How to solve the particle problem on the surface of aluminum alloy material?

Cause analysis of 1. Particle adsorption 1. There are four kinds of particle burrs on the surface of extruded profiles: 1). Air dust adsorption. Dust, aluminium scrap, oil pollution and moisture produced by coal-fired aluminum rod heating furnace condense into particles and attach to the hot profile surface. 2) Impurities in aluminum bars, such as metallic inclusions and nonmetallic inclusions left by insufficient refining. 3), dust adhesion in the aging furnace. 4) The defects in the aluminum bar and the β phase AlFeSi in the composition are precipitated at high temperature, which reduces the plasticity and tensile strength of the metal and produces granular burrs. 2, the reason 1), the influence of aluminum bar quality due to high temperature casting, casting speed is fast, cooling intensity is high, β phase AlFeSi in the alloy can not be transformed into spherical α phase AlFeSi in time. Because β -phase AlFeSi presents needle-like structure in the alloy, it has high hardness, poor plasticity and low tensile strength, which not only induces extrusion cracks, but also produces granular burrs during high-temperature extrusion, which is not easy to clean and has a bad hand feeling. Impurities in aluminum rods will affect aluminum rods. In the casting process, aluminum rod is not fully refined, and dirt, refining agent, covering agent, powder coating and oxide film inclusions are mixed into the rod. These substances significantly reduce the plasticity and tensile strength of metals during extrusion, and are easy to produce granular burrs. The common structural defects of bars are porosity, coarse grains, segregation and bright crystals. All these defects of the cast bar have one thing in common, that is, the poor welding with the cast bar matrix leads to the discontinuous flow of the matrix. During extrusion, slag inclusions are easy to separate from the matrix, pass through the working area of the die, adhere to the inlet end, form sticky aluminum, and are constantly pulled out by flowing metal, which is easy to produce granular burrs. 2) Influence of die In extrusion production, the die works at high temperature and high pressure, and under the influence of pressure and temperature, the die is elastically deformed. The working zone of the die is parallel to the extrusion direction from the beginning. After being pressed, the working zone is deformed into a trumpet shape, and only the cutting edge of the working zone is in adhesive contact with the aluminum formed by the profile, which is similar to the chip tumor of the turning tool. In the process of forming bonded aluminum, particles are constantly taken out by the profile and adhered to the surface of the profile, resulting in "adsorbed particles". With the increasing adhesion of aluminum, the die will rebound instantly, forming bite marks. If there is a lot of aluminum sticking, the profile can't be pulled out, and the die will rebound instantly and the aluminum sticking will not fall off, so the profile surface will be rough, bright, torn and blocked. See figure 1 for the phenomenon of aluminum sticking in the mold. The extrusion die we use now is basically a plane die. Under the condition that the cast rod does not peel, impurities on the surface and inside of the cast rod accumulate in the dead zone of metal flow. With the advance of casting rods and the increase of the number of extrusion rods, the impurities in the dead zone are constantly changing, and some of them are brought out by the normal flowing metal and accumulated in the deformation space of the working area. Some of them are pulled off by profiles, forming granular burrs. Therefore, the mold is the key factor to cause particle burr. In addition, the higher the surface roughness of the die, the lower the surface hardness of the working area, which is also one of the reasons for sticking aluminum and forming granular burrs. 3) The study on the influence of extrusion process found that the correct selection of extrusion process parameters is also an important factor affecting particle burr. Through field observation, if the extrusion temperature and speed are too fast, more burrs will appear. The reason is that the extrusion speed is high at high temperature, the deformation degree of the die is increased, the metal flow is accelerated, and the deformation resistance of the metal is relatively weakened, which makes it easier to form aluminum sticking. For large extrusion coefficient, the deformation resistance of metal increases relatively, and the dead zone increases relatively, which improves the conditions for forming aluminum adhesion and increases the probability of forming "adsorbed particles". The difference between the casting rod heating temperature and the mold temperature is too large, which is also easy to cause the problem of particle burr. 4) Dust, water and oil stains in the air strongly adhere to the surface of aluminum profiles, because hot aluminum profiles will adhere after encountering dust, resulting in chemical reactions and colloidal substances, which will combine with furnace dust in the aging process to generate larger granular burrs, which are difficult to remove in the subsequent oxidation, electrophoresis and spraying processes. Second, measures to reduce granular burr 1. Improving the quality of aluminum bars, starting from the source. For profiles with high surface quality requirements, furnace cleaning should be carried out in the casting process, and raw and auxiliary materials should be optimized, such as spraying profiles and selecting high-quality aluminum ingots. Strengthen the control of casting process, prevent casting defects, improve the high temperature plasticity of metal and reduce the probability of granular burr. 2. Pay close attention to the mold quality, optimize the mold structure design, reduce the inflow of dead metal, improve the strength and rigidity of the mold, reduce the extrusion deformation of the mold, adopt reasonable nitriding process, improve the hardness of the working area, improve the polishing quality and reduce metal adhesion. 3. Optimizing process parameters, different aluminum alloy compositions and profiles, adopting reasonable extrusion process temperature according to aluminum alloy extrusion principle, controlling extrusion speed by stages, reducing the temperature difference between rod temperature and die temperature, and increasing the temperature difference between extrusion cylinder and rod can further reduce the inflow of dead zone metals and metal oxides and inclusions on the surface of cast rod, thus reducing the occurrence of slag inclusion and burr. 4. Take "5S" on-site management for all work sites, improve the environmental quality, clean the surface of cast rods, reduce the adhesion of ash and slag, put an end to "leakage", clean the dust on the surface of profiles in time, and minimize the adhesion of dust.