DE1243398B - Cast or wrought magnesium alloy containing rare earth metals - Google Patents

Description

BUN

EPUBLIC OF GERMANY

PATENT OFFICE

Int. Cl .:

C22c

EDITORIAL

■ = 4

Number:
File number:
Registration date:
Display day:

German class:

M41364VI a / 40b
April 28, 1959
June 29, 1967

The invention relates to a cast or wrought magnesium alloy which is heat-treated by homogenization annealing and hardening at 150 to 250 ^{° C. and contains rare earth metals.}

There are known cast and wrought alloys from 0.1 to 12% thorium, from 0 to 1 to 2% zirconium, up to 5 ° / o cerium, up to 10 ° / ₀ Silver, residual magnesium, under the corresponding reduction of the silver content also Thallium , Beryllium, bismuth, lead, calcium, zinc and / or cadmium.

Also, casting and Gußschweißlegierungen are known which 0.5 to 2% zirconium, up to 3 ° / o cerium and up to 15 ° included / ₀ Silver. These alloys can also contain up to 12% thorium.

Cast and wrought alloys based on magnesium are also known which contain 0.5 to 10%, in particular 2 to 4%, rare earth metals with predominantly neodymium content, also up to 5% silver, up to 2% Manganese, up to 10% thorium and other alloy additives with the exception of gallium and bismuth can hold. In particular, these alloys, provided they are free of manganese, can contain 0.4 to 0.9% Contains zirconium.

The invention is based on the object of specifying alloys of this type which have improved strength properties, in particular have an improved yield strength at 0.1% permanent elongation, because The yield strength of the well-known magnesium alloys is the same for both cast and kneaded fittings not as high as desirable compared to their ultimate tensile strength. Accordingly it was the yield point that set the limit for tensile loads in technical facilities. In particular the alloys should not rely on cold working to produce their properties be. Finally, the alloys should be homogeneous to a high degree.

One possible step in developing such alloys would be to use two-step heat treatment processes (Homogenizing and hardening) as it is widely used with aluminum, copper and other alloys. However, it has proven difficult to find magnesium alloys that match their properties to these Develop cheap way. With many magnesium alloys there is little or no result Advantage over simpler procedures. For example, it is known to cast magnesium-aluminum alloys subject to a two-stage heat treatment, but the alloys so heat-treated have not found any use, since their yield strength is a maximum of 12 kg / mm and they something Cast or wrought magnesium alloy containing rare earth metals

Applicant:

Magnesium Elektron Limited,

Manchester (Great Britain)

Representative:

Dipl.-Ing. F. Weickmann

and Dr.-Ing. A. Weickmann, patent attorneys,

Munich 27, Möhlstr. 22nd

Named as inventor:
Ronald James Malcolm Payne,
Norman Bailey, London

Claimed priority:

Great Britain 16 May 1958 (15 822)

are brittle. Magnesium-zinc-zirconium alloys with a high zinc content react more strongly to a such two-stage heat treatment and show better mechanical properties; however, they are relatively difficult to pour, as cracks and pores easily form in the mold when exposed to heat. Furthermore, alloys of this class are not weldable and therefore large and expensive castings must be made Treated as scrap because it is not possible to weld minor defects in them to eliminate. The consequence of this is that cast magnesium alloys require a two-stage heat treatment process have been subjected to, have so far found little use. The common practice was to make alloys that have been subjected to an aging heat treatment alone. An inadequacy of these alloys is the diversity of their properties from piece to piece, in particular between thick and thin pieces.

The magnesium cast or wrought alloy, which is heat-treated by homogenization annealing and hardening at 150 to 250 ⁰ C and contains rare earth metals, consists of 0.5 to 3.5% rare earth metals with at least 60% neodymium and less than 25% lanthanum and cerium, 1.5 to 3.5% silver, 0 to 1.0% zirconium, 0 to 2.0% manganese,

709 608/354

O to 0.5% zinc, 0 to 1.0 ° / ₀ cadmium, 0 to 6.0% lithium, 0 to 0.8 ° / ₀ calcium, 0 to 2.0% gallium, from 0 to 2.0% Indium, 0 to 5.0% thallium, 0 to 1.0% lead, 0 to 1.0% bismuth, 0 to 5.0% thorium, the remainder magnesium.

