CA2104012A1 - Titanium containing magnesium alloy produced by vapour quenching - Google Patents
Titanium containing magnesium alloy produced by vapour quenchingInfo
- Publication number
- CA2104012A1 CA2104012A1 CA002104012A CA2104012A CA2104012A1 CA 2104012 A1 CA2104012 A1 CA 2104012A1 CA 002104012 A CA002104012 A CA 002104012A CA 2104012 A CA2104012 A CA 2104012A CA 2104012 A1 CA2104012 A1 CA 2104012A1
- Authority
- CA
- Canada
- Prior art keywords
- titanium
- magnesium
- alloys
- alloy
- vapour
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
- C23C14/24—Vacuum evaporation
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C23/00—Alloys based on magnesium
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
- C23C14/14—Metallic material, boron or silicon
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
Abstract
Magnesium based alloy containing 0.5 to 47 % of titanium by weight is produced as a solid solution alloy by vapour quenching. The ingredients are vaporised from separate sources to avoid the problem of titanium insolubility in magnesium melts. Preferred ranges for titanium are 5 to 40 % and 15 to 28 % by weight. The alloy exhibits corrosion resistance particularly at higher levels of titanium. Alloys containing 15 to 28 % titanium with either approximately 5 % aluminium or approximately 1 % silicon are disclosed.
The alloys may contain other elements conventional as ingredients in magnesium based alloys.
The alloys may contain other elements conventional as ingredients in magnesium based alloys.
Description
WO 93tl2262 PCI`/GB92~02279 210~Q12 TITANIUM CONTAINING MAGNESIUM ALLOY PRODUCED BY VAPOUR QUENCHING
This invention relates to alloys which are based upon magnesium and contain titanium, which are produced by the technique of vapour quenching. IThese alloys yield improved resistance to corrosion in comparison with existing alloys of magnesium.
Magnesium is the lightest of the structural metals and hss significant potential utility for aerospace applications, but magnesium alloys have somewhat fallen out of favour for use in such applications, partly because of poor compression properties, but principally because of their poor corrosion resistance. Conventional magnesium alloys (that is those produced by ingot metallurgy methods) have generally poor corrosion resistance due primarily to the water-solubility of the Mg(0~)2 film which forms on the alloy in damp envlronments. This problem of surface corrosion is exacerbated by electrochemical effects as magnesium has a large negative electrode potential. In commercial purity alloys the presence of particles containing common impurity elements such as iron, copper and nickel which have a less negative electrode potential leads to a susceptibility to pitting and general corrosion. Magnesium alloys are also subject to electrochemical corrosion when joined to other structural metals as most have a significantly different electrode potential.
Major improvements in the corrosion resistance of early magnesium alloys were obtained by the addition of small quantities of manganese which reduced the damaging effects of iron, the main impurity, and certain other impurities by combining these within relatively benign intermetallic compounds. More recently further improvements in corrosion resistance have been achieved by reducing the number of particles present in the alloys through improvements in alloy purity.
In addition, a magnesium alloy has been recently developed which is produced by a rapid solidification method to a composition by weight of Mg(base) - 5%Al - 5~Zn - 5%Nd and is claimed to give corrosion W O 93/12262 ~ O 12 PCT~GB92/02279 properties which are superior to any other currently available wrought magnesium alloy. The weight loss of this alloy in a saline corrosion test is comparable to the widely used 2000 series aluminium alloys, but the alloy does not reveal any redurtion in electrode potential in comparison to magnesium so it is still susceptible to electrochemical corrosion.
Some of the alloying ingredients utilised in alloys other than magnesium alloys have minimal or no solubility within magnesium in the melt because of the low boiling point of magnesium and the binary phase diagrams of magnesium with these materials are unknown.
USA patent 4264362 discloses a prior magnesium - titanium alloy produced in the solid state by a mechanical alloying process. In contrast to the alloys of this invention, the alloys disclosed in that specification were alloys in which neither of the two elements was present in solid solution within the other (the two being in the state of a mechanical mixture of the elements) and the alloy product was a supercorroding material intended to react quickly with sea water to provide exothermic heating.
GB patent 1,382,970 discloses a magnesium-based corrosion resistant ~lloy additionally comprising aluminium, zinc, manganese and titanium as well as minute amounts of various doping agents. The alloys disclosed in this document are produced by conventional ingot metallurgy and hence those alloys containing titanium do not have the titanium constituent in solid solution.
~B patent 1,011,585 discloses corrosion resistant magnesium alloys incorporating, in one example, up to 3% titanium silicide.
US patent 5,024,813 discloses magnesium-titanium alloys produced by a powder-metallurgical route from a mixtue of magnesium, titanium and titanium hydride powders. The compositions disclosed are very broad, ranging from 0.04 to 99.96 wt% of titanium. The sintered products are not fully dense and therefore doubts remain concerning the structural properties of these alloys.
3 2 1 0 ~ ~ 1 2 It is therefore an object of this invention to provide a magnesium alloy which provides an improvement in corrosion resistance beyond the level available in current commercial alloys. To achieve this a reduction in both susceptibility to weight loss in saline environments and to electrochemical corrosion (by reduction in its electrode potential) is desirable.
Vapour quenching is a known physical vapour deposition technique which is used primarily for the production of metal films or coatings but is also known as a route to the production of alloys having metastable supersaturated solid solutions on a scale suitable for quite significant structural applications. This invention is concerned with the latter application of vapour quenching technology.
