DE2446933B2 - METHOD OF HEAT TREATMENT OF AIZNMGCU ALLOYS - Google Patents

Description

melt

In the DT-OS 1458 530 is a method for Heat treatment of an object made of an aluminum

S _{en is} made. With the one from ^ un « ₉₉₆ | _known processes for the herder ui- « _objects made of an AlZnMg alloy

stellenJttetzterc maximum of 0.3 Cu Vo to decrease ^we 't ledere ™™> _on

G
tion of the

1 to ₅ x from 0 5% _ and residual terc a maximum of 0.3 Cu Vo ™™> ere _on the Verminde

& ^, _ed i _g fich in two stages. ng is a process for _on AlMgZnCu alloys, beg o ^V ° n _ink , g _§ B ^ - *** J · At least one element * W _{0 05 to} ξ, 3 · /. chromium, 0.1 to ^ _{ofi5 to o> 5} o _{/ o} zirconium - _{in which the} alloy

after

marked that the alloy

^^ fg ^ _{times hardened} on it

GKÜi treatment is subjected to a G ^ handju ^ ^U _{G1 erature and} _ _duration

solctie wenepddic r bbil

and that

^ °, s '63 ^

the second vv « _fi f

_will .

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30th

£ ^ _the two

_w ^ _s J ^ _{g take place} the annealing

tion the value pairs of duration ^ nd ^^^ 0 are chosen that ^ e mdas defined by the corner points £, F, G and W.
^Ώ is advantageous

fall

4, thereby

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The invention relates to a method for the heat Sfi of ⁸ AlZnMgCu alloys, consisting of tr _E xfuÄrnaS

_examples are explained in more detail using the drawings. Show in the drawing

Figures 1 to 3 are electron micrographs of sections in a plate made of an aluminum alloy 7075. The 0.1 »mjpgjri A ^ m

, 0

The remainder is aluminum, in which the alloy is solution annealed and then artificially hardened in several stages.

An aluminum alloy consisting of 5.1 to «, 1 · /. Zinc, 2.1 to 2.9 »/ 0 magnesium, 1.2 to 2 · / β copper, 0.18 to 0.35» / »chromium, maximum 0.30 · /. Manganese, niaximal 0.40 »/» silicon, maximum 0.50 · /. Iron, a maximum of 0.20 ¹ Vo titanium, others a maximum of 0.05% each and a maximum of 0.15% in total, the remainder being aluminum, does not have sufficient resistance to corrosion in the precipitation-hardened state under certain stress conditions.

In this alloy, which is referred to below as alloy 7075, the durability in the precipitation-hardened state against stress corrosion cracking, although the strength is increased considerably reduced compared to the condition of appearance hardening of the solution-annealed alloy.

. . _e . ". solution annealed and

stress-relieved state;

F i g. 2 a known precipitation hardened

State;

F i g. 3 a known, against stress corrosion cracking stable condition;

F i g. Figure 4 is a diagram showing the features of the invention.

The alloy according to the invention has a composition of 4 to 8% zinc, 1.5 to 3.5% magnesium, 1 to 2.5% copper and at least 1 element from the group of 0.05 to 0.3% chromium, 0.1 up to 0.5% manganese and / or 0.05 to 0.3% zirconium. The rest of the composition is essentially Aluminum.

The alloys designated by the aluminum industry as 7075 are preferred for the invention and have a composition of 5.1 to 6.1% zinc, 2.1 to 2.9% magnesium, 1.2 to 2%

3 ' 4

Copper, 0.18 to 0.35 per cent, chromium, maximum 0.30 per cent. Treatment, for example, IVs experienced years earlier.

Manganese, maximum 0.40% silicon, others maximum have to immerse in molten wood metal.

£> 0.05% and a maximum of 0.15% in total, the remainder being aluminum. In Fig. 1 to 3, electron recordings are

miniuEi. different microstructure shown, which are necessary for the

The alloys used in this invention 5 explanation of the invention substantially are also könuen one or more Vornverfeinernde All samples were included from a 6.3 mm thick aluminum elements, including titanium of 0.01 to miniumlegierungsplatte the composition A in 0.2 ⁰ / o and boron from 0.0005 to 0.002%. This EIe Table 1 is taken. FIGS. 1 to 3 show microns producing a fine grain in the cast structure of known states of such an alloy. the alloy. _xo In Fig. 1 is an example of the alloy in the solution

In addition, the annealed condition of 0.001 to 0.005% beryllium can be reproduced. Such a mi-

Joined to the oxidation of the molten kroge structure is made in an aluminum alloy plate

