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The reason why aluminum profiles appear pitted or pitted may be an oxidation reaction. Products made of pure aluminum products generally do not have this phenomenon. It may be that the aluminum material is impure. Such aluminum materials are prone to oxides during production. Speckled white spots form. It is recommended to process it into alloy aluminum during processing. The combined components can change the performance, hardness and corrosion resistance of the material. It can also be surface treated such as anodizing, electroplating, baking paint, sandblasting, etc. Mostly, the surface of aluminum alloy profiles is dull and not smooth, and after oxidation, the surface becomes dark black (does not reflect light).
Another situation is that inclusions in the ingot or metal or debris stuck to the mold working belt are entrained by the high-temperature and high-pressure aluminum during extrusion and fall off, forming pits on the surface of the profile.
Cause
1. In terms of aluminum alloy profile molds, the working belt has insufficient hardness or is not nitrided (the normal hardness is about 48 degrees, and the mold working belt is above 52 degrees) or the working belt is rough and not smooth and sticks to the aluminum. The mold working belt design is too long, which increases the friction resistance. Aluminum The heating and holding time of the extrusion die (limited to no more than 8 hours) is too long, causing annealing on the surface of the work belt. The continuous extrusion of the mold is too long. The originally parallel work belt has a bell mouth, causing the particles to stick to the surface of the profile after extruding from the work belt. . Frequent extrusion of aluminum makes the work belt unable to be repaired and maintained.
2. Excessive temperature in the extrusion of aluminum alloy profiles (three temperatures of cylinder, rod and mold) increases the rise of deformation heat (20~60 degrees), which in turn increases the friction between the inner wall of the cylinder and the working belt and the aluminum, and increases the friction between aluminum and other materials. Due to the viscosity of metal (iron), the more aluminum metal particles stuck to the mold working belt, the rougher the surface of the aluminum material and the more serious the pitting will be. The extrusion speed is too fast (shown as the defect at the tail of the profile is heavier than the head end of the profile), which increases the flow speed of the metal, resulting in increased thermal deformation and die dead zone (aluminum area around the working belt of the lower die, poor fluidity, mostly aluminum on the surface of the aluminum rod) , the impurities and Mg2Si hard crystal particles (more impurities and magnesium silicon Mg2Si hard crystal particles) increase, and the dead zone impurities attached to the surface of the profile become more.
Solution
1. Appropriately reduce the extrusion speed, use reasonable extrusion temperature and mold temperature; standard and reasonable extrusion speed (use the speed when the surface of the profile is rough and pitted multiplied by 0.8 times the extrusion speed to determine the reasonable extrusion speed. ). With the appropriate three extrusion temperatures (the upper pressure at the beginning of extrusion is 210kg/cm2 without stuffiness, the extrusion pressure is around 170kg/cm2).
2. Strictly control the quality of the ingots, reduce the inclusion content in the ingots, and homogenize the ingots;
The raw material in our daily industry is called aluminum ingot. According to the national standard (GB/T 1196-2008), it should be called “aluminum ingot for remelting”, but everyone is used to calling it “aluminum ingot”. It is produced by electrolysis from aluminum oxide-cryolite. After aluminum ingots enter industrial application, there are two major categories: cast aluminum alloys and deformed aluminum alloys. Cast aluminum and aluminum alloys are castings produced by casting methods.
The aluminum ingot casting process uses liquid aluminum to be injected into the mold. After it is cooled into a billet and taken out, the injection process is a key step for the quality of the product. The casting process is the physical process of crystallizing liquid aluminum into solid aluminum.
Therefore, it is necessary to strictly control the ingot casting process and control the quality of aluminum ingots.
3. Strengthen mold repair quality management and design and manufacture qualified molds (the key lies in the strength and length of the mold working belt).
4. The key to reducing surface roughness and pitting of aluminum alloy profiles lies in the control of the working belt strength and length of the aluminum extrusion die as well as the extrusion temperature and extrusion speed.