The process is performed by evaporating alloy constituents from individual or combined sources to produce a flux of vapours, and causing these vapours to be condensed upon a collector which is controlled in temperature to a value which causes extremely rapid quenching of the impinging vapours. All this takes place within a vacuum chamber. A general description of the vapour quenching process for the production of alloys is given in two articles by Bickerdike et a~ in the International Journal of Rapid Solidification, 1985, volume 1 pp 305-325; and 1986, volume 2, pp 001-019. The collector deposit obtained by vapour quenching can be utilised in various product forms.
It can be taken from the collector and processed intact e.g. by forging, rolling, or hot pressing to yield a monolithic product or it can be comminuted to particulate form and subsequently canned and consolidated by hot isostatic pressing or extrusion.
The invention claimed herein is a magnesium based alloy produced by vapour quenching which comprises 0.5X to 47% of titanium by weight, wherein the titanium is substantially held in solid solution in the alloy as deposited.
We have been able to produce magnesium alloys incorporating a variety of such ingredients using a vapour deposition process by evaporating the magnesium base and the alloying ingredients from separate sources and combining the vapour streams to yield an alloyed W O 93/12262 P ~ /GB92/02279
This invention relates to alloys which are based upon magnesium and contain titanium, which are produced by the technique of vapour quenching. IThese alloys yield improved resistance to corrosion in comparison with existing alloys of magnesium.
Magnesium is the lightest of the structural metals and hss significant potential utility for aerospace applications, but magnesium alloys have somewhat fallen out of favour for use in such applications, partly because of poor compression properties, but principally because of their poor corrosion resistance. Conventional magnesium alloys (that is those produced by ingot metallurgy methods) have generally poor corrosion resistance due primarily to the water-solubility of the Mg(0~)2 film which forms on the alloy in damp envlronments. This problem of surface corrosion is exacerbated by electrochemical effects as magnesium has a large negative electrode potential. In commercial purity alloys the presence of particles containing common impurity elements such as iron, copper and nickel which have a less negative electrode potential leads to a susceptibility to pitting and general corrosion. Magnesium alloys are also subject to electrochemical corrosion when joined to other structural metals as most have a significantly different electrode potential.
Major improvements in the corrosion resistance of early magnesium alloys were obtained by the addition of small quantities of manganese which reduced the damaging effects of iron, the main impurity, and certain other impurities by combining these within relatively benign intermetallic compounds. More recently further improvements in corrosion resistance have been achieved by reducing the number of particles present in the alloys through improvements in alloy purity.
In addition, a magnesium alloy has been recently developed which is produced by a rapid solidification method to a composition by weight of Mg(base) - 5%Al - 5~Zn - 5%Nd and is claimed to give corrosion W O 93/12262 ~ O 12 PCT~GB92/02279 properties which are superior to any other currently available wrought magnesium alloy. The weight loss of this alloy in a saline corrosion test is comparable to the widely used 2000 series aluminium alloys, but the alloy does not reveal any redurtion in electrode potential in comparison to magnesium so it is still susceptible to electrochemical corrosion.
Some of the alloying ingredients utilised in alloys other than magnesium alloys have minimal or no solubility within magnesium in the melt because of the low boiling point of magnesium and the binary phase diagrams of magnesium with these materials are unknown.
USA patent 4264362 discloses a prior magnesium - titanium alloy produced in the solid state by a mechanical alloying process. In contrast to the alloys of this invention, the alloys disclosed in that specification were alloys in which neither of the two elements was present in solid solution within the other (the two being in the state of a mechanical mixture of the elements) and the alloy product was a supercorroding material intended to react quickly with sea water to provide exothermic heating.
GB patent 1,382,970 discloses a magnesium-based corrosion resistant ~lloy additionally comprising aluminium, zinc, manganese and titanium as well as minute amounts of various doping agents. The alloys disclosed in this document are produced by conventional ingot metallurgy and hence those alloys containing titanium do not have the titanium constituent in solid solution.
~B patent 1,011,585 discloses corrosion resistant magnesium alloys incorporating, in one example, up to 3% titanium silicide.
US patent 5,024,813 discloses magnesium-titanium alloys produced by a powder-metallurgical route from a mixtue of magnesium, titanium and titanium hydride powders. The compositions disclosed are very broad, ranging from 0.04 to 99.96 wt% of titanium. The sintered products are not fully dense and therefore doubts remain concerning the structural properties of these alloys.
3 2 1 0 ~ ~ 1 2 It is therefore an object of this invention to provide a magnesium alloy which provides an improvement in corrosion resistance beyond the level available in current commercial alloys. To achieve this a reduction in both susceptibility to weight loss in saline environments and to electrochemical corrosion (by reduction in its electrode potential) is desirable.
Vapour quenching is a known physical vapour deposition technique which is used primarily for the production of metal films or coatings but is also known as a route to the production of alloys having metastable supersaturated solid solutions on a scale suitable for quite significant structural applications. This invention is concerned with the latter application of vapour quenching technology.
The process is performed by evaporating alloy constituents from individual or combined sources to produce a flux of vapours, and causing these vapours to be condensed upon a collector which is controlled in temperature to a value which causes extremely rapid quenching of the impinging vapours. All this takes place within a vacuum chamber. A general description of the vapour quenching process for the production of alloys is given in two articles by Bickerdike et a~ in the International Journal of Rapid Solidification, 1985, volume 1 pp 305-325; and 1986, volume 2, pp 001-019. The collector deposit obtained by vapour quenching can be utilised in various product forms.
It can be taken from the collector and processed intact e.g. by forging, rolling, or hot pressing to yield a monolithic product or it can be comminuted to particulate form and subsequently canned and consolidated by hot isostatic pressing or extrusion.
The invention claimed herein is a magnesium based alloy produced by vapour quenching which comprises 0.5X to 47% of titanium by weight, wherein the titanium is substantially held in solid solution in the alloy as deposited.
