CA2196479A1 - Semi-solid metal casting process - Google Patents
Semi-solid metal casting processInfo
- Publication number
- CA2196479A1 CA2196479A1 CA002196479A CA2196479A CA2196479A1 CA 2196479 A1 CA2196479 A1 CA 2196479A1 CA 002196479 A CA002196479 A CA 002196479A CA 2196479 A CA2196479 A CA 2196479A CA 2196479 A1 CA2196479 A1 CA 2196479A1
- Authority
- CA
- Canada
- Prior art keywords
- billet
- semi
- ingot
- temperature
- die casting
- 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
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D18/00—Pressure casting; Vacuum casting
- B22D18/02—Pressure casting making use of mechanical pressure devices, e.g. cast-forging
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
- B21C23/00—Extruding metal; Impact extrusion
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
- B21J5/004—Thixotropic process, i.e. forging at semi-solid state
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/12—Making non-ferrous alloys by processing in a semi-solid state, e.g. holding the alloy in the solid-liquid phase
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Extrusion Of Metal (AREA)
Abstract
A semi-solid metal die casting process using a cast ingot and having the following steps:
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
2. extruding the ingot into an extruded column;
3. cutting the extruded column into at least one billet prior to its cooling;
4. heating the billet from step 3 to a semi-solid state; and 5. squeezing the billet from step 4 into a cavity in a die casting mold to form a part.
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
2. extruding the ingot into an extruded column;
3. cutting the extruded column into at least one billet prior to its cooling;
4. heating the billet from step 3 to a semi-solid state; and 5. squeezing the billet from step 4 into a cavity in a die casting mold to form a part.
Description
2 1 964 7q .. 1 -Title: Semi-Solid Metal Casting Process Inventor: Gordon Woodhouse FIELD OF THE INVENTION
This invention relates generally to semi-solid metal casting and more particularly to the formation and use of magnesium billets in semi-solid 10 metal casting processes.
BACKGROUND
Metal die casting is a process in which molten metal is caused to flow 15 into a cavity defined by a mold. In conventional metal die casting, molten metal is injected into the cavity. In semi-solid metal die casting processes, a metal billet is pre-heated to a point of softening, to a temperature above the solidus and below the liquidus to produce a partially solid, partially liquid consistency prior to placing the billet or "slug" in a shot sleeve in the casting 20 machine.
Semi-solid metal die casting enables control of the microstructure of the finished part to a degree which produces a stronger part than is possible with conventional molten metal die-casting processes. As 25 compared with conventional metal die-casting processes, semi-solid metal casting produces parts of improved casting quality in that they exhibit lower porosity, parts shrink less upon cooling enabling closer tolerances and physical properties are better. In addition, semi-solid metal casting has a 21 9647q reduced cycle time and the lower temperatures utilized result in decreased die wear. Because of the absence of molten metal there is less pollution and safety hazards are reduced.
In semi-solid metal die c~ting~ a billet is first formed which is treated to form fine grained equiaxed crystals as opposed to a dentritic structure.
Subsequent heating, forming and solidification of a formed part using a treated billet avoids the formation of a dentritic structure in the finished part.
To work sl-ccessfully in semi-solid metal casting, the grain structure of a billet must exhibit the necessary degree of lubricity and viscosity to givegood laminar flow in the die cavity. For example an untreated DC cast billet will shear along its dentritic axis rather than flow hence the need for fine grained equiaxed crystals.
Flowability is further affected by grain size and solid/liquid ratio. In addition forming parameters such as die temperatures and gate velocity will affect the casting process. Accordingly, all of the foregoing parameters have to be optimi7eC~ in order to produce successful parts.
The billets were cooled at a high chill rate lltili7ing copper molds and a water spray to provide a chill rate of at least 2~C per second at the billet centre.
This invention relates generally to semi-solid metal casting and more particularly to the formation and use of magnesium billets in semi-solid 10 metal casting processes.
BACKGROUND
Metal die casting is a process in which molten metal is caused to flow 15 into a cavity defined by a mold. In conventional metal die casting, molten metal is injected into the cavity. In semi-solid metal die casting processes, a metal billet is pre-heated to a point of softening, to a temperature above the solidus and below the liquidus to produce a partially solid, partially liquid consistency prior to placing the billet or "slug" in a shot sleeve in the casting 20 machine.
Semi-solid metal die casting enables control of the microstructure of the finished part to a degree which produces a stronger part than is possible with conventional molten metal die-casting processes. As 25 compared with conventional metal die-casting processes, semi-solid metal casting produces parts of improved casting quality in that they exhibit lower porosity, parts shrink less upon cooling enabling closer tolerances and physical properties are better. In addition, semi-solid metal casting has a 21 9647q reduced cycle time and the lower temperatures utilized result in decreased die wear. Because of the absence of molten metal there is less pollution and safety hazards are reduced.
In semi-solid metal die c~ting~ a billet is first formed which is treated to form fine grained equiaxed crystals as opposed to a dentritic structure.
Subsequent heating, forming and solidification of a formed part using a treated billet avoids the formation of a dentritic structure in the finished part.
To work sl-ccessfully in semi-solid metal casting, the grain structure of a billet must exhibit the necessary degree of lubricity and viscosity to givegood laminar flow in the die cavity. For example an untreated DC cast billet will shear along its dentritic axis rather than flow hence the need for fine grained equiaxed crystals.
