JP2010528187A - Aluminum alloy formulations for reducing hot cracking susceptibility - Google Patents

Abstract

The present invention relates to an alloy composition that has been improved to have low hot cracking susceptibility, wherein the aluminum alloy has an Sr in the range of 0.01 to 0.025 wt%; and a boron content measured from 0.001 to It contains TiB ₂ in an amount corresponding to B in the range of 0.005% by mass. The present invention also relates to a method for preventing or eliminating hot cracking in an aluminum alloy, said method comprising measuring aluminum at a Sr in the range of 0.010 to 0.025 mass%; and a boron content. A step of combining TiB ₂ in an amount in the range of 0.001 to 0.005 mass% B.

Description

  The present invention relates to an improved alloy composition for reducing hot cracking susceptibility.

  Hot cracking occurs during the casting process, where cracking between brittle dendritic structures begins during the solidification process. Alloys that are generally considered prone to hot cracking have a relatively long solidification / solidification range, defined as the temperature difference between their liquidus and solidus temperatures. In addition, in the final stage of solidification, these alloys contain a very small amount of residual eutectic liquid and a limited amount of this eutectic liquid is left between the solidified grains. It is necessary to pass through space. The poor supply amount in the final stage of solidification greatly contributes to the hot cracking phenomenon.

One method for reducing hot cracking is described in WO2005 / 056846. This WO2005 / 056846 prior art describes nothing about the combination of strontium and titanium diboride of the present invention, and casts a pure aluminum blend at a first specified temperature, and copper It primarily addresses the hot cracking problem by casting a second aluminum alloy mixed with zinc or magnesium at a second specified temperature. Temperature control of these two alloys is a central aspect of the method described in WO2005 / 056846.
US 4,681,152 is aimed at two-roll casting of 5xxx alloys. The composition uses a crystal refiner comprising aluminum wire, which can contain up to 0.05% Sr and contains about 5% titanium and 0.2% boron. The boron content may be as high as 1% by weight. A sufficiently refined alloy is added to bring the titanium content up to about 0.02 mass%. US 4,681,152 does not aim to reduce hot cracking. The alloy of US 4,681,152 is cast by strip casting.

US 5,453,244 is aimed at bearing alloys (7xxx) containing Al-Zn substrates. This alloy is described in a broad sense as containing Sr in the range of 0.05-0.5% and Ti + B in the range of 0.03-0.5%. US 5,453,244 is not aimed at reducing hot cracking.
US 5,211,910 is a component of 2xxx alloy, from the list consisting of Zn, Ge, Sn, Cd, In, Be, Sr, Sc, Y, and Ca, Sr as a whole is in the range of about 0.5 to about 4 mass% Should be present in an amount and from a list containing Zr, Cr, Mn, Ti, Hf, V, Nb, B and TiB ₂ Ti and / or TiB ₂ is present in an amount ranging from 0.01 to ₂ % It states what should be done. However, specific combinations of the additives of the present invention are not described and are not used within the scope of the present invention. US 5,211,910 is not aimed at reducing hot cracking.
EP 0432184 should be present in an amount ranging from about 0.01 to 1.5 Sr from a list consisting of Zn, Ge, Sn, Cd, In, Be, Sr, Sc, Y and Ca, and Zr, Cr , Mn, Ti, Hf, V , Nb, from a list including B and TiB _2, Ti and / or TiB ₂ are states that should be present in an amount of from 0.01 to 1.5%. However, specific combinations of the additives of the present invention are not described and are not used within the scope of the present invention. EP 0432184 is not aimed at reducing hot cracking.

WO 96/10099 discloses a wide range of possible alloys and includes crystal refiners (Ti and TiB ₂ ) and modifiers (including Sr). The main alloying element of the alloy is Sc. These alloys are useful for modeling casting and are supposed to give properties comparable to wrought alloys.
US 6,562,165 describes an Al-Si alloy, which has a spheroidized structure and is suitable for semi-solid processing, in the range of 0.005 to 0.5% Ti and in the range of 0.005 to 0.030. Contains Sr. US 6,562,165 states that excessive Ti addition can lead to the formation of large and harmful TiB ₂ crystals and does not describe any TiB ₂ concentration. The additive of US 6,562,165 is not intended to reduce hot cracking.

The inventors have found that aluminum-based alloys containing a narrow range of strontium and titanium diboride as additives have a surprisingly low rate of hot cracking, which allows die casting of these alloys. And found that.
The present invention provides improved alloy compositions that can be applied to aluminum alloys to control hot cracking through the selective use of additives, and as a result, these alloys can be die cast. Here, the alloy of the present invention has strength and ductility not present in conventional aluminum alloys. These properties allow for shaping casting of the alloy above the liquidus of the alloy or in the semi-solid region of the alloy.
Without being bound by a particular theory, it is believed that strontium and titanium diboride as additives act in a synergistic manner on the alloy, where the strontium is α- It promotes the formation of spherical crystals in the crystal and the titanium diboride initiates the formation of new crystals. When used in combination in specified amounts, these alloying components cause the liquid aluminum-based alloy to flow until it finally solidifies, thereby preventing hot cracking or substantially preventing its occurrence. Can be reduced.