We have been able to produce magnesium alloys incorporating a variety of such ingredients using a vapour deposition process by evaporating the magnesium base and the alloying ingredients from separate sources and combining the vapour streams to yield an alloyed W O 93/12262 P ~ /GB92/02279
2 1 0 ~ 0 1 ~ 4 deposit on the collector. We have found that msgnesium - titanium alloys produced by this method are capable of yielding a particularly good resistance to corrosion.
Preferably the alloys have a titanium content in the range 5 to 40% by weight.
We have demonstrated a marked improvement in corrosion resistance in these alloys compared to prior art materials and compared to alternative research materials with different alloying ingredients such as aluminium. chromium and silicon.
The magnesium alloy may contain. in addition to the titanium, other ingredients such as those used in prior art magnesium alloys within the following weight limits:
manganese up to 6X; aluminium up to 13%; zinc up to 7X;
zirconium up to 5%; neodymium up to 6%; commercial mixed rare earths up to 5% yttrium up to 6%; silver up to 3%; thorium up to 5%;
lithium up to 10%; and silicon up to 2%.
Preferably the titanium content of the alloy does not exceed 40Z
in alloys intended for du~ies where low density is important for at higher titanium contents the alloy density approaches that obtainable from other alloys such as aluminium-lithium alloys. But it should be noted that the resistance to corrosion and the electrode potential improves with increasing titanium content SG a high titanium content might be preferred for this reason.
A most preferred range of titanium in the alloy is 15 to 28X.
Practical ternary alloys might include titanium in the aforementioned preferred range with either approximately 5% aluminium (to yield a physically stronger magnesium based material still having good corrosion resistance) or else approximately 1% silicon (to increase corrosion resistance still further).
2 1 a ~ ~ 1 2 Alloys within the scope of the claims have demonstrated thermal stability ~as ascertained by differential scanning calorimetry) up to 200-C and can be processed from comminuted particulate form by first can~ing the particulate and then extruding or hot isostatic pressing this.
The invention is further described below by reference to examples of materials made to varying compositions by two alternative vapour quenching methods and by reference to the drawings, of which:
0 Figure 1 is a schematic cross sectional view of one form of small scale evaporation equipment;
Figure 2 is a schematic cross sectional view of a second form of evaporation eguipment;
Figure 3 is a differential scanning calorimetry plot showing the thermal stability for a test sample of AS32 magnesium-titanium alloy heated over a temperature range of 50 to 500-C
at a rate of 10-/minute;
Figure 4 is a plot showing the corrosion resistance of heat treated sample of the magnesium-titanium alloy, and0 Figure 5 is a plot comparing the composition and density for the magnesium-titanium alloy.
Those alloy examples which follow and are designated with the prefix "VM" have been produced using the apparatus depicted in Figure 1. The apparatus has separate evaporators for the magnesium and titanium charges. The evaporator for the titanium charge comprises a water-cooled copper crucible 1 with an underside opening 2 through which is fed a rod charge of titanium 3 and there is an electron beam gun 4 which is beam steered so that the electrons impinge upon the topmost end of the rod charge 3 to cause this to be melted locally. A stream of titanium vapour 5 issues from the melt pool in an upward direction towards a collector 6 and the flux of vapours is controlled by adjustment to the power setting of the electron beam gun 4.
W O 93/12262 PCrtGB92/02279 210~Qi2 6 The evaporator for the magnesium base constituent of the alloy is a heated block 7 of metal of a generally "U" shaped configuration which is located above the level of the titanium source crucible l and is of a size and is positioned such that it encompasses the rising flux of titanium vapour on three sides thereof. Block 7 has an inwardly directed slot 8 within which solid charge pieces 9 of magnesium are placed and the block 7 is heated by means of a radiant heater lO, extending through the mass of the block, to a temperature at which magnesium vapour issues forth from the charge pieces 9 by sublimation. These vapours issue forth laterally through the slot opening to converge upon the rising flux of titanium vapour 5 and vapqur mixing takes place by mingling of the vapour streams and by atomic collisions. Some of the intermixed vapours rise upwards to condense upon the collector 6 to yield a deposit ll.
The collector is heated to and maintained at a suitable temperature to ensure that the impinging vapours are quenched to produce an appropriate microstructure in the alloy deposit ll.
Between the collector plate 6 and the sources of vapours there is a ~0 shutter 12, which is closed in the warm up period of operation of the equipment and opened when the equipment stabilises. This is a safeguard measure intended to avoid unwanted collection of deposits having the wrong compositlon.
In the use of the above-described apparatus in the production of the magnesium-titanium alloys exemplified below, the apparatus was controlled to the following parameters:
collector temperature 125 to 200-C
electron beam gun power 2-3kW
magnesium source temperature approximately 550C
vacuum chamber pressure around 5 x lO-; torr Variation of composition is achieved through alteration of the respective rates of generation of the titanium and magnesium vapours.
The electron beam gun power is ~aried within the range given above to increase or decrease the fiux of titanium vapours and the temperature W O 93/l2262 P ~ /GB92/02279 ~ 7 210~12 to which the magnesium source is heated is varied (but remaining below the melting temperature) to incresse or decrease the flux of magnesium vapour. Simultaneous manipulation of both these provides control over the alloy deposition rate.
Using different sources for the two separate ingredients as described above overcomes the problems of melt insolubility of one ingredient within the other and overcomes also problems which might otherwise be caused by gross differences between the vapour pressures exhibited by different ingredients. Ternary and more complicated alloys can be produced by , instead of having the rod charge comprising just titanium, using a pre-alloyed rod sour~-e containing both the titanium and the other ingredients, except for the magnesium which is provided for as heated blocks as described before.