Flowability is further affected by grain size and solid/liquid ratio. In addition forming parameters such as die temperatures and gate velocity will affect the casting process. Accordingly, all of the foregoing parameters have to be optimi7eC~ in order to produce successful parts.
The billets were cooled at a high chill rate lltili7ing copper molds and a water spray to provide a chill rate of at least 2~C per second at the billet centre.
An earlier process for forming a treated billet involves the use of m~gnetic stirring during the cooling of a cast billet to break up and avoid the formation of a dentritic structure. Magnetic stirring is however a relatively slow and expensive process.
U.S. patent no. 4,415,374 (Young et al) des~ibes an alternate process for forming a billet of aluminum for use in a semi-solid metal die casting process. Young et al describes a process having the following steps:
1. Melting and casting an ingot;
2. Cooling the ingot to room temperature;
3. Reheating the ingot above its recrystallization temperature but below its solidus temperature;
U.S. patent no. 4,415,374 (Young et al) des~ibes an alternate process for forming a billet of aluminum for use in a semi-solid metal die casting process. Young et al describes a process having the following steps:
1. Melting and casting an ingot;
2. Cooling the ingot to room temperature;
3. Reheating the ingot above its recrystallization temperature but below its solidus temperature;
4. Extruding the ingot;
5. Cooling the ingot to room temperature;
6. Cold working the ingot;
7. Reheating the ingot above its solidus temperature; and 8. Forming and quenching the ingot.
The ingot produced according to the process described in Young may 20 then be subsequently heated to semi-solid casting temperature and formed into a part in a die casting process.
Even though Young avoids the requirement for magnetic stirring, it is nevertheless a cumbersome process including a large number of process 25 steps.
More recently a process has been proposed in which a cast ingot is machined down to a billet of approximately one inch in diameter and 21 9647q deformed by subjection to a compressive force. The deformed billet is then heated to a temperature above its recrystallization temperature and below its solidus temperature. The billet is then cooled to room temperature for subsequent re-heating and use in a semi-solid metal casting process. This 5 process however involves an expensive and wasteful ma~hining operation and only appears to work with relatively small billet diameters of less than about one inch (approximately 25 mm) diameter.
It is therefore an object of the present invention to provide a process 10 for semi-solid metal die casting which avoids not only magnetic stirring, butalso eliminates many of the steps that would be required pursuant to the Young process.
It is a further object of the present invention to provide a semi-solid 15 metal die casting process which avoids the maching, cold working heating, cooling and re-heating steps associated with other processes.
It is yet a further object of the present invention to provide a process capable of forming billets for use in semi-solid metal die casting processes 20 that may be significantly greater than about one inch (approximately 25 mm) in diameter.
SUMMARY OF THE INVENTION
A semi-solid metal die casting process using a cast ingot and having the following steps:
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
2. extruding the ingot in an extruded column;
- 21 ~6479 3. cutting the extruded column into at least one billet prior to its cooling;
4. heating the billet from step 3 to a forming temperature corresponding to a semi-solid state; and 5. squeezing the billet from step 4 into a cavity in a die casting mold to form a part.
DESCRIPTION OF DRAWINGS
Plefelled embodin~ents of the present invention are described below with rerelel.ce to the accompanying drawings in which:
Figure 1 is a schematic representation of the process of the present invention;
Figures 2 through 30 are photomicrographs of billets cut from extruded ingots and are individually described in Example 1 below;
Figure 31 illustrates sample locations in a test plate which were tested in Example 3;
Figure 32 illustrates the locations at which photomicrographs were taken in Example 3 below; and Figures 33 through 36 are photomicrographs individually described in Example 3 below.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to Figure 1, molten metal 10 is poured from a ladle into a mold 12 and allowed to solidify into an ingot 14. The ingot 14 is heated, for example by inductive heating coil 16 to a temperature above its recrystallization temperature and below its solidus temperature.
The heated ingot 14 is then extruded through an extruding die 18 to form an extruded column 20. The extruded column 20 is cut to a suitable length billet 22 for use in a semi-solid metal die casting process.
The billet 22 is heated to a forming temperature corresponding to a semi-solid state, for example by induction coils 24, and transferred to a die casting apparatus 26. The heated billet 22 is squeezed by the die casting apparatus into a cavity 28 between mold parts 30 and 32 to form a part 34 conforming in shape to that of the cavity 28.
The present invention is further illustrated by the examples set out below.
The microstructure of two AZ61 alloy, 3 in. diameter by 7 in. length extruded billets in the as extruded and solution heat treated condition were examined.
The billets were produced initially as an 8 1/2 in. direct chill cast billet.
The billets were cut into 2 ft. long sections and the diameter machined down to 8 in. to remove imperfections to the outside edge.
Graining sizing of the 8 inch billet perpendicular to the extrusion axis was 38 microns at the outside, 48 microns at the half radius and 48 microns at the center. As expected, the grain size in the longitudinal or extrusion direction was somewhat larger being approximately 51 microns at the outside, 64 microns at the half radius and 74 microns at the center.
The billets were then heated in 4-6 minute intervals in three induction furnaces. The furnaces heated the billets to 100~C, 200~C, 300~C
(total heating time approximately 15 minutes.) The billet was then placed in the extrusion chamber, which was at 380~C and the billet was extruded at 21 9~47~
between 330~C and 350~C, in one stage down to a 3 in. diameter extrusion billet. The first 14 ft. of extrusion and the last few feet were discarded. The r~m~inc~er of the extrusion was cut into 7 in. sections or "slugs".
