Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
  • B22D17/007—Semi-solid pressure die casting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D21/00—Casting non-ferrous metals or metallic compounds so far as their metallurgical properties are of importance for the casting procedure; Selection of compositions therefor
  • B22D21/002—Castings of light metals
  • B22D21/007—Castings of light metals with low melting point, e.g. Al 659 degrees C, Mg 650 degrees C
• • 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

Definitions

• the present invention relates generally to casting alloys. More particularly, the present invention is directed to an aluminum alloy for semi-solid metal (SSM) casting processes.
• SSM semi-solid metal
• SSM aluminum alloy castings outperform, in both cost and performance, other casting techniques, such as conventional die casting, which is performed under high pressure, gravity permanent mold casting and squeeze casting.
• SSM casting methods when utilized for the manufacturing of aluminum alloy products/castings, have proven advantageous over other casting techniques because SSM castings tend to exhibit higher mechanical properties in the areas of strength and ductility and reduced porosity than castings produced by the above- listed other methods.
• Microstructures of SSM aluminum alloy castings reveal the primary phase particles as round crystals that are often referred to as rosettes or globules.
• the primary phase particles in SSM aluminum alloy castings that contain less than twelve percent silicon are comprised of essentially aluminum. Because solid primary phase particles are part of the semi-solid metal being injected into a mold/die cavity, the microstructure of the primary phase of an aluminum alloy prior to injection into a mold/die is indicative of the microstructure of the primary phase of the resulting aluminum alloy casting.
• SSM methods of casting are utilized, the mechanical properties of a casting can be predicted before a casting is even produced. Accordingly, the production of castings with defects can be avoided.
• non-SSM casting processes involve injection/pouring of a molten metal directly into the die.
• the metal is molten, with no parts of the metal being solid, the microstructure of the resulting casting cannot be ascertained until after the molten metal has solidified in the mold/die cavity.
• the microstructure of the primary phase of a casting cannot be predicted before the casting is formed.
• the microstructures of castings prepared by non-SSM casting processes have dendrites.
• Dendrites are "tree-like" structures, and castings with dendrites are prone to microporosity and have inferior mechanical properties than those that exhibit round crystals.
• Thixocasting and Rheocasting are SSM methods of casting. Thixocasting involves the electromagnetic stirring of metal during solidification/freezing to provide aluminum SSM feedstock billets up to approximately 4" in diameter. The stirring action due to the movement of liquid fragments the aluminum dendrites as they form during solidification and results in the formation of small equiaxed grains in the billets.
• the billets are subsequently cut into slugs, and re-heated to a semi-solid state before being injected into the cavity. It is during the billet re-heating stage that the equiaxed aluminum grains undergo globularization. Chemically grain-refined billets are often used in lieu of electromagnetically stirred billets. Heating of grain-refined billets in the semisolid temperature regime also helps yield globular primary phase particles prior to injection into die cavity.
• Rheocasting which is also known as "slurry” or “slurry-on- demand” casting, involves heating a metal to a liquid state, cooling the molten metal to a semi-solid state, and then injecting the semi-solid metal into the die cavity.
• Rheocasting is more efficient than Thixocasting because Rheocasting involves fewer steps than Thixocasting.
• Rheocasting has also proven to be more economically feasible than Thixocasting because any unused scrap metal can be easily re-melted and reprocessed by an SSM component manufacturer.
• the scrap metal With Thixocasting, the scrap metal has to be reformed into billets by the billet manufacturer via the use of electromagnetic stirring or chemical grain refining before being used again.
• Rheocasting requires only that the scrap metal is re-melted and cooled to a semi-solid state before it is injected into a die cavity. As a result, scrap metal can easily be reused with the Rheocasting method of SSM casting and the expense associated with recycling scrap metal is less.
• SSM casting methods utilizing aluminum alloys have been used for manufacturing brake cylinders, fuel rails, engine brackets steering knuckles, suspension links and auto seat backs because, in addition to the above-discussed advantages over non-SSM casting techniques, SSM casting methods offer non-turbulent filling (i.e., less air entrapment), require lower die temperatures, reduce cycle time, reduce shrinkage, and provide the option of heat treatment (Le., solution treatment).
• A356.2 and 357 are the primary aluminum alloys used for SSM castings, including castings of automotive components.
• the chemistries of A356.2 and 357 are as follows:
• A356.2 and 357 when used with SSM casting methods, generate castings of essentially high toughness, i.e., ability to absorb energy before failure, and thus, have been found suitable for automotive components, such as steering knuckles and suspension links.
• the A356.2 and 357 alloys when used with SSM casting methods, have not been found suitable for automotive components that require essentially high strength, i.e., high load bearing ability, such as axle carriers, rack and pinion housings, and steering column housings.
