U.S. patent application number 13/352595 was filed with the patent office on 2012-08-02 for single-phase solid solution cast or wrought magnesium alloys.
This patent application is currently assigned to Helmholtz-Zentrum Geesthacht Zentrum fun Material-und Kustenforschung GmbH. Invention is credited to Norbert Hort, Yuanding Huang, Karl U. Kainer, Qiumin Peng.
Application Number | 20120195787 13/352595 |
Document ID | / |
Family ID | 45715076 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120195787 |
Kind Code |
A1 |
Huang; Yuanding ; et
al. |
August 2, 2012 |
SINGLE-PHASE SOLID SOLUTION CAST OR WROUGHT MAGNESIUM ALLOYS
Abstract
The present invention relates to single-phase solid solution
magnesium alloys suitable for the applications as cast or wrought.
These alloys are prepared by multi-microalloying with rare earth
elements (including gadolinium, yttrium, dysprosium, samarium,
lanthanum, cerium, neodymium and praseodymium). Each alloy contains
0.5 to less than 5 wt. % rare earth elements with a content of
0.05-2.0% by weight. The total amount of rare earth elements is
controlled below 5% by weight in order for economical
considerations. The amount of grain refiner calcium or zirconium is
in the range of 0.05-0.6% by weight. These alloys can be prepared
by die casting, permanent casting, chill casting, semi-solid
processes, continuous casting and continuous twin roll casting.
Inventors: |
Huang; Yuanding;
(Geesthacht, DE) ; Peng; Qiumin; (Qinhuangdao,
CN) ; Hort; Norbert; (Luneburg, DE) ; Kainer;
Karl U.; (Hohnstorf, DE) |
Assignee: |
Helmholtz-Zentrum Geesthacht
Zentrum fun Material-und Kustenforschung GmbH
Geesthacht
DE
|
Family ID: |
45715076 |
Appl. No.: |
13/352595 |
Filed: |
January 18, 2012 |
Current U.S.
Class: |
420/406 ;
164/113; 164/122; 164/459; 164/47; 164/480; 420/405 |
Current CPC
Class: |
C22C 23/04 20130101;
C22C 23/06 20130101 |
Class at
Publication: |
420/406 ;
420/405; 164/480; 164/113; 164/47; 164/122; 164/459 |
International
Class: |
C22C 23/00 20060101
C22C023/00; B22D 11/00 20060101 B22D011/00; B22D 17/00 20060101
B22D017/00; B22D 27/04 20060101 B22D027/04; C22C 23/06 20060101
C22C023/06; B22D 11/06 20060101 B22D011/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 1, 2011 |
EP |
EP11152827.9 |
Claims
1. A magnesium alloy comprising 0.5 wt. % to less than 5.0 wt. % of
at least two elements selected from the group consisting of La, Ce,
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, wherein
the content of each of said elements La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, if present, is from 0.05 to
2.0% by weight, based on the total weight of the alloy.
2. The magnesium alloy of claim 1 further comprising an element
selected from the group consisting of Zr, Ca, Zn, and mixtures
thereof.
3. The magnesium alloy of claim 1 which contains no aluminium.
4. The magnesium alloy of claim 1 consisting of (a) Mg; (b) 0.5 wt.
% to less than 5.0 wt. % of at least two elements selected from the
group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,
Tm, Yb, Lu and Y; and (c) optionally Zr, Ca and/or Zn; wherein the
content, based on the total weight of the alloy, of each of said
elements La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu
and Y, if present, is from 0.05 to 2.0% by weight; and wherein the
content, based on the total weight of the alloy, of each of said
elements selected from the group consisting of Zr, Ca and Zr, if
present, is from 0.05 to 0.6 wt. %; the remainder being
magnesium.
5. The magnesium alloy according to claim 1, wherein Gd is present
in an amount by weight of 0.05 to 2.0%.
6. The magnesium alloy according to claim 1, wherein Y is present
in an amount by weight of 0.05 to 2.0%.
7. The magnesium alloy according to claim 1, wherein Dy is present
in an amount by weight of 0.05 to 2.0%.