In a preferred embodiment, the alloy consists of 2 to 3% silver, 2 to 3% rare Earth metals, 0.4 to 1% zirconium, the remainder magnesium. In another preferred embodiment there is the alloy of 1.5 to 3.0% silver, 0.5 to 2.0% rare earth metals, 1.0 to 2.5% thorium, 0.4 to 1.0% zirconium, the remainder magnesium. When using the alloy according to the invention for production forged parts, the sum of zirconium and manganese is preferably at least 0.4%, the maximum allowable amount of each of these two metals being supplemented by the amount of the other is.

The homogenization annealing is preferably carried out at a temperature of 100 degrees below the solidification temperature up to this temperature for at least half an hour and hardening at a temperature of 150 to 250 ° C for at least one hour.

The two-stage heat treatment gives the alloys according to the invention a yield point, which is higher than that of the generally used alloys and a greater uniformity of properties between thick and thin pieces. Furthermore, the alloys according to the invention do not tend to to form cracks or pores when heated, and they are also easy to weld.

The element silver has a specific effect in the alloys according to the invention in that it The reaction of the alloying partners in the two-stage heat treatment is improved to the point that the favorable properties listed above actually occur. This effect was alone with Silver achieved in combination with rare earth metals, but not with any other element.

The rare earth metals which can be used for the purposes of the present invention can be present in known mixtures, such as e.g. As "mischmetal" or "didymium" (trade names), or alternatively any single element or group of elements with atomic numbers ranging from 57 to 70 may be used. Yttrium and thorium, although not from this group, can also be used as hardening additives such as rare earth metals in the context of the invention. As indicated below, particular advantages have been obtained by using selected elements or groups of such elements for specific purposes.
If zirconium is present in the alloy, should

ίο elements that have high melting point compounds form with zirconium and thereby prevent grain refinement, be absent.

Iron can be viewed as an impurity for the purposes of the present invention and in the Be present in amounts that are usually allowed in magnesium alloys (up to 0.05%, but much less than this amount if the alloy contains zirconium). Others insoluble or almost insoluble elements, such as copper, add to this

ao tend to make the alloy brittle, should preferably be absent, but they can be in quantities, that do not significantly affect ductility, for example to 0.25%.

The effects of silver in alloys according to the

The invention can be seen from Table I, which shows the properties of magnesium-mischmetal-zirconium-thorium and magnesium-neodymium-zirconium alloys with and without the addition of silver. The mischmetal used was of the commonly used type containing about 50% cerium. The "neodymium" was produced from a technical oxide mixture, which contained a nominal share of 75% neodymium oxide. The term "neodymium" is used here to distinguish the material from "Didymiurno-Mischurtgen, which contain smaller amounts of neodymium. However, the invention includes didymium and all other mixtures of rare earth metals.
The mechanical property values given relate to bars cast in standard sand for test bars with a diameter of 2.54 cm and a length of 15.24 cm, which were machined to a diameter of 1.433 cm and a length of 5.08 cm for the test . The yield point was determined using the "offset" method.

Table I.

alloy MM
Vo Zusai
Th
Vo nmense
Nd ¹ )
% removal
Zr ^! )
V. Ag
Vo Heat treatment Stretch
border
<* 0, l
kp / mm ¹ tensile strenght
If
kp / mm ² fracture
elongation ö
Vo A. 0.45 - - 0.6 - 2 hours at about 560 to
Annealed to 570 ⁰ C, in the water
deterred 7.9 23.4 12th B. 0.45 - - 0.6 2.95 24 hours at 175 ° C warm
outsourced 12.7 25.7 20.5 C. 1.34 0.6 2 hours at about 57O ° C
annealed, abraded in water
frightens 9.0 21.4 7th D. 1.42 - - 0.6 2.19 24 hours at about 175 ° C
artificially aged 15.0 24.4 7.5

MM = mischmetal.

