DE1271996C2 - Process for the heat treatment of castings made of pure aluminum-silicon alloys with a low addition of magnesium for electrotechnical purposes - Google Patents

Description

Number board Silicon content
in Al 99.5
in% 0.3 2 1 i 4th 6th 12.5 Conductivity in
m / Ohm ■ mm ² ... 32 28 27 26th 24 22nd

30th

Numerous studies prove that metals with the highest specific electrical conductivity as low as possible in impurities. This The requirement must also be met in the case of alloys whose use is also due to strength to avoid an increase in resistance. Depending on the intended use and Manufacturing type difficulties. These difficulties exist for the production of cast parts from alloys No longer in the use of the purest base metals, not even in the selection of suitable ones Alloying partners, the addition of which depends on the good mold filling capacity and the required sufficient strength, but in the fact that with these alloy components the electrical Conductivity is often changed to such an extent that the usability of castings made from it for electrotechnical purposes is highly questionable. This applies equally to heavy and light metal alloys.

Thus, by the addition of 12 ° / _o silicon, the electrical conductivity of aluminum with 34 m / AL Recommendation for increasing the conductivity by one to two units intended to Ainet homogenization 6 hours at 300 ° C are started, corresponding to a soft annealing.

Elsewhere, an electrical conductivity for the alloys G - Al Si 13 Mg (hardened) between 20 and 32 m / ohm - mm ^{2 is} given, but no rule for achieving high conductivities.

The aforementioned treatment of the occasion is the only indication. to increase the conductivity.

By adding 12% magnesium, the conductivity of aluminum is reduced from 31 m / ohm · mm ³ to 10.4 m / ohm · mm ^2. In the case of genera of other elements, the electrical conductivity is further reduced.

All recommendations are limited to stabilizing the materials, even in the more recent times and complete depletion of the mixed crystal in order to increase the electrical conductivity, with none Value was placed on special strength properties. This affects the use of GuO parts.

According to the requirements placed on the mechanical properties for electrotechnical Purposes of usable materials came. '' the usual alloy components can be dispensed with, The most interesting of these in aluminum are silicon, magnesium and copper, the former for improvement flowability is essential. In combinations with magnesium, after homogenization a hardenability achieved that of the alloy group Al Si Mg gives technical superiority over others, Hei this type of alloy According to the investigations of the inventors, the electrical properties are also found when the purest starting metals are used Conductivity not yet high enough to ensure its use in the electrical industry. The on The values achieved in the following alloys on permanent mold castings clearly show this in table 2.

Number board 2

No. Cu Mg Si \ nalysis,% ■ Fe Zn Ti in / Ohm mm * HB 0.01 I. 0.50 5.1 Mn 0.06 22.1 kp / mm ¹ 1 0.01 ' 0.25 5.2 η. b. 0.05 77 2 0.01 0.4.7 3.3 0.02 0.04 - 23.9 3 0.01 ' 0.28 3.5 η. b. 0.05 0.02 0.01 25.5 76.3 4th 0.02 70.7

The results in table 2 show that the requirement for higher conductivities is not exclusive is solved satisfactorily by lowering the Si content. Due to the simultaneous The addition of magnesium causes a further reduction in electrical conductivity.

1 27 L 996 ³ I ⁴

The re-examination of the tempered material resulted in the values according to number table 3. The electrical Conductivity is associated with a marked decrease in Brinell hardness.

Number board 3

alloy

No.

thermal treatment

Cu Mg A.
Si analysis,
Mn /.
Fe Zn Ti λ
m / ohm mm ^s HB
kp / mm 0.01 j 0.50 5.1 n. b. 0.06 - 29.9 48 0.01 j 0.25
ι 5.2 0.02 0.05 - - 29.1 45

homogenized + - tempered for 12 hours at 220 ° C

tempered in the as-cast state for 24 hours at 320 ° C

Investigations on aluminum-magnesium-silicon, available investigations in table 4 succeed, show a maximum resistance but di * increase in the electrical conductivity star.dsabrückung at tempering temperatures of 330 ° C, without difficulty above a value of JO m / ohm · So after severe impoverishment of the mixed crystal. As the material gradually softens, the electrical conductivity is increased from 19 m / ohm-mm ² only to 27 mm / Uhm-mm ² . idere investigations on aluminum -t>. Agne-wrought alloys with 10 °, ₀ magnesium showed technically uninteresting tempering times of more than 5000 hours on previously homogenized ashen an improvement in electrical conductivity. The maximum Widei stand decrease is at

mm ³ , also without the drop in hardness according to number table 3.

Number board 4

· ::; When the maximum hardness occurs at the same time, the higher the tempering temperatures, the earlier it is reached, ^ ₁ .. h for alloys with 8% magnesium. At the

As a result, the other mechanical properties are greatly reduced. Depending on the rising temperature, microscopic secretions become visible with a shorter duration or tempering treatment. At 150 C, the increase in hardness above the tensile strength falls to less than 50 ° / ₀ , the elongation to about 15 ° / "of its original value.

The invention was based, for aluminum-silicon / tum-Legierunr;? N with Si contents up to about I3 _cent, and low annealing treatments to Magnesiunuusatz * o linden, the results of IRN contrast to the AIuminium-Magneiium wrought alloys between a total The strengths and their original strengths decrease (see also number table 3 with the greatly reduced hardness values). The electrical conductivity values should be above 27 m / ohm · mm ² and the hardness not below 60 kp / mm ² . preferably 80 kp / mm ² .

