JPH01279712A - Method for removing impurity from aluminum alloy - Google Patents

Abstract

PURPOSE:To reclaim a high-purity Al-Mg alloy from Al scrap by actively incorporating specific amounts of Mg at the time of refining Al scrap by a segregation method and removing impurities by separation so as to remarkably reduce an Si impurity in particular. CONSTITUTION:At the time of refining Al return scrap containing Si, Fe, and Cu as impurities by a segregation method and reducing these impurities, 2-8wt.% of Mg is actively added to Al scrap as raw material, and these are melted and then solidified by cooling at <=15mm/hr average solidification rate, by which Si, Fe, and Cu are segregated and separated and an Al-Mg alloy of extremely high purity can be easily reclaimed from the above Al scrap.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for removing impurities in an aluminum alloy,
In particular, the present invention relates to a method for removing impurities from an aluminum alloy that can contain Mg as an active ingredient.

(Conventional technology) Typical examples of aluminum products made from ultra-high purity aluminum are high purity foil for electrolytic capacitors,
Substrates for magnetic disks are known.

When manufacturing such aluminum products, it is desirable from the viewpoint of effective resource utilization if the product materials can be reused as raw materials (return scraps). However, the aluminum alloy materials melted, cast, and rolled for these products are contaminated with Fe, SL, etc. due to dust mixed in during handling in the furnace and after rolling, and cannot be recycled as raw materials if left as is. However, there is a need for a low-cost method for purifying aluminum.

By the way, several methods have been known for purifying high-purity aluminum, that is, for removing impurities, including 1) three-layer electrolysis method, 2) fractional crystallization method (segregation method), etc. ing.

The former three-layer electrolysis method holds an anode alloy M (raw material layer), an electrolytic bath layer, and an aluminum layer in an electrolytic tank, and immerses the cathode in the topmost aluminum layer for electrolytic refining. This is a method for obtaining purified aluminum by depositing impurities in an electrolytic layer and an anode alloy layer through reaction and anodic reaction. In addition, the fractional crystallization method is a high purification method that utilizes segregation during solidification.
This method involves a process of cooling the molten metal to crystallize minute primary crystals, and compressing the crystals to push out intergranular impurities (see "Metal", January 1988 issue, p. 8-13).

(Problems to be Solved by the Invention) However, the three-layer electrolysis method is not a preferable method for highly purifying return scrap that often contains several types of impurities.

In addition, the one-fraction crystallization method can also be used to improve the purity of return scrap, but even in this method, the refining conditions ( Even if the assimilation period, pressing force, etc.) are changed slightly, the amount of impurities in the obtained aluminum is higher than that of Fe (Si/Fa>1.
5) has been considered a problem. Therefore, if it is required that the content of Si as an impurity be extremely small, (1) increase the truncated portion;

■Increase the overall purity (slow down the average coagulation rate).

■ Add a large amount of aluminum purified by three-layer electrolysis method.

Such measures were taken.

However, these countermeasures result in lower yields, longer refining times, increased raw material costs, etc., all of which increase costs. This is not a desirable method, and there has been a desire to develop a method that can obtain an extremely low Si content at low cost.

The present invention has been made in response to these demands, and provides an impurity removal method that enables return scrap from aluminum materials to be highly purified at low cost.

(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention have developed the conventional fractional crystallization method,
In other words, we analyzed the problems with the segregation method and conducted intensive research to find a method that would make it possible to achieve high purity.

As a result, when reducing the impurity content in aluminum materials by segregation method, if Mg is actively included, impurities other than Mg, especially S, which has been difficult to remove in the past, have been found.
The present invention was made based on the discovery that i can be effectively removed.

The present invention will be explained in more detail below.

When aluminum is highly purified by the segregation method (fractional crystallization method), as shown in the above-mentioned publication, the elements that can theoretically be purified and removed are shown in the equilibrium diagram with AQ (see Figure 1).
In L-=Cs/C<1 Here, C3: Solid phase concentration C: Liquid phase concentration: An element that satisfies the relationship of equilibrium distribution coefficient. Therefore, F
Considerable elements such as e, Si, Cu, Mn, Mg, . . . can be reduced by the segregation method. Despite that,
In the conventional segregation method (fractional crystallization method), Si, Mg, etc., which have a large maximum solid solubility limit, are removed.

