CN101228286A - Hpdc magnesium alloy - Google Patents

Abstract

A magnesium - rare earth - yttrium - zinc alloy consists of 0.2-1.5% by weight zinc and rare earth(s) (RE) and yttrium in amounts which fall within a quadrangle defined by lines AB, BC, CD and DA wherein: A is 1.8% RE - 0.05% Y, B is 1.0% RE - 0.05% Y, C is 0.2% RE - 0.8% Y, and D is 1.8% RE - 0.8% Y.

Description

Hpdc magnesium alloy

Invention field

The present invention relates to magnesium alloy, more specifically relate to pass through the magnesium alloy of Hpdc (HPDC) method casting.

Background of invention

Along with fuel limitation consumption and reduction improve day by day to the requirement of airborne release objectionable impurities, the automaker is seeking the higher vehicle of development fuel efficiency, and the gross weight that reduces vehicle is the key of realizing this goal.What play a major role for the weight of any vehicle is other member of engine and power train.The most important member of engine is a cylinder body, and it accounts for 20～25% of engine gross weight.It is to replace traditional graphitic pig iron body to introduce aluminum alloy cylinder body that past significantly reduces weight, if the temperature that use can stand in the engine operation process to be produced and the magnesium alloy of stress can realize that then weight further reduces about 40%.Can think a kind of like this development of alloy, in conjunction with desired high-temperature mechanical property, consider that before the magnesium power pack manufacturing that is suitable for be necessary with the effective production technique of cost.

HPDC is used for the mass-produced high-efficiency method for producing of light alloy member.Although the casting integrity of sand mold casting and low pressure/gravity metal mold casting generally is higher than HPDC, HPDC is a kind of cheap technology for the mass production of comparatively large vol.Prevailing magnesium base HPDC alloy be AM50 (95%Mg, 5%Al), AM60 (94%Mg, 6%Al) and AZ91 (90%Mg, 9%Al and 1%Zn).Unfortunately, in these alloys, do not have under a kind of temperature that is applicable to raising.

HPDC in the automaker of North America be popularize and Europe and the Asia become the main technique that is used for the cast aluminium alloy power pack.In the last few years, development high temperature magnesium alloy mainly concentrated on the HPDC processing route and had developed several alloys.HPDC is considered to realize that therefore high throughput rate reduces the good selection scheme of manufacturing cost.

The requirement priority date is that the US3718460 on December 4th, 1967 relates to the magnesium-aluminum-silicon alloy of a kind of " being particularly suitable for die casting ".This alloy " basically by the silicon that contains 0.4～1.5% weight of having an appointment, the aluminium of about 3.5～about 7% weight is up to the manganese of about 1% weight and is up to the magnesium institute of the zinc of about 2% weight " is formed.US3718460 does not mention yttrium.

The requirement priority date is magnesium-zincium-rare earth (Mg-Zn-RE) alloy that the PCT/GB96/00261 (W096/24701) in February 6 nineteen ninety-five relates to a kind of suitable HPDC, its middle-weight rare earths has carried out specific qualification from the elemental range angle, but " does not plan to comprise element such as yttrium." so yttrium got rid of especially as the alloying constituent of this HPDC alloy.

Require on December 15th, 1999 for the US6322644 of right of priority relates to a kind of magnesium-Ji alloy for die casting with improved high-temperature behavior, this alloy is by 2～9% aluminium, 0.5～7% strontium, 0～0.6% manganese, 0～0.35% zinc and remainder magnesium are formed.In US6322644, do not mention yttrium.

The various Magnuminiums that contain yttrium propose for many years.

Requiring priority date is that the GB 1067915 on October 26th, 1963 mentions " grain refining that the adding that has now found that yttrium can cause further containing the zirconium magnesium alloy ".This patent relates generally to contain 0.1～1% zirconium (Zr), 0.1～10% yttrium (Y) and be up to 10% at least a magnesium alloy that is selected from the additional alloying element of beryllium (Be), plumbous (Pb), cadmium (Cd), calcium (Ca), cerium (Ce), copper (Cu), silver (Ag), thallium (Tl), thorium (Th), bismuth (Bi) and zinc (Zn).

