ã€China Aluminum Industry Network】 1. Selection of Alloy Compositions 1. Selection of Alloying Element Contents There are a wide range of 6063 alloy compositions. In addition to considering the mechanical properties and processing properties, the specific ingredients must also consider the surface treatment properties. How to perform surface treatment and what kind of surface to get.
For example, to produce abrasives, Mg/Si should be smaller, generally in the range of Mg/Si=1-1.3. This is because there is more relative surplus of Si, which is favorable for the profile to get a sand-like surface; if the production is bright Materials, coloring materials and electrophoretic paints, Mg/Si in the range of 1.5-1.7 is better, because there is less excess silicon, the profile is good corrosion resistance, easy to get a bright surface.
In addition, the aluminum extrusion temperature is generally selected at about 480 °C, therefore, the total amount of alloying elements magnesium silicon should be about 1.0%, because at 500 °C, Mg2Si in the aluminum solid solubility of only 1.05%, too high The content of alloying elements will cause Mg2Si not completely dissolved into the matrix during quenching, and there will be more Mg2Si phase dissolved. These Mg2Si alloys have little effect on the strength of the alloy, which will affect the surface treatment properties of the profiles, oxidation and coloring of the profiles (or Paint) causes trouble.
2. Influence of Impurity Elements 1 Iron and iron are the main impurity elements in aluminum alloys. In 6063 alloys, the national standard specifies no more than 0.35. If primary aluminum ingots are used in production, the general iron content can be controlled below 0.25. However, if a large amount of recycled scrap aluminum or aluminum is used to reduce production costs, the iron will easily exceed the standard.
Fe exists in aluminum in two forms, one is an acicular (or platelet) structure of β phase (Al9Fe2Si2), one is a granular structure of α phase (Al12Fe3Si), a different phase structure, the aluminum alloy There are different effects, the β-phase structure of the sheet structure is much more destructive than the α-phase of the granular structure, β-phase can make the aluminum surface rough, mechanical properties, corrosion resistance become worse, the oxidation of the profile surface blue, shiny When it falls, it will not be purely shaded. Therefore, the iron content must be controlled.
In order to reduce the harmful effects of iron, the following measures can be taken: smelting, casting all tools before the use of paint coating, as much as possible to reduce the molten aluminum solution.
Refine the grains to make the iron phase thinner and smaller, reducing its harmful effects.
Add appropriate amounts of hydrazine to convert the beta phase to alpha, reducing its deleterious effects.
The waste materials are carefully selected to reduce iron, nails, iron, and other debris into the aluminum melting furnace to increase the iron content.
2 Other Impurity Elements Other impurity elements are rare in electrolytic aluminum ingots, far lower than national standards, and may exceed the standard when using recycled waste miscellaneous aluminum; in production, not only must control each element not exceed the standard, but also The total amount of impurity elements can not be exceeded. When the content of individual elements does not exceed the standard, but the total amount exceeds the standard, these impurity elements also have a great impact on the quality of the profile. In particular, it is necessary to put emphasis on the fact that it has been proved that when the zinc content reaches 0.05 (not more than 0.1 in the national standard), white spots appear on the surface of the profile after oxidation, so the zinc content should be controlled to be less than 0.05.
Second, the melting of 6063 aluminum alloy 1. Control the smelting temperature Aluminum alloy smelting is one of the more important process links for producing high-quality cast rods. If the process is not properly controlled, slag inclusions, pores, coarse grains, feathers will be generated in the casting. Crystals and other casting defects, so it must be strictly controlled.
The melting temperature of 6063 aluminum alloy is preferably controlled between 750-760°C. If the temperature is too low, the generation of slag will increase, and if it is too high, hydrogen absorption, oxidation, and nitriding loss will increase. Studies have shown that the solubility of hydrogen in aluminum liquid rises sharply above 760°C. There are many ways to reduce hydrogen absorption when heat is used, such as drying melting furnaces and smelting tools, to prevent the flux from deterioration and deterioration. However, the smelting temperature is one of the more sensitive factors. The smelting temperature is not only a waste of energy, increasing the cost, but also a direct cause of defects such as pores, coarse grains and feather crystals.
