JPS61104043A - Heat resistant and high-strength aluminum alloy - Google Patents

Abstract

PURPOSE:To obtain the Al alloy having superior heat resistance, hot forgeability, and stress corrosion cracking resistance, by incorporating specific percentage of Si, Fe, Mn, Co, and Li to Al. CONSTITUTION:The Al alloy containing, by weight, 10-30% Si, 4-30% Fe, at least least 1 kind of element selected among 1.5-5.0% Mn, 0.5-3.0% Co, and 1.0-5.0% Li, and the balance Al with inevitable impurities is manufactured; the amounts of Cu and Mg in the inevitable impurities should be, respectively, <0.8% and <0.5%. In this way, the Al alloy suitable as parts material for an internal combustion engine can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [1] The present invention relates to an aluminum alloy having excellent heat resistance, hot forgeability, and stress corrosion cracking resistance. The present invention relates to a material that can be applied to connecting rods to make them lighter (6).

Recently, light alloy materials, especially aluminum alloys, have been widely used as parts materials for internal combustion engines in order to reduce the weight of moving parts. In particular, using the powder metallurgy method, various types of alloys are added with a large degree of freedom to achieve heat resistance, strength, strength,
Aluminum alloy H-shaped components designed to improve Young's modulus greatly contribute to improving engine performance.

The material that the applicant investigated in Japanese Patent Application No. 59-166979 is also an aluminum alloy for powder metallurgy that is designed to improve heat resistance, abrasion resistance, heat insulation, and A7 rate.

As a matter of fact, as a result of various subsequent studies on the aluminum alloy containing iron in the range of 4≦Fe≦33@hang%,
Forging materials (preformed products) especially in the range of Fe≧6%
It was found that it was necessary to improve the hot forgeability of J3 and the stress corrosion cracking resistance of the final molded product.

That is, the forging material (Fc≧6%) is subjected to high-speed hot forging processing (processing speed = 75 mm/Sec
), defects such as cracks are likely to occur, and in order to eliminate these defects, it is necessary to take various measures in the forging bill, such as reducing the processing speed and increasing the temperature of the metal. figure,
Mass production will be impaired and parts manufacturing costs will be high.

Additionally, there is a risk of stress corrosion cracking (according to the JIS stress corrosion cracking test) occurring at locations where stress is constantly applied, such as the pin boss portion (small end) or bearing cap fastening portion (large end) of the connecting rod. As the speed of engines has increased in recent years, this has become a factor in reducing the durability of engine component parts.

An object of the present invention is to provide a heat-resistant, high-strength aluminum alloy that can be processed into a forging material by high-speed hot forging and that is less susceptible to stress corrosion cracking due to forging formation. be.

The heat-resistant high-strength aluminum alloy according to the present invention includes Si,
In addition to Fe, at least one element selected from the group consisting of Mn, Co, and Li is added within a composition range (median amount %).
): 10≦Si≦30%, 4≦Fe≦33%, 15≦H
n≦5.0%, 0.5≦CO≦3.0%, 10≦Li≦
Contains 50%.

When iron (Fe) is added to aluminum, FeA I
It is well known that the aluminum ram alloy of the present invention produces acicular crystal compounds of 3, which impairs the malleability and corrosion resistance.
It has been confirmed that the addition of n) suppresses the generation of the above-mentioned needle crystals, improves high-speed hot working @ shipbuilding properties, and improves sinterability, but has a negative effect on stress corrosion cracking resistance. copper (Cu) and magnesium (Ha)
It was decided to improve the stress corrosion cracking characteristics by suppressing the content of F to an impurity level (less than 0.10% by weight).

Silicon (Si) added in the aluminum alloy of the present invention
, Iron (Fe), Manganese (Hn),] Baltic (C
o) The functions of lithium (Li) are as follows.

(a) Si: Silicon is effective in compensating for the lack of wear resistance caused by the addition of iron alone and in improving Young's modulus. However, if the amount is less than 10% by weight, the wear resistance cannot be improved, and if it exceeds 30% by weight, the moldability deteriorates and cracks are likely to occur in the structural member.

As with iron, the Young's modulus changes as the number of silicon-added stitches increases, but it is limited to the above-mentioned F limit value in consideration of formability.