Magnesium alloy ML10 is USSR (Union of Soviet Socialist Republics) development, be used for temperature be up to 250 ℃ aircraft mo(u)lded piece for many years, ML10 is a kind of high-intensity Mg-Nd-Zn-Zr alloy.The ML19 alloy is equally based on the Mg-Nd-Zn-Zr system but contain Y in addition.

People's such as Mukhina title is that one piece of paper publishing of " Investigation of the Microstructure and Propertiesof Castable Neodymium and Yttrium-Bearing Magnesium Alloys at ElevatedTemperatures " is in " science and thermal treatment ", the 39th volume, in 1997, point out that typical case's composition (% weight) of ML10 and ML19 alloy is:

ML10 ML19

Neodymium (Nd) 2.2～2.8 1.6～2.3

Yttrium (Y) does not have 1.4～2.2

Zirconium (Zr) 0.4～1.0 0.4～1.0

Zinc (Zn) 0.1～0.7 0.1～0.6

Magnesium (Mg) surplus surplus

Foreign matter content is:

Iron (Fe)＜0.01

Silicon (Si)＜0.03

Copper (Cu)＜0.03

Nickel (Ni)＜0.005

Aluminium (Al)＜0.02

Beryllium (Be)＜0.01

ML10 and ML19 are two kinds of sand mold casting alloys, and two kinds of alloys are not all found to be accepted by industry as the HPDC alloy.

Require priority date be on March 14th, 1973 GB1378281 " relate to magnesium base light structure alloy, particularly those be used to produce in use stand the parts that heat ".This alloy contains 0.8～6.0%Y, 0.5～4.0%Nd, and 0.1～2.2%Zn, 0.31～1.1%Zr is up to 0.05%Cu, is up to 0.2% manganese (Mn) and surplus magnesium.Relevant US patent, US4116731, the alloy of claimed a kind of same composition, this alloy are the alloys of a kind of warp " thermal treatment and timeliness ", wherein " neodymium and the yttrium additive that are not less than neodymium and yttrium total amount 50% enter sosoloid after thermal treatment "; This alloy, in about 535 ℃ of following thermal treatments after 4～8 hours, in air, cool off, then in about 200 ℃ of following timeliness 12 hours.

The requirement priority date is that the magnesium alloy that the US4401621 on May 25th, 1981 relates to is made up of following:

" (a) the yttrium composition of 1.5～10% weight, its by the yttrium of at least 60% weight and remainder (if any) heavy rare earth metal is formed and

(b) the neodymium composition of 1～6% weight, it is not more than the lanthanum of 25% weight and all basically remainder (if any) praseodymium compositions by the neodymium of at least 60% weight,

The remainder of alloy is made up of magnesium ".

Requiring priority date is the US 6767506 " relate to be adapted at use up under 250～300 ℃ the temperature Magnuminium " on January 10th, 2002.The alloy of US 6767506 contains 2.7～3.3% Nd, and the amount of Y is up to 2.6%, 0.2～0.8% Zr, 0.2～0.8% Zn, 0.03～0.25% Ca, 0～0.001% Be and at least 92% Mg.These alloys allegedly are particularly suitable for sand mold casting, permanent mold casting and direct chill casting, push subsequently and/or forge.Do not illustrate that in US 6767506 this alloy is suitable for HPDC.

The Mg-RE-Y alloy can be used as gravitational casting and the sand mold casting alloy uses, can be by thermal treatment to reach desired characteristic.The addition of their RE and Y is very high, and purpose is forming Mg-RE type crystal boundary phase and two precipitated phases, i.e. Mg ₁₂Nd and Mg ₂₄Y ₅Phase.Even at room temperature Y also has very high solubleness in Mg, and so high Y content is to obtain height to precipitate necessary.Known to the inventor, the Mg base alloy that does not have discovery to contain Y can be accepted by industry as the HPDC alloy.