8. The magnesium alloy according to claim 1, wherein Sm is present
in an amount by weight of 0.05 to 2.0%.
9. The magnesium alloy according to claim 1, wherein La is present
in an amount by weight of 0.05 to 0.3%.
10. The magnesium alloy according to claim 1, wherein Ce is present
in an amount by weight of 0.05 to 0.3%.
11. The magnesium alloy according to claim 1, wherein Nd is present
in an amount by weight of 0.05 to 0.3%.
12. The magnesium alloy according to claim 1, wherein Pr is present
in an amount by weight of 0.05 to 0.3%.
13. The magnesium alloy according to claim 1, wherein Ca is present
in an amount by weight of 0.05 to 0.4%.
14. The magnesium alloy according to claim 1, wherein Zr is present
in an amount by weight of 0.2 to 0.6%.
15. Use of the magnesium alloys according claim 1 as casting
magnesium alloys, wrought magnesium alloys, or degradable
biomaterials.
16. The magnesium alloy of claim 2, wherein Gd is present in an
amount by weight of 0.05 to 2.0%.
17. A method of improving mechanical properties in a magnesium
alloy comprising forming a magnesium alloy part from the
composition of claim 1 by a method selected from the group
consisting of die casting, permanent casting, chill casting, a
semi-solid process continuous casting, and continuous twin roll
casting.
18. A method improving the formability and/or room temperature
ductility of a magnesium alloy part comprising forming the
magnesium alloy part from the magnesium alloy composition of claim
1.
19. A method of purifying a magnesium alloy melt comprising forming
a magnesium alloy part from the magnesium alloy composition of
claim 1 to form a magnesium alloy ingot, whereby the rare earth
elements from the magnesium alloy composition interact with one or
more elements selected from hydrogen, oxygen, chlorine, iron,
cobalt or copper, thereby forming intermetallic compounds that
settle at the bottom of the ingot for removal.
20. A method of improving corrosion resistance of a magnesium alloy
comprising forming a magnesium alloy part from the composition of
claim 1.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to cast and wrought
single-phase solid solution magnesium alloys with high mechanical
properties, formability and corrosion resistance.
BACKGROUND
[0002] Magnesium alloys have not yet been widely accepted by car
manufacturers. Most of the technical barriers preventing magnesium
alloys from widespread applications arise from the low ductility
and toughness at low temperatures, poor corrosion and creep
resistance at high temperatures. Their present commercial products
are normally fabricated by high pressure die casting. The use of
wrought magnesium alloys is limited because of its poor formability
and corrosion resistance.
[0003] It will be necessary to improve the low-temperature
formability of wrought magnesium alloys in order to obtain a higher
acceptance of these alloys in industry. Low ductility and low
toughness are due to the intrinsically brittle nature of the
hexagonal close-packed crystal structure. A further issue which
hinders the acceptance of wrought magnesium alloys is their poor
corrosion resistance.
[0004] Most commercial wrought magnesium alloys belong to
magnesium-aluminium (Mg--Al) and magnesium-zinc (Mg--Zn) series.
The later developed magnesium-rare earth (Mg-RE) series such as
WE43 (Mg-4.1Y-2.2Nd-1HRE-0.5Zr) and WE54
(Mg-5.2Y-1.7Nd-1.7HRE-0.4Zr) alloys were not accepted by the
industry due to their high price arising from the high content of
rare earth elements.
[0005] The alloys of magnesium-aluminium series are the most
commonly used in wrought applications for their relative ease of
extrusion and adequate mechanical properties, but they suffer from
both a pronounced asymmetry in the yield behaviour and a relatively
narrow processing window. Due to the lower eutectic temperature
437.degree. C. for magnesium-aluminium alloys, the hot processing
temperatures are normally selected below 350.degree. C. and the
processing speeds are not so high. If selecting high temperatures
more than 350.degree. C. with high processing speeds, the eutectic
phases dissolve again, leading to the occurrence of hot cracking
and bad surface quality of the products. In addition, until now,
the methods for refining the as-cast microstructures of
magnesium-aluminium alloys are not satisfying and not widely
accepted by the industry.