2. The selection of excellent flux and appropriate refining process flux is an important auxiliary material used in aluminum alloy smelting. Currently, the main components in the fluxes sold on the market are chlorides and fluorides, among which the chlorides have strong water absorption and are prone to moisture. In the production of flux, it is necessary to dry the raw materials used, completely remove the water, seal the packaging, prevent damage during transportation and storage, and pay attention to the production date. If the storage date is too long, moisture absorption phenomenon will occur in 6063 aluminum. In the smelting of alloys, fluxes such as deslagging agents, refining agents, and covering agents, if used, will cause the aluminum fluid to absorb hydrogen in different degrees.
Choosing a good refining agent and selecting the appropriate scouring process are also very important. At present, most of the refining of 6063 aluminum alloys uses powder-refining refining. This refining method can make the refining agent and aluminum liquid fully contact and can make the refining agent play a better role. Great efficiency.
Although this feature is obvious, but the refining process must also pay attention, otherwise it will not be effective, the pressure of nitrogen used in powder refining is small, and it is better to meet the requirement of blowing powder. If the nitrogen used in the refining is not high purity Chlorine (99.99%N2), the more nitrogen that is blown into the liquid aluminum, the more moisture in the fluorine gas causes the aluminum liquid to oxidize and absorb more hydrogen.
In addition, the pressure of the fluorine gas is high, and the rolling waves generated by the aluminum liquid are large, increasing the possibility of oxidation slag formation. If high-purity nitrogen is used in the refining, the refining pressure is large and the resulting bubbles are large. Buoyancy of the large bubbles in the aluminum liquid is large, bubbles quickly float, the residence time in the aluminum liquid is short, and the effect of removing hydrogen is not good. Nitrogen increases costs. Therefore, nitrogen should be used sparingly, refining agents should be used more, and the use of refining agents is only good, there is no harm. The main point of the process of dusting refining is to spray as much of the refining agent as possible with as little gas as possible.
3. Grain refinement Grain refinement is one of the important processes in the casting of aluminum alloys. It is also one of the more effective measures to solve the casting defects such as pores, coarse grains, bright crystals, feather crystals, and cracks. In alloy casting, all are non-equilibrium crystals. Most of the impurity elements (including alloying elements, of course) are concentrated in the grain boundaries. The smaller the grains, the larger the grain boundary area, and the impurity elements (or alloying elements). The higher the uniformity.
For impurity elements, high uniformity can reduce its harmful effects, and even reduce the harmful effects of a small amount of impurity elements. For the alloy elements, the uniformity is high, and alloying elements can be used as alloying elements. To achieve full use of resources.
In the production of 6063 aluminum alloys, the uniform distribution of alloying elements and impurity elements is particularly important for sanding materials because corrosion produces uniform sand surfaces. The finer the grains, the more uniform the distribution of alloying elements (impurity elements) and the more uniform the sand surface obtained after etching.
Third, the 6063 aluminum alloy casting 1. Choose a reasonable casting temperature A reasonable casting temperature is also an important factor in the production of high quality aluminum rod, the temperature is too low, easy to produce slag, pinholes and other casting defects. The temperature is too high, easy to produce coarse grains, feather crystals and other casting defects.
The 6063 aluminum alloy solution after the grain refinement treatment can be appropriately increased in casting temperature, and generally can be controlled between 720-740°C because:
1Aluminous liquid becomes sticky after grain refinement, and it is easy to solidify and crystallize.
2 The aluminum bar has a liquid-solid two-phase transition zone at the front of the casting. The higher casting temperature has a narrow excess zone. The excessive narrow zone is conducive to the evolution of the gas discharged from the front of the crystal. Of course, the temperature cannot be too high. The casting temperature will shorten the effective time of the grain refiner and make the crystal grains relatively larger.