(b) Fe: Iron is necessary to improve high temperature strength, heat insulation properties, and Young's modulus. However, if it is less than 4% by weight, high-temperature strength can be secured to some extent, but the high-temperature strength is insufficient, and if it exceeds 33% by weight, the density will increase and the ability to make a light boat will be impaired, and the soil, hot extrusion processing, heat Formability deteriorates during inter-forging processing, etc. Further, the A7 rate improves as the amount of iron added increases, but the amount of iron added is limited to the upper limit value in consideration of the density.

(c) Hn: In the production of atomized powder, it is necessary to set the cooling rate of aluminum alloy powder to be the highest, but when considering mass production, it is 103 to 10".
C/sec is the limit. In this cooling rate range, when Fe≦6%, the Al-Fe-3i intermetallic compound is sufficiently divided in the hot extrusion process and the precipitated state of the compound is also lumpy, so there is a certain amount of High-speed hot forging is possible, but when Fe>6%, the intermetallic compound has a needle-like precipitate shape and hot deformation resistance increases, making high-speed hot forging impossible.

Manganese is effective for controlling the precipitation form of the intermetallic compound. That is, by adding the specified amount of manganese, instead of the acicular Al31"c phase and the β-AI5 FeSi phase, a lumpy ^1.
Fe, Hn) phase and CI-AL+z(Fe, Hn)
*Si phase.

By preferentially precipitating it, it is possible to improve the high-speed hot truncation processability and improve the strength of the structural member.

However, if it is less than 1.5% by weight, the above effect will be reduced by 1S.
When it exceeds 5.0% by weight, hot deformation resistance increases and high-speed hot forging becomes difficult.

(d) Co: Cobalt has a positive effect on improving high-temperature deflection when reducing iron content to improve forging workability,
It is possible to improve tensile strength, yield strength, and fatigue strength without impairing elongation properties, and it is possible to improve high-temperature strength without deteriorating stress corrosion cracking resistance and forging workability. However, if it is less than 0.5% by weight, the effect will be small, and if it exceeds 30% by weight, the improvement effect will not be as noticeable as the increase in the amount added. Especially since cobalt is expensive, 3.0% by weight limited to %.

(e) Li: Lithium is used to suppress the increase in density of the alloy due to the addition of iron, and its suppressing effect increases as the amount of lithium added increases. Lithium also has the effect of increasing Young's modulus and imparting high rigidity. However, if it is less than 1.0% by weight, the effect of suppressing the increase in density is small, and if it exceeds 5.0% by weight, there is a problem that the manufacturing process becomes complicated because lithium is active.

Copper (Cu) and magnesium (Ha) in the aluminum alloy are kept to the level of unavoidable impurities in consideration of stress corrosion cracking resistance, and copper (Cu) is less than 0.8% by weight and magnesium (Ha) is less than 0.5% by weight. Less than % by weight.

01 for both copper (Cu) and magnesium (h) for structural members that require particularly improved stress corrosion cracking resistance.
It is desirable to suppress the amount to less than % by weight.

Further, a preferred composition of the aluminum alloy according to the present invention is as follows.

■15 ≦Si≦18 double ω%, 4≦“e≦8 double %, 1
．． 5<Hn≦2.5% by weight: Manganese (Hn) in this range can improve the deterioration of formability caused by an increase in iron (Fe) and improve the strength of the member.

■ 15≦Si≦18% by weight, 4≦Fe≦8Φ amount%, 2
≦[i≦4% by weight: Lithium ([i) in this range can suppress the increase in alloy density caused by the addition of iron (Fe).

■15≦Si≦18% by weight, 4≦Fe≦6% by weight, 1.
5<Hn≦2.5% by weight, 2≦[i≦4% by weight: Alloys in this composition range suppress the increase in density, and are excellent in strength and formability.

■ 15≦Si≦18% by weight, 4≦“e≦6% by weight, 1
≦CO≦double ω%: Cobalt (CO) in this range has an iron (Fe) addition rate of
High-temperature strength can be improved within a range that does not adversely affect moldability.

■15≦Si≦18 weight 9%, 4≦Fe≦6 weight% 1.5
<Hn≦2.5 fold ffi%, -2≦[i≦4 fold ffi%1
≦CO≦2% by weight: Alloys in this composition range have suppressed increase in density υ1, improved strength, especially high-temperature strength, and are excellent in elongation properties and formability.