^l ) The values in this column give the total content of rare earth metals, of which about 75 Vo is neodymium. ^a ) Nominal salary.

Table I (continued)

alloy MM
Vo Zusai
Th
· / » nmense
Nd ¹ ) removal
Zr ² )
° / o Ag
Vo Heat treatment Stretch
border
«Ό.Ι
kp / mm * tensile strenght
a _B
kp / mm ² fracture
elongation δ
Vo E. 1.40 1.20 - 0.6 - 2 hours at about 550 to
Annealed to 570 ⁰ C, in the water
deterred 9.9 23.2 10 F. 1.44 1.65 - 0.6 2.04 16 hours at 200 to 225 ° C
artificially aged 17.1 26.1 6.5 G 3.08 0.6 8 hours at about 540 to
Annealed at 560 ° C in water
deterred 12.8 23.9 3 H - - 3.15 0.6 1.96 8 to 16 hours at about
Artificial aged 200 ^{0 C} 18.6 26.4 4th

MM = s misch metal.

¹ J The values in this column give the total content of rare earth metals, of which about 75 Vo is neodymium. ² ) Nominal salary.

It should be noted that in each case the addition of silver leads to a noticeable improvement in the properties, in particular with regard to the yield point. Of the four silver-containing compositions listed in Table I, alloys F and H show yield strengths that exceed ^{15.5 kgf / mm 2.} These alloys are particularly suitable for casting. The properties of the alloys are particularly surprising and exceed those of all known magnesium alloys which have acceptable casting properties.

The alloys can be turned into the kneadable form by the usual techniques of hot and cold working be convicted. A guide to the properties that can be obtained with kneadable alloys is given by the results of the tensile tests given in Table II. Table II relates on pieces kneaded with a hammer from cast ingots 6.35 cm in diameter.

Table II

alloy Together
Rare composition
silver Zirko
nium Heat treatment Stretch
border tensile strenght
If fracture
strain
δ Earth metal Vo ° / o kp / mm ⁸ kp / mm ² % J 0.83%
Mischmetal 1.88 0.6
nominal V _{ge for 2} hours at about 570 ° C
glows, quenched in oil,
24 hours at about 175 ° C
artificially aged 27.1 30.8 4.5 Kl 1.25%
Neodymium ³ ) 2.5 0.6
nominal 1 hour at about 53O ° C ge
glows, subsided in water
frightens, 8 hours at about
Artificial aged 220 ^{0 C} 30.6 34.0 4th K2 1.37%
Neodymium ³ ) 2.5 0.6
nominal 1 hour at about 535 ° C ge
glows, subsided in water
frightens at 16 hours
about 200 ⁰ C warm
stores 35.8 37.6 2

³ ) denotes a mixture of rare earth metals, which contains about 75% neodymium. This designation is used to distinguish this rare earth metal mixture from didymium, which may have a lower content of neodymium.

The benefits resulting from the addition of silver could not be expected, since silver is used as a Metal is considered to be, even when used in substantial amounts, not a noteworthy one Has a tendency to harden magnesium.

Table III shows that the yield strength of a magnesium-zirconium alloy, the 2% silver (typical for

the amounts used in alloys according to the invention) but not rare earth metals contains, is very low, even after a two-stage Heat treatment, and no better than that of a simple magnesium-zirconium alloy. In relation to its tendency to harden and solidify, silver is much less effective than zinc, for example.

Table III
The properties of cast magnesium-zirconium alloys with and without silver

alloy Together
Zr ¹ ) netting
Ag Heat treatment Stretch limit
kp / mm ² tensile strenght
If
kp / mm ² fracture
elongation <5 L.
M. 0.6
0.6 2.13 Annealed for 2 hours at 570 ° C, in
Water quenched
16 hours at about 200 ^° C. warm
outsourced 4.8
6.1 16.6
19.5 21.5
18th

⁴ ) Nominal salary.