Two of the sections of the extrusion billet referred to as billet 1 and billet 2, in AZ61 alloy were examined in the "as extruded" condition by sectioning a 0.5 in. section off the end of each billet, (billets were randomly 10 selected.) A micro was taken perpendicular to the axis of the billet from the centre and from the outside edge. The micros were polished and etched using 2% nitol etchant. The micros were examined at various magnifications to observe grain structure. A photomicrograph was taken at each magnification and the grain size estimated.
The two extrusion billet sections were then given the following solution heat treatment to recrystallize the grain structure;
Ramp 150~C - 338~C 3.0 hrs Hold 338~C 0.1 hrs Ramp 338~C - 413~C 1.5 hrs Hold 413~C 0.5 hrs Ramp 413~C - 426~C 0.5 hrs Hold 426~C 12.0 hrs Air Cool (Furnace atmosphere 10% CO2 to avoid ignition.;
The same procedure was followed in billet sectioning polishing and etching as previously described with the "as extruded" billet sections.
~t 96479 From the same samples micros were made at the centre of each billet parallel to the extrusion axis. These micros were taken from the as extruded and the solution heat treated billets. Photo micrographs were made at from 100 x to 400 x magnifi~ion of these samples.
The purpose for solution heat treating the extrusion billets and analyzing the samples was to determine the effect on grain size and shape resulting from heating and extruding the DC cast billet. The solution heat treating was not carried out under the optimum circumstances as 10 equipment availability necessitated the use of convection heating rather than induction heating. Preferably the heating cycle should not exceed 20 minutes and accordingly multi-state induction heating would be preferable over convection heating. Nevertheless the results were quite favourable as set out below.
RESULTS
The photomicrographs which are set out in Figures 2 through 30 below were 20 taken are as follows:
Figure 2 is a photomicrograph of the outside edge of billet 1, as extruded, at 200 x magnification.
25Figure 3 is a photomicrograph of the outside edge of billet 1, as extruded at 400 x m~gnific~tion;
Figure 4 is a photomicrograph of the centre of billet 1, as extruded under 100 x magnification;
Figure 5 is a photomicrograph of the centre of billet 1, as extruded under 200 x magnification;
g Figure 6 is a photomicrograph of the outside edge of billet 2, as extruded, at 200 x magnification;
Figure 7 is a photomicrograph of the outside edge of billet 2, as 5 extruded, at 400 x magnification;
Figure 8 is a photomicrograph of the centre of billet 1, as extruded, at 400 x m~gnifir~tion;
Figure 9 is a photomicrograph of the centre of billet 2, as extruded, at 200 x m~gnification;
Figure 10 is a photomicrograph of the centre of billet 2, as extruded, at 400 x magnification;
Figure 11 is a photomicrograph of the outside edge of billet 1, extruded and solution heat treated, at 50 x magnification;
Figure 12 is a photomicrograph of the outside edge of billet 1, 20 extruded and solution heat treated, at 100 x magnification;
Figure 13 is a photomicrograph of the outside edge of billet 1, extruded and solution heat treated, at 200 x magnification;
Figure 14 is a photomicrograph of the centre of billet 1, extruded and solution heat treated at 50 x magnification;
Figure 15 is a photomicrograph of the centre of billet 1, extruded and solution heat treated at 100 x m~gnifir~tion;
Figure 16 is a photomicrograph of the centre of billet 1, extruded and solution heat treated, at 200 x m~nification;
~1 96479 Figure 17 is a photomicrograph of the outside edge of billet 2, exkuded and solution heat treated, at 50 x magnification;
Figure 18 is a photomicrograph of the outside edge of billet 2, 5 exkuded and solution heat keated, at 100 x magnification;
Figure 19 is a photomicrograph of the outside edge of billet 2, exkuded and solution heat keated~ at 200 x magnification;
10Figure 20 is a photomicrograph of the cenke of billet 2, exkuded and solution heat keated, at 50 x m~gnific~tion;
Figure 21 is a photomicrograph of the cenke of billet 2, exkuded and solution heat keated, at 100 x m~gnification;
Figure 22 is a photomicrograph of the centre of billet 2, exkuded and solution heat keated, at 200 x m~gnification;
Figure 23 is a photomicrograph of the cenke of billet 1, as exkuded, 20 parallel to the extrusion axis, at 100 x m~gnification;
Figure 24 is a photomicrograph of the cenke of billet 1, as extruded, parallel to the exkusion axis, at 200 x m~gnification;
25Figure 25 is a photomicrograph of the centre of billet 2, as exkuded~
parallel to the extrusion axis, at 100 x m~gnification;
Figure 26 is a photomicrograph of the centre of billet 2, as extruded, parallel to the exkusion axis, at 200 x magnification;
Figure 27 is a photomicrograph of the centre of billet 1 parallel to the extrusion axis, after solution heat tre~tment, at 100 x magnification;
Figure 28 is a photomicrograph of the centre of billet 1 parallel to the extrusion axis, after solution heat treatment, at 200 x magnification;
Figure 29 is a photomicrograph of the centre of billet 2 parallel to the 5 exkusion axis, after solution heat treatment, at 100 x magniffcation;
Figure 30 is a photomicrograph of the cenke of billet 2 parallel to the exkusion axis, after solution heat treatment, at 200 x magnification;
Grain Size Determin~t;on As Exkruded Billets Billet 1 Outside Edge 10.2 microns Billet 1 Cenke 7.6 microns Billet 2 Outside Edge 7.6 microns Billet 2 Cenke 7.6 microns (Skucture is quite broken up with very large and very small grains.) Solution Heat Treated Billets Billet 1 Outside Edge 25.3 microns Billet 1 Centre 22.5 microns Billet 2 Outside Edge 22.5 microns Billet 2 Cenke 20.3 microns (Well ~l~fine~1 solution heat keated grain skucture) DISCUSSION
The microstructure observed consists of magnesium primary magnesium and alllminllnl solid solution crystals and eutectic consisting of two phases, secondary magnesium solid solution crystals and Mgl7Al12 intermetallic compound. The structure was quite broken up in the "as cast"
specimens and grain size measurement is only approximate.
