DE1800067B2 - Aluminum-silicon cast alloy - Google Patents

Description

The invention relates to heat-resistant cast alloys based on aluminum with a low drigen coefficient of linear thermal expansion and can be used for pistons of internal combustion engines as well similar parts are used, which are operated at high temperatures.

Cast alloys based on aluminum are known, ^a 5 which contain 15 to 19 ° ^ Si, 0 to 2% Mg, 2 to 5% Cu, 2 to 5% Ni and, as additives, Mn, Fe, Co, Cr and / or Ti, their total content is between 0 and 5% (British Patent 9 i2 959).

The known alloys have a coefficient of thermal expansion in the temperature range from 20 to 300 ° C., which is equal to 19.5 to 21.5 · 10 ° C., and have a creep strength at 300 ° C. over the course of 100 hours, of σ <5 kp / mm ² and a fatigue strength at 5 ■ 10 ⁷ cycles of ^ ₁ - = 7 to 10 kp / mm ² .

In the German patent 6 70 570 an aluminum alloy is described, which consists of 7 to 25%, preferably 10 to 15% silicon, 0.2 to 3%, preferably 0.2 to 1% magnesium, 0.3 to 2%, preferably preferably 0.75% copper, 0.5 to 6.5%, preferably 2 to 5% nickel, 0 to 1% manganese, 0 to 0.5% chromium, 0 to 0.6% titanium and the remainder aluminum. “The aluminum content is usually not less than 80%, unless the silicon content is at * 5 up to 25% is increased if the machinability of the alloy is not a primary consideration comes.

The known alloy can also contain other alloy components, for example iron, which is usually is contained as an impurity in silicon-rich alloys, in amounts usually found in high-quality bars without the to significantly influence the essential properties of the alloy.

Particular attention is paid to the copper content of the well-known alloy. An alloy of 14% silicon, about 2% nickel, 1% magnesium and 83% aluminum results in a low Brinell hardness of about 85 kp / mm *, while an alloy with the same content of silicon, nickel and magnesium with a simultaneous low content of Under similar conditions, copper has a ^{Brinell hardness 15 to 25 kp / mm 2} higher than that mentioned above. For the mentioned Al-Si-Ni-Mg- ^6s alloy with 0.75% copper, a Brinell hardness of approximately 85 kp / mm ^{2 is} specified for the cast state, which is achieved by a special heat treatment 067

(Annealing treatment for 2 hours at 530 "C, quenching to room temperature, tempering at 125 to 15O ⁰ C for a period of about 25 hours) to 125 to 130 kgf / can be increased mm ^2.

For 2% copper with otherwise the same other components of Si, Mg and Ni and annealing treatment, quenching and tempering, an increase in strength to 34 kp / mm ² and for an addition of 4.5% copper an increase in strength to only 30 kp / mm ^{2 is} specified . It follows that for the known alloy, the increase in strength with increasing copper content decreases.

The preferred copper content for the known alloy is therefore 0.75%. In order to achieve a Brinell hardness of approximately 125 to 130 kp / mm ² for them, the above-mentioned heat treatment is required, which takes a total of at least 27 hours.

The aluminum-silicon cast alloy according to the present invention is different from that known alloy in that narrower ranges are specified for the component, which also for some of the components also lie outside the preferred ranges of the known alloy, aass Manganese, chromium and titanium as well as iron are essential for a purpose to be explained later must be and that the copper content is outside the range of 0.3 to 2% for the copper content of the known alloy lies.

The alloy according to the invention is therefore concerned with both the more narrowly chosen Areas as well as the absolutely necessary components around a selection that is not obvious from a large number of possible alloys. The copper content lying outside the known range in the alloy according to the present invention justifies its novelty and is by the known alloy is not suggested, because the strength there decreases with increasing copper content.

The physical-mechanical properties of the known alloys are relatively low, thereby limiting their use for pistons in automotive and tractor engines which are used under severe conditions.

The purpose of the present invention is to avoid the disadvantages mentioned.