The first aspect of the present invention is directed to an aluminum alloy, which is i) Sr in the range of 0.010 to 0.025 mass%; and ii) B of 0.001 to 0.005 mass%, as measured by boron content. including the scope of the amount of TiB _2. Preferably, the aluminum alloy may further, iii) in the TiB ₂ beyond B and stoichiometrically bound amount, also containing excess Ti of 0.16 wt% or less. Several alloys that are usually prone to hot cracking have been found to be very suitable for use with specified amounts of the additive of the present invention.
A related aspect of the invention comprises aluminum and i) Sr in the range of 0.010 to 0.025 mass%; and ii) TiB _{2 in} an amount in the range of 0.001 to 0.005 mass% B as measured by boron content. It relates to a method for preventing or eliminating hot cracking in an aluminum alloy comprising a compounding step.
It is a further object of the present invention to provide a shaped cast part cast from the alloy defined by the present invention above. In particular, the shaped cast part can be a cast product by a die casting method, and the die casting method is difficult for an aluminum alloy that easily causes hot cracking. A further advantage is provided by the present invention, which is that the alloy-derived casting can be in a semi-solid state.

The present invention also aluminum, i) 0.010 to 0.025 Sr mass% Scope; step measured at and ii) a boron content, is compound and TiB ₂ in an amount of B becomes the range of 0.001 to 0.005 wt% Can be defined as providing a method for producing an aluminum alloy.
A particularly interesting aspect of the invention relates to a method of processing an aluminum alloy, wherein the aluminum alloy is i) Sr in the range of 0.010 to 0.025 wt.%; And ii) measured in terms of boron content, 0.001 to 0.005. The aluminum alloy contains TiB ₂ in an amount ranging from B to mass%, and the aluminum alloy has a liquidus temperature and a solidus temperature. The method comprises the steps of preparing an alloy comprising a semi-solid within the range of the liquidus temperature and solidus temperature of the alloy; bringing the alloy to a high initial alloy temperature above the liquidus temperature. Heating to completely melt the alloy; a temperature of the alloy from a high temperature of the initial metal alloy to a semi-solid temperature below the liquidus temperature and above the solidus temperature And maintaining the alloy at the semi-solid temperature for a period of time sufficient to produce a semi-solid structure in the alloy in which a spherical solid phase is dispersed in the liquid phase. including. Optionally, at least some of the liquid phase present in the semi-solid structure of the metal alloy may be removed to produce a solid-rich semi-solid structure of the alloy. Possible, where the optional removal step includes removing the liquid phase; and shaping the alloy having a solid-rich semi-solid structure into a predetermined shape.

The present invention relates to an aluminum-based alloy. The aluminum-based alloy is mainly an alloy containing aluminum and copper, such as 2xxx and 2xx type alloys; an alloy mainly containing aluminum and manganese, such as 3xxx type alloys; an alloy mainly containing aluminum and silicon, such as 4xxx type alloys; From the group consisting of alloys mainly containing aluminum and magnesium, such as alloys of type 5xxx and 5xx; alloys containing mainly aluminum, magnesium and silicon, such as alloys of type 6xxx; and alloys containing mainly aluminum and zinc, such as alloys of type 7xxx You can choose. In the context of the alloy of the present invention, the term “mainly” means that these elements give the highest mass-based content in the alloy and that aluminum contributes the most to the mass-based content. Means that.
As mentioned above, the aluminum alloy of the present invention contains a unique combination of strontium and titanium diboride, i.e. 0.001 to 0.005 as measured by i) Sr and ii) boron content ranging from 0.010 to 0.025 wt%. It contains TiB ₂ in an amount in the range of B in mass%. TiB ₂ is a known crystal refiner, but in the combination of this specific crystal refiner and strontium, the liquid alloy left in the solidifying alloy is not limited in fluidity.

