JP2602893B2 - Aluminum alloy member with high strength and excellent forgeability - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aluminum alloy member having high strength and excellent forgeability.

[Prior Art] Connecting rods (hereinafter referred to as connecting rods) used in internal combustion engines are required to have high-temperature strength, high reliability, and low cost, and conventionally, steel is used. Since the connecting rod performs high-speed movement accompanying the vertical movement of the piston, energy loss can be significantly reduced by reducing the weight of the connecting rod.Therefore, the use of an aluminum alloy whose specific gravity is about 1/3 that of steel is considered. Have been.

However, at present, aluminum alloys produced by the conventional melting and casting method are only used in some light-load engines because of their insufficient high-temperature strength.

On the other hand, the new type of aluminum alloy produced by rapid solidification and powder metallurgy has a remarkably superior strength, high-temperature strength and wear resistance, compared with the conventional casting alloy or the wrought alloy produced by melt casting. The application to connecting rods has been actively attempted in recent years.

For example, taking advantage of the rapid solidification / powder metallurgy method, this method is a multi-element consisting of “Al-Fe-other transition metal elements” containing much more Fe and Si than aluminum alloys produced by the conventional melting and casting method. Alloys and Al / Si-based alloys have excellent high-temperature strength at about 200 ° C or lower, which is the operating environment for connecting rods.By designing the load cross-sectional shape to be somewhat larger than that of steel connecting rods, manufacture sufficient connecting rods for strength. it can.

[Problems to be solved by the invention]

However, most steel connecting rods are reliable hot forgings. Therefore, it is desirable to use a hot forging material also for a connecting rod made of an aluminum alloy, but an aluminum alloy by rapid solidification / powder metallurgy containing a large amount of Si and Fe or other transition metal elements is iron or steel. The problem is that hot forgeability is inferior to that of an aluminum alloy obtained by a conventional melting forging method.

This is because high temperature strength and hot forgeability are generally contradictory properties. As described above, if the hot forgeability is low, the forging process becomes special and complicated, leading to an increase in manufacturing cost, and the presence of minute forging defects lowers reliability, which is a fatal problem as a connecting rod. .

Therefore, the object of the present invention is particularly for connecting rods.
An object of the present invention is to provide an aluminum alloy member having excellent high-temperature strength at 200 ° C. or lower and excellent hot forgeability.

[Means for solving the problem]

The present inventors have conducted intensive studies on the strength and formability of aluminum alloys of various compositions by rapid solidification and powder metallurgy from room temperature to hot forging temperature. As a result, a limited range of Al-Fe-Mg alloys, alloys containing a relatively small amount of transition metal elements and refractory metal elements, etc., have excellent high-temperature strength up to about 200 ° C, and have a hot forging temperature. At about 400 ° C. or higher, it was found that the moldability was good.

The present invention has been made on the basis of the above findings, and includes Fe: 5.0 wt.% To 12.0 wt.%, Mg: 0.5 wt.% To 4.0 wt.%, And Ti, V, Cr, Zr. And at least one element selected from the group consisting of Mo and Mo: from 0.1 wt.% To 2.0 wt.%, With the balance being aluminum and unavoidable impurities. And Fe: 5.0 wt.% To 12.0 wt.%, Mg: 0.5 wt.% To 4.0 wt.%, And from the group consisting of Ti, V, Cr, Zr and Mo. At least one element selected from the group consisting of: 0.1 wt.% To 2.0 wt.%, And at least one element selected from the group consisting of Mn, Co and Ni; 〜12.0wt.%, Balance: A rapidly solidified powder of aluminum alloy consisting of aluminum and unavoidable impurities, formed and solidified by powder metallurgy And it has a feature.

Next, in the present invention, the reason why the chemical component composition range is limited as described above will be described below.

Iron (Fe): Iron is the most inexpensive transition metal element. Its strength is remarkably improved when it is supersaturated in aluminum or finely dispersed and precipitated in aluminum by rapid solidification and powder metallurgy.