Recrystallized grain structure in the solution heat treated specimens 5 was more accurate and well defined in the microstructure.
The micros taken in the direction of the extrusion axis of the "as extruded" specimens showed long stringers in the microstructure. The corresponding micros taken from the heat treated specimens showed a more 10 evenly distributed recryst~lli7.e-1 structure.
The amount of breakdown that the grain structure of the as-cast billet will undergo is likely a function of the amount of reduction. In the present case 7 to 1 reduction was used. Some sources suggest that the optimum 15 degree of reduction should be on the order of from 10:1 to 17:1. In practice however the degree of reduction required may be less if the starting alloy is relatively fine grained.
OVERVIEW
3 in. diameter x 180 mm long slugs of magnesium alloy AZ61 were tested.
10 of the slugs had been solution heat treated.
SSM casting tests were made using a Buhler SCN66 machine. It was not possible at the time of the trials to store the injection curves due to 30 software issues.
As a test piece, a welding test plate die was chosen, he~te-l by oil to approximately 220~C.
21 ~6479 In general, the material was SSM-castable, but different than other m~gnesium alloys. The thickwall part (lOmm thick) was perhaps not ideal for magnesium casting.
SSM HEATING
Slug heating was performed in a single coil induction heater and 10 optimized such that the slugs were removed from the coil just prior to the onset of burning which co~les~onded to a softness which allowed dissection with a knife. Total heating time was approximately 230 seconds. Very little metal run-off was obtained during the he~ting process.
A single stage induction heater was utilized for the test as multi-stage induction heating was not available at the test facility. It is expected that better heating would have been obtained with multi-stage induction heating. Ideally at the end of the heating cycle the billet should have a uniform temperature throughout with a well controlled solid to liquid ratio.
SSM C~STING
The first parts were cast using a plunger velocity of 0.3 to 0.8 meters per second. These conditions barely filled the die and visual laps were apparent at the end of the part.
With a velocity increase to 1.8m/s (onset of fl~hing), the parts filled better but lapping was still apparent. The best results were obtained using a plunger velocity of 1.2 m/s.
2l 9647q The heat treated slugs appeared lighter in color after heating and had less tendency to burn. The SSM parts produced *om these slugs also appeared lighter in color.
Even at plunge velocities as low as 0.05 m/s and up to above 0.5 m/s, it was not possible to achieve a smooth metal front. In all cases the alloy flowed as individual "glaciers".
Two plates (numbers 34 and 35) which were formed at a plunger velocity of 1.8 m/s were subjected to metallurgical evaluation (see Example 3).
As can be seen, the only parameter varied in making the test plates was the gate or plunger velocity. Accordingly none of the resulting plates could be considered high quality castings. It is expected that much better results would have been obtained if the die temperature had been increased to approximately 300~C and the slugs were heated in the multi-stage induction heater.
As illustrated by the tests, if the gate speed is too high, the metal flow is atomized rather than l~minar. Too low a gate speed results in metal solillification before the mold cavity fills.
Despite the less than optimal casting conditions, as illustrated by example 3 below, the cast plates show good physical properties.
The casting machine was a single cylinder unit having servo control to carfully control the force driving the slug into the closed die. Optimally the casting process will cause the outer skin of the slug which contains surface oxides resulting from the heating process to "skin" from the virgin metal.
, EXAMPT.~ 3 Plates 34 and 35 were sectioned into six sections as illustrated in Figure 30. One quarter inch (1/4 in.) round samples were removed from the sections and tested for mechanical properties. The plates were not heat treated and the results are tabulated in Table 1 below.
PLATE SAMPLE SAMPLE TYPE UTS YS ELONG
NO. NO. ~ksi) ~si) %
34 2 .250" ROUND 31.5 13.9 10.9 34 4 .250" ROUND 33.2 14.2 14.1 34 6 .250" ROUND 32.9 14.5 13.6 2 .250" ROUND 33.6 14.7 12.3 4 .250" ROUND 31.1 13.9 10.3 6 .250" ROUND 33.3 13.9 13.3 Mates 34 and 35 were subsequently solution heat treated for 12 hours at 426~C and still air cooled. One quarter inch (1/4 in.) round samples were cut from the plates and the mechanical properties of those samples were tested. The results of the tests are tabulated in Table 2 below. In Table 2 20 below the sample plan for the heat treated plates is the same as illustrated in Figure 31.
, PLATE SAMPLE SAMPLE TYPE UTS YS ELONG COMMENTS
NO. NO. (ksi) (ksi) %
34 1 .250" ROUND 23.4 14.1 3.0 O~aDEINCL.
