Aluminum alloy common problem

1. The surface of the ingot is not flat, there are many honeycomb holes and cracks.

A. When the silicon content of the alloy reaches about 12%, the crystallization temperature interval of the alloy becomes narrow, and shrinkage and shrinkage occur at the top of the ingot during solidification. This is caused by the nature of the alloy itself, which is eutectic silicon aluminum. Characteristics. This is especially the case with the ADC-12 alloy. When the silicon content is below 10.5%, cracking does not occur.

B. The jitter (vibration) of the conveyor belt accelerates the solidification of the alloy liquid, resulting in an increase in shrinkage cavities and shrinkage depths, resulting in honeycomb-like holes, which are caused by external factors and have no effect on the intrinsic quality.

C. There is a close relationship between the proportion of raw and cooked raw materials.

2. The molten soup has poor fluidity and is difficult to die. If it is heated again, it is easy to overheat.

When any metal is melted into a liquid, it will produce a pot substrate (precipitate), a high grade and a low grade metal, but only how much the bottom of the pot is different. This is closely related to the purity of the raw material. After the alloy is formed, the aluminum About 10% of silicon is added to the silicon alloy. The raw material silicon metal carries impurities such as calcium (Ca) and iron (Fe), and increases impurities such as calcium oxide and ferrous oxide. The bottom of the pot is mainly a metal compound and non- The metal compound is attached with impurities, and the elevated temperature does not work. After the spectroscopic test, the composition is completely gone and can no longer be used for casting. Therefore, it is necessary to pay attention to the operation:

A. When the aluminum alloy ingot is smelted out of the soup, the sinking material must be separated and separated, and the ingot cannot be mixed into the soup;

B. During the die-casting production process, each aluminum pan soup needs to clean the bottom sediment and clean the crucible when pouring a certain amount of residual water. It is not allowed to continuously add the riser, waste castings and fly during the pouring process. With aluminum scraps, the sediment at the bottom of the pot gradually accumulates more and more, and finally a pot of aluminum soup is formed into a paste, which not only loses fluidity, but also clears the pan. This is often the case with many domestic users.

3 The molten soup sinks more than a thick paste, and if it is split, the Fe and Mn components often exceed 2%.

See the answer to the above question: • There is too much sediment in the molten soup, the sediment (pot substrate) is split, the alloy composition is disordered, and manganese (Mn) and iron (Fe) have formed (Fe.Mn) AL6 compound. The bottom of the pot has been repeatedly deposited, requiring the user to correct the smelting method in time, according to the correct process operation of Question 2.

4. Easy to stick mold, poor mold release

A. The quality of the selected release agent is not good, such as the water-based graphite release agent, which causes the casting to slip out of the cavity smoothly.

B. Excessive impurity content in the alloy

C. The mold release angle is too small, so that the demoulding is not smooth;

D. There are too many cracks in the old mold, resulting in sticking

E. The iron content in the alloy is too low, which is lower than the standard range required by the die casting process.

5. The aluminum ingot section has slag inclusions, and the molten soup produces continuous golden yellow scum and black suspended scum.

In the aluminum alloy smelting process, the fluxing agent, the modifier, the magnesium removal agent and the like are commonly used. The raw materials of these additives are mainly composed of fluoride, nitrate, chloride, etc., and these halogen base element compounds cause golden yellow when volatilized. Scum; black suspended particle scum is mainly produced because the melting point of silicon is as high as 1,412 degrees Celsius. In the process of melting aluminum alloy, if the silicon is not completely melted into a solid solution according to the operating rules, the initial ecological silicon is present in the aluminum soup. Then the liquid surface floats in a black suspension. Therefore, the slag removal process must not be sloppy. It must be operated according to the process rules, and the fluxes prepared from carbonates, sulfates, nitrates, etc. are used to form chemical reaction products. Dry slag separated by aluminum liquid.