Summary of the invention

First aspect the invention provides a kind of magnesium-rare earth-yttrium-zinc alloy, and it is made up of following:

Rare earth (RE) (one or more) and yttrium (Y), its amount falls in the tetragon that is limited by line segment AB, BC, CD and DA, wherein:

A is 1.8%RE-0.05%Y,

B is 1.0%RE-0.05%Y,

C be 0.2%RE-0.8%Y and

D is 1.8%RE-0.8%Y;

0.2～1.5% zinc (Zn);

0～0.25% aluminium (Al);

0～0.2% zirconium (Zr);

0～0.3% manganese (Mn);

0～0.1% oxidation suppresses element (one or more), and

Surplus is magnesium (Mg) the impurity except idol is deposited.Unless otherwise stated, all per-cents herein are all weight percent.

Speech " rare earth " should be understood to and refers to that having ordination number is 57～71, i.e. lanthanum (the La)～any element of lutetium (Lu) or the combination of element in the whole process of this specification sheets.

The tetragon that is limited by line segment AB, BC, CD and DA illustrates that in Fig. 1 this figure is the curve of total rare earth content to yttrium content.

Preferably, alloy of the present invention contains:

Be not more than 0.15% titanium,

Be not more than 0.15% hafnium,

Be not more than 0.1% copper,

Be not more than 0.1% nickel,

Be not more than 0.1% silicon,

Be not more than 0.1% aluminium,

Be not more than 0.1% thorium,

Be not more than 0.1% strontium and

Be not more than 0.01% iron.

More preferably, alloy of the present invention:

(a) contain and be lower than 0.1% titanium, better be lower than 0.05% titanium, better be lower than 0.01% titanium, and preferably do not have titanium basically;

(b) contain and be lower than 0.1% hafnium, better be lower than 0.05% hafnium, better be lower than 0.01% hafnium, and preferably do not have hafnium basically;

(c) contain and be lower than 0.05% copper, better be lower than 0.02% copper, better be lower than 0.01% copper, and preferably do not have copper basically;

(d) contain and be lower than 0.05% nickel, better be lower than 0.02% nickel, better be lower than 0.01% nickel, and preferably do not have nickel basically;

(e) contain and be lower than 0.05% silicon, better be lower than 0.02% silicon, better be lower than 0.01% silicon, and preferably do not have silicon basically;

(f) contain and be lower than 0.05% silver, better be lower than 0.02% silver, better be lower than 0.01% silver, and preferably do not have silver basically;

(g) contain and be lower than 0.05% thorium, better be lower than 0.02% thorium, better be lower than 0.01% thorium, and preferably do not have thorium basically; With

(h) contain and be lower than 0.05% strontium, better be lower than 0.02% strontium, better be lower than 0.01% strontium, and preferably do not have strontium basically.

Preferably, alloy of the present invention contains its amount and drops on rare earth and yttrium (Y) in the tetragon that is limited by line segment EF, FG, GH and HE, wherein:

E is 1.5%RE～0.3%Y,

F is 1.0%RE～0.3%Y,

G be 1.0%RE～0.8%Y and

H is 1.5%RE～0.8%Y.

The tetragon that is limited by line segment EF, FG, GH and HE illustrates that in Fig. 1 Fig. 1 is the curve of total rare earth content to yttrium content.

Preferably, alloy of the present invention contains at least 96.7% magnesium, more preferably contains 97～98.5% magnesium, and most preferably contains about 98% magnesium.

Preferably, press the rare earth composition of the alloy of the present invention first or second aspect, be selected from neodymium (Nd), cerium (Ce), lanthanum (La) or its mixture.

Preferably, neodymium content is greater than 0.2%, better greater than 0.4%, and more preferably 0.4～1.8%, and most preferably be 0.4～1.0%, although alloy of the present invention can not contain neodymium.Neodymium content can be from pure neodymium, be contained in neodymium or its composition in lucium such as the mixed rare earth alloy.