[0006] Since magnesium-zinc series contain no aluminium, their
as-cast microstructure can be effectively refined by the addition
of zirconium. However, these magnesium-zinc alloys still have very
limited applications because they are susceptible to microporosity
during casting. The addition of zinc in magnesium increases the
susceptibility to hot tearing. Moreover, due to the high content of
zinc, it was considered that these alloys are difficult to be
welded.
[0007] Therefore, at present only AZ31 (Mg-2.9Al-0.8Zn) alloy is
used in industry to an significant extent. However, AZ31
(Mg-2.9Al-0.8Zn) alloy exhibits some problems with
recrystallisation during the hot working and has insufficient
mechanical and corrosion properties.
[0008] It is therefore the object of the present invention to
develop new magnesium alloys with high corrosion resistance and
formability using innovative alloy design concept.
SUMMARY OF THE INVENTION
[0009] Accordingly, the present invention provides a magnesium
alloy comprising 0.5 wt. % to less than 5.0 wt. % of at least two
elements selected from the group consisting of La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y, wherein the content
of each of said elements La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb, Lu and Y, if present, is from 0.05 to 2.0% by
weight, based on the total weight of the alloy.
[0010] Preferably, the amount of the at least two elements selected
from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb, Lu and Y, is from 1.0 wt. % to less than 5.0
wt. %.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The strengthening effects of rare earths in the previous
magnesium alloys have been explained by two mechanisms, precipitate
strengthening and solid solution strengthening. Precipitate
strengthening, especially the age hardening, has been emphasised to
improve the mechanical properties. Without being bound to any
theory, it is believed that in alloys of the present invention,
precipitate strengthening is avoided and that solid solution
strengthening is the main mechanism which improves the mechanical
properties in the magnesium alloys according to the present
invention.
[0012] It is further believed that the solid solution strengthening
depends on the contents of alloying elements in the matrix of
magnesium and the difference in atomic radius between the alloying
elements and magnesium such that a high content of alloying
elements and large difference in atomic radius increase the effect
of solid solution strengthening.
[0013] In addition, it has been found that there exists a
synergistic effect caused by the interaction of the different rare
earth elements. With the same total content of rare earth elements
in the magnesium alloy, the improvement in mechanical properties is
higher when two different rare earth elements are present in
comparison to the improvement achieved with the presence of only on
e rare earth element.
[0014] Furthermore, the addition of rare earth elements can purify
the melt during casting. The addition of rare earth elements can
remove impurity elements such as hydrogen, oxygen, chlorine, etc.
Moreover, they interact with iron, cobalt, nickel or copper
elements during melting, and these elements are removed by the
formation of intermetallic compounds which settle at the bottom of
the ingot. The decrease of impurities in the matrix also
contributes to the high corrosion resistance.
[0015] Preferably, the magnesium alloy of the present invention
further comprises an element selected from the group consisting of
Zr, Ca, Zn, and mixtures thereof. The stress corrosion of magnesium
alloys could be alleviated by the addition of zirconium (Zr) and
rare earth elements. Zirconium (Zr) can be used as an element to
decrease the stress corrosion cracking.
[0016] Preferably, the magnesium alloys according to the present
invention contain no aluminium; therefore, their as-cast
microstructure can effectively be refined by the addition of
zirconium or calcium.
[0017] In principle, two groups of rare earth elements can be
classified in periodic table: light rare earth elements and heavy
rare earth elements. In each group, rare earth elements have the
similar chemical and physical properties. Due to the similar
properties of yttrium and scandium to heavy rare earth elements,
for the purposes of the present invention Y and Sc are treated as
they were heavy rare earth elements. The light rare earth elements
include samarium, lanthanum, cerium, neodymium, and praseodymium,
and the heavy rare earth elements include gadolinium, yttrium and
dysprosium. Besides the rare earth elements, zirconium and/or
calcium are preferably added as a grain refiner.