Titanium, zirconium and their borides and carbides are all known crystal refiners. Surprisingly, when used in combination with strontium, titanium diboride, a crystal modifier, provides a surprising improvement in the properties of the aluminum alloy, preventing the occurrence of hot cracks, Or eliminated.
In a preferred embodiment of the invention, the aluminum alloy further comprises an excess of Ti of 0.16 wt% or less, and more preferably an excess of Ti of 0.12 wt% or less. An excessive amount of Ti means an amount of Ti that exceeds the amount of TiB ₂ produced. This Ti can be introduced by a number of means known to those skilled in the art, but this is typically introduced by adding metallic titanium or through the use of a “crystal refiner” rod, the crystal fines. The agent rod is an aluminum rod or wire containing a specific concentration of Ti and B, stoichiometrically designed to produce TiB ₂ with an excess of Ti, as known to those skilled in the art. It is.
Suitably, the aluminum alloy of the present invention has, for a wide range of purposes, strontium and titanium diboride, and optionally additives other than titanium, such as Mg, Cu and Zn to improve strength, strength improvement and die casting. May contain Mn and Fe to reduce die adhesion and Ca, Na and Sb to improve crystallinity.

As can be understood from the following examples, an effect on crystal nucleation is not observed in an alloy having a TiB ₂ content (measured by boron content) of less than 0.001% by mass. Conversely, in alloys where the TiB ₂ content (measured by boron content) exceeds 0.005% by mass, there is no measurable benefit for hot cracking, but TiB ₂ (boron content exceeding 0.005% by mass). Levels (measured by rate) are expected to have a negative effect on some semi-solid methods. Excessive titanium diboride can negatively affect the degree of control in some embodiments of the semi-solid process and can reduce the strength of the resulting cast part. Accordingly, the present invention relates to TiB _{2 in} an amount corresponding to B in the range of 0.001 to 0.005 mass% (measured by boron content), preferably TiB _{2 in the} range of 0.002 to 0.004 mass% (measured by boron content). ) Containing alloys.
Similarly, as can be seen from the following examples, in alloys with a Sr content of less than 0.010%, spheroidization or spheronization is insufficient (too many pointed or needle-shaped crystals remain. ) When it exceeds 0.025%, the Sr has a negative effect on the strength of the final cast part. Therefore, the present invention relates to an aluminum alloy containing Sr in the range of 0.010 to 0.025% by mass, preferably Sr in the range of 0.010 to 0.020% by mass.

In addition, as can be seen from the examples below, the use of excess titanium (other than that in the TiB ₂ form) is hot cracking because this contributes to the formation of excessively large and long crystals. It is not advantageous with regard to action control. Excess Ti has a negative effect on hot cracking, and if the excess exceeds 0.16%, it leads to the formation of Al-Ti intermetallic compounds, which are in a sharp crystalline form, It also contributes to hot cracking of the cast part and an increase in its fragility. The alloys of the present invention preferably contain an excess of Ti of 0.16% by weight or less, more preferably an excess of Ti of 0.12% by weight or less.
These additives according to the invention are very suitable for aluminum alloys containing mainly aluminum, magnesium and silicon. Accordingly, one of the interesting aspects of the present invention is that it contains mainly aluminum, magnesium and silicon, and further contains Sr in the range of 0.010 to 0.025% by mass and TiB ₂ (boron in an amount corresponding to B in the range of 0.001 to 0.005% by mass. In relation to an aluminum alloy including (measured by content). Further interesting embodiments of the present invention are mainly aluminum, magnesium and silicon, Sr in the range of 0.010-0.025% by mass, TiB _{2 in} an amount corresponding to B in the range of 0.001-0.005% by mass (measured by boron content) and preferably greater than the amount of B and stoichiometrically bonded in TiB _2, containing Ti of 0.16% or less excess relates aluminum alloy.

Furthermore, the additive of the present invention is remarkably suitable for aluminum alloys containing mainly aluminum and copper. Accordingly, one of the interesting embodiments of the present invention comprises Sr in the range of 0.010-0.025% by mass and TiB _{2 in} an amount corresponding to B in the range of 0.001-0.005% by mass (measured by boron content). It relates to an aluminum alloy. One of the more interesting aspects of the present invention is mainly comprised of aluminum and copper, and TiB _{2 in} an amount corresponding to Sr in the range of 0.010 to 0.025% by mass, B in the range of 0.001 to 0.005% by mass (depending on the boron content). measured) and preferably greater than the amount of B and stoichiometrically bonded in TiB _2, containing Ti of 0.16% or less excess relates to an aluminum alloy.
In one more suitable embodiment, the additive of the present invention is significantly suitable for aluminum alloys containing primarily aluminum and magnesium. Accordingly, one of the interesting embodiments of the present invention is mainly comprised of aluminum and magnesium, and further, Sr in the range of 0.010 to 0.025% by mass, and TiB ₂ (boron-containing amount) corresponding to B in the range of 0.001 to 0.005% by mass. Relates to an aluminum alloy, including One of the more interesting aspects of the invention is that it contains mainly aluminum and magnesium, and TiB _{2 in} an amount corresponding to Sr in the range of 0.010 to 0.025% by mass, B in the range of 0.001 to 0.005% by mass (depending on the boron content). measured) and preferably greater than the amount of B and stoichiometrically bonded in TiB _2, containing Ti of 0.16% or less excess relates to an aluminum alloy.