2. When conditional, fully preheat, dry casting system such as gutters, diverter plates, etc. to prevent moisture from reacting with aluminum liquid to cause hydrogen absorption. 3. During casting, avoid turbulent flow and rolling of aluminum liquid as much as possible. Do not use lightly. The tool agitates the aluminum liquid in the flow cell and the diverter disc, allowing the molten aluminum to crystallize smoothly under the protection of the surface oxide film. This is because the tool agitates the aluminum liquid and turns the liquid flow to break the oxide film on the molten aluminum surface. New oxidation, while rolling the oxide film into aluminum liquid. Studies have shown that the oxide film has a strong adsorption capacity, it contains 2% of the water, when the oxide film is involved in aluminum liquid, the water in the oxide film reacts with the aluminum liquid, resulting in hydrogen absorption and slag inclusion.
4. Filtration of aluminum liquid, filtration is a more effective method to remove non-metal inclusions in aluminum liquid. In the casting of 6063 aluminum alloy, it is generally filtered by multi-layer glass cloth or ceramic filter, no matter what kind of filtration Method, in order to ensure that the aluminum liquid can be properly filtered, the aluminum liquid should be removed before filtering the surface scum, because the surface scum easily plug the filter material filter mesh hole, so that the filter can not be carried out normally, remove the aluminum liquid surface scum is relatively simple The method is to set a slag block in the flow tank so that the molten aluminum removes the scum before filtration.
IV. Homogeneous treatment of 6063 aluminum alloy There are two problems in the internal structure of the aluminum alloy rod produced by casting:
1 Casting stress exists between grains;
2 Non-equilibrium crystallization causes imbalance in chemical composition within the grains. Due to the existence of these two problems, extrusion becomes difficult, and at the same time, the extruded product has a decline in mechanical properties and surface treatment properties. Therefore, the aluminum rod must be homogenized before extrusion to eliminate the unbalance between the casting stress and chemical composition in the grains.
Homogenization treatment is the heat treatment of aluminum rods at high temperatures (below the over-firing temperature) to eliminate the unbalance between the casting stress and chemical composition in the grains. The overheating temperature of Al-Mg-Si series alloys should be 595°C, but due to the presence of impurity elements, the actual 6063 aluminum alloy is not a ternary system but a multicomponent system. Therefore, the actual over-firing temperature is higher than 595°C. Lower, 6063 aluminum alloy homogenization temperature can be selected between 530-550 °C, high temperature, can shorten the holding time, save energy, improve the productivity of the furnace.
Homogenization treatment energy-saving measures: Homogenization treatment needs to be kept at a high temperature for a long period of time, which has a large energy demand and a high processing cost. Therefore, at present, most aluminum profile bars are not homogenized. The more important reason is that the homogenization process requires higher costs. The main measures to reduce the cost of homogenization are:
1 Grain refinement: Grain refinement can effectively shorten the holding time, and the finer the grains, the better.
2 lengthen aluminum rod heating furnace, according to uniform and extrusion temperature control, meet different process requirements. The main advantages of this process are: no increase in homogenization treatment furnace; full use of the heat energy after homogenization of aluminum to avoid reheating the aluminum rod during extrusion; aluminum holding heat for a long time, uniform temperature inside and outside, conducive to extrusion and subsequent Heat treatment.
In summary, the production of high-quality 6063 aluminum alloy cast rods, the first is based on the production of profiles to select a reasonable composition, followed by strict control of the melting temperature, casting temperature, do a good job of grain refinement, refinement of the alloy solution, filtration, etc. Technological measures, careful operation, to avoid the breakdown and entrapment of the oxide film. Later, the aluminum rods are homogenized so that high-quality aluminum rods can be produced, which provides a reliable material basis for producing high-quality profiles.
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