A kind of high-strength casting Mg-Zn-Cu-Zr alloy and preparation method thereofTechnical field
The invention belongs to metal material engineering technical field, be related to a kind of high-strength casting Mg-Zn-Cu-Zr alloy and itsPreparation method.
Background technique
Magnesium alloy has good specific strength, specific stiffness, thermal conductivity, shock resistance and machinability, is widely used in high-end vapourIn the lightweights industrial production such as vehicle, aerospace, it has also become the potential substitute of aluminium alloy and steel industry most attraction, quiltIt is described as " 21 century green metal material ".However, since the intensity of magnesium alloy is lower, plasticity is poor and alloy addition is expensive etc.Reason greatly limits its promotion and application in industrial production.
Mg-Zn-Cu alloy is the more successful Mg-Zn system heat-resisting alloy of commercial applications so far, below at 150 DEG CHigh-temperature behavior is preferable, and being successfully used for automotive engine component, propeller etc. needs on high temperature resistant components.But due to castingMg-Zn-Cu alloy structure is coarseer, and main hardening constituent Mg (Zn, Cu)2Eutectic phase is linked to be net distribution in interdendritic, no moreBut Mg (Zn, Cu)2The invigoration effect of phase can not give full play to, and can also reduce the mechanical property of casting Mg-Zn-Cu alloy.ForMg-Zn-Cu alloy items mechanical property is further increased, technical staff attempts around techniques such as alloying, heat treatment and extrudingExpansion research, such as: 102071345 A of patent CN discloses a kind of Mg-Zn-Cu alloy containing Zr, the weight percent of componentThan are as follows: Zn 5~7%, Cu 0.5~2%, Zr 0.3~0.8%, surplus Mg, after being sufficiently heat-treated the maximum tensile strength,Yield strength, elongation percentage are respectively up to 240~270MPa, 160~190MPa and 11~17%；J.Buha has studied ageing treatment pairThe influence of Mg-6Zn-2Cu-0.1Mn alloy property, peak timeliness alloy the maximum tensile strength, yield strength, elongation percentage reach respectively220~253MPa, 121~168MPa and 2.8~8.6% (J.Buha, MechanicalpropertiesofnaturallyagEdMg-Zn-Cu-Mnalloy, Materials Science andEngineering A, 2008,489:127-137)；Zhao ChongHave studied influence of the extrusion process to Mg-Zn-Cu-Ce alloy property, through different extrusion process processing after alloy tensile strength,Yield strength and elongation percentage are respectively up to 293~321MPa, 215~282MPa and 2.04~15.7% (Zhao Chong, Mg-Zn-Cu-CeAlloy structure and performance study, University Of Chongqing's master thesis, 2012).
Although the above method makes moderate progress to the mechanical property of Mg-Zn-Cu alloy, the hardening constituent under high temperature in alloy is easyLong greatly overaging phase, strengthening effect is still undesirable, and the introducing of precious metal element (such as Ce) also increases cost of alloy.And it studies the discovery preferable high-temperature behavior of Mg-Zn-Cu alloy and is present in eutectic phase Mg (Zn, Cu) with Cu2It is related, therefore refine castingIt makes Mg-Zn-Cu alloy structure, improve Mg (Zn, Cu)2Eutectic phase morphology and distribution can significantly improve alloy mechanical property, and atThis is cheaper.
Summary of the invention
In view of the deficiencies of the prior art, the present invention proposes the systems of a kind of novel low-cost, high-performance Mg-Zn-Cu-Zr alloyStandby technique, wherein the addition of inexpensive element Zr can not only refine crystal grain, moreover it is possible to reduce other impurities element to alloy structureWith the damage of performance.By solidifying under GPa grades of high pressures to routine casting Mg-Zn-Cu-Zr alloy, it is solidifying alloy has been refinedGu tissue improves Mg (Zn, Cu)2The form and distribution of phase, the mechanical property and height of further expansion Mg-Zn-Cu-Zr alloyWarm use scope.
The present invention adopts the following technical scheme that:
A kind of high-strength casting Mg-Zn-Cu-Zr alloy, the mass percent of each component are as follows: Zn 4%~10%, Cu0.1%~1.0%, Zr 0.1%~0.5%, surplus Mg.