Preferably, the content of rare earth except that neodymium is 0～1.6%, more preferably 0.5～1.0%, although alloy of the present invention can not contain the rare earth except that neodymium.Preferably, any rare earth (multiple) except that neodymium is cerium, lanthanum or its mixture.Rare earth except that neodymium can derive from mixture such as mixed rare earth alloy or its composition of pure rare earth, rare earth.Preferably, the rare earth except that neodymium derives from the cerium mixed rare earth alloy of other rare earth that contains cerium, lanthanum, optional neodymium, an amount of praseodymium (Pr) and trace.

Be not wishing to be bound by theory, think that the doping of yttrium is useful to melting protection, ductility and creep resistance.

Preferably, zinc content is 0.2～0.7%, more preferably 0.3～0.5%, especially be preferably 0.4～0.6%.

Zirconium is the optional member of alloy of the present invention.The reduction of iron level can be separated out iron from molten alloy by the interpolation zirconium and be realized.It is desirable to, alloy contains the iron of minimum quantity.Preferably, alloy of the present invention contains and is lower than 0.005% iron, does not preferably have iron basically.Therefore, the zirconium content of the present invention's regulation is remaining zirconium content.Yet, it should be noted that zirconium can add two different stages.At first, when alloy is made, secondly, just before casting after the alloy molten.Preferably, zirconium content is to reach other people needed minimum quantity of de-ferrous effect satisfactorily.Be typically, zirconium content be about 0.1% or below.

Manganese is the optional member of alloy.When existing, manganese content typically is about 0.1%.

Preventing or suppress at least the element of molten alloy oxidation, as beryllium (Be) and calcium (Ca), is optional member, especially when in the time of can not adequately protecting melt, alloy can comprise these optional members by protective atmosphere control (cover gas atmosphere control).Particularly casting technique does not relate under the situation of closed system, and is all the more so.

When existing, beryllium content preferably is lower than 50ppm, and more preferably 4～25ppm especially is preferably 4～20ppm, and more preferably 4～15ppm especially is preferably 6～13ppm, as 8～12ppm.Typically,, introduce beryllium, aluminium is existed to be up to 0.25% a small amount of by means of aluminium-beryllium mother alloy such as Al-5%Be.Preferably, aluminium content is lower than 0.2%, more preferably less than 0.1%.Be not wishing to be bound by theory, think that the doping of beryllium and/or calcium can improve the die casting of alloy.

Ideally, the content that idol is deposited impurity is zero, but it is impossible to know that this comes down to.Therefore, preferred idol is deposited foreign matter content and is lower than 0.15%, more preferably less than 0.1%, especially preferably is lower than 0.01%, is more preferably to be lower than 0.001%.

For the HPDC alloy, be that some alloy of the present invention has benefited from thermal treatment at least unexpectedly, as T6 thermal treatment, described T6 thermal treatment is usually directed to be up to 6 hours 450～550 ℃ of following solution treatment, then quenches, and is up to 24 hours in 150～300 ℃ of following artificial agings more afterwards.

Second aspect the invention provides the assembly of the oil engine of being made by the alloy of first aspect present invention.The assembly of oil engine can be power pack or its parts such as coverture.

The alloy of first aspect present invention can be cast as sand mold casting or low pressure/gravity metal mold casting by the technology except that HPDC.

The third aspect the invention provides a kind of power pack that is used for the oil engine produced by the alloy of Hpdc first aspect present invention.

Specifically mention power pack above, but it should be noted that alloy of the present invention can obtain purposes as using at automobile power-transmission system and in low temperature uses in other high temperature uses.Also specifically mention HPDC above, yet it should be noted that alloy of the present invention can cast by the technology except that HPDC, these technology comprise thixotropy casting, thixotropy casting, permanent mold casting and sand mold casting.