The values achieved are shown in table 4. With an extension of the annealing times and application of the usual low but also higher tempering temperatures, the result of electrical conductivities over 27 m / ohm mm ² was achieved after just 48 hours of tempering at 175 ° C., in contrast to known investigations (see also numerical die casting from the alloy.! nor the strength table 3) hardness values of 102 kp / mm 'Brinell are available. can be achieved according to meter table 5. If all the values found are plotted as a function of the tempering time (see A b b. 1 to 3), it can be seen that at higher tempering temperatures of 200 ° C, half the duration of an annealing treatment at 175 ° C is sufficient (see Fig . 3).

The untreated alloys according to table 2 showed insufficient electrical conductivity despite the high purity of the aluminum used for production. The Al Si! ^ - alloys according to DIN 1725 achieve in the hardened state at best only 22 m / ohm · mm ² , namely both the high and low Si content, pden alloys. After the

Artificial aging after ;. kp / mm ^: Homogenization ni / lacking ² Alloy I. 122 12 hours at 175 C .... 24.9 114 24 hours at 175 C. 25.9 116 48 hours at 175 C .... 27.4 102 96 hours at 175 ° C 27.9 65 48 hours at 200 C .... 30.0 59 96 hours at 200 ° C 30.1 Alloy 2 82 48 hours at 175 C .... 28.2 82 96 hours at 175 C .... 29.5 63 48 hours at 200 C .... 30.4 57 96 hours at 200 C .... 30.5 Alloy 3 90 48 hours at 175 C .... 28.1 91 96 hours at 175 ° C 2 ¹ U 70 48 hours at 200 C .... 31.0 60 96 hours at 200 C .... 31.2 Alloy 4 84 48 hours at 175 C .... 29.2 82 96 hours at 175 C .... 30.8 63 48 hours at 200 C .... 32.0 58 96 hours at 200 C .... 32.1

After 48 hours of tempering at 200 ° C you can-; on

ZahieiiMfel 5

Homogenized and tempered at 200.degree. C. for 48 hours

<) 0.2 15.4 kp / mm ² 20.5 kp / mm ¹ 10.1 63 kp / mm-

<T N

HB

1

The investigations were continued at limit temperatures that were higher. The result is shown on number table 6.

Number board 6th ;. HB Artificial aging after m / ohm mm * kp / mm ¹ Homogenization Alloy 1 24.7 80 15 minutes at 25O "C ... 26.1 68 30 minutes at 25O "C ... 28.2 70 1 hour at 250 "C ... 28.0 52 3 hours at 25O ^Ü C ... 29.8 51 12 hours at 25O ° C ... Alloy 2 26.4 76 15 minutes at 25O "C ... 27.0 70 30 minutes at 250 ° C ... 28.7 66 1 hour at 25O'C ... 30.0 54 3 hours at 25O ° C ... 30.1 44 12 hours at 25O ° C ... Alloy 4 26.9 75 15 minutes at 250 ° C ... 29.0 69 30 minutes at 250 ° C ... 29.2 54 1 hour at 25O ° C ... 30.5 55 3 hours at 25O ° C ... 31.7 40 12 hours at 25O "C ...

Number board 7

Artificial aging after /. HB Homogenization m / ohm min ¹ kp / mm ¹ Alloy 1 12 hours at 150 ° C ... 23.5 82 24 hours at 150 "C ... 23.9 103 48 hours at 150C ... 25.8 110 96 hours at 150 "C ... 26.5 112 120 hours at 150 "C ... 27.1 117 Alloy 3 24 hours at 150 C ... 25.9 103 48 hours at 150 "C ... 26.6 112 96 hours at 150 "C ... 27.7 112 120 hours at 150 ° C ... 28.3 117

The delimitation of the low temperatures around 150 ° C is shown by the experiments in table 7.

The characteristic results are shown as a whole in A b b. 1 to 3 have been recorded. It is clear It can be seen that it is possible to obtain high electrical conductivity in addition to high hardness.

A b b. 1: Hardness and conductivity of the Al-Si-Mg alloys 1 to 4 (permanent mold casting, homogenized and tempered according to table 4), depending on represented by the duration of the start;

A b b. 2: Hardness of the Al-Si-Mg alloys 1 to 4, permanent mold casting, homogenized and tempered), opposite the conductivity plotted;

Fig. 3: Hardness and conductivity of Al-Si-Mg-Lc alloy 1 (homogenized chill casting) at tempering temperatures of 150, 175, 200 and 250 ⁰ C as a function of the tempering duration.

1 sheet of drawings

Claims (1)

Claim: Ohm · ram ¹ lowered to about 22 m / Ohm · mm '. Process for the heat treatment of cast parts made of pure, largely manganese, zinc and titanium-free aluminum-silicon alloys with a small addition of magnesium (max. 0.5Vo) in order to achieve an electrical conductivity of 27 to 32 m / ohm · mm ² and a Brinell hardness of at least 60kp / mm ² _? preferably 80kp / mm ² , characterized in that the cast parts are tempered after a homogenization treatment, namely at temperatures above 150 ° C and not above 250 ° C, at the latter temperature at least 30 minutes and at most 3 hours, at the first-mentioned temperature at least 06 , preferably least ¹ hours at 175 C. '. s 48 hours or at 200 ° C not less than 1 hour. ao