The preferred scope of the mass percent of aforementioned alloy compositions are as follows: Zn 7%, Cu 0.5%, Zr 0.2%, surplus areMg。
The preparation method of above-mentioned high-strength casting Mg-Zn-Cu-Zr alloy, comprising the following steps:
(1) use purity for 99.99% Mg ingot, purity be 99.99% Zn ingot, Cu/Zn mass ratio be 7:3 brassWith Mg-30%Zr intermediate alloy as raw material, mass percent needed for calculating each raw material according to subject alloy ingredient；
(2) step (1) described raw material is preheated at 250 DEG C；
(3) heating temperature of crucible electrical resistance furnace is set as 750~770 DEG C, when crucible temperature reaches 300~350 DEG CMg ingot, Zn ingot is added, is passed through volume ratio CO2/SF6The mixed gas of=99:1 protects gas as melting；To Mg ingot, Zn in crucibleIt is to close among the brass and Mg-30%Zr of 7:3 that Cu/Zn is sequentially added when ingot melts completely and crucible temperature reaches 650~700 DEG CGold simultaneously keeps the temperature 2min~5min；Molten surface dross, heat preservation 20 are stirred and removed when furnace temperature reaches 750 DEG C~770 DEG CThen molten metal is poured onto preheated metal mold by~30min, metal mold preheating temperature is 450~500 DEG C, obtains instituteNeed Mg-Zn-Cu-Zr cast alloy material；
(4) the Mg-Zn-Cu-Zr cast alloy material of above-mentioned preparation is put into vacuum resistance furnace and carries out homogenizing annealing,Temperature is set as 240~300 DEG C, and soaking time 12~24 hours, then wire cutting was at high pressure sample；
(5) the high pressure sample that step (4) obtains is fitted into graphite group encapsulation, then by assembled graphite group encapsulationIt is put into the cavity position of high pressure cubic apparatus, starts High Pressure Solidification after tup alignment: first by pressure rise to setting freezing pressure2GPa~6GPa, while starting temperature measuring equipment, and be heated rapidly to 770 DEG C~970 DEG C of preset heating temperature, at such a temperature15~20min of heat-insulation pressure keeping closes power supply and stops heating, release and takes out after naturally cooling to room temperature, obtain final alloySample.
In abovementioned steps (5), High Pressure Solidification experiment is carried out using CS-1B type high pressure cubic hinge press, is pushed up with two sidesPress system is compared, and cubic hinge press saves a pre-stress die and a heavy duty mill housing, while the pressure field in high pressure chestIt is even more ideal.
In abovementioned steps (5), before high pressure is packed into graphite group encapsulation with sample, it is the introducing for effectively avoiding impurity element, needsIt cleans sample surfaces: first with impurity such as each surface and oil contaminant of 600~2000# fine sandpaper removal sample and oxide layers, being then placed inIt is cleaned in supersonic wave cleaning machine, is finally putting into 110 DEG C of drying boxes dry 12h or more.
In abovementioned steps (5), need to test liquidus curve of each specimen sample in the case where GPa grades of high pressures act on before setting heating temperatureTemperature.According to Clausius-Clapeyren equation, melting point substance is with pressure change by the shadow of volume change when solid-liquid phase changeIt rings.Since fusion process of the Mg under high pressure effect is expansion reaction, therefore Mg fusing point is increased with pressure increase.By laboratory sampleThe heating and heat preservation for carrying out different temperatures under the effect of 2~6GPa high pressure respectively, are rapidly cooled to room temperature under pressure maintaining, solidifying according to itGu tissue signature determines liquidus temperature；The heating temperature set is each+30 DEG C of high pressure sample liquidus temperature or so.
In abovementioned steps (5), what the crucible for containing High Pressure Solidification sample was selected is boron nitride crucible, boron nitride crucibleIt the use of temperature is under vacuum 1800 DEG C, thermal shock resistance is good, not easy to crack under chilling；Boron nitride crucible size should basisSpecimen size selection or machining, the excessive sample that will affect contain and are heated, too small then to send out in the process because of METAL HEATING PROCESSHeat expands and spalling crucible.
In abovementioned steps (5), whether the stringent each tup for wiping and checking CS-1B type high pressure cubic hinge press before testingThere is crackle.
In abovementioned steps (5), CS-1B type high pressure cubic hinge press is using preceding needing to preheat 30min in advance；The heating process momentAmmeter variation is paid close attention to, electric current should not be too large；When release, first using unload at a slow speed be depressed into 20MPa after be changed to fast pressure relief again.
Compared with prior art, the invention has the following advantages that
1, Zr is a low-cost alloy addition element, and suitable Zr is added in Mg-Zn-Cu alloy can not only refineAlloy grain, moreover it is possible to reduce damage of the other impurities element to alloy structure and performance, improve the plasticity of Mg-Zn-Cu alloy simultaneouslyImprove corrosion resistance.