Alloys of the type described retain their properties well when cast in thick pieces are and are superior to the known alloys in this respect. The properties of a magnesium-silver-mischmetal-thorium-zirconium alloy tion (alloy N), on test bars and in heavy blocks with a diameter of 10.16 cm in Table IV with those made from a conventional magnesium-zinc-zirconium alloy (alloy O) and a magnesium-zinc-thorium-zirconium alloy (alloy P), produced under the same conditions are cast, compared.

The values given are mean values of a number of test results.

Table IV

Heat treatment Properties of test bars tensile strenght fracture Properties of blocks tensile strenght fracture 2.54 cm in diameter kp / mm ² elongation δ 10.16 cm in diameter kp / mm ⁸ elongation <5 alloy Stretch limit 24.1 7o Stretch limit 20.6 % 8 hours at »0.1 2.5 σ _ο , ι 1 about 550 ⁰ C ge kp / mm ² kp / mm ² Alloy N glows in water 17.6 15.3 Mg 2.03%, deterred, Ag 1.27%, 16 hours at Mischmetal about 200 ° C 1.57%, artificially aged 25.1 21.9 Th 0.6%, Zr like alloy N. 6th 3.4 Alloy O 14.1 27.6 11.3 20.8 Mg 4.5%, 2 hours about 12th 2.8 Zn 0.6%, Zr 330 ⁰ C, air-cooled Alloy P cools, and 15.0 11.4 Mg 5.57ο, 16 hours about Zn 1.8%, 200 ° C Th 0.67o, Zr

The properties of a Sandgußstücken Mg 2.56 7o - 2.73 Ag ° / ₀ - Nd 0.7 7 ₀ - Zr - alloy were also studied and compared with those of test bars prepared from Sandgußstücken, which were cast from the same heat .

The results of the yield strength test with specimens obtained from a heat-treated cast body that had parts up to 3 inches thick are the following:

Table V

description

Yield strength Ct ₀₁₁

kp / mm ²
Maximum mean minimum tensile strength a _B

kp / mm ²
Maximum mean I minimum

Elongation at break δ

ο / / ο

Maximum mean I minimum

Samples from castings
(Establish mean values
7 attempts)

Individual test bars
(actual values)

18.3

17.5

17.2
17.2

16.6 25.8

25.0

26.2
24.6

22.9

ίο

The heat treatment lasted 4 hours at 530 ° C. It was quenched in water and 8 hours Artificially aged at 200 ° C. Alloys of the type under consideration have creep resistance at temperatures of the order of 200 ° C, which is comparable to that of magnesium-mixed metal-zirconium alloys (with or without the addition of zinc) that are commonly used.

The alloy ZRE1 (DTD 708) is the most widely used of these alloys. The following table shows that a Mg 2.5% -Ag 2.2% -Nd 0.6% -Zr alloy has a far superior combination of static strength at room temperature and creep resistance at elevated temperature than the previously used ZREI alloy . Incidentally, the Mg 2.5 ⁰ I ₀ -Ag 2.2 ° / ₀ -Nd 0.67 ₀ -Zr alloy shows a much higher yield point than ZRE1 when it was tested at temperatures of 200 to 250 ° C, that is Temperatures at which castings made of ZREl are often used operationally.