The explanation of the preferred embodiment of the invention

Embodiment 1

Prepare two kinds of alloys of the present invention and the chemical analysis of alloy is listed in the table below 1.The rare earth of adding except that neodymium is as cerium base mishmetal, and it contains cerium, lanthanum and some neodymiums.Add other neodymium and zinc with its element form.In whole alloy preparation process, use the melt treatment program of standard.

The alloy of table 1-preparation

Element	Alloy A	Alloy B
			Nd(wt％)	0.6	0.54
Ce(wt％)	0.37	0.36
			La(wt％)	0.32	0.31
Zn(wt％)	0.4	0.41
			Y(wt％)	0.5	0.18
Mg(wt％)	Except that even surplus of depositing the impurity	Except that even surplus of depositing the impurity

The tensile property of room temperature and 177 ℃ of following alloy A and B is listed in the following table 2.

Table 2-tensile property

	210℃			1770℃
								0.2% yielding stress	UTS	Unit elongation	0.2% yielding stress	UTS	Unit elongation
Alloy A
		120	146	4.0	106	132	6.6
Alloy B								114	164	5.7	102	133	9.0

With casting condition and T6 heat-treat condition in the creep test of carrying out alloy A and B under 90MPa constant load and 177 ℃ and the creep test of under 75MPa load and 200 ℃, carrying out alloy A with casting condition.Steady state creep speed is listed in the table 3.

Table 3-steady state creep speed

	As cast condition steady state creep speed (s -1)
				90Mpa 1770℃	75MPa	200℃
Alloy A	2.5×10 -10	4.3×10 -10
			Alloy B	3.0×10 -10	-

Fig. 2 shows the creep result under 177 ℃ and 90MPa with casting condition alloy A and B.From Fig. 2 as seen, although two kinds of alloys have similar secondary creep speed, the instantaneous strain when alloy A is loaded under these conditions has more patience than alloy B.

Fig. 3 shows the creep result under 177 ℃ and 90MPa at T6 heat-treat condition interalloy A and B.Alloy A and B through solution treatment 8 hours, then use cold-water quench under 525 ℃, afterwards in 215 ℃ of following timeliness 4 hours.The creep resistance of alloy A under these conditions is also significantly greater than alloy B.

T6 thermal treatment is illustrated by Fig. 2 and Fig. 3 contrast the influence of the creep property of the HPDC test sample of alloy A of the present invention and B.Can see T6 thermal treatment to the alloy of low Y content (＜0.4wt.%Y) almost be no advantage.Yet for the composition that contains 0.5wt.%Y or bigger content, T6 thermal treatment has significant favourable influence for the creep property of alloy.

Embodiment 2

Produce a series of alloys of the present invention and its composition is listed in the table 4, it comprises alloy A and B among the embodiment 1.