The remaining alloys of the examples which follow were produced using the equipment depicted in Figure 2 and these alloy examples are identified with a prefix of "AS". More detailed information regarding th~s form of equipment is given in UK patent application GB 2240852.
This second form of equipment comprises an inner evaporation crucible 31 surrounded by a another evaporation crucible 32. A charge 33 of the titanium is con~ained within the crucible 31. This crucible is open topped and the charge of titanium within it is heated by means 25 of an electron beam 37. This electron beam 37 is focussed and steered by means of a magnet 38 to impinge upon the uppermost surface of the charge 33 to heat it to a temperature at which an appreciable flux of titanium vapours escapes from the charge. The other evaporation crucible 32 holds a charge 34 of magnesium within it and this charge is heated by a radiant heater 39. Crucible 32 has a lid 4O and there are nozzles 41 present in the lid through which a flux of magnesium vapours issues forth. The two crucibles are placed as depicted (one within the other) beneath a collector 35. The nozzles 41 are so directed as to cause the individual streams of magnesium vapours to 35 converge towards each other on paths which intersect the direct path between the other evaporator 31 and the collector 35 so that vapour mixing between the two species of vapours occurs before either species W O 93/l2262 PCT/GB92/02279 210~12 8 `-lands upon the collector. A deposit 36 of alloy is built up on the lower surface of the collector 35. The lid 40 is heated by a separate radiant heater 42 to a higher temperature than that of the magnesium charge. Moreover the nozzles are of re-entrant form as depicted in the figure and by this combination o~ re-entrant form and higher temperature, condensation within or upon the nozzle of magnesium vapours is minimised. The nozzles 41 serve the dual function of directing the streams of magnesium vapours and choking the volume flow-rate somewhat allowing the magnesium charge to be superheated to yield sufficient vapour pressure to disperse surface oxide contaminants from the surface of the melt without saturating the deposit with an excess of magnesium. In the deposition of the claimed magnesium-titanium alloys by this second form of equipment the evaporator 32 is charged with pieces of magnesium and heated to produce a melt of metal at a temperature of approximately 750-C. The temperature of the titanium charge 33 within evaporator 31 is not controlled directly, instead control of titanium evaporation rate and hence of alloy deposit composition is achieved by variation of electron beam power up to a maximum power of 20 kW. Ternary and more complex alloys can be produced by this second equipment by using a different form of inner crucible 31 accepting an under-fed rod source in the manner of the first type of equipment, and using a pre-alloyed titanium alloy rod charge of appropriate composition.
Vapour-quenched magnesium-titanium binary alloys to the following compositions have been produced by means of the two equipments described above. All compositions are given in proportions by weight.
Alloy designation Composition VM49 Mg base - 9.5X Ti VM46 Mg base - 21Z Ti VM47 Mg base - 26.5% Ti VM48 Mg base - 37% Ti VM44 Mg base - 47% Ti ASl9 Mg base - 1.5%Ti ASZ0 Mg base - Z.0%Ti AS18 Mg base - 7.4XTi AS21 Mg base - 8.4ZTi AS23 Mg base - 15.3ZTi AS22 Mg base - 22.0XTi AS14 Mg base - 27.5ZTi 9 210~1 2 Tensile tests have been performed on specimens prepared from certain of the alloys. The alloy deposit was first removed from the collector then comminuted to particles, canned then hot isostatically pressed and subsequently extruded at 180-C. Tensile properties are as 5 rOllOws:
.... .. ...
Alloy 0.2% Tensileelongation Reduction proof stress strength(~) in area (MPa) (MPa) (%~
AS 23 212 283 3.4 10 AS 22 243 317 1.6 2.5 Corrosion resistance tests have been performed on various examples of the claimed alloy and also a comparison specimen of puré magnesium prepared by the sflme vapour quenching route. These materials were all tested in the as-deposited condition. Some other comparison materials were tested also in their normal commercially avsilable form. These additional comparison materials are listed below: WE 43 (nominal composition: Mg base - 4%Y - 3%Nd ~ other rare earths - 0.5ZZr);
AZ9lE (nominal composition: Mg base - 9%Al - 0.5%Zr - 0.3ZMn); and EA55RS a rapid solidification route alloy (nominal composition: Mg base - 5XAl - 5XZn - 5%Nd). The corrosion resistance tests comprised a total immersion of standard coupons of the material in 600mM/l sodium chloride solution for a period of 7 days followed by cleaning (in accordance with ASTM Gl-81) to remove corrosion products and weighing to determine weight change. A rate of corrosion in terms of weight loss per day was calculated (mg/dm2 per day) and from this a corrosion rate expressed in terms of millimetres per year -representative of the rate of corrosion penetration - was derived using the following expression:
~orrosion rate = corrosion rate x 0.0365/density of alloy (mm/year) (mg/dm2 per day) 2~ ~40~2 lo Results of the corrosion resistance tests are given below:
Alloy Corrosion rate (mm/year) _ As 19 0.30 AS 20 0.33 AS 18 weight gain~
AS 22 0.03 AS 14 weight gain VM 44 0.005 pure magnesium 0.49 WE43 (commercial corrosion 0.42 resistant Mg alloy) AZ9lE ( ditto ) 0.24 EA55RS ( ditto ) 0.14 NOTES
~ weight gain indicates that corrosion products are stable.
2 AZ9lE relies for its corrosion resistance upon its high purity and this low value of corrosion rate may not be representative of resistance to corrosion in practical situations where contact with contaminants cannot be avoided.
- The other aspect to corrosion resistance is the electrode potential exhibited by the material. This value has been measured for the alloy examPles listed below. The values of electrode potential given represent the open circuit potentisl (relative to a standard saturated calomel electrode) exhibited by the alloys in a 600mM/l solution of sodium chloride after 30 minutes immersion therein.
