Aluminum alloy flat ingot side crack and prevention method

【China Aluminum Industry Network】 1.Characteristics of side cracks in flat ingots (1) Cold cracks;

(2) usually occurs in hard alloys (such as 7A04, 2A12, etc.);

(3) Direct water-cooled semi-continuous casting occurs after the length of the ingot reaches 1.5 to 2 m;

(4) Cracks are often mixed with slag, stratification, cracking, or microcracking;

(5) The angle between the crack plane and the horizontal plane depends on the casting speed and the aspect ratio of the ingot. The smaller the casting speed, the wider the ingot, the smaller the included angle.

In continuous casting, the small face of the flat ingot is cooled on three sides, and the central part of the large face is cooled on both sides. The temperature gradient and cooling speed of the small face in the axial direction of the ingot greatly exceed the temperature gradient along the axial direction of the ingot in the center of the large surface. The cooling rate thus causes the facets of the ingot to exert a tensile stress acting in the height direction. At the beginning, it may be due to cold stress or non-metallic inclusions that act as stress concentrators, resulting in a very shallow initial crack in the facet area. With the gradual cooling of the ingot, the sensitivity of the metal to the incision is greatly increased, the residual stress in the ingot is at the original crack, and local concentration occurs. When the strength of the metal exceeds the allowable degree, the sudden development of the side crack is caused. .

(2) To prevent side cracks (1) To reduce the tensile stress in the small face of the ingot 1. Use a mold with a small face to open the notch so that the metal in the facet area is cooled ahead of time when it is in the same level as the facet area. The metal in the central area of ​​the wide face of the ingot only forms a hard shell near the mold wall and does not cause large resistance to the contraction of the facet region, thereby reducing the tensile stress in the facet region. At the same time, as a result of the early cooling of the facet area, the quality of the metal that resists tensile stress increases. (2) In the case of an incision in the face of the crystallizer, the water pressure of the facet is appropriately increased to enhance the effect of the incision. (3) Properly increase the casting speed and move the larger tensile stress point in the ingot to the center of the wide surface. At this time, the metal temperature in the central area of ​​the wide surface of the ingot is higher, the plasticity is better, and the generated stress is easily influenced by the metal. Deformation eliminated. At the same time, the amount of metal that resists tensile stress increases, so the tendency of cracking at the side of the ingot decreases. 4 Select the appropriate ingot section. The tensile stress of the facet region increases with the increase of the width-thickness ratio when the thickness of the ingot is constant, and increases with the increase of the thickness when the aspect ratio is constant. Therefore, for alloys with a large tendency to cold cracks, a smaller width to thickness ratio of the ingot should be selected.

(2) Special attention should be paid to the prevention of facet formation, facet cracking, and facet slag inclusion.

(3) Control the chemical composition strictly according to internal standards to improve the ability of the alloy to resist hot and cold cracks.

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