Alloy	Nd (weight %)	Ce (weight %)	La (weight %)	Y (weight %)	Zn (weight %)	Be (ppm)	Al (weight %)	Fe (ppm)	Zr (dissolved weight %)	Zr (total weight %)
											A	0.60	0.37	0.32	0.50	0.40	-	-	-	-	-
B	0.54	0.36	0.31	0.18	0.41	-	-	-	-	-
											C	0.63	0.41	0.36	1.06	0.43	15	0.10	-	＜0.005	0.02
D	0.64	0.42	0.38	1.52	0.45	18	0.10	-	0.005	0.035
											E	1.18	0.41	0.38	0.75	0.42	19	0.10	-	0.005	0.03
F	0.53	0.63	0.18	0.95	0.43	26	0.11	-	0.008	0.08
											G	0.54	1.11	0.18	0.95	0.42	40	0.11	-	0.018	0.15
H	0.62	0.48	0.37	0.27	0.54	15	0.07	17	＜0.005	＜0.005
											I	0.56	0.44	0.33	0.26	0.57	15	0.07	16	＜0.005	＜0.005
J	0.46	0.36	0.28	0.25	0.57	16	0.07	14	＜0.005	＜0.005
											K	0.65	0.49	0.38	0.37	0.56	15	0.07	25	＜0.005	0.009
L	0.58	0.44	0.34	0.39	0.57	18	0.08	27	0.005	0.010
											M	0.49	0.37	0.28	0.40	0.54	17	0.08	20	0.005	0.010
N	0.67	0.50	0.37	0.54	0.58	16	0.07	26	＜0.005	0.006
											O	0.58	0.42	0.33	0.57	0.54	18	0.07	22	0.005	0.008
P	0.48	0.34	0.27	0.60	0.54	18	0.07	27	0.005	0.008
											Q	0.48	0.35	0.28	0.64	0.80	20	0.07	34	0.006	0.010
R	0.46	0.34	0.27	0.61	1.12	19	0.07	28	0.005	0.010
											S	0.68	0.51	0.39	1.17	0.57	＜1	0.01	34	＜0.005	＜0.005
T	0.71	0.51	0.40	1.10	0.56	5	0.04	33	＜0.005	＜0.005
											U	0.70	0.51	0.39	0.99	0.54	9	0.10	27	＜0.005	＜0.005
V	0.68	0.49	0.38	0.89	0.54	13	0.22	23	＜0.005	＜0.005

The chemical constitution of table 4 alloy A～V

Concerning mechanical property is estimated, the production test sample by these alloys of Hpdc (HPDC) on 250 tons TOSHIBA cold-chamber die casting machine.The performance of estimating alloy comprises the creep property under tensile strength under the microtexture of castability, as-cast condition, room temperature and 177 ℃ and 177 ℃ and 200 ℃.

Fig. 4 shows the representative instance of alloy of the present invention (alloy N) microtexture with as-cast condition.Because the character of HPDC, the fine grained structure on the surface (' top layer ') of the close casting sample of existence is to central section (' the core ') transition than coarse-grained structure.Yet two districts all are made up of nascent rich magnesium crystal grain or dendrite, have the Mg-RE intermetallic phase at intergranular and interdendritic district.

Alloy of the present invention is fire-retardant high antioxidant, as shown in Figure 5.

Fig. 5 (d), 5 (e) and 5 (f) relate to alloy H and form closely similar alloy, and Fig. 5 (a), 5 (b) and 5 (c) relate to the alloy of forming except the equivalence that does not contain yttrium.Fig. 5 (b) and 5 (e) are shown in Fig. 5 (a) and 5 (d) grand design through foundry goods center polished section respectively, and this image shows the degree of depth that the oxide compound that forms from the teeth outwards infiltrates foundry goods inside.Fig. 5 (c) and 5 (f) are respectively that the identical high magnification map of Fig. 5 (b) and 5 (e) resembles.Can see that in Fig. 5 (c) alloy of no yttrium presents the strong penetration of oxide compound hairline; Otherwise alleged occurrence infiltration situation is atomic in Fig. 5 of alloy of the present invention (f).

For having the alloy that the present invention typical case forms, the degree of depth that the degree of surface oxidation and oxide compound hairline infiltrate the foundry goods main body greatly reduces.This fire retardation can be very favorable in all actual casting operations.

Table 5 provides the table look-up of alloy tension test data of the present invention, from then on as can be seen under two kinds of test temperatures being investigated tensile property be rational.The example of the stress-strain curve of alloy N, ALLOY O and alloy P is shown among Fig. 6 and Fig. 7, is respectively the test of carrying out under room temperature and 177 ℃.The Y content of component is shown among Fig. 8 the influence of tensile stress-strain property, this shows that tensile strength improves along with the raising of Y content.