Also, since iron has a slow thermal diffusion, Al / Fe alloys are also excellent in high-temperature strength.

Therefore, it is suitable as a main component of rapid solidification / powder metallurgy for connecting rods requiring high-temperature strength.

However, if the Fe content is less than 5.0 wt.%, The desired strength from room temperature to about 200 ° C. cannot be sufficiently obtained. Meanwhile, F
If the content of e exceeds 12.0 wt.%, not only the strength improving effect is hardly observed, but also the ductility and hot forgeability around room temperature are significantly reduced.

Therefore, the content of Fe should be limited to the range of 5.0 wt.% To 12.0 wt.%.

Magnesium (Mg): When Mg is added to an Al / Fe alloy by rapid solidification and powder metallurgy, the strength from room temperature to about 200 ° C increases.

Conventionally, even for aluminum alloys by melt casting
It has been known that the addition of Mg is effective for improving the strength.
This is understood to be due to the fact that Mg forms a solid solution in Al and resists the movement of lattice dislocation required for plastic deformation, that is, solid solution hardening. Al by rapid solidification and powder metallurgy
It is considered that the effect of increasing the strength of Mg up to about 200 ° C. in the case of / Fe-based alloys is also due to solid solution hardening.

On the other hand, at about 200 ° C. or higher, it was found that the strength of the Al—Fe—Mg alloy was greatly reduced as compared with the Al—Fe alloy, and that the formability at high temperatures was improved.

Al-Fe alloys are basically dispersion strengthened alloys. That is, the fine Al-Fe intermetallic compound is dispersed in the Al matrix by the rapid solidification / powder metallurgy method, and the fine Al-Fe intermetallic compound is hindered by kinetic dislocation and strengthened.

However, when solid solution hardening is added to such a dispersion strengthened alloy, the above two strengthening mechanisms are added from room temperature to a certain temperature, but offset hardening seems to occur at a certain temperature or more.

In fact, the strength of Al-Fe-Mg-based alloys at room temperature is higher than that of Al-Fe-based alloys containing the same amount of Fe and other small amounts of transition metal elements, but rather decreases at a certain temperature or higher. It was found that the ductility was improved.

It was also found that as the Mg content increased, the temperature at which the strength was significantly reduced shifted to the lower temperature side.

Utilizing these findings, Al-Fe in an appropriate composition range to show high strength within the operating temperature of the connecting rod and to show high formability at the hot forging temperature when manufacturing the connecting rod.
-Mg based alloy can be selected.

That is, if the Mg content is less than 0.5 wt.
In the temperature range up to 200 ° C., the desired improvement in strength cannot be obtained, and further, there is no effect in improving the moldability at a high temperature. On the other hand, if the Mg content exceeds 4.0 wt.%, The strength decreases greatly even at around 200 ° C., and the desired strength cannot be obtained.
The formation and coarsening of Al-Fe-Mg intermetallic compound and Al-Fe-other transition metal-Mg intermetallic compound also significantly reduce the room-temperature ductility.

Therefore, the content of Mg relative to the Al-Fe-other transition metal alloy should be limited to the range of 0.5 wt.% To 4.0 wt.%.

Titanium (Ti), Vanadium (V), Chromium (Cr), Zirconium (Zr), Molybdenum (Mo): These transition metal elements are peritectic with aluminum, and are eutectic with aluminum such as iron The effect of improving strength is greater with the addition of a relatively small amount. However, each of them is a rare element, is expensive, and has an effect of raising the melting point of the alloy to a remarkably high temperature. Therefore, there is a problem in productivity and economy in putting it into practical use as a binary alloy with aluminum.

However, Al-Fe alloys with small amounts of these elements added to Al-Fe alloys
Fe—X (X: Ti, V, Ci, Zr, Mo) alloys have a Fe + X content in an Al—Fe—X ternary or higher alloy that is at least room temperature rather than the Fe content in an Al—Fe binary alloy. -It is known that high-temperature strength increases. Therefore, various Al-Fe-X alloys by rapid solidification and powder metallurgy have been proposed. However, even in these multi-element alloys, the strength increases as the X content increases, but the ductility, the formability in hot forging decrease, and the raw material costs rise, the alloy production due to the rise in melting point, and the powder production. Problem arises.