34 3 .250" ROUND SAMPLE DAMAGED IN MACHINING
34 5 .250" ROUND 37.6 14.6 18.5 1 .250" ROUND 37.0 12.8 15.7 3 .250" ROUND 36.9 13.8 16.4 .250" ROUND 36.8 12.8 19.3 Photomicrographs of one of the plates were taken at locations M1 and 5 M2 as illustrated in Figure 32. The photomicrographs are reproduced in Figures 33 through 36 as follows.:
Figure 33 is a photomicrograph of sample M1 at 50x magnification;
Figure 34 is a photomicrograph of sample M1 at 100x magnification;
Figure 35 is a photomicrograph of sample M2 at 50x magnification;
Figure 36 is a photomicrograph of sample M2 at 100x magnification.
The above description is intended in an illustrative rather than a restrictive sense. One skilled in the art would recognize that the specific process perameters used in the examples would have to be varied to adapt 20 the present invention to particular alloys, equipment and parts being cast.
For example, although AZ61 magesium alloy was ulilized in the tests no doubt other magesium alloys could be used. It is quite likely that the process could be adaped to metal systems other than magesium so long as the metal is capable of forming a two-phase system comprising a solid particles in a - 21 9647q lower melting matrix. Examples of such metal systems include aluminum and copper. It is intended that any such variations be deemed as within the scope of the present patent as long as such are within the spirt and scope of the claims set out below.
The ingot produced according to the process described in Young may 20 then be subsequently heated to semi-solid casting temperature and formed into a part in a die casting process.
Even though Young avoids the requirement for magnetic stirring, it is nevertheless a cumbersome process including a large number of process 25 steps.
More recently a process has been proposed in which a cast ingot is machined down to a billet of approximately one inch in diameter and 21 9647q deformed by subjection to a compressive force. The deformed billet is then heated to a temperature above its recrystallization temperature and below its solidus temperature. The billet is then cooled to room temperature for subsequent re-heating and use in a semi-solid metal casting process. This 5 process however involves an expensive and wasteful ma~hining operation and only appears to work with relatively small billet diameters of less than about one inch (approximately 25 mm) diameter.
It is therefore an object of the present invention to provide a process 10 for semi-solid metal die casting which avoids not only magnetic stirring, butalso eliminates many of the steps that would be required pursuant to the Young process.
It is a further object of the present invention to provide a semi-solid 15 metal die casting process which avoids the maching, cold working heating, cooling and re-heating steps associated with other processes.
It is yet a further object of the present invention to provide a process capable of forming billets for use in semi-solid metal die casting processes 20 that may be significantly greater than about one inch (approximately 25 mm) in diameter.
SUMMARY OF THE INVENTION
A semi-solid metal die casting process using a cast ingot and having the following steps:
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
2. extruding the ingot in an extruded column;
- 21 ~6479 3. cutting the extruded column into at least one billet prior to its cooling;
4. heating the billet from step 3 to a forming temperature corresponding to a semi-solid state; and 5. squeezing the billet from step 4 into a cavity in a die casting mold to form a part.
DESCRIPTION OF DRAWINGS
Plefelled embodin~ents of the present invention are described below with rerelel.ce to the accompanying drawings in which:
Figure 1 is a schematic representation of the process of the present invention;
Figures 2 through 30 are photomicrographs of billets cut from extruded ingots and are individually described in Example 1 below;
Figure 31 illustrates sample locations in a test plate which were tested in Example 3;
Figure 32 illustrates the locations at which photomicrographs were taken in Example 3 below; and Figures 33 through 36 are photomicrographs individually described in Example 3 below.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to Figure 1, molten metal 10 is poured from a ladle into a mold 12 and allowed to solidify into an ingot 14. The ingot 14 is heated, for example by inductive heating coil 16 to a temperature above its recrystallization temperature and below its solidus temperature.
The heated ingot 14 is then extruded through an extruding die 18 to form an extruded column 20. The extruded column 20 is cut to a suitable length billet 22 for use in a semi-solid metal die casting process.
The billet 22 is heated to a forming temperature corresponding to a semi-solid state, for example by induction coils 24, and transferred to a die casting apparatus 26. The heated billet 22 is squeezed by the die casting apparatus into a cavity 28 between mold parts 30 and 32 to form a part 34 conforming in shape to that of the cavity 28.
The present invention is further illustrated by the examples set out below.
The microstructure of two AZ61 alloy, 3 in. diameter by 7 in. length extruded billets in the as extruded and solution heat treated condition were examined.
The billets were produced initially as an 8 1/2 in. direct chill cast billet.
The billets were cut into 2 ft. long sections and the diameter machined down to 8 in. to remove imperfections to the outside edge.
Graining sizing of the 8 inch billet perpendicular to the extrusion axis was 38 microns at the outside, 48 microns at the half radius and 48 microns at the center. As expected, the grain size in the longitudinal or extrusion direction was somewhat larger being approximately 51 microns at the outside, 64 microns at the half radius and 74 microns at the center.
The billets were then heated in 4-6 minute intervals in three induction furnaces. The furnaces heated the billets to 100~C, 200~C, 300~C
(total heating time approximately 15 minutes.) The billet was then placed in the extrusion chamber, which was at 380~C and the billet was extruded at 21 9~47~
between 330~C and 350~C, in one stage down to a 3 in. diameter extrusion billet. The first 14 ft. of extrusion and the last few feet were discarded. The r~m~inc~er of the extrusion was cut into 7 in. sections or "slugs".
