Choice of alloy composition
1. Selection of alloy element content
6063 alloy components have a wide range. The specific components should consider not only mechanical properties and processing performance, but also surface treatment performance, that is, how the profile is processed and what kind of surface is to be obtained.
For example, in order to produce abrasive materials, Mg/Si should be smaller. Generally, Mg/Si should be selected in the range of Mg/Si=1-1.3. This is because there are more relatively excessive Si, which is conducive to the sand-like surface of the profile. If bright material, colored material and electrophoretic paint are produced, Mg/Si is good in the range of 1.5-1.7, which is because there is less excess silicon and the profile is resistant to corrosion, so it is easy to get the shiny surface.
In addition, aluminum extrusion temperature generally chosen at 480 ℃ or so, therefore, should be around 1.0%, total magnesium alloy element silicon at 500 ℃, Mg2Si only 1.05% solid solubility in aluminium, high content of alloy elements can cause the Mg2Si cannot be absorbed during quenching substrate, there are more dissolved Mg2Si phase at the end of the Mg2Si relative to the strength of the alloy don't have much effect, it will affect the profile surface treatment performance, oxidation, coloring to profile (or paint) cause trouble.
2. Influence of impurity elements
Ferric, iron is the main impurity element in aluminum alloy, in 6063 alloy, the national standard is no more than 0.35, if the production is using grade I industrial aluminum ingots, the general iron content can be controlled below 0.25, but if in order to reduce the production cost, a large number of recycled aluminum or aluminum outside, iron root is easy to exceed the standard.
Existence form of Fe in aluminum has two kinds, one kind is needle (or sheet) of the structure of the beta phase (Al9Fe2Si2), a kind of to the granular structure of alpha (Al12Fe3Si), different phase structure, has a different effect on aluminium alloy, the lamellar structure of alpha beta phase than granular structure more destructive, beta phase can make the aluminum surface roughness, mechanical properties, corrosion resistance, oxidation of profile surface of the blue, luster, color is not pure color, therefore, iron content must be controlled.
In order to reduce the harmful effects of iron, the following measures can be taken: melting, casting of all tools before use of paint, as far as possible to reduce iron dissolved human aluminum liquid.
Refining the grain to make the iron phase thin, small, reduce its harmful effects.
The addition of appropriate amount of strontium, which can make Chinese silkworm phase to fruity phase, reduce its harmful effects.
Select waste and miscellaneous materials carefully, reduce iron wire, iron nails, iron filings and other sundries as far as possible into melting aluminum furnace, resulting in increased iron content.
Other impurity elements
Other impurity elements are very few in electrolytic aluminum ingots, which are far below the national standard. In production, not only should each element be controlled not to exceed the standard, but also the total amount of impurity elements should be controlled. When the content of a single element is not exceeding the standard, but the total amount is exceeding the standard, these impurity elements also have a great impact on the profile quality. In particular, it should be emphasized that when the zinc content reaches 0.05 (no 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 below 0.05.
Ii. Smelting of 6063 aluminum alloy
Control the melting temperature
Aluminum alloy smelting is one of the most important processes for producing high quality casting bar. If the process is not controlled properly, various casting defects such as slag inclusion, pores, thick grains and feather crystals will be produced in the casting holding. Therefore, strict control is required.
6063 aluminum alloy melting temperature control between 750-760 ℃ is beautiful, too low will increase the production of slag, high increase hydrogen, oxygen, nitrogen absorption loss. Research shows that the solubility of hydrogen in aluminum liquid in sharp rise above 760 ℃, when heat by means of reducing hydrogen absorption and many, such as drying smelting furnace and smelting tool, to prevent the use flux be affected with damp be affected with damp metamorphism, etc. However, the melting temperature is one of the sensitive factors. The melting temperature of over-separation not only wastes energy and increases cost, but also directly causes defects such as pores, thick grains and feather crystals.
2. Select excellent flux and proper refining process
Flux is one of the important auxiliary materials used in aluminium alloy smelting, the flux are sold on the market at present the main ingredients for chloride, fluoride, chloride water imbibition is strong, easy to be affected with damp be affected with damp, therefore, must be in the production of flux, the drying materials, thoroughly remove moisture, packing should be sealed, and to prevent the damage of the transportation, storage, but also pay attention to the date of production, such as keeping the date is too long, the same will happen phenomenon of moisture absorption, in 6063 aluminum alloy smelting, the use of slag agent, refining agent, coating agent, such as flux if moisture absorption, can produce different degree of the aluminum liquid hydrogen absorption.
It is also very important to select a good refining agent and a proper refining process. Currently, the vast majority of 6063 aluminum alloy refining is conducted by powder spraying. This refining method can make the refiner fully contact the aluminum liquid and make the refiner play a greater role.
Although this characteristic is obvious, but the refining process must also note, otherwise can not get due effect, the nitrogen pressure used in powder refining is good with small, blow out can meet the powder to be beautiful, refined if used in the nitrogen is not high purity chlorine (99.99% N2), the more nitrogen gas into liquid aluminum, fluorine in water to make the more liquid aluminum oxide and hydrogen absorption.
In addition, the high pressure of fluorine gas, large rolling wave of aluminum liquid, increases the possibility of producing oxidized slag inclusion. If high purity nitrogen is used in refining, the refining pressure is high, the bubbles are large, and the large bubbles have high buoyancy in aluminum liquid, and the bubbles rise rapidly. The residence time in aluminum liquid is short, the effect of hydrogen removal is not good, nitrogen is wasted and the cost is increased. So nitrogen should be used sparingly, and the refiner should be used more. The key point of powder spraying is to use as little gas as possible and to spray as much refining agent as possible.