Table 5 under room temperature and 177 ℃ for the typical tensile property of the scope of embodiment of the invention alloy

Alloy	RT-21℃			177℃
							0.2% yielding stress. (Mpa)	UTS，(MPa)	％E	0.2% surrender. stress, (MPa)	UTS， (Mpa)	％E
	A	120.1±2.1	146.3±2.8	4.0±0.3	106.2±2.7	131.6±7.1							6.6±1.0
B							114.0±7.0	163.6±11.2	5.7±0.9	102.5±2.9	133.4±1.4	9.0±0.6
	C	122.4±1.7	167.6±4.6	5.2±0.7	112.5±0.5	150.2±8.1							8.8±1.6
D							127.5±4.4	176.1±5.9	5.6±0.6	117.2±1.6	151.7±3.0	7.0±0.3
	E	128.6±1.6	164.8±12.6	4.5±1.1	117.6±1.5	146.0±3.5							6.4±0.9
F							120.7±2.0	153.1±6.2	4.3±0.5	111.0±1.8	137.0±4.0	6.5±0.8
	G	130.7±2.7	159.2±7.2	4.2±0.6	113.5±1.9	142.1±4.1							6.5±0.9
H							118.1±1.4	158.1±4.7	4.6±0.5	104.7±1.6	131.8±3.4	6.9±0.2
	I	115.0±2.2	152.9±11.6	4.5±1.0	96.8±1.9	130.4±5.2							7.6±0.8
J							110.5±1.0	148.3±7.5	4.5±0.6	97.8±3.0	127.5±7.9	7.7±1.8
	K	126.3±0.9	159.0±6.1	4.65±0.6	104.6±6.9	130.7±7.9							5.8±1.1
L							120.6±1.0	152.8±4.8	4.2±0.5	101.6±5.5	126.7±5.3	6.1±0.7
	M	114.5±1.8	137.9±2.1	3.34±0.1	100.2±1.9	123.5±4.6							5.9±0.3
N							127.3±2.0	151.8±11.1	3.67±0.95	109.0±3.5.	137.7±4.8	6.1±0.3
	O	126.1±0.9	155.2±1.7	4.1±0.2	107.8±2.1	133.0±2.1							5.9±0.9
P							116.8±2.8	133.8±4.2	2.7±0.4	103.7±2.4	120.3±6.5	4.5±0.9
	Q	123.3±1.3	150.8±2.6	4.2±0.3	105.8±2.5	127.4±4.9							5.2±0.8
R							119.7±2.2	147.9±1.2	3.8±0.3	102.9±2.0	122.0±4.0	4.8±0.7
	S	131.5±4.5	159.8±6.6	4.5±0.5	121.1±4.3	145.7±2.3							5.2±0.5
T							131.3±3.7	155.3±6.9	3.9±0.7	118.9±2.4	142.0±4.7	5.0±0.8
	U	129.6±4.0	151.1±5.3	3.3±0.5	114.6±2.8	134.0±9.0							4.6±1.0
V							132.3±4.2	155.3±7.3	3.4±0.7	115.1±2.4	131.6±6.6	3.9±0.7

Table 6 is included in the steady state creep speed of alloy of the present invention under many different tests conditions (alloy A, as-cast condition), and the example of relevant creep curve also is shown among Fig. 9.

The steady state creep speed of table 6 alloy A of the present invention under various test conditionss and same test conditions in different heat treatment.

Alloy	Steady state creep speed (s -1)
					90MPa 177℃		2000 ℃ of 55MPa (as cast condition)	200 ℃ of 75MPa (as cast condition)
	As cast condition	T6
			A	2.5×10 -10	3.6×10 -11	1.1×10 -10			4.3×10 -10

Table 7 is included in steady state creep speed table look-ups that all compositions of being surveyed down with casting condition change under the same terms of 177 ℃ and 90MPa.

The steady state creep speed of the many alloy variablees of the present invention of table 7.