Two of the sections of the extrusion billet referred to as billet 1 and billet 2, in AZ61 alloy were examined in the "as extruded" condition by sectioning a 0.5 in. section off the end of each billet, (billets were randomly 10 selected.) A micro was taken perpendicular to the axis of the billet from the centre and from the outside edge. The micros were polished and etched using 2% nitol etchant. The micros were examined at various magnifications to observe grain structure. A photomicrograph was taken at each magnification and the grain size estimated.
The two extrusion billet sections were then given the following solution heat treatment to recrystallize the grain structure;
Ramp 150~C - 338~C 3.0 hrs Hold 338~C 0.1 hrs Ramp 338~C - 413~C 1.5 hrs Hold 413~C 0.5 hrs Ramp 413~C - 426~C 0.5 hrs Hold 426~C 12.0 hrs Air Cool (Furnace atmosphere 10% CO2 to avoid ignition.;
The same procedure was followed in billet sectioning polishing and etching as previously described with the "as extruded" billet sections.
~t 96479 From the same samples micros were made at the centre of each billet parallel to the extrusion axis. These micros were taken from the as extruded and the solution heat treated billets. Photo micrographs were made at from 100 x to 400 x magnifi~ion of these samples.
The purpose for solution heat treating the extrusion billets and analyzing the samples was to determine the effect on grain size and shape resulting from heating and extruding the DC cast billet. The solution heat treating was not carried out under the optimum circumstances as 10 equipment availability necessitated the use of convection heating rather than induction heating. Preferably the heating cycle should not exceed 20 minutes and accordingly multi-state induction heating would be preferable over convection heating. Nevertheless the results were quite favourable as set out below.
RESULTS
The photomicrographs which are set out in Figures 2 through 30 below were 20 taken are as follows:
Figure 2 is a photomicrograph of the outside edge of billet 1, as extruded, at 200 x magnification.
25Figure 3 is a photomicrograph of the outside edge of billet 1, as extruded at 400 x m~gnific~tion;
Figure 4 is a photomicrograph of the centre of billet 1, as extruded under 100 x magnification;
Figure 5 is a photomicrograph of the centre of billet 1, as extruded under 200 x magnification;
g Figure 6 is a photomicrograph of the outside edge of billet 2, as extruded, at 200 x magnification;
Figure 7 is a photomicrograph of the outside edge of billet 2, as 5 extruded, at 400 x magnification;
Figure 8 is a photomicrograph of the centre of billet 1, as extruded, at 400 x m~gnifir~tion;
Figure 9 is a photomicrograph of the centre of billet 2, as extruded, at 200 x m~gnification;
Figure 10 is a photomicrograph of the centre of billet 2, as extruded, at 400 x magnification;
Figure 11 is a photomicrograph of the outside edge of billet 1, extruded and solution heat treated, at 50 x magnification;
Figure 12 is a photomicrograph of the outside edge of billet 1, 20 extruded and solution heat treated, at 100 x magnification;
Figure 13 is a photomicrograph of the outside edge of billet 1, extruded and solution heat treated, at 200 x magnification;
Figure 14 is a photomicrograph of the centre of billet 1, extruded and solution heat treated at 50 x magnification;
Figure 15 is a photomicrograph of the centre of billet 1, extruded and solution heat treated at 100 x m~gnifir~tion;
Figure 16 is a photomicrograph of the centre of billet 1, extruded and solution heat treated, at 200 x m~nification;
~1 96479 Figure 17 is a photomicrograph of the outside edge of billet 2, exkuded and solution heat treated, at 50 x magnification;
Figure 18 is a photomicrograph of the outside edge of billet 2, 5 exkuded and solution heat keated, at 100 x magnification;
Figure 19 is a photomicrograph of the outside edge of billet 2, exkuded and solution heat keated~ at 200 x magnification;
10Figure 20 is a photomicrograph of the cenke of billet 2, exkuded and solution heat keated, at 50 x m~gnific~tion;
Figure 21 is a photomicrograph of the cenke of billet 2, exkuded and solution heat keated, at 100 x m~gnification;
Figure 22 is a photomicrograph of the centre of billet 2, exkuded and solution heat keated, at 200 x m~gnification;
Figure 23 is a photomicrograph of the cenke of billet 1, as exkuded, 20 parallel to the extrusion axis, at 100 x m~gnification;
Figure 24 is a photomicrograph of the cenke of billet 1, as extruded, parallel to the exkusion axis, at 200 x m~gnification;
25Figure 25 is a photomicrograph of the centre of billet 2, as exkuded~
parallel to the extrusion axis, at 100 x m~gnification;
Figure 26 is a photomicrograph of the centre of billet 2, as extruded, parallel to the exkusion axis, at 200 x magnification;
Figure 27 is a photomicrograph of the centre of billet 1 parallel to the extrusion axis, after solution heat tre~tment, at 100 x magnification;
Figure 28 is a photomicrograph of the centre of billet 1 parallel to the extrusion axis, after solution heat treatment, at 200 x magnification;
Figure 29 is a photomicrograph of the centre of billet 2 parallel to the 5 exkusion axis, after solution heat treatment, at 100 x magniffcation;
Figure 30 is a photomicrograph of the cenke of billet 2 parallel to the exkusion axis, after solution heat treatment, at 200 x magnification;
Grain Size Determin~t;on As Exkruded Billets Billet 1 Outside Edge 10.2 microns Billet 1 Cenke 7.6 microns Billet 2 Outside Edge 7.6 microns Billet 2 Cenke 7.6 microns (Skucture is quite broken up with very large and very small grains.) Solution Heat Treated Billets Billet 1 Outside Edge 25.3 microns Billet 1 Centre 22.5 microns Billet 2 Outside Edge 22.5 microns Billet 2 Cenke 20.3 microns (Well ~l~fine~1 solution heat keated grain skucture) DISCUSSION
The microstructure observed consists of magnesium primary magnesium and alllminllnl solid solution crystals and eutectic consisting of two phases, secondary magnesium solid solution crystals and Mgl7Al12 intermetallic compound. The structure was quite broken up in the "as cast"
specimens and grain size measurement is only approximate.