The invention has the object of providing a cast alloy based on aluminum with a low coefficient of linear thermal expansion, high heat resistance and fatigue strength create that can be used for pistons of the severely operated automotive and tractor engines.

This object is achieved by an aluminum-silicon cast alloy which, according to the invention, consists of 20 to 22% silicon, 2.2 to 3.0% copper, 0.2 to 0.5% magnesium, 2.2 to 2.8% nickel, 0.2 to 0.4% manganese, 0.2 to 0, 4% chromium, 0.1 to 0.3% titanium as well an iron content of up to 0.9%, the remainder being aluminum.

According to the present invention, the alloy is obtained in the usual metallurgical process. Like all hypereutectic aluminum-silicon alloys, it is modified with a substance containing phosphorus and refined with chlorine or chlorides. The modification and refining temperature is 790 to 850 ° C. The alloy is cast at a temperature of 780 to 85O ⁰ C.

° 4

Said silicon content in the aluminum a) After high-temperature annealing at 370 ± 10 ° C

In addition to the good casting properties, the alloy allows a

low coefficient of thermal expansion when cooled in air:

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8Fi ³ SP-? r ^Nid "'; ⁿ *? ^Meo v °" SA

2.2 to 2.8% in the alloy is for alloying with fixed alternating strength

Aluminum solution through copper and for the formation of _{ihd 5} . ₁₀ 7 cycles 9 to 12 ko / mm ²

Nickel-containing phases T (Al ₈ Cu ₃ Ni) and S [Al ₁ (CuNi) J Zdtstandfestiekek in 'one

to increase the high temperature strength of the alloy * o temperature 5on300 ° C "m

require ^, the addition * of magnesium in a ^ TlIt ^ _n Si. 5 to 6 kp / mm *

Amount of 0.2 to 0.5% calls for an increase in

mechanical properties of the alloy at Zim- b) After low-temperature annealing at 230 ± 10 ° C

mertemperature and at higher temperatures. in the course of 12 hours with subsequent

The addition of manganese in the range from 0.2 to 0.4% 15 cooling in air:

increases the resistance of the solid aluminum leakage. Tensile strength 19 to 23 kp / mm *

A certain amount of manganese and the addition Bruchdehnune 0 2bis0 5r

from 0.2 to 0.4% chromium eliminate the possibility of the BrinellhS 100 to 130TkoW

Formation of ferrous ternary phase (AISiFe), wSdSfckrit

which otherwise crystallizes in the form of lamellae, the ₃ o _{{W 5} . ^ | _k , _{} I0 b] S 13 k / mm} 2

the mechanical properties and in particular the creep strength at a

Reduce the fatigue strength of the alloy. TemSur of 300 ° C "ηϊ

Chromium, manganese and iron make up the four-component ΐ ^ Γνοη 125 hours 6.0 to 6.5 kp / mm *

phases of AlSiCrFe and AlSiMnFe, soft the

Increase the high temperature strength of the alloy. »5 The alloy has a linear thermal expansion

The introduction of titanium into the alloy in the voltage range in the range of temperatures of

Amount of 0.1 to 0.3% promotes fine grain formation is 20 to 300 ⁰ C, which from 18.5 to 19.5 · 10 "degrees C" ¹

of primary silicon crystals and is essentially the same.

the increase in the creep rupture strength. Due to the properties mentioned, the

The aluminum-silicon cast alloy according to the invention 30 aluminum-silicon cast alloy according to the invention alloy guarantees the following mechanical properties for pistons operated under severe conditions, the motor vehicle and tractor engines that were determined on chill casting samples be turned.

Claims (1)

1800 % Claim: Aluminum-silicon casting alloy, consisting of 20 to 22% silicon, 2.2 to 3.0% copper, 0.2 to 0.5% magnesium, 2.2 to 2.8% nickel, 0.2 to 0.4% manganese, 0.2 to 0.4% chromium, 0.1 to 0.3% titanium and an iron content of up to 0.9%, the remainder being aluminum.