In this patent application, the alloy relies on the Aluminum Association International Alloy Designations. Thus, 2xxx alloy means a wrought alloy based on aluminum that contains Cu as the main alloying element (wherein the Cu may be present in an amount of up to about 7% by weight, for example). 2xx alloy means a foundry alloy based on aluminum containing Cu as a main alloy element (wherein the Cu is present in an amount of up to about 9% by mass, for example) Can do). An example of an aluminum-Cu alloy is 206 alloy, which is expressed in mass%, less than 0.1 Si, less than 0.15 Fe, Cu in the range of 4.2 to 5.0, Mn in the range of 0.20 to 0.50, 0.15 to Mg in the range of 0.35, Ni less than 0.05, Zn less than 0.10, Sn less than 0.05, and the balance Al, each less than 0.05, and less than 0.15 overall incidental impurities, and 0.010- Sr in the range of 0.025% by weight, TiB _{2 in} an amount corresponding to B in the range of 0.001 to 0.005% by weight (measured by boron content) and preferably the amount stoichiometrically bound to B in TiB ₂ In excess of 0.16% or less of excess Ti. Another example of an aluminum-Cu alloy is the 2024 alloy, expressed in mass percent, less than 0.5 Si, less than 0.5 Fe, Cu in the range of 3.8 to 4.9, Mn in the range of 0.30 to 0.9. , Mg in the range of 1.2-1.8, Cr less than 0.10, Zn less than 0.25, and the balance Al, each less than 0.05 and incidental impurities less than 0.15 as a whole, and 0.010-0.025 mass Sr in the range of%, TiB _{2 in} an amount corresponding to B in the range of 0.001 to 0.005% by mass (measured by boron content) and preferably exceeding the amount stoichiometrically bound to B in TiB ₂ , Contains an excess of 0.16% Ti or less.

The 3xxx alloy is called a wrought alloy, which is mainly composed of aluminum and contains Mn as the main alloying element up to about 1.5% by mass. The 4xxx alloy is called a wrought alloy, which is mainly composed of aluminum and contains Si as the main alloying element up to about 14% by mass.
The 5xxx alloy is called a wrought alloy, which is mainly composed of aluminum and contains Mg as the main alloying element up to about 6% by mass. The 5xx alloy is called a casting alloy, which is mainly composed of aluminum and contains Mg as the main alloying element up to about 11% by weight. An example of an aluminum-Mn alloy is 5182 alloy, which is expressed in mass percent, less than 0.2 Si, less than 0.35 Fe, less than 0.15 Cu, Mn in the range of 0.20 to 0.50, 4.0 to 5.0. A range of Mg, less than 0.1 Cr, less than 0.25 Zn, and the balance Al, each less than 0.05, and less than 0.15 incidental impurities as a whole, and a range of 0.010-0.025 mass% Sr, TiB _{2 in} an amount corresponding to B in the range of 0.001 to 0.005 mass% (measured by boron content) and preferably more than 0.16%, exceeding the amount stoichiometrically bound to B in TiB ₂ Contains excess Ti.

The 6xxx alloy is called a wrought alloy, which contains aluminum as the main component, Mg and Si as the main alloying elements, and contains up to about 1.6% by mass of Mg and up to about 1.7% by mass of Si. Form magnesium silicide. An example of an aluminum-Mg-Si alloy is 6061 alloy, expressed in mass percent, Si in the range of 0.40 to 0.80, Fe of less than 0.7, Cu in the range of 0.15 to 0.40, Mn of less than 015, Mg in the range of 0.8 to 1.2, Cr in the range of 0.04 to 0.35, Zn of less than 0.25, and the balance Al, each less than 0.05, and incidental impurities less than 0.15 as a whole, and 0.010 to Sr in the range of 0.025% by weight, TiB _{2 in} an amount corresponding to B in the range of 0.001 to 0.005% by weight (measured by boron content) and preferably the amount stoichiometrically bound to B in TiB ₂ In excess of 0.16% or less of excess Ti.
The 7xxx alloy is referred to as a wrought alloy, which contains aluminum as the main component and Zn as the main alloying element, typically present in an amount up to about 9% by weight.
The above alloys contain TiB ₂ , Sr, and optional Ti within the above ranges in addition to the specified elements, resulting in reduced hot cracking. These alloys can also include additional alloying elements including Si, Fe, Cu, Mn, Mg, Cr, Ni, Zn and V.