Material ¦ Open-circuit potential _ pure Mg -1675mV
VM49 -1378mV
VM46 -1360mV
VM47 -1354mV
VM44 -1301mV
_ W O 93/12262 21~ ~ O 12 PCTJGB92/02279 The experimental results documented above indicate that alloys containing titanium even at low levels such as 1.5% produce 8 useful tegree of corrosion resistance compared to both pure magnesium and prior art alloy WE43. At higher levels of titanium, such as 7.4%
plus, the alloys demonstrate a marked improvement in corossion resistance compared with the best comparative materials AZ9lE and EA55RS. Significant reductions in the high negative electrode potential of pure magnesium are achieved with titanium levels as low as 8 to 11%. The strength and ductility are reasonable for binary magnesium based alloys. Additions of Zn (up to 2X) or Al (up to loX) or Si (up to 2X) can provide significant strengthening with little adverse effect on predicted corrosion resistance. Also Zr will give a useful grain refinement effect with consequential strengthening or toughening and no significant predicted adverse effect on corrosion resistance. Mn will be expected to yield some increase in corrosion resistance but no significant increase in strength.
The thermal stability of the alloys is important because most applications require use at temperatures significantly above room temperature and it is important that there is no degradation in mechanical properties and corrosion resistance. An early indication of the thermal stability of these alloys can be obtained from differential scanning calorimetry (DSC). DSC of these magnesium titanium alloys indicates that their short term stability extends to at least 230-C as is shown in Figure 3.
Corrosion tests on a magnesium - 42.6X titanium alloy which had been heat treated for one hour at temperatures in the range 140 -240-C show that there is no detrimental effect on corrosion resistance as shown in the table below and in Figure 4.
W O 93/12262 P ~ /GB92/02279 2 1~
Corrosion test results for heat treated Mg - 42.6wtX Ti alloy.
Heat Treatment Corrosion Rate 1 hour at mm/year as deposited 0.315 140' 0.59 160- 0.32 200- 0.33 22~- 0.35 240- 0.35 pure vapour 0.59 deposited magnesium Maintaining the low density of magnesium alloys is important for -aerospace applications. It is essential that the levels of titanium required to reduce the corrosion rate oi the alloys do not increase the density to unacceptable levels. Analysis shows a maximum value of around 2.1 g/cm3 should be an objective for these alloys.
Measurements of the density of the deposited alloys, when compared with the accepted value for pure magnesium and values calculated from lattice parameter measurement, suggest that there is some porosity but that alloys containing less than around 28 wtX. of titanium should have good specific properties. This is shown in the table below and also in Figure 5. The corrosion tests results indicate that an upper limit of 28% titanium should not limit the development of a good corrosion resistant alloy.
W O 93/12262 P ~ /G892/02279 13 ;~ 2 Measured and calculated relative densities for Mg-Ti alloys.
__............ . .
~omposition Measured Relative CPlculated Relative wtZ Ti Density Density . . _ 0 1.68 1.74 8.4 1.77 .
8.4 1.82 11 1.89 15-3 1.81 18 3 1.91 1.95 243-7 12 93 2.13 27.8 1.99 31.2 . 1.94 .
42.6 2.44
Preferably the alloys have a titanium content in the range 5 to 40% by weight.
We have demonstrated a marked improvement in corrosion resistance in these alloys compared to prior art materials and compared to alternative research materials with different alloying ingredients such as aluminium. chromium and silicon.
The magnesium alloy may contain. in addition to the titanium, other ingredients such as those used in prior art magnesium alloys within the following weight limits:
manganese up to 6X; aluminium up to 13%; zinc up to 7X;
zirconium up to 5%; neodymium up to 6%; commercial mixed rare earths up to 5% yttrium up to 6%; silver up to 3%; thorium up to 5%;
lithium up to 10%; and silicon up to 2%.
Preferably the titanium content of the alloy does not exceed 40Z
in alloys intended for du~ies where low density is important for at higher titanium contents the alloy density approaches that obtainable from other alloys such as aluminium-lithium alloys. But it should be noted that the resistance to corrosion and the electrode potential improves with increasing titanium content SG a high titanium content might be preferred for this reason.
A most preferred range of titanium in the alloy is 15 to 28X.
Practical ternary alloys might include titanium in the aforementioned preferred range with either approximately 5% aluminium (to yield a physically stronger magnesium based material still having good corrosion resistance) or else approximately 1% silicon (to increase corrosion resistance still further).
2 1 a ~ ~ 1 2 Alloys within the scope of the claims have demonstrated thermal stability ~as ascertained by differential scanning calorimetry) up to 200-C and can be processed from comminuted particulate form by first can~ing the particulate and then extruding or hot isostatic pressing this.
The invention is further described below by reference to examples of materials made to varying compositions by two alternative vapour quenching methods and by reference to the drawings, of which:
0 Figure 1 is a schematic cross sectional view of one form of small scale evaporation equipment;
Figure 2 is a schematic cross sectional view of a second form of evaporation eguipment;
Figure 3 is a differential scanning calorimetry plot showing the thermal stability for a test sample of AS32 magnesium-titanium alloy heated over a temperature range of 50 to 500-C
at a rate of 10-/minute;
Figure 4 is a plot showing the corrosion resistance of heat treated sample of the magnesium-titanium alloy, and0 Figure 5 is a plot comparing the composition and density for the magnesium-titanium alloy.
