JPS60165332A - Preparation of cast aluminum alloy article - Google Patents

Abstract

PURPOSE:To prevent the lowering in the toughness of a cast article due to Fe, in preparing the cast article by casting an Al-Si alloy containing Fe as an impure substance, by applying over-heating treatment to the above mentioned Al- Si alloy. CONSTITUTION:In casting an Al-Si alloy containing 4-24wt% of Si and 0.25- 1.4wt% of Fe being an impure substance, this Al-Si alloy is melted by heating the same to 780-950 deg.C higher than a usual temp. Because Fe in the Al-Si alloy is precipitated as an Al-Si-Fe alloy in an amorphous or kanji form without forming a needle like crystal by casting said Al-Si alloy, the cast article of the Al-Si alloy having toughness markedly excellent as compared with the case of being precipitated as a needle-like crystal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing aluminum alloy castings, particularly aluminum-silicon alloy castings.

Aluminum-silicon alloy castings with high toughness have been manufactured using base metals that are low in impurities, especially iron.

Many of the impurities mixed into the metal cannot be removed without refining it. It is known that iron is the element that is most likely to be mixed in, and is the most problematic impurity because it crystallizes as a needle-shaped aluminum-iron-silicon compound, which not only reduces the toughness of the casting but also tends to induce casting defects. It is being

When manufacturing castings using secondary ingots, scraps, returned materials, etc., as a way to alleviate the harm caused by the increased amount of iron mixed in, it is necessary to add an appropriate amount of manganese to make the iron not needle-like but irregularly shaped or kanji. Aβ-(Fe.

A method is known in which Mn)-8i is crystallized as a compound to recover toughness. However, even this method does not eliminate the harmful effects of iron, and there is a problem in that when the amount of manganese exceeds a certain level, it impairs castability.

Therefore, the present invention has been developed to achieve the following: without adding other elements such as manganese, and without sacrificing castability or strength of the casting.
An object of the present invention is to provide a method for producing aluminum alloy castings with excellent toughness by reducing the damage caused by iron in the base metal. More specifically, even if a base metal containing iron is used, which would cause needle crystals to occur in the casting and reduce toughness in the conventional method,
The object of the present invention is to provide a method by which a casting having excellent toughness can be obtained.

Aluminum alloy castings are generally manufactured by melting base metal at a temperature of around 750°C, subjecting the molten metal to deoxidation, degassing, etc. treatments, and casting into a mold.

In the melting process, the present invention lowers the temperature of the molten metal to
The above object is achieved by heat treatment at a temperature of 780° C. to 950° C. (hereinafter referred to as superheat treatment).

The present invention contains silicon at 4% to 4% (indicates weight%, the same applies hereinafter).
It can be applied to aluminum-silicon alloy castings having a wide composition range including about 24%.

In addition, the effect of the present invention is that the content of iron, which is an impurity, is 0.25%.
This effect is noticeable in alloys with an iron content of about 1.4% or more.

The present invention was achieved as a result of many studies and experiments, and the inventors have discovered that by the molten metal superheating treatment of the present invention, the iron content is relatively small in the range of 0.25% to 1.4%. In the case of , the iron compound crystallizes in a kanji-like or amorphous shape with a small notch effect, and in the case of a relatively large amount, it crystallizes in a needle-like shape, but it is extremely fine, and this improves the toughness. They discovered this and achieved the present invention.

Experimental Example 1゜Al-6XSi-0,3%Mg-0,4X shown in the table below
Fe alloy casting (first alloy), and kl-6%51-v
, 5x Cu-O, a%Fe alloy castings (second alloy), the molten metal temperature during melting was 750°C, and the molten metal temperature was superheated to increase to 850°C. The impact bending strength was measured in the as-cast state.

The method for preparing the test piece is as follows. That is, in the first alloy, pure Al, Al-12%Si, Al-10,'7
A master alloy of %Mg1An-15%Fe was used, and in the second alloy, A/-34XCu was used in place of the above A/-10,'7%Mg as the master alloy, and the above was adjusted so that the total amount was 1.5119. After blending into the alloy composition and melting in an electric resistance heating furnace at 750°C using alumina-coated graphite crucibles, one was kept at that temperature and the other was further heated to 850°C.
1, followed by NaCl and AIFm for deoxidation.
The molten metal was treated using a flux containing a mixture of 3:1.

