JPS6155576B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for refining primary silicon in a hypereutectic aluminum-silicon alloy.

It is known to those skilled in the art that aluminum-silicon alloys are classified into three groups according to the content of added elements. An alloy containing about 12.5% by weight of Si is called a eutectic, and an alloy containing Si in an amount smaller or larger than this value is called a hypoeutectic or a hypereutectic, respectively.

In the present invention, only binary and multi-component hypereutectic alloys are considered in which a solid phase containing substantially primary silicon and then an aluminum-silicon eutectic system are formed successively during cooling during the manufacturing process. .

Such alloys are used in particular in the production of jackets for internal combustion engines by casting. The reason is that this type of crystal structure, in which hard primary silicon is embedded in a softer eutectic matrix, tends to form a microporous surface that is especially favorable for lubricant retention and frictional action. It is. however,
For favorable results these crystals should be 100μ
The size must not exceed m.

However, this requirement is difficult to meet, especially for cast parts of large dimensions.

For this purpose, when producing these alloys, elements or compounds called "refiners" are added that increase the number of development centers in the liquid metal and form crystals of small size during the cooling process. It became like that.

A large number of refining agents are described in the literature.
However, each of these atomizing agents has its own unique effect and therefore cannot be used indiscriminately.

Some refining agents act on primary silicon, while other refining agents act only on eutectic silicon crystals. Some may even be able to refine the crystals of one phase while simultaneously increasing the crystals of the other phase.

STCHIU METALKUNDE 1966 5
His paper “The effect of various elements on the improvement of Al-Si alloys” in issue 57
elements on the modification of Al―Si
In particular, Table 4 on page 399 lists the elements along with their concentrations that can refine primary silicon.This table includes chromium, molybdenum, manganese , tungsten, phosphorus, sulfur, iodine, copper, silver, zinc, tin, lead, nickel, cadmium, and mercury.

In this paper, Table 2 on page 396 states that, contrary to all the elements mentioned above, magnesium added to hypereutectic alloys has the effect of increasing primary silicon and refining eutectic crystals. It is shown.

By the way, the present applicant has extensively researched the crystal refinement of hypereutectic alloys using phosphorus, and has surprisingly found that when magnesium is added to an alloy to which a refiner has already been added, the refinement is not impaired. He acknowledged that it would actually be strengthened. This thing is
Contrary to teachings by CHIU. Furthermore, the Applicant has determined that this supplementary refining effect disappears immediately, i.e. it disappears over time, and therefore, in order to obtain the maximum benefit from its effect, this magnesium should be removed immediately before casting. I discovered that I had to add it.

As described above, the present invention relates to a method for refining the primary silicon of a hypereutectic aluminum-silicon alloy in which a refining agent containing phosphorus is added in advance, and a feature of the present invention is that a refining agent containing magnesium is added immediately before casting of the alloy. It is the addition of a substance that The alloy is prepared in a conventional manner and has one of the phosphorus-containing substances added in an amount of 50 to 1000 ppm phosphorus or an equivalent amount, to which is added magnesium. The magnesium may be in the elemental state or as an aluminum-magnesium master alloy, and may be in the form of scrap metal, powder, or in chunks large enough to dissolve at a sufficient rate.

The amount used depends on the magnesium content in the final alloy.
500 ppm, but when processing alloys containing magnesium in the composition, the amount necessary to reach the desired content may be added. Magnesium content value in the final alloy referred to in this specification (500ppm)
refers to the remaining amount of magnesium added to the alloy and does not include the amount of magnesium that was present in the original (starting) alloy.
The addition takes place as close as possible to the moment of casting and in any case within 30 minutes before casting. This is because after this period, the miniaturization effect decreases and becomes zero in practice. In order to obtain optimum refinement conditions, it is preferable to add it within 5 minutes before casting.

In this way, the size of primary silicon can be reduced by about half compared to that obtained in the presence of phosphorus alone. It is also possible to reduce the amount of phosphorus required for such refinement to achieve the desired crystal size and compensate this amount by the amount of magnesium. This has the advantage of reducing the consumption of this metalloid and reducing the amount present in the production furnace.

The invention is illustrated by the following examples.

Example 1 A sample was taken from a metal bath of extremely pure AS17 (binary alloy of 17% by weight Si, balance Al) at a temperature of 765° C., containing several tens of ppm of phosphorus, and solidified in 13 seconds. As a result of testing this sample, an average of approximately 50μ
It was found that the material had primary crystal silicon with a size of m.

Then 0.1% magnesium was added to the same bath and 2 minutes after introduction a new sample was taken under the same conditions as before, allowed to solidify and examined. At this time, the crystal size had reached 25 μm. When the same operation was repeated one hour after the introduction of magnesium, 40 μm crystals were observed, indicating the ease with which the effect of this refinement element disappeared.

Example 2 Divide the AS17 metal bath into three parts, each with 10
Different amounts of phosphorus were added from 50 ppm to 50 ppm. A sample was taken of each, allowed to solidify in 13 seconds, and its structure examined. The sizes of the observed primary silicon were 20-40-60 μm, respectively.

Add 0.1% Mg to each of the above, and add 2 of the elements introduced.
Minutes later, the same operation as was performed on the untreated magnesium alloy was performed. The grain size of each sample was 11-19-32 μm, respectively.

Therefore, it can be seen that magnesium has the effect of reducing the crystal grain size of primary silicon to approximately half.

Example 3 AS17U4G (Si17%, Cu approx. 4%,
Copper phosphorus containing 15% phosphorus was added to a bath of alloy (alloy consisting of approximately 1% Mg and balance Al) such that the phosphorus content of the bath reached 700 ppm, and some amount of the liquid was applied to the traction specimen. Taken for casting in shape. After solidification, the size of primary silicon crystals observed for these specimens exceeded 50 μm.

0.6% magnesium was added to the remaining bath and another sample was taken immediately after this introduction and dissolution.
The grain size of these samples after solidification is 30
μm, thus confirming the role of magnesium as an element for refining.

The present invention can be used to refine hypereutectic aluminum alloys and is particularly useful when these alloys are intended for the manufacture of internal combustion engine jackets or any other parts that are subject to friction.

Claims (1)

[Claims] 1. Adding a magnesium-containing substance to an alloy to which a phosphorus-containing substance has already been added before casting in such an amount that the magnesium content in the final alloy can reach at least 500 ppm.
A method for refining primary silicon in a hypereutectic aluminum-silicon alloy using a phosphorus-containing substance and a magnesium-containing substance, which are added within 30 minutes. 2. The method according to claim 1, characterized in that the magnesium-containing substance is added within 5 minutes before casting.