Additives according to the invention, i.e. Sr in the range of 0.010 to 0.025% by weight, and TiB _{2 in} an amount corresponding to B in the range of 0.001 to 0.005% by weight (measured by boron content) are also 2xxx and 2xx aluminum- It is considered to be remarkably suitable for copper alloys. 2xxx and 2xx Al-Cu alloys are known to have a tendency to crack. The Sr and TiB ₂ additives enable die casting of the 2xxx and 2xx alloys in each specified amount, and as a result, allow complex part shapes and designs. By controlling hot cracking in aluminum-copper alloys (2xxx and 2xx alloys), the die casting process, which is usually considered difficult to use with conventional alloys, has become possible for 2xxx and 2xx alloys. These alloys of the present invention retain the same strength and ductility as unaltered alloys, even in the die casting process. In one embodiment of the present invention, the alloy is cast by a molding casting method or a die casting method.

Similarly, alloys containing mainly aluminum and magnesium, such as the above 5xxx and 5xx type alloys, are known to have a tendency to crack. TiB _{2 in} an amount corresponding to Sr in the range of 0.010 to 0.025 mass% and B in the range of 0.001 to 0.005 mass% in the aluminum and magnesium alloys such as the 5xxx and 5xx type alloys (measured by the boron content) Use allows die casting of the 5xxx and 5xx type alloys and, as a result, complex part shapes and designs. By controlling hot cracking in alloys containing mainly aluminum and magnesium, such as the 5xxx and 5xx type alloys, die casting, which is usually considered difficult to use for conventional alloys, is about 5xxx and 5xx alloys. It has become possible. These alloys of the present invention retain the same strength and ductility as unaltered alloys, even in the die casting process. In one embodiment of the present invention, the alloy is cast by a molding casting method or a die casting method.

The alloy formulations of the present invention are suitable for use in any form casting process including, but not limited to, sand casting, permanent casting and die casting. Examples of casting methods include gravity permanent casting, low pressure permanent casting, and vacuum permanent casting. Most notably, these alloy formulations are compatible with high pressure die casting methods, including both conventional high pressure die casting methods and high integrity die casting methods such as high vacuum die casting, semi-solid forming, and squeeze casting methods. It is also suitable for this.
Hot cracking is, of course, not a phenomenon inherent to molding casting methods for near-net parts, but billets, blooms, or T-shaped ingot parts can be semi-continuous or continuous casting (e.g. , DC casting or horizontal continuous casting method), which has limitations that are often encountered. The blends of the present invention are of course applicable in reducing hot cracking when casting these types of products.

Of note, by controlling hot cracking in Al-Mg-Si alloys (6xxx alloys), it is possible to die cast 6xxx alloys, which are usually difficult to use with conventional alloys. It was. The alloy of the present invention maintains the same strength and ductility as the unaltered alloy, even in the case of die casting, yet imparts properties not normally found in conventional aluminum shaped cast alloys. In one embodiment of the present invention, the alloy is cast by a molding casting or a die casting method.
It has been found that the casting can be carried out either in the region above the liquidus temperature of the alloy or in its semi-solid region. Surprisingly, for aluminum alloys, the present invention, in one aspect, contemplates casting in the semi-solid region. This is because not only hot crack resistance has been observed, but it has been found that casting in the semi-solid region also provides improvements in die fillability and general suitability for casting. The semi-solid structure can have a spherical solid phase under some processing conditions, which is particularly preferred for casting.

Starting from a temperature above the liquidus (where the alloy is in a sufficiently molten state), casting the alloys of the present invention into useful shaped articles is done by any technique known to those skilled in the art. be able to.
Most of the alloys of the present invention have a temperature at which the alloy is partially solid and partially liquid (a temperature between the “solidus” and “liquidus” temperatures of the alloy). It is also possible to cast in a semi-solid form.

6xxx alloys that are particularly suitable for casting by semi-solid or complete melting methods, expressed in mass%, Si in the range of 0.6 to 0.8, Fe up to 0.12, Cu in the range of 0.15 to 0.40, Range of 0.8 to 1.2 Mg in the range of 0.04 to 0.10, Sr in the range of 0.006 to 0.025, TiB _{2 in the} range of 0.005 to 0.025% by mass (measured by its boron content), B in the range of 0.001 to 0.005% by mass and preferably it exceeds the amount bound to B stoichiometrically in TiB _2, with Ti having a composition of 0.16% or less excess. For processing by the semi-solid method, a particularly preferred 6xxx alloy contains Al as its balance, each containing less than 0.05, and overall containing less than 0.15 incidental impurities, while in the fully molten state In particular, the particularly preferred 6xxx alloy additionally contains up to 0.45% by weight of Mn, provided that the sum: Mn + Fe is in the range of 0.55 to 0.65%, with the remainder as Contains Al, each less than 0.05, and overall less than 0.15 incidental impurities. Semi-solid processing methods can advantageously use low levels of Fe and Mn. This is because this method is less sensitive to die-sticking. For processing at temperatures above the liquidus, control of the total Mn + Fe amount is advantageous to reduce die-sticking.