2, the preferable high-temperature behavior of Mg-Zn-Cu alloy and Cu are present in eutectic phase Mg (Zn, Cu)2It is related, but cast Mg-Zn-Cu As-cast Microstructure is coarseer, and main hardening constituent Mg (Zn, Cu)2For eutectic phase and it is linked to be net distribution in dendrite moreBetween.Mg-Zn-Cu-Zr alloy on the one hand can be made to obtain more crystallization nucleus numbers using High Pressure Solidification technology, significant refinement is solidifyingGu tissue, on the other hand Mg (Zn, the Cu) during High Pressure Solidification2The netted form of eutectic phase is interrupted, and becomes and is discontinuously distributedGraininess or island form are distributed more uniform.Therefore, the intensity of alloy is increased dramatically.
3, the Mg-Zn-Cu system alloy through ageing treatment, the hardening constituent when high temperature range is on active service in alloy are easily grown upFor overaging phase, alloy mechanical property is made to decline to a great extent；And the Mg-Zn-Cu-Zr alloy of High Pressure Solidification technology preparation is used, by forceDegree and hardness significantly improve and high-temperature behavior is more stable, and maximum compressive strength, yield strength and elongation percentage be respectively 320.6~430.3MPa, 280.2~370.1MPa, 16.3~21.3%.
Detailed description of the invention
Fig. 1 is the microscopic structure under routine casting Mg-7Zn-0.5Cu-0.2Zr alloy different amplification；
Fig. 2 is the microscopic structure under the Mg-7Zn-0.5Cu-0.2Zr alloy different amplification of High Pressure Solidification preparation(6GPa)。
Specific embodiment
The present invention is further illustrated With reference to embodiment, but the contents of the present invention are not limited to following realitiesApply example.
Embodiment 1: a kind of high-strength casting Mg-Zn-Cu-Zr alloy, each component and mass percent are as follows: Zn 7%,Cu 0.8%, Zr 0.4%, surplus Mg, gross mass 100%.
Preparation method is as follows:
(1) Mg ingot, Zn ingot of the purity for 99.99% are used, the brass and Mg-30%Zr intermediate alloy that Cu/Zn is 7:3 are madeFor raw material, Zn is 7%, Cu 0.8% by weight percent, and Zr 0.4%, surplus is that the alloy compositions of Mg are matchedMaterial；
(2) step (1) described raw material is preheated at 250 DEG C；
(3) heating temperature of crucible electrical resistance furnace is set as 760 DEG C, Mg ingot, Zn is added when crucible temperature reaches 350 DEG CIngot is passed through CO2/SF6The mixed gas of=99:1 protects gas as melting；Melt completely to Mg ingot, Zn ingot in crucible and crucible temperatureDegree sequentially adds the brass that Cu/Zn is 7:3 and Mg-30%Zr intermediate alloy and keeps the temperature 5min when reaching 670 DEG C；When furnace temperature reachesMolten surface dross is stirred and removed at 760 DEG C, keeps the temperature 20min, then molten metal is poured onto preheated metal moldIn (metal mold preheating temperature be 500 DEG C), obtain required Mg-Zn-Cu-Zr cast alloy material；
(4) the Mg-Zn-Cu-Zr cast alloy material of above-mentioned preparation is put into vacuum resistance furnace and carries out homogenizing annealing,Temperature is set as 280 DEG C, and soaking time 14 hours, then wire cutting was at high pressure sample；
(5) the high pressure sample that step (4) obtains is fitted into graphite group encapsulation, then by assembled graphite group encapsulationIt is put into the cavity position of high pressure cubic apparatus, starts High Pressure Solidification after tup alignment: first by pressure rise to setting freezing pressure2GPa, while starting temperature measuring equipment, and be heated rapidly to 800 DEG C of preset heating temperature, at such a temperature heat-insulation pressure keeping18min closes power supply and stops heating, release and takes out after naturally cooling to room temperature, obtain high-strength casting Mg-7Zn-0.8Cu-0.4Zr alloy sample.
Embodiment 2: a kind of high-strength casting Mg-Zn-Cu-Zr alloy, each component and mass percent are as follows: Zn 8%,Cu 1%, Zr 0.3%, surplus Mg, gross mass 100%.