Recrystallized grain structure in the solution heat treated specimens 5 was more accurate and well defined in the microstructure.
The micros taken in the direction of the extrusion axis of the "as extruded" specimens showed long stringers in the microstructure. The corresponding micros taken from the heat treated specimens showed a more 10 evenly distributed recryst~lli7.e-1 structure.
The amount of breakdown that the grain structure of the as-cast billet will undergo is likely a function of the amount of reduction. In the present case 7 to 1 reduction was used. Some sources suggest that the optimum 15 degree of reduction should be on the order of from 10:1 to 17:1. In practice however the degree of reduction required may be less if the starting alloy is relatively fine grained.
OVERVIEW
3 in. diameter x 180 mm long slugs of magnesium alloy AZ61 were tested.
10 of the slugs had been solution heat treated.
SSM casting tests were made using a Buhler SCN66 machine. It was not possible at the time of the trials to store the injection curves due to 30 software issues.
As a test piece, a welding test plate die was chosen, he~te-l by oil to approximately 220~C.
21 ~6479 In general, the material was SSM-castable, but different than other m~gnesium alloys. The thickwall part (lOmm thick) was perhaps not ideal for magnesium casting.
SSM HEATING
Slug heating was performed in a single coil induction heater and 10 optimized such that the slugs were removed from the coil just prior to the onset of burning which co~les~onded to a softness which allowed dissection with a knife. Total heating time was approximately 230 seconds. Very little metal run-off was obtained during the he~ting process.
A single stage induction heater was utilized for the test as multi-stage induction heating was not available at the test facility. It is expected that better heating would have been obtained with multi-stage induction heating. Ideally at the end of the heating cycle the billet should have a uniform temperature throughout with a well controlled solid to liquid ratio.
SSM C~STING
The first parts were cast using a plunger velocity of 0.3 to 0.8 meters per second. These conditions barely filled the die and visual laps were apparent at the end of the part.
With a velocity increase to 1.8m/s (onset of fl~hing), the parts filled better but lapping was still apparent. The best results were obtained using a plunger velocity of 1.2 m/s.
2l 9647q The heat treated slugs appeared lighter in color after heating and had less tendency to burn. The SSM parts produced *om these slugs also appeared lighter in color.
Even at plunge velocities as low as 0.05 m/s and up to above 0.5 m/s, it was not possible to achieve a smooth metal front. In all cases the alloy flowed as individual "glaciers".
Two plates (numbers 34 and 35) which were formed at a plunger velocity of 1.8 m/s were subjected to metallurgical evaluation (see Example 3).
As can be seen, the only parameter varied in making the test plates was the gate or plunger velocity. Accordingly none of the resulting plates could be considered high quality castings. It is expected that much better results would have been obtained if the die temperature had been increased to approximately 300~C and the slugs were heated in the multi-stage induction heater.
As illustrated by the tests, if the gate speed is too high, the metal flow is atomized rather than l~minar. Too low a gate speed results in metal solillification before the mold cavity fills.
Despite the less than optimal casting conditions, as illustrated by example 3 below, the cast plates show good physical properties.
The casting machine was a single cylinder unit having servo control to carfully control the force driving the slug into the closed die. Optimally the casting process will cause the outer skin of the slug which contains surface oxides resulting from the heating process to "skin" from the virgin metal.
, EXAMPT.~ 3 Plates 34 and 35 were sectioned into six sections as illustrated in Figure 30. One quarter inch (1/4 in.) round samples were removed from the sections and tested for mechanical properties. The plates were not heat treated and the results are tabulated in Table 1 below.
PLATE SAMPLE SAMPLE TYPE UTS YS ELONG
NO. NO. ~ksi) ~si) %
34 2 .250" ROUND 31.5 13.9 10.9 34 4 .250" ROUND 33.2 14.2 14.1 34 6 .250" ROUND 32.9 14.5 13.6 2 .250" ROUND 33.6 14.7 12.3 4 .250" ROUND 31.1 13.9 10.3 6 .250" ROUND 33.3 13.9 13.3 Mates 34 and 35 were subsequently solution heat treated for 12 hours at 426~C and still air cooled. One quarter inch (1/4 in.) round samples were cut from the plates and the mechanical properties of those samples were tested. The results of the tests are tabulated in Table 2 below. In Table 2 20 below the sample plan for the heat treated plates is the same as illustrated in Figure 31.
, PLATE SAMPLE SAMPLE TYPE UTS YS ELONG COMMENTS
NO. NO. (ksi) (ksi) %
34 1 .250" ROUND 23.4 14.1 3.0 O~aDEINCL.