In some embodiments, a solid rod or ingot, which can be specially cast to have a fine spherical structure within its solid phase, is again brought to a temperature between the solidus temperature and the liquidus temperature. Heat, then transfer to mold for casting casting.
In other embodiments, the alloy in a sufficiently liquid state is cooled to a temperature between the solidus temperature and the liquidus temperature to produce a semi-solid slurry, which is then cast. In general, this method is controlled to ensure that the solid fraction has a spherical structure rather than a dendritic structure. This can be accomplished by vigorous stirring (eg, by electromagnetic stirring) when rapidly cooling, optionally adding solid nuclei, or cooling to a predetermined temperature. The semi-solid mixture can be maintained at this temperature (a few seconds to a few minutes) to allow the solid particles to grow into a spherical structure. The semi-solid slurry with a spherical structure is generally thixotropic, which increases the mold filling capacity of the slurry.
The container in which the slurry is produced can be heated and / or cooled by external means to ensure the maintenance of the exact predetermined temperature. In a particularly preferred embodiment, when the temperature and mass of a completely liquid alloy is adjusted and consequently added to a container with a known mass, heat capacity and temperature, the alloy will have a predetermined amount in the semi-solid region. It is stabilized there for a predetermined period of time that achieves a predetermined temperature and allows the structure to spheroidize.

In some preferred embodiments, some of the unsolidified liquid alloy is removed (e.g., via a filter or orifice) while maintaining the predetermined temperature or after the passage of that period. Can be removed). This provides a further improvement in the structure of the semi-solid alloy and makes it easier to remove the semi-solid material and transfer it to the casting apparatus.
The semi-solid slurry after preparation can be cast by a known shaping cast casting technique. The die casting method is one of the particularly preferable methods.
The present invention provides an aluminum alloy having a low incidence of hot cracking. Without being bound by any particular theory, the addition of modifiers and crystal refiners in combination in the stated amounts controls both the primary α-phase and the secondary phase of the alloy. The high degree of control over the grain size and morphology provided by the present invention is achieved using a narrow range of titanium diboride, preferably well dispersed within the melt. A high degree of control of the primary α-phase allows the eutectic liquid to move more freely (as compared to the absence of titanium diboride) within the solidifying network. To do. Furthermore, intermetallic compounds (e.g., Mg ₂ Si in the 6xxx alloy) containing, precipitation of the secondary phase affects the fluidity of the eutectic liquid between said spherical structure, also any initial thermal between cracks It is thought to prevent supply.

As stated previously, the crystal refiner and improver control the particle size and morphology of both the secondary and primary phases. Since the primary α-phase is generally the last phase formed during solidification, the present invention specifically controls the particle size and shape of the α-phase so that the eutectic liquid is in the solidified state. Guarantees free movement in the network. The secondary phase between the α-crystals affects the fluidity of the eutectic fluid, and as a result the tempering and improvement of the secondary phase also ensures sufficient alloy supply and prevention of initial hot cracking. It is important to
If crystal refinement is not very effective, hot cracking is likely to start and propagate easily. On the other hand, if the alloy is tempered excessively, it is difficult to initiate hot cracking, but once this has occurred, it will propagate more easily. Eventually, when tempering is performed appropriately, the initiation of the hot cracking becomes more difficult, and propagation of these becomes difficult.

Example 1
Two types of Al-Mg-Si type base alloys, two types of Al-Cu type alloys, and one type of Al-Mg type alloy were prepared as follows (composition expressed in units of mass%).

Various amounts of Sr, TiB ₂ and excess Ti were added to these base alloys. The Ti and Sr were added to the casting furnace as an aluminum master alloy. The TiB ₂ was added to the casting ladle as an Al-5Ti-1B crystal refiner rod just before casting in order to avoid sedimentation of TiB ₂ . This also slightly increases the amount of Ti. This is because there is an excess of Ti in the grain refiner rod and this amount is added to the Ti in the alloy composition described above. These alloys were cast from a fully liquid state in a Constrained Rod Casting (CRC) mold. The hot cracking sensitivity index was measured in each case using the following method.
Cracks on the CRC casting bar were inspected with the naked eye. Five categories related to the severity of hot cracking are described below and assigned an index number Cj for the cracking:
・ No cracking: Cast body that seems to have no cracks (Cj = 0);
・ Narrow crack: A narrow crack (Cj = 1) spreading in half of the circumference of the bar;
-Mild cracks: thin cracks (Cj = 2) that extend all around the bar;
-Severe cracking: cracking over the entire circumference of the bar (Cj = 3);
Complete cracking: The bar is completely or almost separated (Cj = 4).
Two different CRC molds were used with casting bars (AD) with different lengths and were assigned length parameters as shown in the following table:

ここで、「C」は、該バーにおける該割れの重度に対して割り当てられた数値であり、「L」は、該バーの長さに相当する、割り当てられた数値であり、また「i」は、該バーA、B、C及びDを表す。特定の合金組成物に関する該HTSの値は、該CRC金型を用いて鋳造されたこれら5つの鋳造品の平均値であった。
以下のような結果が得られた： Then the HTS value for the sample is given by the following formula:

Here, “C” is a numerical value assigned to the severity of the crack in the bar, “L” is an assigned numerical value corresponding to the length of the bar, and “i”. Represents the bars A, B, C and D. The HTS value for a particular alloy composition was the average of these five castings cast using the CRC mold.
The following results were obtained:

In Table, the boron is present as TiB _2. All Ti is the total amount of Ti from any source, also Ti (excess) is the amount of Ti that is not bound in the TiB _2.
Alloys A15-A19, B7-B12, C10-C19, D9-D18 and E10-E18 represent alloys whose additives are within the scope of the present invention, while the remaining alloys are outside that range. Alloys A1, B1, C1, D1, and E1 represent the above base alloys that do not contain additive elements.
The hot cracking susceptibility index for alloys within the scope of the present invention is lower than that of those outside the range. This change is sufficient to substantially reduce the presence of cracks due to hot cracks in the alloys of the present invention in actual casting.
Example 2
Die-cast parts (artificial suspension arms) in the shape of a U-shape were produced from base alloys A and B and several improvements with the preferred composition of this patent application.

Samples were prepared using both the liquid alloy die casting method and the preferred semi-solid method described above. Here, the alloy material exceeding the liquidus is rapidly cooled to the temperature of the semi-solid region, the temperature determined by the materials and the temperature of the alloy, and held in a crucible for a predetermined period of time, The stock was maintained and then a portion of the residual liquid was removed from the crucible before casting. The amount of liquid alloy removed from the semi-solid material before casting was in the range of 15-18%. These cast parts were heat treated by two different methods.
Treatment I: Heat treatment: 530 ° C for 3 hours + rapid cooling + 160 ° C for 18 hours.
Treatment II: Heat treatment: 3 hours at 530 ° C + rapid cooling + 8 hours at 170 ° C.

  A hot die index for the cast part was determined using liquid die penetrant analysis. The straight side portion of the U-shaped profile was inspected and the hot crack index was determined for these locations. Tensile tests were performed on samples cut from these same parts. The hot crack index is a semi-quantitative index that is assigned a score for each defect found at the inspected location. A score of 0 means no defect, a score of 1 means a point defect (no propagation), and a score of 2 means the propagation length of the defect is less than or equal to the width of the side part A score of 3 means that the propagation length of the defect exceeds the width of the side portion. The index was the sum of these scores for four locations along the straight side portion of the U-shaped profile.

The results in the above table indicate that the hot cracking susceptibility of the alloys A19, A16 and B9 of the present invention is lower than that of the base alloy A1. In general, parts cast using the semi-solid process exhibit better hot cracking performance than liquid cast alloys, and the semi-solid process is more susceptible to the heat treatment than that produced by the liquid process. Resulted in tensile properties that are less sensitive to.
Example 3
Die cast parts were made from the alloy A16 of the present invention. Samples were made using the preferred semi-solid method described above. Here, the alloy material that exceeds the liquidus is rapidly cooled to the temperature of the semi-solid region, the temperature determined by the materials and the temperature of the alloy, and any residual material from the crucible before casting. Without removing the liquid, it was held in a crucible for a predetermined period to maintain the metal material. These residues and parts were heat-treated by the following method.
Treatment III: Heat treatment: 540 ° C for 8 hours + quenching + 170 ° C for 6 hours.
A tensile test was performed and the results are shown in the table below.

  The results in the above table indicate that the hot cracking susceptibility of alloy A16 of the present invention is lower than that of base alloy A1. Furthermore, these results also demonstrate that alloy A16 of the present invention has an elastic limit and mechanical strength that exceeds the typical value for wrought alloy 6061 by 5-15%. From the fatigue test, the alloy A16 of the present invention in the semi-solid state. It can also be seen that it has the same fatigue life length as the wrought alloy 6061.