3. Grain refinement
Grain refinement is one of the important processes in aluminum alloy casting, and also one of the effective measures to solve the casting defects such as pores, coarse grains, bright crystals, feather crystals and cracks. In alloy casting, all the impurity elements (including alloying elements, of course) are mostly distributed in grain boundaries. The smaller the grains, the larger the grain boundary area and the higher the uniformity of impurity elements (or alloying elements).
For the impurity element, high uniformity can reduce its harmful effect and even change the harmful effect of a small amount of impurity element into beneficial effect. On the surface of alloying elements, high uniformity can be used to make the alloying element more powerful, so as to make full use of resources.
In the production of 6063 aluminum alloy, the uniform distribution of alloy elements and impurity elements is particularly important for the abrasive materials to produce uniform sand surface through corrosion. The finer the grains, the more uniform the distribution of the alloy elements (impurity elements), and the more uniform the sand surface obtained after corrosion.
Casting of 6063 aluminum alloy
1. Select reasonable casting temperature
Reasonable casting temperature is also an important factor for the production of high quality aluminum bar. The temperature is too low, and it is easy to produce casting defects such as slag inclusion and pinhole. The temperature is too high, easy to produce heavy grain, feather crystal and other casting defects.
The grain refinement process of 6063 aluminum alloy liquid, casting temperature can be appropriately increased, generally can be controlled between 720-740 ℃, this is because:
The aluminum solution becomes viscous and solidifies easily after grain refining.
The aluminum bar has a liquid-solid two-phase transition zone at the crystallization front in casting, and the higher casting temperature has a narrow transition zone, which is conducive to the release of gas from the crystallization front. Of course, the temperature cannot be too high, and the excessive casting temperature will shorten the effective time of grain refiner and make the grain relatively large.
2. When the conditions are available, fully preheat the casting system, such as drying the flow groove and distributing plate to prevent the reaction of moisture with aluminum liquid to cause hydrogen absorption
(3) in the casting, as far as possible avoid turbulent liquid aluminum and folding, you don't want to disturb the chute and easy to use tool shunt liquid aluminum plate, let the liquid aluminum surface oxidation film flow smoothly under the protection of the crystallizer crystallization, this is because the tool agitation aluminum liquid and liquid flow, twisting can make liquid aluminum surface oxidation film is broken, and create new oxidation, at the same time will be involved in liquid aluminum oxide film. Studies have shown that the oxide film has a strong adsorption capacity, it contains 2% water. When the oxide film is sucked into the aluminum liquid, the water in the oxide film reacts with the aluminum liquid, resulting in hydrogen absorption and slag inclusion.
4. To filter of liquid aluminum, filter is to remove non-metallic slag is a effective method in aluminum liquid, in 6063 aluminum alloy casting, general filter with multilayer glass cloth or ceramic filter plate, whether what filtering methods, in order to ensure the normal order of the liquid aluminum can filter, liquid aluminum should be removed before the filter surface scum, because the surface scum easily blocked filter material filter hole, the filtering unable to proceed normally, remove the scum on the surface of the liquid aluminum is a simple method is set in the chute blocking slag board, make the liquid aluminum scums in front of the filter.
The homogenization of 6063 aluminum alloy
The inner structure of aluminum alloy bars produced by casting has two problems:
There is casting stress between the grains of the cores.
Imbalance of chemical composition in grains caused by non - equilibrium crystal. Due to the existence of these two problems, it will be difficult to squeeze. At the same time, the extruded product will have a decline in mechanical performance and surface treatment performance. Therefore, aluminum bar must be homogenized before extrusion to eliminate the casting stress and chemical imbalance in the grain.
Homogenization is the heat treatment of aluminum rod at high temperature (lower than overheat temperature) through heat preservation to eliminate the casting stress and chemical imbalance in the grain. Al - Mg - Si alloy series burnt temperature is 595 ℃, but because of the existence of the impurity elements, the actual 6063 aluminum alloy is not a ternary system, but a multicomponent system, therefore, the actual burnt temperature were lower than 595 ℃, 6063 aluminum alloy homogenization temperature of optional between 530-550 ℃, the temperature is high, can shorten the time of heat preservation, save energy and improve the productivity of the furnace.
Energy saving measures of homogenization treatment: the homogenization treatment needs to pass the long-term heat preservation under the high temperature, which has a large energy demand and high treatment cost. Therefore, most of the profile factories do not homogenize the aluminum bar at present. The more important reason is the higher cost of homogenization. The main measures to reduce the cost of uniform treatment are as follows:
Grain refining: grain refining can effectively shorten the holding time, the finer the better.
The lengthened aluminum rod heating furnace in the holder can be controlled in different stages according to the homogenization and extrusion temperature to meet different technological requirements. The main advantages of this process are: no homogenization furnace is added; Make full use of the heat energy after homogenization to avoid reheating aluminum rod when extruding. Long heating time and uniform internal and external temperature are conducive to extrusion and subsequent heat treatment.
To sum up, the production of high quality 6063 aluminum alloy casting bar is based on the selection of reasonable components based on the profiles produced, followed by the strict control of melting temperature and casting temperature, fine processing of grains, refining of alloy liquid, filtration and other technological measures, careful operation to avoid the rupture and involvement of oxide film. After that, the aluminum bar is homogenized to produce high quality aluminum bar, which provides a reliable material basis for the production of high quality profiles.