produce oxidation film;

In the process of converting 4- melt metal melt without full pipe flow, the impact is too large or the fall was not closed due to oxide melt into pieces.

5- melt temperature is low, the time of slag removal and degassing is short, and the casting time is not enough in the static furnace;

The various tools used by 6- are not good for preheating and drying;

The casting temperature of 7- is on the low side, and the oxide film is hard to float;

In the 8- casting process, the metal level fluctuates greatly, and the beginning and ending operations are improper.

6. cracks

The internal causes of crack formation can be divided into two categories: hot crack and cold crack.

According to the shape of crack in the ingots and parts can be divided into center (tongxinfang) crack, surface crack (subcutaneous), radial crack, cyclic crack, transverse cracks, crack, crack at the bottom of the gate, the crack for proofreading waste.

Causes:

1- adjust the main chemical composition reasonably, strictly control harmful impurity content and \"mutual relation\"\";

2- improves the purity of molten metal, eliminates gas and slag completely, and prevents the metal melt from overheating at the same time;

3- all kinds of casting tools are suitable for use. They are firm and smooth, with good surface finish;

4- reasonably adjust the manufacturing speed, casting temperature, cooling strength and their relationship;

5- crack alloy, large size ingot casting, beginning with pure aluminum or the basic technologies of bedding.

7. porosity and porosity

The molten metal contains a large amount of gas, and the inner surface of the ingot is formed with a round cavity called a blowhole.

At the grain boundary and the dendrite network, macroscopic or microscopic porosity is formed, which is called porosity.

This defect damage strong binding ingot between grains, the microstructure is compact, in the process of welding (if not more difficult, while stomatal) severely degrades the mechanical properties of the products. Such defects are not allowed to exist.

Causes:

1- alloy, when some alloys are cast, start the solidification temperature and the end of the solidification temperature difference, that is, the transition belt size is large, so that the contraction and gas escape difficult;

2- metal melt has long residence time, poor coverage or local overheating,

which causes a large amount of gas to be absorbed by melt;

3- furnace, tools, nitrogen and chlorine content is high, refining gas is not complete;

4- has low casting temperature, fast casting speed and little cooling strength, so it is difficult to escape gas in the melt;

5- high temperature and high humidity season, the air humidity is large, the metal melt suction volume increased.

8.: white edge Aluminum Alloy bottom, and the cross section of the gate, there is a white spot defect, scattered, cottony, known as white spots (also called white).

This kind of defect is most likely to occur in high magnesium alloys, and it greatly reduces the elongation of alloys.

Causes:

1- white reasons and related to the composition (including magnesium alloy) such as LF2, LF3, LF6, LY12, LC4, LD5 alloy large size ingot.

2- raw material is humid, the melt has high gas content, and the gas is not completely eliminated during refining.

The residence time of 3- melt is long, the coating is poor, and the intake of

metal melt is increasing.

4- mold is high and has little cooling strength.

5- casting speed is too slow, cooling water temperature is too high.

9. white spot

The white spot is in the initial stage of casting, because the liquid flow impulse, the suspension of pure aluminum in aluminum liquid crystal bed full condensation in the casting funnel bottom, and gradually grow up, gradually into a small number of elements when subjected to some external force vibration or erosion and colony formation in white cast.

The appearance of the white spot reduces the mechanical strength of the product and can not be well pressed after the processing deformation, so it is not allowed to exist.

Causes:

1- casting begins when the bedding operation must be carefully, to prevent the suspension of pure aluminum in the funnel bottom or the mold wall, don't shake after the start of casting process and funnel.

2- bed temperature and improve the aluminum, hit in bed before the scum.

3- funnel should be paved with paint, fully preheated

10. bright grain

The primary segregation of poor solid melts results in the formation of bright grains.

It has bright, color, uncertainty, and a few times larger than the surrounding crystal tree crystal, this crystal is referred to as optical crystal.

Because bright grains contain alloy elements are very low, will seriously reduce the mechanical properties of the product, so it is not allowed to exist.

Causes:

The surface of the funnel used at the beginning of the casting of the 1- is not smooth or the heat conductivity is not good. The funnel is too high from the bottom or does not preheat well;

When the 2- funnel sinks too deep, the supercooled zone of the liquid portion of the ingot expands to the entire volume of the liquid cavity, in favor of the order in volume;

In the course of 3- casting, the funnel is shaken for some reason, and the bottom of the bottom of the hopper falls into the crystalline surface and condenses into the ingot;

The casting temperature of 4- is low and the speed is slow. The cooling of ingot surface is strong, and the crystal is easy to produce.

11. primary segregation of intermetallic compounds and metallic compounds

The inclusion of refractory components in the ingot structure, the high melting point intermetallic compound, and the primary segregation of the metal compounds found in LF21, LD7, LD8, LD9, LF11, LC4, LF6, LF12 and other alloys.