[0018] The magnesium alloys of the present invention comprise 0.5
wt. % to less than 5.0 wt. % of at least two rare earth elements
with a content of 0.05 to 2.0% by weight of each of the rare earth
elements. The total content of rare earths is maintained below 5
wt. %, mainly for economical reasons. The content of grain refiner
calcium and/or zirconium is preferably in the range of 0.05-0.6% by
weight.
[0019] The manufacturing processes of the magnesium alloys
according to the present invention are not restricted. The alloys
can be prepared by die casting, permanent casting, chill casting,
semi-solid processes, continuous casting or continuous twin roll
casting.
[0020] The magnesium alloys according to the present invention
exhibit excellent room temperature ductility with a value of about
25%.
[0021] Tensile tests show that as-cast alloy Mg0.4Gd0.4Y0.4Dy0.2Zr
and Mg0.4Gd0.4Y0.4Dy0.2Zn0.2Zr exhibit excellent ductility. The
elongation is more than 20%, which is much higher than that of AZ31
alloy. These two alloys have shown a good deformability.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0022] The above and other characteristics and advantages of the
invention will be more readily apparent through the following
examples, and with reference to the appended drawings, where:
[0023] FIG. 1 compares the optical microstructure of the
investigated, as cast alloys ((a) Mg, (b) Mg-0.4Y, (c)
Mg-0.4Gd-0.4Y, (d) Mg-0.4Gd-0.4Y-0.4Dy, (e)
Mg-0.4Gd-0.4Y-0.4Dy-0.2Zr, (f) Mg-0.4Gd-0.4Y-0.4Dy-0.2Zn, (g)
Mg-0.4Gd-0.4Y-0.4Dy-0.2Ca, (h) Mg-0.4Gd-0.4Y-0.4Dy-0.2Zn-0.2Zr and
(I) AZ31);
[0024] FIG. 2 shows the grain size, hardness and corrosion
properties of the investigated alloys;
[0025] FIG. 3 shows the tensile properties of selected as-cast
alloys; and
[0026] FIG. 4 shows the microstructural situation and the
microsegregation of the alloying elements.
EXAMPLES
[0027] Three rare earth elements gadolinium, yttrium, dysprosium
with high solubility in magnesium were selected to develop the
single-phase solid solution magnesium alloys. Table 1 lists the
compositions of the investigated alloys. A conventional alloy,
Mg-3Al-1Zn (AZ31), was included for comparison.
[0028] All alloys were prepared by zone solidification. Their
optical microstructures are shown in FIG. 1. The average grain size
decreases with the increment in the content of rare earths.
Compared to the gadolinium and dysprosium, the yttrium element is
the most effective element to decrease the grain size. The average
grain sizes of E and H alloys containing zirconium are 55 .mu.m and
67 .mu.m. The average grain size of Mg-3Al-1Zn (AZ31 is 480
.mu.m.
TABLE-US-00001 TABLE 1 Nominal compositions of the investigated
alloys (Composition (weight percent, wt. %) Alloys Mg Gd Y Dy Zn Al
Zr Ca A--Pure Mg 100 -- -- -- -- -- -- B--Mg0.4Y Bal* -- 0.4 -- --
-- -- C--Mg0.4Gd0.4 Y Bal 0.4 0.4 -- -- -- -- D--Mg0.4Gd0.4 Y0.4Dy
Bal 0.4 0.4 0.4 -- -- -- E--Mg0.4Gd0.4Y0.4DyO.2Zr Bal 0.4 0.4 0.4
-- -- 0.2 F--Mg0.4Gd0.4 Y0.4Dy0.2Zn Bal 0.4 0.4 0.4 0.2
G--Mg0.4Gd0.4 Y0.4Dy0.2Ca Bal 0.4 0.4 0.4 0.2 H--Mg0.4Gd0.4 Bal 0.4
0.4 0.4 0.2 -- 0.2 Y0.4Dy0.2Zn0.2Zr I--AZ31 Bal -- -- -- 1.0 3.0 --
*Balance.
* * * * *