• an aluminum alloy that can be utilized with SSM methods of castings, especially with the increasingly popular Rheocasting method of SSM casting, that can produce high integrity, high-strength automotive components, such as axle carriers, rack and pinion housings, and steering column housings.
• an alloy in accordance with the present invention includes 6.5 to 8.5 percent silicon, 0.60 to 1.0 percent iron, 0.3 to 0.5 percent manganese, 0.35 to 0.65 percent magnesium, 0.01 to 1.0 percent of zinc, 0.11 to 0.2 percent titanium, 2.0 to 2.5 percent copper, and aluminum as the remainder with further one or more other elements 0.001 to 0.15 percent of the weight.
• a die cast product in another exemplary embodiment of the present invention includes 6.5 to 8.5 percent silicon, 0.60 to 1.0 percent iron, 0.3 to 0.5 percent manganese, 0.35 to 0.65 percent magnesium, 0.01 to 1.0 percent of zinc, 0.11 to 0.2 percent titanium, 2.0 to 2.5 percent copper, and aluminum as the remainder with further one or more other elements 0.001 to 0.15 percent of the weight.
• a method of making a die cast product includes forming a semisolid aluminum alloy, wherein the semi-solid aluminum alloy contains 6.5 to 8.5 percent silicon, 0.60 to 1.0 percent iron, 0.3 to 0.5 percent manganese, 0.35 to 0.65 percent magnesium, 0.01 to 1.0 percent of zinc, 0.11 to 0.2 percent titanium, 2.0 to 2.5 percent copper, and aluminum as the remainder with further one or more other elements 0.001 to 0.15 percent of the weight, and placing the semi- solid aluminum alloy in a die cavity.
• FIG. 1 illustrates microstructures of an exemplary embodiment an aluminum alloy in accordance with the present invention.
• FIG.2 illustrates microstructures of an exemplary embodiment of an aluminum alloy in accordance with the present invention.
• FIG. 3 illustrates microstructures of an exemplary embodiment of an aluminum alloy in accordance with the present invention.
• An aluminum alloy in accordance with the present invention is a high copper, manganese and iron (HiCMF) aluminum alloy.
• HiCMF high copper, manganese and iron
• an aluminum alloy in accordance with the present invention is composed of the below-listed elements, by percentage of weight, as follows:
• the "others" are lead and/or chromium.
• the amount of manganese is more preferably 0.30 to 0.50 percent by weight.
• the ranges of manganese as described herein facilitate a reduction in the amount of solder when adhering the aluminum alloy to die steel. Furthermore, the ranges described herein contribute to the formation of 'Chinese- script' intermetallics and are therefore less detrimental to ductility of the aluminum alloy. Particular examples of preferred amounts of manganese include 0.30, 0.35, and 0.45 percent by weight.
• Preferred amounts of zinc include 0.01 to 1.00 percent by weight.
• the range of zinc described herein facilitates minimizing or substantially eliminating 'hot cracking' of the aluminum alloy during solidification.
• Particular examples of preferred amounts of zinc include 0.01, 0.03, 0.05, and 0.08 percent by weight.
• Preferred amounts of titanium include 0.11 to 0.20 percent by weight.
• the range of titanium described herein promotes effective grain refinement and thereby generally contributes to increased mechanical properties. More particularly, toughness is increased by effective grain refinement.
• Particular examples of preferred amounts of titanium include 0.11, 0.15, 0.18, 0.19, and 0.20 percent by weight.
• the response to artificial aging is unexpectedly improved.
• the response to artificial aging following solution treatment is unexpectedly improved by including 0.001 to 0.10 percent tin by weight.
• Particular examples of preferred amounts of tin include 0.003, 0.045, and 0.09 percent by weight.
• Preferred amounts of chromium include 0.001 to 0.10 percent by weight.
• the range of chromium described herein facilitates a reduction or substantially eliminates sludge formation in the aluminum alloy.
• the term, 'sludge' as used herein refers to a complex of essentially iron, chromium and manganese.
• Particular examples of preferred amounts of chromium include 0.003, 0.04, and 0.09 percent by weight.
• An aluminum alloy in accordance with the present invention is suitable for SSM methods of casting because the microstructure of the primary aluminum phase of the metal slurry prior to its injection into a die cavity is comprised of globular and/or rosette crystals.
• An alloy in accordance with the present invention is hypoeutectic because its silicon content is less than 12 percent.
• the primary phase metal of an alloy in accordance with the present invention is aluminum.
• Alloys with silicon composing less than twelve percent of their weight are hypoeutectic and alloys with silicon composing more than twelve percent of their weight are hypereutectic.
