[China Aluminum Network] I. Basic features of Al-Mg-Si alloys:
The chemical composition of 6063 aluminum alloy in the GB/T5237-93 standard is 0.2-0.6% of silicon, 0.45-0.9% of magnesium, iron higher limit of 0.35%, the remaining impurity elements ( Cu, Mn, Zr, Cr, etc.) are all less than 0.1%. This is a very wide range of ingredients and it has a great deal of choice.
6063 aluminum alloy belongs to the aluminum-magnesium-silicon series heat-treatable aluminum alloy. In the ternary system composed of AL-Mg-Si, there is no ternary compound, only two binary compounds Mg2Si and Mg2Al3, with alpha (Al) Pseudo-binary cross section of Mg2Si is the boundary, forming two ternary systems, α(Al)-Mg2Si-(Si) and α(Al)-Mg2Si-Mg2Al3, as shown in Figs. 1 and 2: in Al-Mg- In Si-based alloys, the main strengthening phase is Mg2Si. When the alloy is quenched, the more Mg2Si solid-dissolved in the matrix, the higher the strength of the alloy after aging, and vice versa, the lower, as shown in Figure 2, in α ( On the pseudo-binary phase diagram of Al)-Mg2Si, the eutectic temperature is 595°C, the larger Mg2Si solubility is 1.85%, and it is 1.05% at 500°C. It can be seen that the temperature is solid solution of Mg2Si in Al. The degree of influence is great. The higher the quenching temperature, the higher the strength after aging. Conversely, the lower the quenching temperature, the lower the strength after aging. Some aluminum profiles factory production of the chemical composition of qualified parts, strength can not meet the requirements, the reason is that the aluminum heating temperature is not enough or outside the internal cooling, resulting in profile quenching temperature is too low.
In the Al-Mg-Si alloy series, the weight ratio of magnesium to silicon in the strengthening phase Mg2Si is 1.73. If there is an excess of magnesium in the alloy (ie, Mg:Si>1.73), magnesium will reduce the solid solubility of Mg2Si in aluminum. , thereby reducing the strengthening effect of Mg2Si in the alloy. If there is excess silicon in the alloy, ie, Mg:Si<1.73, then the solid solubility of Mg2Si in the aluminum is not affected by silicon. Therefore, in order to obtain a higher strength alloy, Mg:Si<1. 73.
two. Alloy composition selection 1. Alloy Element Content Selection There is 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, ie, how the profile should be surface treated and what surface it needs to obtain. 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; Bright materials, coloring materials, and electrophoretic paints are used, and Mg/Si is preferably in the range of 1.5-1.7. This is because there is less excess silicon, and the profile has good corrosion resistance and easy to obtain a bright surface.
In addition, the extrusion temperature of aluminum extrusions is generally about 480°C. Therefore, the total amount of alloying elements magnesium and silicon should be about 1.0%, because at 500°C, the solid solubility of Mg2Si in aluminum is only 1.05%. The excessively high content of alloying elements will cause Mg2Si to not dissolve 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 and the oxidation of the profiles. Coloring (or painting) causes trouble.
2. Impact of Impurity Elements 1 Iron and iron are the main impurity elements in aluminum alloys. In the 6063 alloy, the national standard specifies that it is not more than 0.35. If a primary industrial aluminum ingot is used in production, the general iron content can be controlled at 0. Below 25, but if in order to reduce production costs, the large amount of recycled scrap aluminum or aluminum, iron is easy to 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), 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.
a) Smelting, casting All materials should be coated with a coating before use to minimize the amount of molten aluminum.
b) Refine the grains to make the iron phase thinner and smaller, reducing its harmful effects.
c) Add an appropriate amount of hydrazine to convert the beta phase to the alpha phase and reduce its deleterious effects.
d) Carefully select waste miscellaneous materials, reduce as much as possible iron, nails, iron filings and other impurities into the aluminum furnace to increase iron content.
2 Other impurity elements Other impurity elements are rare in electrolytic aluminum ingots, far lower than national standards. When using recycled aluminum scrap, it may exceed the standard; 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.
three. Melting of 6063 aluminum alloy Controlling the smelting temperature Aluminum alloy smelting is one of the more important process steps for producing high-quality cast rods. If the process is not properly controlled, slag inclusions, pores, coarse crystal grains, feather crystals and other casting defects will occur in the casting. Strictly control. 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 fluxes and appropriate refining fluxes are important auxiliary materials used in the melting of aluminum alloys. The main components in the fluxes currently available on the market are chlorides and fluorides, in which the chlorides are highly water-absorptive and susceptible to moisture. Therefore, fluxes The production must be dried in the production of raw materials, completely remove the water, packaging should be sealed, transport, storage, to prevent damage, but also pay attention to the production date, such as the storage of the date is too long, the same moisture absorption phenomenon occurs in the 6063 aluminum alloy In the smelting process, fluxes such as deslagging agent, refining agent, and covering agent, if used, will cause the aluminum liquid to absorb hydrogen to varying 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-blasting refining. This refining method can make the refining agent and the 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 dusting 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 curling waves generated by the leech liquid are large, increasing the possibility of oxidized slag. 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, the bubbles float quickly, 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.
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