6063 aluminum alloy is mainly used for extrusion of building profiles. Its metallurgical defects include cracks, pores, inclusions, loose, bright grains, feather-like crystals, and coarse grains. These metallurgical defects have affected the production rate of round ingot production and the finished product ratio during extrusion to a great extent, and have caused significant economic losses to the company. Therefore, the aforementioned metallurgical defects must be prevented.
The bright grains were discovered when examining 6063 aluminum alloy ingots with low magnification. They showed some irregular light-colored bright spots on the cross-section of the sample, mainly concentrated in the root of the ingot, and the coarse grain structure was observed. There are few solid solutions and the color is pale white, which is quite different from the normal crystalline structure. It is produced during the casting stage.
1 Causes of Bright Crystals
1. 1 Chemical composition
6063 is a low-alloyed A1-Mg-Si series high-plasticity alloy. Due to misoperation, "(Cu):0.24%-0.32% of 6061 alloy scrap was added to the 6063 aluminum alloy casting. Ingots create conditions for bright grain defects, see Table 1.
1. 2 casting temperature is low
In order to improve the formability and appearance quality of the ingot, the casting temperature is often low, so that the temperature of the liquid cavity during casting is low, and the supercooling zone in the liquid cavity expands to the bottom area of ​​the adapter plate, and it will advance at the bottom of the adapter plate. The dendrites crystallize and they grow in the liquid cavity for a long time to produce bright grains. Because the growth rate of the bright grains is very slow, and because the metal flow around it is continuously updated, the liquid phase components there are not changed greatly during the crystallization process, and the crystals always start to crystallize between the bright grains and the liquid phase. The difference in concentration at the time causes the bright grains to become an lean-solute aluminum solid solution (1).
1.3 Casting tray temperature is low
Because the production characteristics of 6063 aluminum alloy round ingot casting is that the production time between the heat and the casting time is long, the casting plate is always in a cold state. When the casting is started, the temperature of the liquid is lower, and the bright crystal grains that are crystallized first are Attached to the adapter plate, it will gradually grow. When it grows to a certain degree, it will drop out of the ingot and form a bright grain structure defect at the base of the ingot.
1.4 Crystallizer
The crystallizer used in the casting of 6063 aluminum alloy is a water-eye dwarf crystallizer. The water quality of the circulating water is dirty, the water temperature is high, and the concentration of Ca2+ and Ms2' ions is high. During casting, some water eyes are blocked and the melt around the ingot is melted. The temperature varies, causing fluctuations in the metal flow and uneven distribution of the liquid flow in the crystallizer. The melt crystallisation speed is different at locally low casting temperatures, resulting in bright grains.
2 Preventive measures
Through the above analysis, we have taken the following measures:
(1) Wash the furnace thoroughly when changing the product type.
(2) Different types of alloy scraps are stored separately and only wastes of the same species or composition are allowed to be added during the preparation.
(4) Strengthen the process operation management, use the liquefied petroleum gas torch lamp to bake the flow trough, distribution plate, flow tube and adapter plate to red hot state before casting.
(5) Renovate the circulating water filtration system and cooling system, make full use of the demineralized water station, make the circulating water quality, water temperature and Cab, M wide ion concentration meet the requirements of the casting operation, and eliminate the metallurgical defects brought by the circulating water to the ingot. The content of Cu in the charge is high, the temperature is low when the melt flows into the liquid cavity, the preheating of the distribution plate is not good, and the circulation water causes poor cooling of the ingot.
(6) By adjusting the Cu content in the charge, appropriately increasing the casting temperature and casting speed, preheating and baking the casting tool before casting, and strengthening the control of the circulating water quality, the bright grain defect of the 6063 aluminum alloy ingot can be completely eliminated. .
The bright grains were discovered when examining 6063 aluminum alloy ingots with low magnification. They showed some irregular light-colored bright spots on the cross-section of the sample, mainly concentrated in the root of the ingot, and the coarse grain structure was observed. There are few solid solutions and the color is pale white, which is quite different from the normal crystalline structure. It is produced during the casting stage.
1 Causes of Bright Crystals
1. 1 Chemical composition
6063 is a low-alloyed A1-Mg-Si series high-plasticity alloy. Due to misoperation, "(Cu):0.24%-0.32% of 6061 alloy scrap was added to the 6063 aluminum alloy casting. Ingots create conditions for bright grain defects, see Table 1.
1. 2 casting temperature is low
In order to improve the formability and appearance quality of the ingot, the casting temperature is often low, so that the temperature of the liquid cavity during casting is low, and the supercooling zone in the liquid cavity expands to the bottom area of ​​the adapter plate, and it will advance at the bottom of the adapter plate. The dendrites crystallize and they grow in the liquid cavity for a long time to produce bright grains. Because the growth rate of the bright grains is very slow, and because the metal flow around it is continuously updated, the liquid phase components there are not changed greatly during the crystallization process, and the crystals always start to crystallize between the bright grains and the liquid phase. The difference in concentration at the time causes the bright grains to become an lean-solute aluminum solid solution (1).
1.3 Casting tray temperature is low
Because the production characteristics of 6063 aluminum alloy round ingot casting is that the production time between the heat and the casting time is long, the casting plate is always in a cold state. When the casting is started, the temperature of the liquid is lower, and the bright crystal grains that are crystallized first are Attached to the adapter plate, it will gradually grow. When it grows to a certain degree, it will drop out of the ingot and form a bright grain structure defect at the base of the ingot.
1.4 Crystallizer
The crystallizer used in the casting of 6063 aluminum alloy is a water-eye dwarf crystallizer. The water quality of the circulating water is dirty, the water temperature is high, and the concentration of Ca2+ and Ms2' ions is high. During casting, some water eyes are blocked and the melt around the ingot is melted. The temperature varies, causing fluctuations in the metal flow and uneven distribution of the liquid flow in the crystallizer. The melt crystallisation speed is different at locally low casting temperatures, resulting in bright grains.
2 Preventive measures
Through the above analysis, we have taken the following measures:
(1) Wash the furnace thoroughly when changing the product type.
(2) Different types of alloy scraps are stored separately and only wastes of the same species or composition are allowed to be added during the preparation.
(4) Strengthen the process operation management, use the liquefied petroleum gas torch lamp to bake the flow trough, distribution plate, flow tube and adapter plate to red hot state before casting.
(5) Renovate the circulating water filtration system and cooling system, make full use of the demineralized water station, make the circulating water quality, water temperature and Cab, M wide ion concentration meet the requirements of the casting operation, and eliminate the metallurgical defects brought by the circulating water to the ingot. The content of Cu in the charge is high, the temperature is low when the melt flows into the liquid cavity, the preheating of the distribution plate is not good, and the circulation water causes poor cooling of the ingot.
(6) By adjusting the Cu content in the charge, appropriately increasing the casting temperature and casting speed, preheating and baking the casting tool before casting, and strengthening the control of the circulating water quality, the bright grain defect of the 6063 aluminum alloy ingot can be completely eliminated. .
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