Issues to pay attention to before the casting of aluminum liquid.

Release time:

2024-12-28

Sodium is an effective metamorphic agent for eutectic silicon.

　　Sodium Salt Modifier:

　　Sodium is an effective modifier for eutectic silicon, which can be added in the form of sodium salt or pure metal (but it may be unevenly distributed when added in pure metal form, so it is rarely used in production). The sodium mixed salt composition includes NaF, NaCl, Na3AlF, etc. During the modification process, only NaF is effective, and its reaction is as follows:

　　6NaF+Al→Na3AlF6+3Na

　　The purpose of adding mixed salts is, on one hand, to lower the melting point of the mixture (the melting point of Na is 992°C), thereby increasing the modification speed and effectiveness; on the other hand, to provide solvent protection for sodium in the melt, preventing sodium loss. The mass fraction of sodium in the melt is generally controlled at 0.01%~0.01400. Considering that not all NaF participates in the reaction under actual production conditions, the mass fraction of sodium can be appropriately increased in calculations, but it should generally not exceed 0.02%.

　　When using sodium salt modifiers, the following disadvantages exist: it is difficult to control the sodium content, a small amount may lead to insufficient modification, while a large amount may cause over-modification (worsening alloy performance, increasing slag inclusion tendency, and severely deteriorating ingot structure); sodium modification has a short effective time, requiring protective measures (such as alloying protection, solvent protection, etc.); the residual sodium in the furnace after modification greatly affects the subsequent production of alloys, causing high melt viscosity, increasing the tendency for cracks and tearing in the alloy, especially affecting the sodium brittleness of high magnesium alloys; NaF is toxic and affects the health of operators.

　　The key to the modification treatment process is to control the modification temperature, time, modifier dosage, and modification operation method.

　　1. Modification Temperature

　　For sodium salt modifiers, after the modifier comes into contact with the aluminum melt, the following reaction occurs:

　　6NaF+AI→Na3AlF6+3Na

　　Na enters the aluminum melt to play a modifying role. On one hand, the higher the modification temperature, the more favorable it is for the reaction to proceed, the higher the recovery rate of Na, and the faster the modification speed; on the other hand, excessively high modification temperatures waste fuel and labor, increase oxidation and gas absorption of the aluminum melt, cause iron penetration in the alloy melt, reduce the service life of the crucible, and at high temperatures, sodium is prone to volatilization and oxidation. Therefore, the modification temperature should be slightly higher than the pouring temperature.

　　2. Modification Time

　　The modification time depends on the modification temperature; the higher the modification temperature, the shorter the modification time. When using the salt pressing and cutting method, the modification time generally consists of two parts: covering time of 10-12 minutes and pressing salt time of 3-5 minutes.

　　3. Modification Operation Method

　　For sodium salt modifiers, after refining, remove the oxide skin and slag from the surface of the aluminum alloy melt, evenly sprinkle a layer of powdered modifier, and maintain this temperature for 10-12 minutes. The layer of modifier that comes into direct contact with the aluminum melt sinters into a hard shell or becomes liquid under high temperature. After maintaining for 10-12 minutes, gently press the modifier into the aluminum alloy melt to a depth of about 100-150mm using a pressing spoon, and after 3-5 minutes, samples can be taken to test the modification effect. If using the cutting salt method, first cut the sintered hard shell modifier into small pieces on the surface of the alloy melt, then press the pieces into the melt until the modification effect appears. If using the stirring method, powdered modifier can be added to the aluminum melt and stirred, adding the modifier while stirring until the modification effect appears.

Key words:

Alumnium Downstream Processing

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