Those alloy examples which follow and are designated with the prefix "VM" have been produced using the apparatus depicted in Figure 1. The apparatus has separate evaporators for the magnesium and titanium charges. The evaporator for the titanium charge comprises a water-cooled copper crucible 1 with an underside opening 2 through which is fed a rod charge of titanium 3 and there is an electron beam gun 4 which is beam steered so that the electrons impinge upon the topmost end of the rod charge 3 to cause this to be melted locally. A stream of titanium vapour 5 issues from the melt pool in an upward direction towards a collector 6 and the flux of vapours is controlled by adjustment to the power setting of the electron beam gun 4.
W O 93/12262 PCrtGB92/02279 210~Qi2 6 The evaporator for the magnesium base constituent of the alloy is a heated block 7 of metal of a generally "U" shaped configuration which is located above the level of the titanium source crucible l and is of a size and is positioned such that it encompasses the rising flux of titanium vapour on three sides thereof. Block 7 has an inwardly directed slot 8 within which solid charge pieces 9 of magnesium are placed and the block 7 is heated by means of a radiant heater lO, extending through the mass of the block, to a temperature at which magnesium vapour issues forth from the charge pieces 9 by sublimation. These vapours issue forth laterally through the slot opening to converge upon the rising flux of titanium vapour 5 and vapqur mixing takes place by mingling of the vapour streams and by atomic collisions. Some of the intermixed vapours rise upwards to condense upon the collector 6 to yield a deposit ll.
The collector is heated to and maintained at a suitable temperature to ensure that the impinging vapours are quenched to produce an appropriate microstructure in the alloy deposit ll.
Between the collector plate 6 and the sources of vapours there is a ~0 shutter 12, which is closed in the warm up period of operation of the equipment and opened when the equipment stabilises. This is a safeguard measure intended to avoid unwanted collection of deposits having the wrong compositlon.
In the use of the above-described apparatus in the production of the magnesium-titanium alloys exemplified below, the apparatus was controlled to the following parameters:
collector temperature 125 to 200-C
electron beam gun power 2-3kW
magnesium source temperature approximately 550C
vacuum chamber pressure around 5 x lO-; torr Variation of composition is achieved through alteration of the respective rates of generation of the titanium and magnesium vapours.
The electron beam gun power is ~aried within the range given above to increase or decrease the fiux of titanium vapours and the temperature W O 93/l2262 P ~ /GB92/02279 ~ 7 210~12 to which the magnesium source is heated is varied (but remaining below the melting temperature) to incresse or decrease the flux of magnesium vapour. Simultaneous manipulation of both these provides control over the alloy deposition rate.
Using different sources for the two separate ingredients as described above overcomes the problems of melt insolubility of one ingredient within the other and overcomes also problems which might otherwise be caused by gross differences between the vapour pressures exhibited by different ingredients. Ternary and more complicated alloys can be produced by , instead of having the rod charge comprising just titanium, using a pre-alloyed rod sour~-e containing both the titanium and the other ingredients, except for the magnesium which is provided for as heated blocks as described before.
The remaining alloys of the examples which follow were produced using the equipment depicted in Figure 2 and these alloy examples are identified with a prefix of "AS". More detailed information regarding th~s form of equipment is given in UK patent application GB 2240852.
This second form of equipment comprises an inner evaporation crucible 31 surrounded by a another evaporation crucible 32. A charge 33 of the titanium is con~ained within the crucible 31. This crucible is open topped and the charge of titanium within it is heated by means 25 of an electron beam 37. This electron beam 37 is focussed and steered by means of a magnet 38 to impinge upon the uppermost surface of the charge 33 to heat it to a temperature at which an appreciable flux of titanium vapours escapes from the charge. The other evaporation crucible 32 holds a charge 34 of magnesium within it and this charge is heated by a radiant heater 39. Crucible 32 has a lid 4O and there are nozzles 41 present in the lid through which a flux of magnesium vapours issues forth. The two crucibles are placed as depicted (one within the other) beneath a collector 35. The nozzles 41 are so directed as to cause the individual streams of magnesium vapours to 35 converge towards each other on paths which intersect the direct path between the other evaporator 31 and the collector 35 so that vapour mixing between the two species of vapours occurs before either species W O 93/l2262 PCT/GB92/02279 210~12 8 `-lands upon the collector. A deposit 36 of alloy is built up on the lower surface of the collector 35. The lid 40 is heated by a separate radiant heater 42 to a higher temperature than that of the magnesium charge. Moreover the nozzles are of re-entrant form as depicted in the figure and by this combination o~ re-entrant form and higher temperature, condensation within or upon the nozzle of magnesium vapours is minimised. The nozzles 41 serve the dual function of directing the streams of magnesium vapours and choking the volume flow-rate somewhat allowing the magnesium charge to be superheated to yield sufficient vapour pressure to disperse surface oxide contaminants from the surface of the melt without saturating the deposit with an excess of magnesium. In the deposition of the claimed magnesium-titanium alloys by this second form of equipment the evaporator 32 is charged with pieces of magnesium and heated to produce a melt of metal at a temperature of approximately 750-C. The temperature of the titanium charge 33 within evaporator 31 is not controlled directly, instead control of titanium evaporation rate and hence of alloy deposit composition is achieved by variation of electron beam power up to a maximum power of 20 kW. Ternary and more complex alloys can be produced by this second equipment by using a different form of inner crucible 31 accepting an under-fed rod source in the manner of the first type of equipment, and using a pre-alloyed titanium alloy rod charge of appropriate composition.
Vapour-quenched magnesium-titanium binary alloys to the following compositions have been produced by means of the two equipments described above. All compositions are given in proportions by weight.