IO

Table VI

warmth
treatment Check
temperature Stretch
border train
strength fracture
strain
S. Train that Train that <Ό, ι If O is required, is required alloy by 0.1 "/ Ό
To crawl
in 100 hours by 0.1 ■> / "
To crawl
in 500 hours ⁰ C kp / mm ² kp / mm ^a % at about 200 ^° C at about 200 ^° C 16 hours space to create to create about 180 ° C temperature 8.5 15.5 4th kp / mm ² kp / mm Mg 2.7% 200 ° C 7.0 12.6 29 S. E 2.27 ₀ 250 ⁰ C 5.9 10.7 39 Zn 0.6% 6.5 5.7 Zr 4 hours about space ZREl) 53O ⁰ C ab temperature 17.5 25.3 3 2.57 mg Ag ₀ frightens 200 ° C 15.0 18.9 24 2.2% Nd 0.6% 8 hours about 250 ° C 10.8 14.0 33 Zr (invent 200 ⁰ C 7.4 6.7 proper Legie 8 hours about space tion) 550 ° C temperature 16.7 24.0 4th Mg 2.17o Ag frightens 200 ⁰ C 14.2 17.7 11 1.1% MM 16 hours 250 ° C 13.2 15.7 18.5 1.7% Th 0.6% about 250 ° C 9.6 Zr (invent proper Legie tion)

The rare earth metals are the main hardening agents in these alloys, and the content at them is generally of the same order of magnitude like the maximum solubility of these metals in solid magnesium, so that maximum responsiveness on heat treatment is achieved. However, more or less of these metals can be used depending on the form in which the alloy is used and the combination of those desired Properties. For example, it can be advantageous to use a smaller amount of rare earth metals to be used in wrought as in cast alloys. On the other hand, it can if a high hardness is desired, it should be expedient to use a larger proportion of rare earth metals than in solid solution can be included and in other cases in order to improve ductility the Sacrificing the yield strength (by using a reduced content of rare earth metals, as in alloy B of Table I).

The silver content is most advantageously chosen in the range of 2.3 7 ".

The temperature and duration of the treatment are generally as follows:

For homogenization annealing, the temperature can range from 100 degrees below the solidus temperature to approximately this temperature and the duration can be ¹ _1/2 hours up to 12 hours or more. For the hardening treatment, the temperature can be between 150 and 250 ^° C. and the duration can be 1 to 16 hours or more.

In all alloys that have a composition within the scope of the invention, the double heat treatment produces a yield strength of at least 12 kp / mm ² . The exact temperatures and times depend on the specific composition. At most, a few tests must be made to determine the optimum.

Claims (5)

Patent claims: 1. By homogenization annealing and hardening at 150 to 250 ⁰ C, rare earth metal containing magnesium cast or wrought magnesium alloy, consisting of 0.5 to 3.5% rare earth metals with at least 60% neodymium and less than 25% lanthanum and cerium , 1.5 to 3.5% silver , 0 to 1.0% zirconium, 0 to 2.0% manganese, 0 to 0.5% zinc, 0 to 1.0% cadmium, 0 to 6.0% lithium , 0 to 0.8% calcium, 0 to 2.0% gallium, 0 to 2.0% indium, 0 to 5.0% thallium, 0 to 1.0% lead, 0 to 1.0% bismuth, 0 up to 5.0 70 thorium, remainder magnesium. 2. Alloy according to claim 1, consisting of 2 to 3% silver, 2 to 3% rare earth metals, 0.4 to 1% zirconium, the remainder magnesium. 3. Alloy according to claim 1, consisting of 1.5 to 3.0% silver, 0.5 to 2.0% rare earth 709 608/354 metals, 1.0 to 2.5 ° / ₀ thorium, 0.4 to 1.0 ° / ₀ zirconium and the balance magnesium. 4. Use of the alloy according to claims 1 to 3 for the production of forged Parts, where the sum of zirconium and manganese is at least 0.4% and the maximum allowable amount of each of these two metals is limited by the amount of the other. 5. Process for the heat treatment of a casting or a forged article made of an alloy according to one of Claims 1 to 4, characterized in that the homogenization annealing at a temperature of 100 degrees below the solidus temperature up to this temperature for at least half an hour and the curing is carried out at a temperature of 150 to 250 ⁰ C for at least one hour. Considered publications: German Patent No. 932,987; Patent Specification No. 755 918 of the Office for Invention and Patents in the Soviet Zone of Occupation Germany; British Patent Nos. 637 040, 759 411. 709 608/354 6.67 © Bundesdruckerei Berlin