However, as a result of various experimental studies, the present inventor has found that the above problem is only a problem in the high purification method of obtaining pure aluminum raw material (base metal), and from the viewpoint of removing impurities from return scrap, it is not necessarily a problem. We have now determined that this is not a disorder.

That is, Mg, which is an element that has a large solid solubility limit in Au and is difficult to reduce, is considered to be an additive element (essential element), and other elements are considered to be impurities. In other words, conventionally, A
Q-8i, AQ-Fe, AQ-Cu, etc. 3
Instead of the impurity removal method used in the original system, [A Q -
Mgl-Fe, [AR-Mg coco-i, [AQ-Mg
An impurity removal method using a pseudo-binary system such as l-Cu, . . . is adopted.

If we apply the segregation method to this pseudo-binary system.

■Fe, Mn, etc. have almost no affinity with [AQ-Mgl, and are hardly affected by Mg.

(2) Regarding Cu and Zn, it is expected that [they have a higher affinity with Au-Mgl, and the higher the Mg content, the lower the amount of Cu and Zn.

■For Si, AQ-Mg-3 with more than Mg2νt%
Although the behavior of i is not clear, it is expected to behave similarly to Cu and the like.

In other words, it can be concluded that the inclusion of Mg is actually preferable when removing impurities, provided that the inclusion of Mg itself does not harm the intended use of the product. therefore,
AQ- products obtained using high-purity aluminum ingots
In the case of Mg-based alloys, especially in the case of bright materials and magnetic disk base materials, it is desirable to remove impurities using this segregation method.

Next, the conditions of this segregation method will be explained.

This segregation method actively adds an appropriate amount of M to the molten aluminum.
The method can be carried out in the same manner as the conventional method except that g is included.

The amount of Mg to obtain the effect of Mg inclusion in this method is not particularly limited as long as it substantially contains Mg, but 2
It is desirable to contain more than 8wt%, and although there is no theoretical upper limit, the oxidation of the molten metal will become significant.
% or less is preferable. In addition, M during return scrap
If the content of g is too small, an appropriate amount may be added.

Impurities in the aluminum material before impurity removal, that is, impurities such as Si other than Mg, are theoretically acceptable no matter how much they are contained, but in terms of work efficiency,
Fe and SL are desirably 0.05% or less. Also Ti
Since the content of Cr and Cr is not reduced by this segregation method, it is desirable to have a small amount.There is no problem as long as the amount of other elements is also below the impurity amount (0.05% it%).

Further, since the slower the average solidification rate, the more impurities are removed, it is desirable to set the average solidification rate to 15 mm/hr or less.

Next, examples of the present invention will be shown.

(Example) For molten aluminum or aluminum alloy having the chemical components shown in Table 1, the average solidification rate was approximately 6 mm/hr.
Impurities were removed by the segregation method by applying a thermal gradient such that . The results are also listed in Table 1.

As is clear from Table 1, in the case of molten aluminum alloy containing Mg, the effect of reducing the Si content is remarkable. Of course, the content of Fe, Cu, etc. is also reduced. On the other hand, pure aluminum molten metal containing substantially no Mg has a high Si content.

[Blank below c] (Effects of the Invention) As detailed above, according to the present invention, when removing impurities from an aluminum material by the segregation method, since Mg is actively included, impurities other than Mg, especially Si The content can be significantly reduced, making it possible to provide a high-purity Mg-containing aluminum alloy at low cost. Therefore, it is suitable for removing impurities from aluminum alloys containing Mg as an active ingredient.

[Brief explanation of the drawing]

FIG. 1 is an equilibrium phase diagram (horizontal axis: concentration, vertical axis: temperature) of an alloy system with an equilibrium distribution coefficient (k) smaller than 1. Patent applicant Takashi Nakamura, Patent attorney representing Kobe Steel, Ltd. Figure 1′, j1 degree →

Claims (1)

[Claims] A method for removing impurities from an aluminum alloy, characterized in that when impurities in an aluminum material are removed by a segregation method, impurities other than Mg are removed by incorporating Mg to achieve high purity.