34 3 .250" ROUND SAMPLE DAMAGED IN MACHINING
34 5 .250" ROUND 37.6 14.6 18.5 1 .250" ROUND 37.0 12.8 15.7 3 .250" ROUND 36.9 13.8 16.4 .250" ROUND 36.8 12.8 19.3 Photomicrographs of one of the plates were taken at locations M1 and 5 M2 as illustrated in Figure 32. The photomicrographs are reproduced in Figures 33 through 36 as follows.:
Figure 33 is a photomicrograph of sample M1 at 50x magnification;
Figure 34 is a photomicrograph of sample M1 at 100x magnification;
Figure 35 is a photomicrograph of sample M2 at 50x magnification;
Figure 36 is a photomicrograph of sample M2 at 100x magnification.
The above description is intended in an illustrative rather than a restrictive sense. One skilled in the art would recognize that the specific process perameters used in the examples would have to be varied to adapt 20 the present invention to particular alloys, equipment and parts being cast.
For example, although AZ61 magesium alloy was ulilized in the tests no doubt other magesium alloys could be used. It is quite likely that the process could be adaped to metal systems other than magesium so long as the metal is capable of forming a two-phase system comprising a solid particles in a - 21 9647q lower melting matrix. Examples of such metal systems include aluminum and copper. It is intended that any such variations be deemed as within the scope of the present patent as long as such are within the spirt and scope of the claims set out below.
Claims (7)
1. A semi-solid metal die casting process using a cast ingot and having the following steps:
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
2. extruding the ingot into an extruded column;
3. cutting the extruded column into at least one billet prior to its cooling;
4. heating the billet from step 3 to a semi-solid state; and
5. squeezing the billet from step 4 into a cavity in a die casting mold to form a part.
2. A semi-solid metal die casting process as claimed in claim 1 wherein:
AZ61 magnesium alloy is used;
In step 1 the ingot is heated to a temperature of approximately 300°C;
The ingot is extruded in step 2 at a temperature of from about 330 -350°C;
The heating in step 4 corresponds to a softness which allows dissection with a knife.
3. A semi-solid metal die casting process using a direct chill cast ingot and having the following steps:
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
2. reducing the diameter of the ingot and breaking down its grain structure by extruding it through an extruding die to form an extruded column;
3. cutting the extruded column into billets;
4. heating a billet from step 3 to a forming temperature above its liquidus temperature;
5. placing the heated billet from step 4 into an injection chamber in a semi-solid die casting machine;
2. A semi-solid metal die casting process as claimed in claim 1 wherein:
AZ61 magnesium alloy is used;
In step 1 the ingot is heated to a temperature of approximately 300°C;
The ingot is extruded in step 2 at a temperature of from about 330 -350°C;
The heating in step 4 corresponds to a softness which allows dissection with a knife.
3. A semi-solid metal die casting process using a direct chill cast ingot and having the following steps:
1. heating the ingot to a temperature above its recrystallization temperature and below its solidus temperature;
2. reducing the diameter of the ingot and breaking down its grain structure by extruding it through an extruding die to form an extruded column;
3. cutting the extruded column into billets;
4. heating a billet from step 3 to a forming temperature above its liquidus temperature;
5. placing the heated billet from step 4 into an injection chamber in a semi-solid die casting machine;
6. injecting the heated billet section into a mold to form a part; and
7. removing the part from the mold.
4. A semi-solid metal die casting process as claimed in claim 3 wherein the direct chill cast ingot during its production was cooled at a rate exceeding2°C per second.
5. A semi-solid metal die casting process as claimed in claim 4 wherein the direct chill cast billet has a maximum grain size of less than 100 microns.
4. A semi-solid metal die casting process as claimed in claim 3 wherein the direct chill cast ingot during its production was cooled at a rate exceeding2°C per second.
5. A semi-solid metal die casting process as claimed in claim 4 wherein the direct chill cast billet has a maximum grain size of less than 100 microns.
Priority Applications (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002196479A CA2196479A1 (en) | 1997-01-31 | 1997-01-31 | Semi-solid metal casting process |
| CA002227828A CA2227828C (en) | 1997-01-31 | 1998-01-23 | Semi-solid metal forming process |
| PCT/CA1998/000062 WO1998033610A1 (en) | 1997-01-31 | 1998-02-02 | Semi-solid metal forming process |
| JP53240798A JP2001509085A (en) | 1997-01-31 | 1998-02-02 | Semi-solid metal forming method |
| EP98901901A EP1011897B1 (en) | 1997-01-31 | 1998-02-02 | Semi-solid metal forming process |
| AU58500/98A AU5850098A (en) | 1997-01-31 | 1998-02-02 | Semi-solid metal forming process |
| DE69818282T DE69818282D1 (en) | 1997-01-31 | 1998-02-02 | METAL SHAPING METHOD WITH SEMI-SOLID MATERIAL |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002196479A CA2196479A1 (en) | 1997-01-31 | 1997-01-31 | Semi-solid metal casting process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2196479A1 true CA2196479A1 (en) | 1998-08-01 |
Family
ID=4159798
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002196479A Abandoned CA2196479A1 (en) | 1997-01-31 | 1997-01-31 | Semi-solid metal casting process |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2196479A1 (en) |
-
1997
- 1997-01-31 CA CA002196479A patent/CA2196479A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |