JPH0734168A - Aluminum alloy for casting and method thereof - Google Patents

Abstract

PURPOSE:To provide a cast Al alloy small in the content of gaseous hydrogen and in which the generation of pinholes is prevented and to provide a producing method thereof. CONSTITUTION:The molten metal of an Al alloy is incorporated with total 0.005 to 0.3% wt. of one or more kinds among Ca, Sr, Ba and Li. Since these elements are easy to form hydrides when being added to the Al molten metal and are stable at the temp. of the aluminum molten metal in a practical range, they are brought into reaction with hydrogen in the molten metal to form hydrides. Thus, hydrogen in the molten metal reduces to <=0.3cc/100g. Furthermore, since at least one kind among Ca, Sr, Ba and Li are added to the aluminum alloy molten metal at the latest 30min before casting for the aluminum alloy, hydrogen in the molten metal can be reduced to <=0.3/100g. Thus, pinholes in the product can be prevened to improve its strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting aluminum alloy capable of preventing generation of pinholes due to hydrogen gas and obtaining a sound casting, and a method for producing the same.

[0002]

2. Description of the Related Art An Al melt in a state of being remelted for casting reacts with moisture existing in the surrounding atmosphere to generate hydrogen and absorbs this hydrogen. The hydrogen absorbed in the liquid Al melt is significantly released as a gas in the solid phase when the Al melt solidifies due to the significant difference in solubility between the Al liquid phase and the solid phase. And remain as pinholes in the solid.

When an Al alloy having such pinholes is used as a structural material, stress concentration occurs at the tips of these pinholes, and cracks may occur from there, which may lead to destruction of the material. Therefore, conventionally, in order to prevent the occurrence of this pinhole, measures have been taken to remove hydrogen by subjecting the molten aluminum to various treatments as described below.

That is, degassing with a flux of chloride, fluoride or the like, degassing by blowing chlorine gas, freon gas, argon or nitrogen gas, etc. There is also a method in which the molten aluminum is placed in a closed chamber and a vacuum is drawn.

[0005]

However, in the above degassing method, the method of using flux and chlorine gas deteriorate the environment of the factory, and the use of CFC gas in the global environment becomes difficult. In addition, bubbling with argon gas, nitrogen gas, etc. has problems that the degassing efficiency is poor and slag is generated, a rotary degassing device or the like is required, and the cost is high and the process is complicated. When evacuating, a temperature drop occurs in the process, which requires complicated auxiliary equipment such as a heating and heat retaining device, resulting in high cost.

The present invention has been made in order to solve the above-mentioned problems of the conventional degassing method of molten Al, and does not pollute the environment and does not require large-scale equipment, and the product has a pin shape. An object of the present invention is to provide an aluminum alloy for casting which prevents the generation of holes and a method for producing the same.

[0007]

The inventor has conceived to solve the above-mentioned problems by using an additive to an Al alloy. Therefore, earnest studies have been conducted on additional elements that form hydrides. As a result, the inventors have newly found that Ca, Sr, Ba and Li easily form hydrides and are stable under the temperature of molten Al in a practical range, and thus completed the present invention.
In addition, in actual use, the hydrogen concentration increases with time after addition, so the present invention has been completed through repeated research on the timing of addition of these additional elements.

The casting aluminum alloy of the present invention contains 0.005 to 0.3% by weight of at least one kind of Ca, Sr, Ba and Li in a total weight ratio, and a hydrogen content of 0. The gist is that the amount is 3 cc / 100 g or less.

The method of producing an aluminum alloy for casting according to the present invention is characterized by adding at least one or more of Ca, Sr, Ba and Li to the molten aluminum alloy at least 30 minutes before casting the aluminum alloy. To do.

The casting aluminum alloy to which the present invention is applied may be of any type as long as it is for casting or die casting, and may be, for example, Al--Cu type, Al--Si type,
It is applied to each alloy system such as Al-Cu-Si system and Al-Mg system.

The additive elements such as Ca, Sr, Ba and Li are
Since any element is easily oxidized, care must be taken when disturbing the molten metal such as stirring. Specifically, the molten metal melted in the melting furnace is moved to the holding furnace. At that time, slag is removed before transfer to the holding furnace or in the holding furnace. In addition, the metal is added as a single metal or as an aluminum master alloy, and if it is a metal or the like, it is wrapped in an aluminum foil and placed in the molten metal. It is also a good method to spray an inert gas on the surface of the molten metal to prevent oxidation during processing. Also, since it easily absorbs moisture, it is necessary to be careful when storing.

[0012]

When Ca, Sr, Ba and Li are added to the molten aluminum, they easily form hydrides and are stable under the practical temperature of the molten aluminum. Therefore, when 0.005 to 0.3% in total of at least one of the above elements is turbid in the molten metal, it reacts with hydrogen in the molten metal to form a hydride. Therefore, hydrogen in the molten metal is reduced to 0.3 cc / 100 g or less.

After the amount of hydrogen in the molten aluminum is reduced, hydrogen is introduced from the water in the air while the molten aluminum is held. After about 2 hours, it returns to the state before processing. By adding the additional element at least 30 minutes before the casting of the molten aluminum, it is possible to cast the molten aluminum in a state where the hydrogen in the molten aluminum is reduced to 0.3 cc / 100 g or less.

As described above, Ca and the like that have entered the molten metal form hydrides with hydrogen in the molten metal and reduce the hydrogen concentration in the molten metal. By casting the lowered molten metal, it is possible to prevent pinholes in the product and improve the strength.

The total content of at least one of Ca, Sr, Ba and Li to be added is set to 0.005 to 0.3% because the molten metal usually contains 0.5 cc / 100 g of hydrogen. Therefore, 0.005% at least is necessary in consideration of loss, and even if added over 0.3%, the effect is saturated, so the upper limit was made 0.3%.

In the present invention, the hydrogen content is 0.3 cc.
/ 100 g or less is because if it exceeds 0.3 cc / 100 g, pinholes are generated and the soundness of the product is impaired.

In the method of the present invention, Ca, Sr, B should be cast at least 30 minutes before casting the aluminum alloy.
The reason for adding at least one or more of a and Li to the molten aluminum alloy is that the hydrogen concentration in the molten metal rises again and pinholes are generated after 30 minutes or more have elapsed after the addition of the additive element. Because.

[0018]

EXAMPLES Examples of the present invention will be described in comparison with conventional examples to clarify the effects of the present invention. As a conventional example, aluminum alloy JIS AC4H was melted, and the molten aluminum alloy was bubbled with argon gas for dehydrogenation. At this time, a badge treatment was required, and the molten metal could initially be reduced to about 0.25 cc / 100 g of hydrogen after 30 minutes of bubbling.
Since it was sedated for 30 minutes and cast in a mount part of an automobile 1.5 hours later, the amount of hydrogen increased up to about 0.4 cc / 100 g, and a pinhole defect occurred.

On the other hand, as an example of the present invention, aluminum alloy JISAC4C was melted and Al5 was added to the molten aluminum alloy so that the weight ratio was 0.05%.
% Ca mother alloy was added, and the treatment time was 3 minutes to obtain an Al alloy molten metal having a hydrogen content reduced to 0.2 cc / 100 g. Within 30 minutes after the Ca addition treatment, the molten aluminum alloy was cast into automobile mount parts by a low pressure casting method. The amount of hydrogen in the molten metal at the end of casting was 0.25 cc / 100 g. Therefore, no pinhole was generated and no defect was found.

FIG. 1 shows an aluminum alloy JISAC.
4C is melted and 0 to 0.3% based on this molten Al alloy
Al 5% Ca master alloy was added at various weight ratios between
The hydrogen content was measured after a treatment time of 3 minutes. As shown in FIG. 1, when the Ca addition amount is 0.005% or more, the hydrogen gas content is 0.3 cc / 100 g or less,
After that, the hydrogen content decreased due to the increase of Ca addition amount, and C
It can be seen that the addition amount a is 0.3% and the reduction amount is saturated.

FIG. 2 shows the relationship between the amount of molten metal gas and the standing time after the molten metal degassing process in this embodiment. As shown in FIG. 2, when the Al5% Ca mother alloy was added and the amount of molten metal gas was 0.2 cc / 100 g after the degassing treatment, it exceeded 30 minutes after the treatment due to absorption of moisture from the air. , 0.3 cc / 100 g is exceeded.

The same experiment as in the above example was conducted for Ba, Sr and Li, but almost the same results as for Ca were obtained. Further, the same experiment as in the above-mentioned example was performed for the composite addition of two or more kinds of Ca, Sr, Ba and Li, but almost the same results as in the case of Ca were obtained.

[0023]

As described above, the casting aluminum alloy of the present invention and the method for producing the same are at least one of Ca, Sr, Ba and Li in the molten Al alloy in a weight ratio.
The total content of the above elements is 0.005 to 0.3%. When these elements are added to the molten aluminum, they easily form hydrides and are stable at the temperature of the molten aluminum in the practical range. Reacts with hydrogen to produce a hydride. Therefore, hydrogen in the molten metal is reduced to 0.3 cc / 100 g or less. Further, at least 30 minutes before casting the aluminum alloy, at least one of Ca, Sr, Ba and Li is added to the molten aluminum alloy, so that the hydrogen in the molten metal is reduced to 0.3 cc / 100 g or less. You can Therefore, product pinholes can be prevented and the strength is improved. In addition, the degassing processing time is shorter than that of the conventional one, no special equipment is required, the equipment cost is low, and the layout can be simplified.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an additive element and a molten metal gas amount of the present invention.

FIG. 2 is a diagram showing a change in molten metal gas amount after a processing time.

Claims (2)

[Claims] 1. A total weight ratio of at least one of Ca, Sr, Ba, and Li of 0.005 to 0.3%, and a hydrogen content of 0.3 cc / 100 g or less. Aluminum alloy for casting characterized by. 2. A casting of an aluminum alloy at the latest 3
A method for producing an aluminum alloy for casting, which comprises adding at least one of Ca, Sr, Ba and Li to the molten aluminum alloy by 0 minutes.