Also in the present invention, these X (X: Ti, V, Cr, Zr, Mo)
Is an essential element for obtaining strength up to about 200 ° C for use in connecting rods. If these elements are not contained, the solidification of powder described later and the heat and processing history in the molding process In addition, there is also a problem that the strength of the alloy is greatly reduced due to the above, and the alloy cannot be put to practical use.

On the other hand, the present invention contains an appropriate amount of Mg as an essential element.
Since Mg is effective in improving the strength up to about 200 ° C., the total content of at least one of these elements X (X: Ti, V, Cr, Zr, Mo) is determined based on productivity and economic efficiency. It is possible to keep the problem within a range that does not become excessive.

However, if the total content of X is less than 0.1 wt.%, The effect of improving the strength is insufficient, and the reduction in the strength of the connecting rod member due to the heat and processing history is too large. On the other hand, if the total content of X exceeds 2.0 wt.%, The ductility decreases near room temperature,
It is not preferable because the hot workability is reduced, the raw material cost is increased, and the difficulty in producing the alloy powder is increased.

Therefore, Al-5.0 wt.%-12.0 wt.% Fe-0.5 wt.%-4.0
The total content of Ti, V, Cr, Zr, and Mo in the wt.% Mg alloy is 0.
It should be limited to the range 1 wt.% To 2.0 wt.%.

Manganese (Mn), Cobalt (Co), Nickel (Ni): These transition metal elements, like Fe, form a eutectic system with aluminum, and when contained in an Al-Fe alloy, form the peritectic system described above. The strength improvement effect is not as great as the group.

However, Al-Fe alloy and Al by rapid solidification and powder metallurgy
-Fe-Y (Y: Mn, Co, Ni) alloys, the former Fe and the latter
When the amount of Fe + Y is the same, the latter Al-Fe-Y alloy is often superior in strength and ductility.

Similar effects can be obtained when a part of iron is replaced with Y in the Al-Fe-Mg-X alloy of the present invention. On the other hand, Fe + Mn + Co +
If the total content of Ni is excessive, ductility near room temperature and formability such as hot forgeability also deteriorate.

Therefore, the content of Fe + Mn + Co + Ni is 5.1 wt.% In total.
It should be limited to the range of ~ 12.0 wt.%.

However, since Ni and Co are relatively expensive, it is preferable to suppress the content thereof sufficiently lower than that of Fe.

Although the configuration relating to the composition of the alloy of the present invention is as described above, changes in the details of the configuration can be easily made by those skilled in the art.

For example, Cu and Si contribute to both solid solution hardening and dispersion strengthening and Al-Fe-Mg-X by rapid solidification and powder metallurgy.
It has the potential to improve the strength of the alloy and the Al-Fe-Mg-XY alloy.

Therefore, the addition of small amounts of these elements is effective as long as the strength and ductility from room temperature to about 200 ° C. of the present invention and the hot forgeability are not impaired.

Next, a method for molding and solidifying the aluminum alloy member of the present invention from an aluminum alloy, that is, a method for producing a rapidly solidified powder and a method for solidifying the powder by powder metallurgy will be described.

As described above, the aluminum alloy member of the present invention is:
It is formed by rapidly solidifying a rapidly solidified aluminum alloy powder by powder metallurgy.

Manufacturing method of rapidly solidified powder: Currently, aluminum alloys by the melt casting method, which are widely used industrially, have a solidification rate of about 10 ° C / sec.
It is as follows.

On the other hand, in the present invention, the solidification rate of the aluminum alloy needs to be at least 10 ² ° C / sec or more, preferably 10 ³ / sec or more. For this purpose, a known air atomization method is used.
At present, it is a method for producing rapidly solidified powder that is most suitable for mass production and economy, and is also suitable for the present invention. When the coarse powder is sieved in the aluminum alloy powder by the air atomization method, a solidification rate of about 10 ³ ° C / sec or more can be obtained.