After processing the molten metal, let it calm down for 10 minutes, remove it, and immediately put it at 75%.
It was transferred to a vacuum furnace maintained at 0°C, and degassed for 20 minutes under reduced pressure of 0.2 Torr.

Next, the bath water was taken out into the atmosphere and placed in a silica sand shell mold for 700'
A bar-shaped casting having a length of 10 mm, a width of IQms+, and a height of 130 pieces was obtained. This casting was cut into 55 lengths,
Furthermore, a cut hole with a diameter of 2 fins was attached as a notch in the center to form a cast skin test piece. The solidification time of these specimens was approximately 40 seconds for the first alloy and approximately 55 seconds for the second alloy.

The measurement results are shown in the table, and the impact value of both alloys was approximately 4 to 4 when the molten metal was superheated to 850°CK.
It has improved by 50%, and the breaking load showing the strength at this time is 750
There was almost no change from the case at °C.

Figure 1 is an optical micrograph (X400) showing the solidified structure of the first alloy among the test pieces, and Figure 1 (8) shows the molten metal at 75mm.
0°C, and Fig. 1 0 shows the molten metal heated to 850°C.

If no overheating is applied, the impurity Fe will be AJ7-F.
While it crystallizes as a needle-like compound of e-8i, when superheating is applied, crystallization as needle-like FeO crystals is extremely rare, and most of the crystals are kanji-like crystals of Al-Fe-8i. It can be seen that crystallization occurs. In this way, it is clear that changing the solidification structure of the casting so that the Fe impurity becomes not acicular crystals but Kanji-shaped crystals with less notch effect leads to improved toughness. It was confirmed by X-ray diffraction that the Kanji-shaped crystals were a different compound from the needle-shaped crystals.

Also, regarding the second alloy, needle-like crystals were crystallized at 750°C, but when heated to 850"C, there were very few needle-like crystals, and most of them were kanji. It was confirmed that the crystals were crystallized in irregular shapes.

Experimental Example 2 FIG. 3 shows the experimental results of the relationship between the tensile properties and the maximum heating temperature of the molten metal for the second alloy.

The tensile test piece was in the shape of a J-Ko S No. 2 proportional test piece with the cast surface made by casting into a silica sand shell mold. The parallel part of the test piece has a width of 15 mm and a thickness of 8 mm. The method of melting and casting the test piece was the same as in Experimental Example 1.

Tensile test specimens were made of as-cast materials, which were solution-treated at 500°C for 5 hours, quenched in ice water, and then immediately
Two types of Ts materials aged at 60°C for 5 hours were tested. The results are shown in Figure 3. In the figure, line A (marked Q) is the as-cast material, and line B (marked *) is the T-treated material.

As shown in Figure 3, the maximum heating temperature of molten metal is 750.
Tensile strength hardly changes even when changing from °C to 850 °C, but elongation gradually increases above 775 °C. T6 material is about 50% larger.

Figure 3 also shows an alloy with a low Fe content of 0.15%.
This figure shows the elongation of a Ts material (marked C in the figure) that was made using the conventional method of melting at 0°C without superheating, and was subjected to the same heat treatment as above. It was confirmed that the elongation of this casting was inferior to that of a casting subjected to the superheat treatment according to the present invention, particularly to a high temperature superheat treatment of 825°C or higher.

When observing the solidification structure of each test piece with different molten metal temperatures,
The crystallization of the Fe compound was as follows, and it was found that it corresponded well to the elongation.

That is, in the Ad-6XSi-3,5XCu alloy, whether the Fe content is 0.25% or 0.4%, if it is melted at 750°C and no overheating is applied, Mle will crystallize as a needle-shaped compound. was. As the maximum heating temperature exceeds '750'O for alloy castings containing 0.4% Fe,
Fe often crystallized as kanji-shaped or amorphous compounds rather than needle-shaped, and at 850°C, there were very few needle-shaped crystals and crystallized as kanji-shaped or amorphous compounds.

Experimental Example 3゜Figure 4 shows the case where the maximum heating temperature of the molten metal is 750°C, which is the same as the melting temperature (marked by line CSO), and the case where it is higher than that, 850°C (marked by line, ・), and 950°C. 0 (9AE,
In the case of A7 with T-processing? -6x
This figure shows the tensile properties of a si-mx Cu-Fe alloy when the amount of Fe is changed from 0.25% to 1.6%. The method for producing the tensile test piece and the heat treatment conditions were the same as in Experimental Example 2.