Alloy designation Composition VM49 Mg base - 9.5X Ti VM46 Mg base - 21Z Ti VM47 Mg base - 26.5% Ti VM48 Mg base - 37% Ti VM44 Mg base - 47% Ti ASl9 Mg base - 1.5%Ti ASZ0 Mg base - Z.0%Ti AS18 Mg base - 7.4XTi AS21 Mg base - 8.4ZTi AS23 Mg base - 15.3ZTi AS22 Mg base - 22.0XTi AS14 Mg base - 27.5ZTi 9 210~1 2 Tensile tests have been performed on specimens prepared from certain of the alloys. The alloy deposit was first removed from the collector then comminuted to particles, canned then hot isostatically pressed and subsequently extruded at 180-C. Tensile properties are as 5 rOllOws:
.... .. ...
Alloy 0.2% Tensileelongation Reduction proof stress strength(~) in area (MPa) (MPa) (%~
AS 23 212 283 3.4 10 AS 22 243 317 1.6 2.5 Corrosion resistance tests have been performed on various examples of the claimed alloy and also a comparison specimen of puré magnesium prepared by the sflme vapour quenching route. These materials were all tested in the as-deposited condition. Some other comparison materials were tested also in their normal commercially avsilable form. These additional comparison materials are listed below: WE 43 (nominal composition: Mg base - 4%Y - 3%Nd ~ other rare earths - 0.5ZZr);
AZ9lE (nominal composition: Mg base - 9%Al - 0.5%Zr - 0.3ZMn); and EA55RS a rapid solidification route alloy (nominal composition: Mg base - 5XAl - 5XZn - 5%Nd). The corrosion resistance tests comprised a total immersion of standard coupons of the material in 600mM/l sodium chloride solution for a period of 7 days followed by cleaning (in accordance with ASTM Gl-81) to remove corrosion products and weighing to determine weight change. A rate of corrosion in terms of weight loss per day was calculated (mg/dm2 per day) and from this a corrosion rate expressed in terms of millimetres per year -representative of the rate of corrosion penetration - was derived using the following expression:
~orrosion rate = corrosion rate x 0.0365/density of alloy (mm/year) (mg/dm2 per day) 2~ ~40~2 lo Results of the corrosion resistance tests are given below:
Alloy Corrosion rate (mm/year) _ As 19 0.30 AS 20 0.33 AS 18 weight gain~
AS 22 0.03 AS 14 weight gain VM 44 0.005 pure magnesium 0.49 WE43 (commercial corrosion 0.42 resistant Mg alloy) AZ9lE ( ditto ) 0.24 EA55RS ( ditto ) 0.14 NOTES
~ weight gain indicates that corrosion products are stable.
2 AZ9lE relies for its corrosion resistance upon its high purity and this low value of corrosion rate may not be representative of resistance to corrosion in practical situations where contact with contaminants cannot be avoided.
- The other aspect to corrosion resistance is the electrode potential exhibited by the material. This value has been measured for the alloy examPles listed below. The values of electrode potential given represent the open circuit potentisl (relative to a standard saturated calomel electrode) exhibited by the alloys in a 600mM/l solution of sodium chloride after 30 minutes immersion therein.
Material ¦ Open-circuit potential _ pure Mg -1675mV
VM49 -1378mV
VM46 -1360mV
VM47 -1354mV
VM44 -1301mV
_ W O 93/12262 21~ ~ O 12 PCTJGB92/02279 The experimental results documented above indicate that alloys containing titanium even at low levels such as 1.5% produce 8 useful tegree of corrosion resistance compared to both pure magnesium and prior art alloy WE43. At higher levels of titanium, such as 7.4%
plus, the alloys demonstrate a marked improvement in corossion resistance compared with the best comparative materials AZ9lE and EA55RS. Significant reductions in the high negative electrode potential of pure magnesium are achieved with titanium levels as low as 8 to 11%. The strength and ductility are reasonable for binary magnesium based alloys. Additions of Zn (up to 2X) or Al (up to loX) or Si (up to 2X) can provide significant strengthening with little adverse effect on predicted corrosion resistance. Also Zr will give a useful grain refinement effect with consequential strengthening or toughening and no significant predicted adverse effect on corrosion resistance. Mn will be expected to yield some increase in corrosion resistance but no significant increase in strength.
The thermal stability of the alloys is important because most applications require use at temperatures significantly above room temperature and it is important that there is no degradation in mechanical properties and corrosion resistance. An early indication of the thermal stability of these alloys can be obtained from differential scanning calorimetry (DSC). DSC of these magnesium titanium alloys indicates that their short term stability extends to at least 230-C as is shown in Figure 3.
Corrosion tests on a magnesium - 42.6X titanium alloy which had been heat treated for one hour at temperatures in the range 140 -240-C show that there is no detrimental effect on corrosion resistance as shown in the table below and in Figure 4.
W O 93/12262 P ~ /GB92/02279 2 1~
Corrosion test results for heat treated Mg - 42.6wtX Ti alloy.
Heat Treatment Corrosion Rate 1 hour at mm/year as deposited 0.315 140' 0.59 160- 0.32 200- 0.33 22~- 0.35 240- 0.35 pure vapour 0.59 deposited magnesium Maintaining the low density of magnesium alloys is important for -aerospace applications. It is essential that the levels of titanium required to reduce the corrosion rate oi the alloys do not increase the density to unacceptable levels. Analysis shows a maximum value of around 2.1 g/cm3 should be an objective for these alloys.
Measurements of the density of the deposited alloys, when compared with the accepted value for pure magnesium and values calculated from lattice parameter measurement, suggest that there is some porosity but that alloys containing less than around 28 wtX. of titanium should have good specific properties. This is shown in the table below and also in Figure 5. The corrosion tests results indicate that an upper limit of 28% titanium should not limit the development of a good corrosion resistant alloy.
W O 93/12262 P ~ /G892/02279 13 ;~ 2 Measured and calculated relative densities for Mg-Ti alloys.