The intermetallic compound has high hardness and brittleness, and is mostly blocky, acicular and unevenly distributed in the crystal, which seriously affects the lateral properties of the products.

Causes:

1- strictly controls the content of refractory component and impurity content in alloy composition;

2- uses a low melting point master alloy to melt refractory elements into the melt to ensure that it is fully dissolved in the alloy;

3- appropriately improves casting temperature and casting speed;

4- fully preheated casting funnel and transfer tool, not in a hole in the liquid funnel placed too deep.

12. segregation tumor

The fusible precipitates ingot surface condensation is called to segregation, also called segregation.

The segregation within the fusible ingredients and eutectic compounds, the composition is not uniform, and the surface of the ingot to eliminate the bulge, cold processing.

Causes:

1- casting temperature is high and speed is fast;

The gap between the ingot and mould of 2- is large, the mould is big and the mould is high;

3- mold internal surface is not smooth, oil lubrication is not good;

The casting funnel of 4- is not placed properly and the flow distribution is uneven;

5- low cooling rate or partial water shortage in mold;

6- ingot diameter is large.

13. feathery crystals - lace

In a continuous casting ingot, a patterned structure is formed. Some call it a fan-shaped, cone-shaped, flaky, radial, feathery, lacy structure, commonly known as feathery crystals or laces. Feathery crystals are a variety of columnar crystals.

The alloy with feather like alloy may break down along its twin when rolling and free forging, and seriously affect the technological performance and mechanical properties of the product.

Causes:

1- melting temperature is too high, too long, melt long residence time in the furnace, the non self crystal nucleus reduced;

2- refining gas excessive nucleation material separation, non self crystal nucleus reduced;

3- is related to the amount of grain refining elements, such as LC4 alloy ingots. When the content of Ti is less than 0.025, the appearance of feathery crystals can not be completely suppressed

4- when the metal melt is injected centrally and is equal to the crystal front, the tangent direction flows into the liquid cavity, so that the local temperature is high, and it is easy to produce feather like crystal.

5- when casting temperature is high, easy to produce feather like crystal

14. coarse grains and large columnar crystals

Coarse grains refer to large equiaxed grains. Coarse columnar crystals refer to large columnar crystals.

The presence of coarse grain defects seriously reduces the mechanical properties of alloy casting, and eventually affects the mechanical properties of the products.

Causes of coarse grain:

When the 1- alloy is overheated or partially overheated, the non spontaneous nucleation is destroyed and the crystalline core decreases;

2- casting temperature is high, crystallization speed is small

Improper adjustment of composition and impurities in 3- alloy.

Causes of coarse columnar grains:

1- reasonably adjust alloy composition and impurity content, for example, in 5XXX alloy, Mg content is reduced, easy to form columnar crystal;

The cooling intensity of 2- is large, the nucleation time is short, the nucleation is reduced, and columnar crystals are easy to form;

3- melt overheating or overheating, the non nuclear liquates self Rutilated Quartz crystal core, easy reduction, columnar crystal growth;

4- is easy to grow with columnar crystals because of its unequal concentration and unequal flow.

15. the ingot has been overheated

When the ingot is homogenized during annealing, the temperature is too high (beyond the range specified in the process).

When the alloy ingot is burned, the mechanical properties deteriorate, the elongation and fatigue strength decrease obviously, which is absolutely waste.

Causes:

1- did not perform the process correctly and the heating temperature was too high;

2- instrument malfunction or error;

3- soaking District uneven temperature or discharge is not;

4- pit is not normal, bad ventilation equipment, so that each section of the uneven temperature.

Sixteen

A common casting defect:

The defects in the casting process often appear in the macrostructure of the extruded products:

Bright grain: poor alloy component, poor solid melt, primary crystal.

Treatment methods: pure aluminum, LF2 and LF21 are not examined. Other alloy extrusions allow for two points of 2mm, beyond the two points, treated by intermetallic compounds.

Intermetallic compound: a metal compound with a refractory component and a high melting point

Treatment methods: all profiles permit the presence of metal compounds with 0.3mm, and the strip allows for 0.3-0.5mm intermetallic compounds to be two points.

Porosity, slag inclusion and porosity: there are tiny shrinkage holes or pores in the product, which makes the crystalline structure not compact, and sometimes the three are produced.

Treatment method: to a certain extent, destroy the grain firmness, is not allowed to exist.

Oxide film: aluminum oxide is found in metal alloy.

Treatment method: allow 0.3-0.5mm oxide 5 points (3 points are not calculated), exceed the standard, according to the metal compound approach.

The chemical composition is over standard: the calculation of ingredients is incorrect or uneven mixing or excessive burning during smelting. This defect is entirely scrapped.