First step: using each alloy powder with the composition shown in Table 1, it was formed into a mold with a density ratio of 75% and a diameter of 225 mm by cold isostatic pressing (C11, P, method) or mold compression molding. , an extrusion material having a length of 300IRIR is formed.

In the cold isostatic press molding method, alloy powder is placed in a rubber tube and 1.5 to 3. Molding is carried out under hydrostatic pressure with Ot/Ci culm. In mold compression molding, alloy powder is placed in the mold and 1.5 to 3.0 t/h is molded in the atmosphere at room temperature.
Molding is carried out under a pressure of about i.

Second stage: Each extrusion material is placed in a soaking furnace with an internal temperature of 350°C and held for 10 hours.Next, each extrusion material is hot extruded to form a forging material. The extrusion method in this case is direct extrusion nrr i)
Extrusion), indirect extrusion or backward extrusion) may be used, but the extrusion ratio must be 5 or more. If the extrusion ratio is less than 5, the strength will vary widely, which is not preferable. The temperature of the extrusion material is set at 300 to 400°C. Below 300°C, the deformation resistance of the material increases and extrusion processability deteriorates, and above 400°C, l1
ii! coarsening occurs, making it impossible to obtain a high-strength product. After the extrusion process, the &i construction material is cooled at a predetermined cooling rate by air cooling or water cooling.

Third stage: After that, each tR building material is heated to 460-470℃
Then, high-speed hot forging l:z processing was performed using a crank press at a processing speed of 75 mm/sec (almost the same processing speed as forging of duralumin).

Table 1 For each of the R molding amounts thus determined, the presence or absence of forging cracks and the hardness after air cooling were examined, and a stress corrosion cracking test was conducted, and the results are shown in Table 1.

Note that the stress corrosion cracking test was conducted according to JIS H8711. In other words, the length a o from each @molding amount
Cut out a plate-shaped test piece with a width of 10 mm and a thickness of 2 m.
Assuming that the applied stress is σ, JLx O,9 (however, σ1.2 is the 0.2% yield strength of each alloy ad, T to V), the liquid temperature is 30°C and the concentration is 3.5%. After being left in an aqueous sodium chloride solution for 28 days, the presence or absence of cracks was checked.

As is clear from Table 1, the alloys (T to V) according to the present invention have excellent forging workability and hardness, and have a stress of +17! .

Erosion cracking is less likely to occur.

In addition, when comparing samples d and ■, it is found that magnesium (h
> and copper (no cracks occur due to low Cur@),
It can be seen that hardness increases by increasing the amount of cobalt (CO) added.

In addition, by comparing sample b1■, manganese (Hn
), it was found that forging workability was impaired if the iron content exceeded 6% by weight, and by comparing lj-mples a and T, it was found that the iron content was increased and manganese (Hn) was added. It can be seen that Wfill and machining f1 are improved.

Furthermore, when looking at Sample V, it can be seen that both forging workability and hardness are excellent, and the special stress corrosion cracking resistance has been improved.

As is clear from the above explanation, in the aluminum alloy according to the present invention, the decrease in forging workability caused by the addition of iron is improved by the addition of manganese, and! The reduction in high-temperature strength caused by suppressing the addition of iron in order to improve processability was compensated by the addition of cobalt, and the stress corrosion cracking resistance was improved by keeping the copper and magnesium content to the level of unavoidable impurities. Therefore, high-speed hot forging can be performed, and a high-strength structural member with good heat resistance and durability can be obtained.

Claims (2)

[Claims] (1) In addition to Si and Fe, at least one element selected from the group consisting of Mn, Co, and Li is added in the composition range (wt%): 10≦Si≦30%, 4≦Fe≦
33%, 1.5≦Mn≦5.0%, 0.5≦Co≦3.
0%, 1.0≦Li≦5.0%, and the remainder is Al containing inevitable impurities. (2) The heat-resistant, high-strength aluminum alloy according to claim 1, wherein the amount of Cu in the inevitable impurities is less than 0.8 wt%, and the amount of Mg is less than 0.5 wt%. .