How to prevent 6063 aluminum alloy round casting ingots from shining grains

6063 aluminum alloy is mainly used for extruded building profiles, and its ingot metallurgical defects include cracks, porosity, slag inclusions, looseness, bright grains, feather-like crystals, coarse grains, etc. These metallurgical defects affect the yield of round ingot production and the yield of extrusion to varying degrees, and bring great economic losses to the company, so the occurrence of the above metallurgical defects must be prevented.
　　

The bright grains are found when the low-magnification structure of the 6063 aluminum alloy ingot is examined, and some irregular light bright spots appear on the cross-section of the specimen, mainly concentrated in the root of the ingot, the grain structure is coarse, the solid solution in the grain is less, the color is light white, and the normal crystalline structure is quite different, which is produced in the casting stage.

1 Causes of bright grains
　　1.1 Chemical composition
　　6063 is a low-alloyed A1-Mg-Si high-plastic alloy, and the 6061 alloy scrap of "(Cu): 0.24%-0.32% is added due to misoperation in the process of furnace feeding, which creates conditions for the 6063 aluminum alloy ingots to produce bright grain defects, see Table 1.
　　1.2 Low casting temperature
　　In order to improve the formability and appearance quality of the ingot, the casting temperature is often low, so that the temperature of the cavity is low during casting, and the supercooling zone in the cavity expands to the bottom area of the adapter plate, and dendrites will crystallize at the bottom of the adapter plate in advance, and they grow in the cavity for a long time and produce bright grains. Because the growth rate of the bright grain is very slow, and because the surrounding metal flow is constantly updated, the liquid phase composition there does not change significantly during the crystallization process, and the concentration difference between the bright grain and the liquid phase is always maintained at the beginning of crystallization, so that the bright grain becomes a solute-poor aluminum solid solution (1).

      1.3 The temperature of the casting disc is low
　　Because the production of 6063 aluminum alloy round ingots is characterized by a long production interval between furnace and casting, the casting disc is always in a cold state, resulting in the start of casting, the temperature of the melt in the cavity is low, and the bright grains that crystallize first will be attached to the adapter plate and gradually grow.
　　1.4 Crystallizer
　　The crystallizer used in the casting of 6063 aluminum alloy is a water-eye dwarf crystallizer, the circulating water quality is dirty, the water temperature is high, the concentration of Ca2 and Ms2' ions is high, and some of the water eyes are blocked during casting, resulting in the melt temperature around the ingot is different, so that the metal flow fluctuates in the crystallizer and the liquid flow distribution is uneven, and the melt crystallization speed is different at the local low casting temperature, resulting in bright grains.

2 Preventive measures
　　Through the above analysis, we have taken the following measures:
　　(1) Wash the furnace thoroughly when changing production varieties.
　　(2) Separate storage of different varieties of alloy waste, and only waste of the same variety or similar composition is allowed to be added during preparation.
　　(4) Strengthen process operation management, and bake the flow tank, distribution plate, flow pipe and adapter plate to a red hot state with a petroleum liquefied steam blowtorch before casting.
　　(5) Transform the circulating water filtration system and cooling system, make full use of the softening water station, so that the water quality, water temperature and Cab and M wide ion concentration of the circulating water meet the requirements of casting operations, and eliminate the metallurgical defects caused by the circulating water to the ingot caused by the circulating water. The Cu content in the charge is high, the temperature is low when the melt flows into the cavity, the distribution pan is not well preheated, and the circulating water is not cooled well on the ingot.
　　(6) By adjusting the Cu content in the furnace charge, appropriately increasing the casting temperature and casting speed, preheating and baking the casting tool before casting, and strengthening the control of circulating water quality, the bright grain defects of 6063 aluminum alloy ingots can be completely eliminated.