Alloy	As cast condition steady state creep speed (s -1) 90MPa 177℃
		A	2.5×10 -10
B	3.0×10 -10
		C	2.1×10 -10
D	1.9×10 -11
		E	3.4×10 -10
F	3.0×10 -10
		G	2.6×10 -10
H	1.3×10 -9
		I	6.3×10 -10
J	4.6×10 -8
		K	2.6×10 -10
L	2.0×10 -10
		M	2.5×10 -10
N	1.4×10 -10
		O	9.0×10 -11
P	2.3×10 -11
		Q	4.0×10 -11
R	1.6×10 -10
		S	4.2×10 -10
T	1.7×10 -10
		U	3.1×10 -10
V	2.0×10 -10

Contain low total rare earth (TRE) (TRE) content (in 1.1～1.2wt.% scope) for composition, medium TRE content (in 1.3～1.4wt.% scope), and the selected creep curve of the alloy that improves of high TRE content (in 1.5～1.6wt% scope) and Y content is shown in Figure 10, Figure 11 and Figure 12.According to overview, the Y content that improves alloy of the present invention can obviously improve (177 ℃ and 90MPa) observed creep behaviour under these test conditionss.Alloy composition with low TRE content and low Y content presents relatively poor creep property under these strict test conditionss, indicated as the curve of Figure 10 interalloy J.Therefore such composition is compared more suitable less demanding power train with engine.For the composition that contains above 0.45wt.%Y, its creep property is very good, as (the seeing Fig. 9, Figure 11 and Figure 12 respectively) that confirmed by alloy A, alloy C and alloy T.

Quoted the publication of prior art although it should be clearly understood that this paper, this quoting not is to admit these, and file becomes the common sense of this area in Australia or what its country in office.

Claims (18)

1. magnesium-rare earth-yttrium-zinc alloy, form by following:

Its amount falls into rare earth (RE) and the yttrium in the tetragon that is limited by line segment AB, BC, CD and DA, wherein:

A is 1.8%RE-0.05%Y,

B is 1.0%RE-0.05%Y,

C be 0.2%RE-0.8%Y and

D is 1.8%RE-0.8%Y;

0.2～1.5% zinc;

0～0.25% aluminium;

0～0.2% zirconium;

0～0.3% manganese;

0～0.1% oxidation suppresses element, and

Residual content is magnesium (Mg) the impurity except that idol is deposited.

2. according to the described alloy of claim 1, contain its amount and fall into rare earth and yttrium in the tetragon that limits by line segment EF, FG, GH and HE, wherein:

E is 1.5%RE-0.3%Y,

F is 1.0%RE-0.3%Y,

G be 1.0%RE-0.8%Y and

H is 1.5%RE-0.8%Y.

3. according to the alloy described in claim 1 or the claim 2, it contains at least 96.7% magnesium.

4. according to each the described alloy in the aforementioned claim, wherein, rare earth element is selected from neodymium, cerium, lanthanum, praseodymium or its combination.

5. according to each the described alloy in the aforementioned claim, it has 0.4～1.0% neodymium content.

6. according to each the described alloy in the aforementioned claim, wherein, except that neodymium, content of rare earth is 0.5～1.0%.

7. according to each the described alloy in the aforementioned claim, it has 0.1～1.6% yttrium content.

8. according to the described alloy of claim 7, it has 0.25～1.25% yttrium content.

9. according to the described alloy of claim 8, it has 0.5～1.0% yttrium content.

10. according to each the described alloy in the aforementioned claim, it has 0.2～0.7% zinc content.

11. according to the described alloy of claim 10, it has 0.4～0.6% zinc content.

12. according to each the described alloy in the aforementioned claim, it contains the aluminium that is lower than 0.25% amount.

13. according to each the described alloy in the aforementioned claim, it contains the zirconium that is lower than 0.2% amount.

14. according to each the described alloy in the aforementioned claim, it contains the manganese that is lower than 0.3% amount.

15. according to each the described alloy in the aforementioned claim, it contains the beryllium that is lower than the 50ppm amount.

16. according to each the described alloy in the aforementioned claim, it contains the calcium that is lower than 0.1% amount.

17. the assembly of oil engine or automotive power transmission system, it is made of each the described alloy in the aforementioned claim.

18. a power pack or its parts, it is made by each the described alloy in the Hpdc claim 1～16.

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