6. After the smelting process is strictly degassed, the gas cannot be removed.

The degassing process of aluminum alloy has been perfected, including inert gas degassing method and solid flux degassing method. Gas degassing has chlorine gas, argon gas, nitrogen gas, and three gas degassing method; solid flux deaerator has hexachloroethane , carbon tetrachloride, sodium nitrate non-toxic deaerator, etc.. As long as the operation is reasonable, the gas (H2) in the aluminum liquid can be removed. The first condition of the degassing agent is that it cannot contain gas, the gas here is Refers to hydrogen (H2) from moisture (H2O), so the degassing agent itself has extremely strict requirements on the gas content, and it must be dehydrated when it is formed. Sometimes it is impossible to remove the gas after degassing operation, which is often The degassing agent is too poor in quality. If the water content in the deaerator is too high, the deaerator is placed too long, the tide is not fresh, etc. It is necessary to observe the specific use and operation process of the other manufacturer.

7. During gravity casting, a large amount of pores occur near the riser of the finished piston.

This is caused by improper casting process and mold design: the piston casting process has already formed a complete design (JINGREN method), that is, the gooseneck gate system. According to the diameter of the piston and the wall thickness, set one on each side or on both sides. Or two risers (side risers). Some production plants only need to design small gates and small risers to save aluminum liquid, so that the risers are too small, the shrinkage is poor, and the pores are generated.

8. After the die-casting of the finished product is peeled off after the die-casting, the riser “eats” the finished product, resulting in an increase in the defect rate.

A. Mainly related to the unreasonable design of die-casting molds. If the gate size is too thick, it will cause "belt" phenomenon.

B. The position of the gate is set at the thin wall of the casting, which will also cause the phenomenon of "with meat" during cleaning.

C. The cake (*) is too thin, there are shrinkage holes and inclusions at the fracture.

< The casting system of die castings is divided into inner gates, overflow tanks, and cakes (blocks). It is not set up with "riser", so it is called "riser" is wrong, it should be called block (cake) >

9. Cracking at the nozzle when opening the mold

A. The mold design and production are unreasonable. The length of the ejector pin is uncoordinated when the mold is opened (not synchronized) B. The design of the ejector position is unreasonable C. The raw material is brittle and the toughness is not enough. Sampling analysis means knowing the details. Casting the object, to determine which is the cause

10. The casting is brittle when it is post-treated, polished, drilled, and the casting is fragile.

A. Aluminum-bismuth alloy has high bismuth content, brittle material and easy to break

B. The aluminum alloy liquid is kept warm and the shelf life is too long or the alloy liquid is overheated, which may cause brittleness and cracking.

11. The joints of the castings cannot be completely fused and the residual marks remain.

A. The temperature of the alloy liquid is low or the mold temperature is low, and the fluidity of the alloy liquid is poor, which will cause such defects, mainly because the two streams cannot be welded.

B. Low filling speed

C. The mold design is unreasonable, and the overflow groove is improperly distributed.

D. The pressure is lower than the pressure; each casting has a different structure, and the correct casting process should be designed according to the physical design.

12. The product cannot be formed during die casting

The whole set of die-casting technology has not been mastered, and it is recommended that the other die-casting plant strengthen its technical strength.

13. Castings have irregular black stripes on the surface, with water ripples

A. Too much coating (using water-based graphite coating)

B. The mold temperature is too low (below 180 degrees Celsius, it will produce flow marks)

C. Filling speed is too high to produce water ripples

14. The surface of the casting is dark and black, with oxidation, sometimes white hair.

A. Improper preservation of castings, stacking in the open air, exposure to the sun; or stacking castings close to electroplating, heat treatment workshops, etc.

B. The working environment is too bad, there is moisture in the air, and the acid and alkali gas are too heavy, which will cause the surface of the aluminum casting to oxidize.

C. The release agent has deteriorated

15. The surface of the casting has "lack of meat" or "rough surface", the cause of the depression on the surface of the casting. The academic term "depression", also known as "concave" and "helium", causes

A. The overflow tank is too small, too little or there is no overflow tank in a thick place

B. The mold temperature is too high

C. The pressure is too low