Magnesium alloy electromagnetic low-temperature semicontinuous casting method

Abstract

The magnesium alloy electromagnetic low-temp. semicontinuous casting method includes the steps of melting magnesium, adding compound fire-resisting elements, adding alloy elements, heat-insulating, standing still and semicontinuous casting under the electromagnetic field. It utilizes the addition of compound fire-resisting elements to implement smelting of magnesium alloy free from coverage or protection so as to shorten technological process and raise melt quality, and utilizes the application of electromagnetic field and optimization of crystallizer structure to implement the low-temp. and high-speed semicontinuous casting of magnesium alloy.

Description

Technical field [0001] The invention belongs to the technical field of magnesium alloy casting. Background technique [0002] The melting and casting process is an important process before the material is formed, and has an important genetic influence on the subsequent process of the material. Semi-continuous casting is an efficient billet-making process for magnesium alloys. Due to the flammability of magnesium alloys, a complex melting process is required; due to the magnesium hcp crystal structure and relatively low thermal conductivity, it is easy to cause coarse dendrites, composition segregation and thermal cracking. How to solve these problems is the key to obtaining high-quality cast ingots and subsequent forming of magnesium alloys. [0003] At present, the smelting method and casting process of magnesium alloy semi-continuous casting process have the following problems: [0004] Problems with the smelting method [0005] 1. SO 2 It has a stimulating effect on ...

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Problems solved by technology

[0005] 1. SO 2 It has a stimulating effect on the operator's respiratory tract; it is highly corrosive; when there is slag, SO 2 Gas instead causes combustion; liquid SO 2 It needs to be heated and vaporized and the temperature and flow rate should be strictly controlled, so there are many procedures and there is a danger of explosion;

[0006] 2. SF 6 The gas is non-toxic and tasteless, and is currently a commonly used protective gas for domestic and foreign enterprises. However, the gas has a greenhouse effect and will be decomposed into toxic gases during protection. Today, with the increasing calls for environmental protection, it is an urgent method to be replaced;

[0007] 3. Flux protection is easy to cause casting slag inclusion, which requires refined operation, which leads to several hours of standing operation, which greatly reduces production efficiency and product quality. Even so, it is difficult to avoid waste products caused by slag inclusion ; The surface of the billet obtained by the above method is seriously oxidized, showing rough, blackened surface, and requires a large amount of milling

[0009] 1. High casting temperature (730-750°C): the tendency of magnesium alloy to oxidize and burn increases; the solidification time is long, because magnesium alloy has low thermal conductivity (at 300°C, the thermal conductivity of pure aluminum is 234W·m -1 ·℃ -1 , while pure magnesium is 150W·m -1 ·℃ -1 , and only 64% of Al), the temperature gradient inside and outside the solidification of the ingot is large, and the liquid cavity is deep, resulting in serious element segregation; the difference between the internal and external structures is significant; this is also the main reason for the significant trend of hot cracking in traditional semi-continuous casting of magnesium alloys;

[0010] 2. The casting speed is not high: Generally, the maximum speed of semi-continuous casting does not exceed 10cm / min, otherwise it is easy to produce central cracks or even split; at the same time, it is difficult to obtain an ingot with high surface flatness even if the surface is not oxidized and blackened ;Production efficiency is very low;

[0011] 3. High crystallizer height: Due to the low thermal conductivity of magnesium alloys, in order to ensure no leakage, a high crystallizer height must be ensured. As a result, the liquid cavity is deep, the temperature gradient inside and outside the billet is large, and the uniformity of the internal and external structures is poor.

From the published literature and patents, there is almost no research on semi-continuous casting of magnesium alloys, let alone the relevant research and patents on the application of electromagnetic fields in semi-continuous casting of magnesium alloys

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