[ALUMINIUM NETWORK] The inhomogeneity of the ingot structure affects the performance of the ingot, and ingots for forging, rolling, and extruding are particularly undesirable in reducing the columnar structure of the alloy process. In general, alloys with fine grain structure, fine grain internal structure, and uniform distribution of surplus phases have better as-cast properties and higher pressure processing ductility. The use of increased cooling rate, low temperature casting, ultrasonic oscillation casting, electromagnetic casting and other measures are conducive to obtaining the above-mentioned ideal organization, but these methods have limitations, only the use of metamorphic treatment of the alloy is the fundamental means of adjusting the ingot structure. First, the deterioration process overview The so-called metamorphic treatment is the process of changing the microstructure of the as-cast alloy under the action of a small amount of special additives (modifiers) to increase the degree of dispersion of the metal or alloy. At present, the technical terms of this treatment method are not uniform, some are called refinement processing, and others are called gestation processing. The classification of deterioration processing is also different. Some people classify the deterioration process into three categories according to the characteristics of the final structure changes of metals and alloys: the treatment of changing primary dendrites and other primary crystal sizes is called the former metamorphic treatment, and the treatment that changes the internal structure of primary dendrites is called second Metamorphic treatment, to change the treatment of eutectic tissue called the third type of metamorphic treatment. Some people also classified the deterioration process into three types of four groups according to the properties of the modifying agents (see Table 2—5—3). It is also classified according to the physical and metallurgical effects on the crystallized alloy. Obviously, the boundaries between these concepts are indistinguishable. In this manual, metamorphism is understood as the increase in the dispersion of metal and alloy ingots. Table 2-5-3 Categories of Modified Agents and Their Properties category Modification agent Groups Nature of action Possible deterioration mechanism I Nucleation modifier l No chemical effect, but structurally coherent Nucleation or nucleation base effect, such as TiC in aluminum and other high melting point inclusions 2 Chemical and structurally coherent The peritectic reaction produces nucleation sites and changes the concentration of the components in the surrounding liquid, such as TiAl formed by the interaction of titanium and aluminum. II Adsorption modifier 3 Active adsorption or physical adsorption Adsorption on the crystal surface, hinder grain growth, promote supercooling, increase nuclear, such as sodium in aluminum-silicon alloy III Change the structure Smoothing agent 4 From mechanical or materialization, change the liquid phase structure and distribution Uniform liquid composition and temperature change the activity of nucleation sites At present, there are various theories that describe the process of metamorphism. Among them, there are well known nucleation theory, carbide theory, peritectic reaction theory, atomic structure theory, etc. However, no one theory can fully explain this process. . This is because, on the front, the process of modification is complex, not only related to the smelting conditions, but also related to the casting conditions. Second, uncontrollable impurities have an effect, and the interaction of certain elements in the aluminum alloy also has an effect. They are enhanced. Or weaken the effect of grain refinement. According to the theory of nucleation theory, grain refinement is due to the presence of nuclei, and the melt begins to crystallize on the nuclei. These particles may be transition metal carbides, borides, and aluminides, and their lattice constants are similar to those of aluminum solid solutions (4.04 Å) (see Table 2—5—4). According to this theory, additives added as modificators should meet the following requirements: 1 Chemical composition at high temperatures does not change, there is sufficient stability in the aluminum melt; 2 the melting point of the additive should be higher than that of aluminum; 3 additives and aluminum The crystal lattice should adapt to the structure and size; 4 forms a strong and strong adsorption bond with the melt atoms being processed. At present, in addition to aluminum-titanium additives, aluminum-titanium-boron additives are generally used in aluminum-titanium-boron additives (wires or cakes). In addition, newly developed aluminum-titanium-boron-rare earth modifers and aluminum-titanium-carbon modifiers have also been used. Table 2-4-5 lattice constants of carbides, borides and aluminides Compound name chemical symbol Lattice constant/Α Character type Melting point/°C a c c/a Aluminum 1 Titanium carbide Zirconium carbide Vanadium carbide Titanium boride Aluminum boride Zirconium boride Vanadium boride Aluminum Titanium Aluminum zirconium Aluminum phosphide Sodium 1 Al TiC ZrC VC (V2C3) TiB2 AlB2 ZrB2 VB2 TiAl3 ZrAl3 AlP Na 4.04 4.32 4.69 4.182 3.026 3.01 3.162 3.001 5.42 4.013 5.42 4.22 - - - - 3.213 3.26 3.523 3. O6l 8.57 17.32 - - - - - - 1.06 1.08 1.114 1.02 1.58 4.316 - - Face centered cube Face centered cube cube cube Six parties Six parties Six parties Six parties Quartet Quartet cube Body-centered cubic 660 3140 3175 3160 2980 2700? 