In addition, various methods for producing rapidly solidified powders, flakes and ribbons are known, and among them, there is a method capable of obtaining a solidification rate of 10 ⁵ ° C / sec or more.

However, as described later, hot compaction is indispensable for solidifying the aluminum alloy powder, and at this time, thermal decomposition of the rapidly solidified structure occurs. Therefore, the advantage of the high solidification rate as described above is not always achieved, and the problems of mass productivity and economic efficiency often remain.

Powder solidification method by powder metallurgy method: In order to solidify powder obtained by rapid solidification, powder obtained by crushing flakes or ribbons, it is necessary to perform hot forming at least once. The surface of the aluminum alloy powder is covered with a thin strong oxide film, and cannot be solidified by a normal sintering method.

Further, as a highly reliable strength member, it is necessary to perform solidification with no voids and a relative density of 100%. Further, in order to break the oxide film and obtain a metal bond between the powders, it is necessary to give a certain amount or more of plastic deformation during heating.

As a solidification molding process of an aluminum alloy powder satisfying these conditions, it is most common to sequentially perform a billet molding by compression molding, degassing, hot extrusion and hot forging in the order described.

If hot extrusion is omitted as a method of forming into an aluminum alloy member for connecting rods, compression molding of the preformed body, a shortening process consisting of hot forging, if sufficient strength and reliability are obtained, productivity and This is advantageous in both economical aspects. However, at the present time, those excluding the hot extrusion step have not yet achieved the same properties as those including the hot extrusion step.

The heat and working history of these solidification, forming and forging processes affects the properties of the connecting rod. Most importantly, the reduction in strength due to coarsening of the dispersion strengthened particles in the alloy is minimized.

In the present invention, the temperature of these hot steps is set to 500 ° C.
By keeping the temperature at or below, preferably at 460 ° C. or lower, desired characteristics are maintained.

(Example of the invention)

 Next, the present invention will be described with reference to examples.

Alloys having a component composition within the scope of the present invention shown in Table 1
No. 1 to No. 10 and comparative alloys No. 1 to No. 9 having component compositions outside the range of the present invention were produced, respectively. Each of these alloys was redissolved and made into a rapidly solidified powder by an air atomizing method. By setting the atomizing conditions and sieving the atomized powder, a powder having a mesh size of -100 mesh (a sieve opening of 149 μm or less) and an average particle size of 45 μm was obtained. As a result of analyzing the alloy structure of the cross section of each of these powders,
The solidification rate of these powder was 10 ³ ~10 ⁴ ℃ / sec approximately.

After vacuum degassing each of these powders at 400 ° C., they were hot pressed to form billets having a diameter of 150 mm. Then, each of these billets was heated to 420 ° C. and hot-extruded to prepare an extruded round bar having an extrusion ratio of 11 and a diameter of 45 mm.
Specimens of alloy members of the present invention (hereinafter referred to as specimens of the present invention) No. 1 to No. 10, and specimens of alloy members for comparison (hereinafter referred to as comparative specimens) No. 1 to No. It was set to 9.

Tensile test specimens were taken from each of these extruded round bar specimens, and the tensile properties at room temperature and 200 ° C. were measured and are shown in Table 1.

In addition, each of the extruded round bar specimens was cut into a cylindrical specimen having a height of 80 mm, heated and held at 450 ° C., set in a hydraulic press, heated to 300 ° C., and then coated with graphite-based lubricant. These cylindrical specimens were subjected to upsetting and compression using a pair of flat molds, and the hot forging property was evaluated by obtaining the critical upsetting ratio at which cracks occur. The results are also shown in Table 1. .

As shown in Table 1, the comparative specimen N containing no Mg
o.1 does not have the desired strength at room temperature and 200 ° C. Comparative specimens No. 2 and No. 3 containing no Mg or having a content less than the range of the present invention and having a low content have a low marginal upsetting ratio. Thus, alloy members that do not contain Mg or contain only a small amount have insufficient strength, or the hot forgeability decreases as the content of transition metal elements is increased to improve strength. showed that.