Preparation method is as follows:
(1) Mg ingot, Zn ingot of the purity for 99.99% are used, the brass and Mg-30%Zr intermediate alloy that Cu/Zn is 7:3 are madeFor raw material, Zn is 8%, Cu 1% by weight percent, and Zr 0.3%, surplus is that the alloy compositions of Mg are matchedMaterial；
(2) step (1) described raw material is preheated at 250 DEG C；
(3) heating temperature of crucible electrical resistance furnace is set as 770 DEG C, Mg ingot, Zn is added when crucible temperature reaches 350 DEG CIngot is passed through CO2/SF6The mixed gas of=99:1 protects gas as melting；Melt completely to Mg ingot, Zn ingot in crucible and crucible temperatureDegree sequentially adds the brass that Cu/Zn is 7:3 and Mg-30%Zr intermediate alloy and keeps the temperature 4min when reaching 700 DEG C；When furnace temperature reachesMolten surface dross is stirred and removed at 770 DEG C, keeps the temperature 25min, then molten metal is poured onto preheated metal moldIn (metal mold preheating temperature be 450 DEG C), obtain required Mg-Zn-Cu-Zr cast alloy material；
(4) the Mg-Zn-Cu-Zr cast alloy material of above-mentioned preparation is put into vacuum resistance furnace and carries out homogenizing annealing,Temperature is set as 260 DEG C, and soaking time 16 hours, then wire cutting was at high pressure sample；
(5) the high pressure sample that step (4) obtains is fitted into graphite group encapsulation, then by assembled graphite group encapsulationIt is put into the cavity position of high pressure cubic apparatus, starts High Pressure Solidification after tup alignment: first by pressure rise to setting freezing pressure4GPa, while starting temperature measuring equipment, and be heated rapidly to 850 DEG C of preset heating temperature, at such a temperature heat-insulation pressure keeping15min closes power supply and stops heating, release and takes out after naturally cooling to room temperature, obtain high-strength casting Mg-8Zn-1Cu-0.3Zr alloy sample.
Embodiment 3: a kind of high-strength casting Mg-Zn-Cu-Zr alloy, each component and mass percent are as follows: Zn 6%,Cu 1%, Zr 0.2%, surplus Mg, gross mass 100%.
Preparation method is as follows:
(1) Mg ingot, Zn ingot of the purity for 99.99% are used, the brass and Mg-30%Zr intermediate alloy that Cu/Zn is 7:3 are madeFor raw material, Zn is 6%, Cu 1% by weight percent, and Zr 0.2%, surplus is that the alloy compositions of Mg are matchedMaterial；
(2) step (1) described raw material is preheated at 250 DEG C；
(3) heating temperature of crucible electrical resistance furnace is set as 750 DEG C, Mg ingot, Zn is added when crucible temperature reaches 300 DEG CIngot is passed through CO2/SF6The mixed gas of=99:1 protects gas as melting；Melt completely to Mg ingot, Zn ingot in crucible and crucible temperatureDegree sequentially adds the brass that Cu/Zn is 7:3 and Mg-30%Zr intermediate alloy and keeps the temperature 4min when reaching 660 DEG C；When furnace temperature reachesMolten surface dross is stirred and removed at 750 DEG C, keeps the temperature 20min, then molten metal is poured onto preheated metal moldIn (metal mold preheating temperature be 450 DEG C), obtain required Mg-Zn-Cu-Zr cast alloy material；
(4) the Mg-Zn-Cu-Zr cast alloy material of above-mentioned preparation is put into vacuum resistance furnace and carries out homogenizing annealing,Temperature is set as 250 DEG C, and soaking time 20 hours, then wire cutting was at high pressure sample；
(5) the high pressure sample that step (4) obtains is fitted into graphite group encapsulation, then by assembled graphite group encapsulationIt is put into the cavity position of high pressure cubic apparatus, starts High Pressure Solidification after tup alignment: first by pressure rise to setting freezing pressure5GPa, while starting temperature measuring equipment, and be heated rapidly to 900 DEG C of preset heating temperature, at such a temperature heat-insulation pressure keeping20min closes power supply and stops heating, release and takes out after naturally cooling to room temperature, obtain high-strength casting Mg-6Zn-1Cu-0.2Zr alloy sample.
Embodiment 4: a kind of high-strength casting Mg-Zn-Cu-Zr alloy, each component and mass percent are as follows: Zn 7%,Cu 0.5%, Zr 0.2%, surplus Mg, gross mass 100%.