Reduce alloy to a minimum. obtained when heated to 482 ° C and then put in

Iron and silicon are considered impurities before water is quenched at room temperature. That

act. 15 plate material is then permanent to 1.5 to 3%

Up to 0.5% iron can be tolerated and stretched to relieve stress. In

Silicon content should not exceed 0.4%, around which Fig. 1 are E-phase particles of an Al-Mg-Cr structure

Formation of a substantial amount of interme- diate, matrix areas R of single-phase AIu-

metallic compound Mg ₂ Si to avoid. minium solid solution, grain boundaries B and offset

A heat treatment according to the invention for ER- 20 D tongues shown. The grained background, the

aiming at improved resistance to chip appearing in the matrix area in Fig. 1 is one

corrosion consists in the solution-annealed effect of the dilution solution, which is used to prepare

Alloy in the precipitation hardened state iering the sample used for over microscopy

in molten metal for a period and has been.

Temperature within the circumference of the rectangle as

EFGH in Fig. 4 and then table I again

perform precipitation hardening. Composition of the alloys (° / o)

This state is largely achieved by

Precipitation hardening of a solution-annealed Le <jie element alloy

at 80 to 163 ° C. Typical conditions can be 30 A Ji_

to be:

a) for alloys containing less than 7.5% zinc, heating a solution annealed Object at 93 to 135 ° C and holding for a period of 5 to 30 hours;

b) for alloys containing more than 7.5% of zinc, heating a iösungsgeglühten article to 80 to 135 ⁰ C and holding for a period of 3 to 30 hours.

Usually this condition is obtained by placing a sample in an air circulation oven while

Is heated to 121 ° C for 24 hours. F i g. 2 shows the alloy according to FIG. 1 after

According to another embodiment of the invention, the alloy is solution heat treated to the artificially age-hardened state, then the solution heat-treated and stress-relieved material is heat-treated at a temperature of 80 to 163 ° C in an air-circulating furnace during hardening, then for a duration and temperature of 24 hours 121 ⁰ C has been brought. The EFGH Ε phase, which is preferably within the scope A BCD, remains essentially unchanged. Suspended and then again during 2 to subsidence D and a grain boundary B appear. Here, for 30 hours at a temperature of 132 to 160 "C.

The article by T. Staley, "Heat Treating and Accumulations of Magnesium and Ink-Characteristics of High Strength Al-Zn-Mg-Cu-Alloys Atoms, Generally in a Ratio of With and Without Silver Additions," which is based on 2 Zinc atoms per magnesium atom. Pp. 191 to 199 in the January 1972 edition of 55 FIG. 3 shows a sample which appeared from "Metallurgical Transactions", compare the plate according to FIG. 1 and 2 in the against the public by ASM / AIME, shows that the heating stress corrosion cracking stable state demining / quenching speed, the time lapse has been taken, which by heating in between the heating / quenching and the air circulation furnace initially for 24 hours at the beginning of heating for precipitation hardening is ⁶ ° IzI ⁰ C and then for 8 hours to 177 ° C and the heating rate for aging is generated. A grain boundary precipitate 10 is crystalline hardness affecting the maximum yield strength, and the Guinier-Preston zones are overgrown, can flow, which can be achieved with alloy 7075. The latter zones have begun, plasticity is barely possible. It is to be demonstrated within the gist of the invention by designing x-ray diffraction patterns, yielding the teachings of Staley for optimization, and they will be used by those skilled in the art as a metric of the results. Thus it can be called and M-phase. Solution potential studies to improve strength indicate that the M 'and M phases contain some copper samples which contain their solution annealing and quenching atoms. It is believed that the

Cu 1.45 1.63 Fe 0.19 0.30 Si 0.09 0.12 35 mn 0.02 0.07 Mg 2.40 2.48 Zn 5.92 5.68 Ni 0.00 0.00 Cr 0.18 0.19 40 Ti 0.02 0.05 Be 0.001 0.001

Guinier-Preston zones advance to crystalline rock, by initially becoming the M 'phase, which is still partially connected to the matrix structure is. The M 'phase then changes to the M phase, which has a structure that differs from that of the Matrix is different. It is arrived at that progressing through the M 'phase to the M phase makes the original Guinier-Preston zones increasingly anodic with respect to the matrix and that the Protect the resulting anodic areas in the matrix against stress corrosion cracks.

The invention is further illustrated by the following examples.

Examples 1 to 8

For each example, two tensile bars of 9.5mm 9.5mm X 63.5mm were made from one piece of one 63.5 mm thick alloy plate 7075 (metallurgical development as described in Fig. 2) cut, so that their lengths are in the direction of the short side, i.e. H. in the direction perpendicular to that Surface of the plate.