A comparative sample No. 4 or No. 5 containing no aluminum peritectic element or having an Fe content less than the range of the present invention and having an insufficient amount has a strength at about 200 ° C. Was enough.

Comparative specimens No. 6 and No. 7, in which the content of Fe or the total content of Fe and an element forming a eutectic system with aluminum similarly to Fe are excessive beyond the scope of the present invention, are room temperature. The elongation was low and the hot forgeability was poor.

The comparative sample No. 8 in which the content of the element forming the peritectic system with aluminum exceeded the range of the present invention was too poor in hot forgeability.

Comparative sample No. 9 having an excessively high Mg content beyond the scope of the present invention exhibited a significantly low room temperature elongation.

As described above, the alloy member out of the alloy composition range of the present invention is unsuitable for connecting rods because at least one property among room temperature strength, room temperature elongation, strength at 20066, and hot forgeability is deteriorated. . In addition, those containing too much Fe and those containing too many elements without aluminum and peritectic system are practically used as alloy members for connecting rods, either because they are difficult to dissolve or because the base metal is expensive. Lack of sex.

On the other hand, the specimens No. 1 to No. 10 of the present invention all had a room temperature tensile strength of 47 kgf / mm ² or more, a tensile strength at 200 ° C. of 32 kgf / mm ² or more, and It had suitable strength.

Incidentally, since the tensile strength at 200 ° C. of the extruded material which is one 5083 alloy excellent in most high-temperature strength alloys by conventional melting and casting method alloy is about 24kgf / mm ^2, the present invention than it It can be said to exhibit a high temperature strength of about 30-50% increase.

In addition, 2218 alloy, which is a heat treatment type alloy by the conventional method,
When held briefly at 200 ° C. is showing a tensile strength of about 33 kgf / mm ^2, a long time (for example, 1000 hours) and held引長strength decrease is large, about 18 kgf / mm ² Become. On the other hand, the alloy member formed by the rapid solidification / powder metallurgy method of the present invention does not cause a decrease in strength due to long-time heating at a temperature of at least 300 ° C.

The critical upsetting ratios at 450 ° C. of the test specimens No. 1 to No. 10 of the present invention are all 75% or more, and have practically sufficient hot forgeability.

[Effects of the Invention] As described in detail above, the aluminum alloy member of the present invention has a remarkably high strength within the operating temperature range of the connecting rod as compared with the alloy obtained by the conventional melting casting method, and is formed into a connecting rod. It is suitable as an alloy member for a lightweight aluminum alloy connecting rod instead of a conventional steel connecting rod because of its good forgeability in hot forging. Therefore, according to the alloy member of the present invention, an internal combustion engine having excellent high-speed operation performance and high efficiency can be manufactured, and industrially excellent effects are brought about.

Claims (2)

(57) [Claims] (1) Fe: 5.0 wt.% To 12.0 wt.%, Mg: 0.5 wt.% To 4.0 wt.%, And at least one selected from the group consisting of Ti, V, Cr, Zr and Mo.
High strength, characterized by being formed by solidifying a rapidly solidified powder of an aluminum alloy comprising the following elements: 0.1 wt.% To 2.0 wt.%, Balance: aluminum and unavoidable impurities by powder metallurgy.
An aluminum alloy member with excellent forgeability. (2) Fe: 5.0 wt.% To 12.0 wt.%, Mg: 0.5 wt.% To 4.0 wt.%, And at least one selected from the group consisting of Ti, V, Cr, Zr and Mo.
At least one element selected from the group consisting of: 0.1 wt.% To 2.0 wt.%, And Mn, Co and Ni, in a total amount with the Fe: 5.1 wt.% To 12.0 wt. %, The balance: an aluminum alloy member having high strength and excellent forgeability, which is obtained by molding and solidifying a rapidly solidified powder of an aluminum alloy comprising aluminum and unavoidable impurities by powder metallurgy.