__............ . .
~omposition Measured Relative CPlculated Relative wtZ Ti Density Density . . _ 0 1.68 1.74 8.4 1.77 .
8.4 1.82 11 1.89 15-3 1.81 18 3 1.91 1.95 243-7 12 93 2.13 27.8 1.99 31.2 . 1.94 .
42.6 2.44
Claims (6)
1. A magnesium based alloy produced by vapour quenching, comprising 0.5% to 47% of titanium by weight, and within which the titanium is substantially held in solid solution in the alloy as deposited.
2. A magnesium based alloy as claimed in claim 1, characterised by comprising 5% to 40% of titanium by weight.
3. A magnesium based alloy as claimed in claim 1, characterised by comprising 15% to 28% of titanium by weight.
4. A magnesium based alloy as claimed in any one of the preceding claims, characterised by additionally comprising ingredients other than titanium and magnesium from within the group which follows and within the stated individual proportional limits by weight: manganese up to 6%; aluminium up to 13%; zinc up to 7%; zirconium up to 5%:
neodymium up to 6%; commercial mixed rare earths up to 5%; yttrium up to 6%; silver up to 3%; thorium up to 5%; lithium up to 10%;
and silicon up to 2%.
neodymium up to 6%; commercial mixed rare earths up to 5%; yttrium up to 6%; silver up to 3%; thorium up to 5%; lithium up to 10%;
and silicon up to 2%.
5. A magnesium based alloy as claimed in claim 3 or claim 4, characterised by comprising 5% aluminium.
6. A magnesium based alloy as claimed in claim 3 or claim 4, characterised by comprising 1% silicon.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9126619.7 | 1991-12-16 | ||
| GB9126619A GB2262539A (en) | 1991-12-16 | 1991-12-16 | Titanium containing magnesium alloy produced by vapour quenching. |
| PCT/GB1992/002279 WO1993012262A1 (en) | 1991-12-16 | 1992-12-09 | Titanium containing magnesium alloy produced by vapour quenching |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2104012A1 true CA2104012A1 (en) | 1993-06-17 |
Family
ID=10706308
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002104012A Abandoned CA2104012A1 (en) | 1991-12-16 | 1992-12-09 | Titanium containing magnesium alloy produced by vapour quenching |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0571595A1 (en) |
| JP (1) | JPH06506505A (en) |
| CA (1) | CA2104012A1 (en) |
| GB (1) | GB2262539A (en) |
| WO (1) | WO1993012262A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1996004409A1 (en) * | 1994-08-01 | 1996-02-15 | Franz Hehmann | Selected processing for non-equilibrium light alloys and products |
| EP1260545A1 (en) | 2001-05-21 | 2002-11-27 | Borealis Technology OY | Industrial polyolefin piping system |
| EP1260528A1 (en) | 2001-05-21 | 2002-11-27 | Borealis Technology OY | Propylene polymer pipes for pipelines |
| US7651732B2 (en) * | 2007-09-07 | 2010-01-26 | Gm Global Technology Operations, Inc. | Magnesium-titanium solid solution alloys |
| DE102013108997A1 (en) * | 2013-08-20 | 2015-02-26 | Von Ardenne Gmbh | Crucible arrangement and vacuum coating system |
| CN105401030A (en) * | 2015-11-10 | 2016-03-16 | 太仓捷公精密金属材料有限公司 | Anti-corrosion titanium-magnesium alloy material |
| CN108456813B (en) * | 2018-01-22 | 2020-02-21 | 上海交通大学 | Mg-Li-Al-Zn-Y series cast magnesium-lithium alloy and heat treatment method thereof |
| CN111118364B (en) * | 2020-01-16 | 2021-08-24 | 江苏理工学院 | Mg-Y-Nd-Gd-Zr-Li alloy capable of being rapidly age-strengthened and preparation method thereof |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2178582A (en) * | 1936-11-23 | 1939-11-07 | Dow Chemical Co | Magnesium alloy |
| US2340795A (en) * | 1942-03-25 | 1944-02-01 | Wander Company | Magnesium alloy |
| US3240593A (en) * | 1961-06-02 | 1966-03-15 | Knapsack Ag | Corrosion resistant magnesium alloys having a grain-refined structure |
| GB1382970A (en) * | 1973-09-04 | 1975-02-05 | Tikhonova V V | Magnesium based alloys |
| US4264362A (en) * | 1977-11-25 | 1981-04-28 | The United States Of America As Represented By The Secretary Of The Navy | Supercorroding galvanic cell alloys for generation of heat and gas |
| JPH0617524B2 (en) * | 1988-11-08 | 1994-03-09 | 勝廣 西山 | Magnesium-titanium sintered alloy and method for producing the same |
| GB2230792A (en) * | 1989-04-21 | 1990-10-31 | Secr Defence | Multiple source physical vapour deposition. |
| GB2252979A (en) * | 1991-02-25 | 1992-08-26 | Secr Defence | A metastable solid solution titanium-based alloy produced by vapour quenching. |
-
1991
- 1991-12-16 GB GB9126619A patent/GB2262539A/en not_active Withdrawn
-
1992
- 1992-12-09 EP EP19920924804 patent/EP0571595A1/en not_active Ceased
- 1992-12-09 WO PCT/GB1992/002279 patent/WO1993012262A1/en not_active Application Discontinuation
- 1992-12-09 CA CA002104012A patent/CA2104012A1/en not_active Abandoned
- 1992-12-09 JP JP5510707A patent/JPH06506505A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0571595A1 (en) | 1993-12-01 |
| GB2262539A (en) | 1993-06-23 |
| WO1993012262A1 (en) | 1993-06-24 |
| GB9126619D0 (en) | 1992-02-12 |
| JPH06506505A (en) | 1994-07-21 |
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