Compared to the conventional method with a melting temperature of 750'C, when the molten metal is superheated to a high temperature of 850'C or 950°C, the Fe content ranges widely from 0.25% to 1.6%. Elongation has been improved across the board.

However, when the amount of Fe exceeds 1.4X and further reaches 1.6%, the effect of improving elongation becomes smaller. On the other hand, the tensile strength does not decrease due to overheating.

Figure 2 shows the optical microscopic structure (X
200) t - Figure 2 (8) shows the molten metal temperature at 75
The temperature was set to 0°C, and FIG. 2 (c) shows the temperature set to 950°C.

Comparing the molten metal temperature of 750°C with that of 950°C, the F'e compound crystallized at 950°C also has a needle-like shape, but its size is clearly smaller. . If we compare the size of these needle crystals with the size of Si crystallized by eutectic solidification (which has become rounded due to solution treatment), it is 75.
In many cases, when it is simply melted at 0°C, it is several times larger than Sl, but when it is heated to 950°C, it is almost as small as 5ol-.

As shown in Experimental Example 1, by heating the molten metal to a temperature higher than the conventional melting temperature, when the Fe content is relatively small, around 0.4 do. If Fe is included up to around 0.6%, Fe
The compound begins to crystallize in both needle-like shapes, kanji-like shapes, and amorphous shapes. In this way, the impurity Fe is crystallized not in the form of needles but in the form of Kanji-like or amorphous crystals with a small notch effect, thereby improving the elongation of the alloy casting.

Furthermore, as is known from Experimental Example 3, elongation is improved by overheating the molten metal even when Fe is contained in a larger amount, although crystals crystallize into needles, but these needles are fine. , it is clear that this contributes to improving growth.

As explained above, in conventional Al-5i alloy castings, if Fe is contained as an impurity in the base metal, the toughness is greatly reduced. However, in the process of melting the base metal, the present invention increases the temperature of the molten metal to 80°C to 90°C higher than that of the conventional method.
By heating to 50°C! They succeeded in significantly improving the toughness of the material without sacrificing its strength.

At the same time, the inventors discovered that in castings obtained by conventional melting, Fe compounds contained as impurities crystallize in the form of needles, which causes a decrease in toughness. When the amount of 1゛θ is relatively small, the JF'e compound crystallizes in a kanji-like or kanji-like amorphous shape, and when it is relatively large, it crystallizes in needle-like but extremely fine crystals, which contributes to improved toughness. They discovered this.

The present invention not only improves the reliability of Al-8i alloy castings, but also enables the effective use of inexpensive base metals containing a large amount of ye, and greatly contributes to the economic efficiency of manufacturing Ae-8i alloy castings. It is something to do.

[Brief explanation of the drawing]

Figure 1 shows the microscopic structure (x400) of an A/-8i alloy casting containing 0.4X iron! i@1 Figure (6) shows the structure of the casting obtained by the conventional method, and Figure 1 (c) shows the structure of the casting obtained by the present invention. Figure 2 shows the microscopic structure (X200) of an A/-Si alloy casting containing 1.4% iron, and Figure 2 (8) shows the structure of the casting obtained by the conventional method. (c) shows the structure of the casting obtained according to the present invention. Figure 3 is a diagram showing the relationship between the maximum temperature of molten metal, tensile strength, and elongation of alloy castings obtained by the present invention and the conventional method, and Figure 4 shows the iron content in the alloy castings obtained by the present invention and the conventional method. It is a figure showing the relationship between the amount, tensile strength, and elongation. To the agent and patent attorney Mokuma Ito: 2)

Claims (2)

[Claims] (1) When producing castings from aluminum-silicon alloy castings containing 4% to 24% silicon by weight and containing iron and other unavoidable impurities, the molten metal'k'I 8oC~950 during melting. A method for producing an aluminum alloy casting, the method comprising casting after heat treatment at a temperature of °C. (2) The method for producing an aluminum alloy casting according to claim 1, wherein the iron content in the casting alloy is 0.25% to 1.4% by weight.