• FIG. 1 and FIG. 2 shown are microstructures of the primary phase from various locations of an aluminum alloy in accordance with the present invention prior to its injection into a die cavity.
• the illustrations of FIG. 1 and FIG. 2 were ascertained in accordance with the conventional evaluation method of "water-quenching," which "locks in” the microstructure.
• the microstructures of FIG. 1, from top to bottom, are from the middle edge 10, middle 12 and center 14 of a water-quenched slug. It can be seen from FIG. 1 that the primary aluminum phase particles consist of round crystal/globular 16, and/or rosette 18 formations.
• FIG. 2 depicts microstructures of the primary phase of an aluminum alloy in accordance with the present invention prior to its injection into a die cavity.
• the microstructures of FIG.2, from top to bottom, are from the bottom edge 20, middle 22 and center 24 of a water-quenched slug.
• the primary aluminum phase particles of an aluminum alloy in accordance with the present invention consist of round crystal/globular 26 and/or rosette 28 formations.
• FIG. 3 depicts microstructures of the primary phase of an aluminum alloy in accordance with the present invention after it has been injected into a die cavity.
• the primary aluminum phase particles of an aluminum alloy in accordance with the present invention consist of round crystals/globular 32 and/or rosette 34 formations.
• FIG. 1 and FIG. 2 are compared with FIG. 3, it can be seen that the morphology of the primary aluminum phase prior to injection into a die cavity is similar to that of the aluminum alloy in the resulting casting.
• the microstructure of the primary phase of an alloy in accordance with the present invention can be determined before it is utilized to form a casting. Thus, the number of casts with microstructures unsuitable for their purpose can be reduced.
• silicon is restricted to 7.2 percent to 8 percent of the weight to efficiently achieve formation of the primary aluminum phase during the cooling of the molten metal to the semi-solid state.
• the amount of silicon present in an aluminum alloy may be directly related to the strength of the aluminum alloy.
• the higher the content of silicon the higher the strength of the aluminum alloy.
• the average silicon content of the alloy is higher than other alloys, such as the A356.2 and 357 aluminum alloys.
• the strength of an aluminum alloy in accordance with the present invention is higher than other alloys, such as A 3562.2 and 357.
• an aluminum alloy in accordance with the present invention reveals the presence of fine aluminum-silicon eutectic and entrapped intermetallic particles 30 within the round crystals, globular and/or rosette primary aluminum phase.
• the entrapped intermetallic particles 30 essentially consist of iron, silicon and manganese.
• a path fracture path
• the intermetallic particles 30 are entrapped within the round crystal/globular 32 and/or rosette 34 structures, the fracture path is now restricted. Accordingly, fractures occur with less frequency, especially when an aluminum alloy in accordance with the present invention is compared to the A356.2 and 357 aluminum alloys that do not reveal entrapped particles in their microstructures in the primary aluminum phase.
• the formation of the intermetallic particles in an aluminum alloy in accordance with the present invention can be attributed to the high content of iron in the aluminum alloy.
• iron is 0.6 to 1.0 percent of the weight.
• iron is 0.6 to 0.8 percent of the weight.
• the iron content of an aluminum alloy in accordance with the present invention is higher than other alloys, such as A 356.2 and 357 which are, at a maximum, 0.12 percent of the weight. Accordingly, an alloy in accordance with the present invention is less expensive than A 356.2 and 357 because the iron content does not have to be maintained low. Additionally, because the iron content is not low, the potential of soldering is reduced.
• magnesium is approximately 0.35 to 0.65 percent of the weight.
• the magnesium content of an aluminum alloy in accordance with the present invention is higher than the magnesium content of other aluminum alloys, such as the A 356.2 and 357, which is 0.30 to 0.45 and 0.45 to 0.6 percent of the weight, respectively.
• the strength of a casting made from an aluminum alloy in accordance with the present invention will be even greater after the alloy has been heat treated, i.e., subjected to a solution treatment and artificially aged.
• the magnesium content is approximately 0.45 to 0.6 percent of the weight.
• an aluminum alloy in accordance with the present invention is suitable for the manufacturing of products that require high strength, such as axle carriers, rack and pinion housings and steering column housings by both Rheocasting and Thixocasting.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Conductive Materials (AREA)

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• 2005
  • 2005-03-22 US US11/085,086 patent/US20050161128A1/en not_active Abandoned
• 2006
  • 2006-03-22 EP EP06739457A patent/EP1871555A4/de not_active Withdrawn
  • 2006-03-22 WO PCT/US2006/010666 patent/WO2006102550A2/en active Application Filing

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