Table II

Annealing duration and annealing temperatures in Woodmetall for Examples 1 to 8

and the coordinates of points A to H

Example number duration temperature or period min ⁰ C 1 0.5 24 (p 2 1.0 2415 3 1.5 231) 4th 4.0 230 5 7.0 204 6th 15.0 204 7th 7.0 191 8th 15.0 191 A. 20.0 182 B. 0.2 260 C. 1.0 260 D. 150.0 id2 E. 20.0 193 F. 0.8 249 G 1.2 249 H 40.0 193

The chemical composition of the alloy is as shown for Alloy B in Table I.

The tensile specimens for each example were made in molten Wood metal with a composition of 50% bismuth, 25% lead, 12.5% tin and 12.5 per cent cadmium immersed. The immersion temperatures and the durations are given in Table II and in FIG. 4 drawn. After immersion The cooled samples were then precipitation hardened by placing in the molten Wood metal them in a forced air oven for 24 hours

ίο have been heated to 121 ° C. In each of Examples 1 to 8, a tensile specimen was processed into a tensile rod with a diameter of 3.18 mm in order to add it to a 3.5% strength sodium chloride solution by means of alternating immersion at a load of 2950 kg / cm ² according to the Military Specification MIL-A-22771 B «. The samples were held until fracture with successive immersion in the saline solution for 10 minutes and then in air for 50 minutes. The number of

ao days to break under such treatment is shown in FIG. 4 above the time-temperature point reproduced for each example. On the remaining sample of each example, the yield strength was determined checked. The yield strength data for Examples 1

“5 to 8 are in FIG. 4 below the time-temperature points in percentages of a yield point of 43.8 kp / mm ² for the state which is explained on page 8 above.
Further examples of an embodiment according to the invention follow, wherein the second precipitation hardening is carried out for 2 to 30 hours at a temperature of 132 and 160 ° C.

Examples 9-14

The procedure was as described for Examples 1 to 8 except that all samples were immersed in a molten Wood metal for 90 seconds at 230 ° C prior to the second precipitation hardening. Other parameters and results are as given in Table III .

Examples 9 through 11 form a group of Comparative examples, which in the second precipitation hardening stage for 3 hours on temperature while in Examples 12-14 the second precipitation hardening was held during Took place 24 hours. The superior strength and corrosion resistance achieved by a second precipitation hardening can be achieved for 2 to 30 hours at 132 to 160 ° C, result from comparisons of the examples within the groups.

Table ΠΙ

Parameters and data for Examples 9-14, including immersion of the solution annealed, Precipitation hardened aluminum alloy 7075 in molten Woodmetall for 90 seconds at 230 ° C, followed by a second precipitation hardening

Example no.

Duration and temperature of the second Precipitation hardening

Tensile strength kp / mm ¹

Stretch limit kp / cm *

Days to break load 2710 kg / cm ¹

2260 kgf / cm ¹

9 3h / 121 ° C 43.4 37.7 27 80 10 3h / 135 ° C 44.4 37.8 43 62 11th 3 hours / 149 ° C 43.0 37.5 60 84 12th 24 hours / 121 ° C 45.5 40.6 49 « 50 13th 24h / 135 ° C 44.8 39.4 47 61 14th 24 hours / 149 ° C 44.8 39-6 56 63

For this purpose 2 sheets of drawings

Claims (2)

Claims: W 1. A method for _Z Heat Treatment! of AlZnMgCu alloys, consisting of 4 tons 8 · / · zinc, 1.5 to 3.5 «/ ο magnesium, 1 to 2, * '/ · copper and at least one element from the group 0.05 to 0 , 3% chromium, 0.1 to 0.5 · /, manganese and / or 0.05 to 0.5 · /. Zirconium and the remainder aluminum, in which the alloy is solution-annealed and then hot-hardened in several stages, characterized in that the alloy is hardened for the first time after the solution heat treatment in a first stage at 80 to 163 ° C, then subjected to an oil treatment that weep formed by such value pairs of annealing temperatures and duration, which are shown in the in FIG. 4 shown Te ^ pemtur-Ze ^ diagram fall within the rectangle defined by the corner points A, B, C and D and that finally the alloy is artificially age hardened a second time at 80 to 163 ° C 2. The method according to claim 1, characterized in that that the second artificial hardening is carried out for 2 to 30 hours at 132 to 160 ° C ^ Traufen according to claims or due to this marked that at the between the two The annealing treatment takes place during the heat-curing stages, the value pairs of duration and temperature You are chosen to be in that through the Corner points E, F, G and H Defined vertical corner fMethod according to one of Claims 1 to 3, characterized in that the between the two war-hardening stages that take place Annealing treatment by dipping the alloy · Τ ϊΐ ΤΕΤ ?? ^{bfidiih F1Üiß b} tär ^d