3040 2400 1340 1580 1,000 97.5 Note: 1 Aluminum is refined and sodium is an aluminum-silicon alloy modifier. For ease of comparison, the data are listed together. Second, aluminum-titanium-boron modification agent The aluminum-titanium-boron modification mechanism is a problem that has not yet been clarified. Some researchers believe that the refinement of aluminum-titanium-boron is caused by TiAl3, and TiB2 and AlB2 do not participate in the modification process. The addition of boron only promotes the formation of TiAl3, because boron makes the liquidus linear curvature of the binary alloy of titanium and titanium drastically increase, so that the solubility of titanium in the liquid aluminum is reduced, which expands the range of primary crystallizing of TiAl3, and thus makes crystals. Grain refinement is better. The development of aluminum-titanium-boron modification agents has gone from salt mixtures to bulk additives to the length of linear intermediate alloys, and the melting technology of aluminum-titanium-boron intermediate alloys has also undergone a process of gradual development and improvement. Until now, the process of producing salt-based master alloys and conventional fusion casting and extrusion has been basically eliminated. Today, the aluminum industry mainly uses two types of aluminum-titanium-boron modifiers: linear and block. The trend is toward the use of linear modifiers. This is because: 1 The linear modification agent used for on-line treatment, can obtain continuous inoculation effect, refinement efficiency is high, the amount of addition is small, compared with adding in the furnace in the block-like manner, about 50% of the amount can be reduced; 2All of the added wire material enters the casting process, the metal yield is large, and the added amount is more accurate; 3 The deposition of titanium and boron compounds in the furnace is avoided, so that the content of the refining agent in the ingot is constant throughout the casting process. , In order to ensure that the entire ingot grain refinement uniform, and has a good distribution of fine-grained particles, this high-speed and high-efficiency even if the 7Z-based alloy containing zirconium can also get a good grain refinement effect; 4 because no furnace Internal treatment, there is no boride accumulation and other agglomeration phenomenon in the furnace, thus saving cleaning time; 5 in the continuous casting system, can eliminate the problem of fine failure due to a long time, and can achieve online automatic adjustment material. There are many factors affecting the refinement effect, durability, and attenuation of aluminum-titanium-boron alloys. The major ones are: 1) Titanium-Boron ratio. All commercially available aluminum-titanium-boron modifiers have a titanium to boron ratio greater than the stoichiometric ratio of TiB2 of 22, greater 50:1, and smaller 3:1. This is because TiB2 alone is not an effective grain refiner, and the titanium to boron ratio has a large influence on the number of mesophases (see Figure 2—5-15). The domestic and foreign data show that TiAl3 content is high when the production conditions are basically the same and the boron content is the same. On the contrary, if the titanium content is the same, the Ti content is high, the quantity of TiB2 is large, and the quantity of TiAl3 is small. . What kind of ratio is better should be based on specific conditions. Under normal conditions, 5TilB works well. However, it should be pointed out that a single chemical composition does not guarantee the effective and economical refinement of the product. Figure 2-5-15 Effect of Titanium-Boron Ratio on the Number of Mesophases 2) The shape, size, quantity, and evenness of the mesophase. In the aluminum-titanium-boron intermediate alloy, there are three different forms of TiAl3 particles: "mass", "petal" and "plate". Different forms of TiAl3 expose different crystal planes in the liquid phase but still maintain Strict TiAl3 stoichiometry. Bulk particles have several crystal faces facing the liquid phase, increasing the statistical opportunity for nucleation, but the bulk aluminates dissolve more quickly and therefore their effectiveness decreases over time. The bulk TiAl3 crystals predominate in the fast-reacting Al-Ti-B modification. In the high quality aluminum-titanium-boron master alloy, the average size of TiB2 particles is about 0.8 μm, with about 90% of the size being less than 1 μm. The typical size of bulk TiAl3 particles is 80 μm larger for 5 TilB. , Generally between 10 ~ 65 μm, for 3TilB, the larger is 60μm, their distribution on the aluminum matrix is ​​uniform. The size of the TiAl3 particles has a significant effect on the refining effect, because when the additive is added to the metal stream, the TiB2 particles are insoluble, while the TiAl3 is soluble and it dissolves rapidly in the flowing metal in the flow cell. Plate-shaped aluminides have only one crystal plane facing the liquid phase. When there are massive particles, they will effectively limit their potential for direct nucleation. It should be noted that the morphology of TiAl3 depends on the process parameters at the time of manufacture. The main one is the reaction rate and reaction temperature during alloying smelting. The shape of the mesophase is the main factor that determines the quality of the modifier. 3) The type of alloy being processed and the casting conditions. When the type of alloy being processed and the casting conditions are different, there are different grain refinement effects. For this reason, the addition amount of the refiner should be adjusted according to the test results in order to obtain a more ideal refinement effect. Generally for ordinary grades of pure aluminum, such as 110000 alloys and alloys containing magnesium, silicon, manganese, and iron, refinement is relatively easy. When using 5TilB or 3TilB for linear modification, the amount of titanium added is only 0.0025%. 0.005% can be; and for higher grade pure aluminum and alloys containing zirconium and chromium, refinement is much more difficult and the amount added is much greater. Generally, the rolling slab has a large section, a low solidification rate, and is difficult to refine. The amount of addition should be increased accordingly. Continuous casting slabs have a small cross section, but have a high solidification rate, a large temperature gradient, and a very narrow supercooling zone. In order to obtain a good refinement effect and also to prevent edge cracking, the amount of additives should also be increased. For the extrusion of the ingot, the solidification rate is higher due to the smaller cross-section, the refinement is easier, and the addition amount can be less. At present, there are many types of commercially available aluminum-titanium-boron modification agents. According to the production method, they can be classified into alloying products and powder press molding products. According to the chemical composition, they can be classified into standard, low-boron and low-titanium. According to the shape of supply, it can be divided into three types: linear, spindle and cake; according to the response time, it can be divided into two types: rapid response type and slow response type.