Preparation method is as follows:
(1) Mg ingot, Zn ingot of the purity for 99.99% are used, the brass and Mg-30%Zr intermediate alloy that Cu/Zn is 7:3 are madeFor raw material, Zn is 7%, Cu 0.5% by weight percent, and Zr 0.2%, surplus is that the alloy compositions of Mg are matchedMaterial；
(2) step (1) described raw material is preheated at 250 DEG C；
(3) heating temperature of crucible electrical resistance furnace is set as 760 DEG C, Mg ingot, Zn is added when crucible temperature reaches 300 DEG CIngot is passed through CO2/SF6The mixed gas of=99:1 protects gas as melting；Melt completely to Mg ingot, Zn ingot in crucible and crucible temperatureDegree sequentially adds the brass that Cu/Zn is 7:3 and Mg-30%Zr intermediate alloy and keeps the temperature 3min when reaching 680 DEG C；When furnace temperature reachesMolten surface dross is stirred and removed at 760 DEG C, keeps the temperature 25min, then molten metal is poured onto preheated metal moldIn (metal mold preheating temperature be 500 DEG C), obtain required Mg-Zn-Cu-Zr cast alloy material；
(4) the Mg-Zn-Cu-Zr cast alloy material of above-mentioned preparation is put into vacuum resistance furnace and carries out homogenizing annealing,Temperature is set as 250 DEG C, and soaking time 18 hours, then wire cutting was at high pressure sample；
(5) the high pressure sample that step (4) obtains is fitted into graphite group encapsulation, then by assembled graphite group encapsulationIt is put into the cavity position of high pressure cubic apparatus, starts High Pressure Solidification after tup alignment: first by pressure rise to setting freezing pressure6GPa, while starting temperature measuring equipment, and be heated rapidly to 950 DEG C of preset heating temperature, at such a temperature heat-insulation pressure keeping20min closes power supply and stops heating, release and takes out after naturally cooling to room temperature, obtain high-strength casting Mg-7Zn-0.5Cu-0.2Zr alloy sample.
Performance comparison:
Following table is the room temperature tensile properties of heterogeneity Mg-Zn-Cu-Zr alloy in above-described embodiment, wherein comparative alloy1, comparative alloy 2 is respectively the nearly peak value Mg- that state-run Materials Research Laboratories J.Buha of Japan et al. is obtained through T4 and T6 ageing treatment6Zn-2Cu-0.1Mn alloy (Materials Science and Engineering A2008,489:127-137), comparison are closedThe Mg-Zn-Cu-Zr alloy (patent CN 102071345A) that gold 3 obtains for bright red plum et al. cast and subsequent heat treatment, it is rightThan room temperature tensile properties (Zhao Chong, the Mg-Zn-Cu-Ce conjunction that alloy 4 is the Mg-Zn-Cu-Ce alloy that Zhao Chong is obtained through extrusion processPayment organization and performance study, University Of Chongqing's master thesis, 2012), Examples 1 to 4 is to be obtained using the technology of the present inventionMg-Zn-Cu-Zr alloy.
As seen from the above table, the casting Mg-Zn-Cu-Zr alloy that the present invention is prepared by High Pressure Solidification technology, maximum resistance to compressionIntensity is 320.6~430.3MPa, and maximum yield strength is 280.2~370.1MPa, and maximum extension rate is 16.3~21.3%.Compared with comparative alloy 1,2,3, the present invention has better compression strength, yield strength and elongation percentage, and is provided simultaneously with more preferableThermal stability, overaging phenomenon will not be generated during high temperature long service；Compared with comparative alloy 4, in the present invention notContaining high cost addition element (Ce), casting cost is lower.
Fig. 1 is routine casting Mg-7Zn-0.5Cu-0.2Zr alloy microscopic structure, shows that its nascent crystalline substance α-Mg is coarse treeArborescent structure, " dendrite group " average-size is about 365 μm, the interdendritic α-Mg it is continuously distributed eutectic the second phase Mg (Zn, Cu)2。
Fig. 2 is the Mg-7Zn-0.5Cu-0.2Zr alloy microscopic structure of 6GPa High Pressure Solidification preparation.With routine shown in FIG. 1The comparison of technic metal solidified structure is cast it is found that the nascent crystalline substance α-Mg in the lower technic metal solidified structure of high pressure effect is mostly tinyIsometric " dendrite group ", dendritic morphology is relatively regular, complete, and molten disconnected Fragmentation Phenomena is few, and branch is undeveloped, and " dendrite group " average-size is aboutIt is 56 μm；The reticular structure that the second phase of intergranular is formed is interrupted, and the second phase of intergranular is in that long island or graininess are discontinuously distributed in moreThe interdendritic α-Mg.