Claims (28)

i) Sr in the range of 0.010 to 0.025 mass%, and
ii) TiB _{2 in} an amount in the range of 0.001 to 0.005 mass% B as measured by boron content
An aluminum alloy comprising: The aluminum alloy according to claim 1, further comprising i) an excess of 0.16% by mass or more of Ti exceeding the amount stoichiometrically bound to B in TiB ₂ .   Alloy mainly containing aluminum and copper; Alloy mainly containing aluminum and manganese; Alloy mainly containing aluminum and silicon; Alloy mainly containing aluminum and magnesium; Alloy mainly containing aluminum, magnesium and silicon; Mainly aluminum, magnesium 3. The aluminum alloy according to claim 1, wherein the aluminum alloy is selected from the group consisting of alloys containing zinc and copper.   The aluminum alloy according to any one of claims 1 to 3, comprising aluminum, magnesium and silicon. 5. The aluminum alloy according to claim 4, further comprising Sr in a range of 0.010 to 0.020 mass% and TiB ₂ in an amount of B in a range of 0.002 to 0.004 mass% as measured by boron content.   The aluminum alloy according to any one of claims 1 to 5, which is an alloy for modeling casting.   The aluminum alloy according to any one of claims 1 to 5, which is an alloy for die casting.   The aluminum alloy according to any one of claims 1 to 5, wherein the alloy is an alloy casting manufactured using a semi-solid casting method. Expressed in mass%, measured as 0.6 to 0.8 Si, Fe up to 0.12, Cu from 0.15 to 0.40, Mg from 0.8 to 1.2, Cr from 0.04 to 0.10, Sr from 0.006 to 0.025, and boron content 0.001 0.005 to 0.025% TiB ₂ , equivalent to B in the range of ~ 0.005% by mass, more than 0.16% of excess Ti, less than the amount of TiB ₂ stoichiometrically combined with B, each less than 0.05 3. The aluminum alloy according to claim 1, wherein the aluminum alloy has a composition of incidental impurities of less than 0.15 as a whole and the balance of Al.   10. The aluminum alloy according to claim 9, for casting by a semi-solid method. Expressed in mass%, measured as 0.6 to 0.8 Si, Fe up to 0.12, Cu from 0.15 to 0.40, Mg from 0.8 to 1.2, Cr from 0.04 to 0.10, Sr from 0.006 to 0.025, and boron content 0.001 To 0.005% by mass of TiB ₂ , equivalent to B in the range of 0.005% by mass, exceeding the amount stoichiometrically combined with B in TiB ₂ , 0.16% excess Ti, up to 0.45% by mass The aluminum alloy according to claim 1, wherein Mn, provided that the total Mn + Fe is in the range of 0.55 to 0.65% by mass, each is less than 0.05, and has an incidental impurity of less than 0.15 as a whole, and the balance Al. .   The aluminum alloy according to claim 1, for processing in a completely molten state. A method for preventing or eliminating hot cracking in an aluminum alloy, comprising:
Aluminum,
i) Sr in the range of 0.010 to 0.025 mass%, and
ii) TiB _{2 in} an amount ranging from 0.001 to 0.005 mass% B, as measured by boron content;
A method comprising the step of combining. Furthermore, iii) beyond the amount bound in the TiB ₂ in B stoichiometrically, also comprising the step of compounding excess Ti below 0.16%, The method of claim 13.   A shaped cast product cast from the alloy according to any one of claims 1 to 12.   16. The shaped casting according to claim 15, which is a casting by a die casting method.   16. A shaped casting according to claim 15, which is a casting derived from the alloy in a semi-solid state. A method for producing an aluminum alloy, comprising:
Aluminum,
i) Sr in the range of 0.010 to 0.025 mass%, and
ii) TiB _{2 in} an amount ranging from 0.001 to 0.005 mass% B, as measured by boron content;
The manufacturing method characterized by including the process to combine. Furthermore, iii) beyond the amount bound in the TiB ₂ in B stoichiometrically, also comprising the step of compounding excess Ti below 0.16%, The method of claim 18, wherein.   The method of claim 18, wherein the alloy comprises primarily aluminum, magnesium and silicon.   The method of claim 18, comprising casting the alloy.   The method of claim 18, comprising die casting the alloy.   19. The method of claim 18, comprising casting the alloy in a semi-solid state.   19. The method of claim 18, wherein the alloy is cooled from its liquidus state to its semi-solid state prior to casting.   19. The method of claim 18, wherein the alloy in a molten state can be maintained at a predetermined temperature for a time sufficient to produce a semi-solid state in the alloy.   26. The method of claim 25, wherein the period is from 1 second to about 2 minutes.   When the alloy is in its semi-solid state, corresponding to a state in which the spherical solid phase is dispersed in the liquid phase, it removes at least some of the liquid phase rather than all of it before casting. 24. The method of claim 23. A method for processing an aluminum alloy according to any one of claims 1 to 12, having a liquidus temperature and a solidus temperature,
Preparing an alloy comprising a semi-solid within the range of the liquidus temperature and solidus temperature of the alloy;
Heating the alloy to a high alloy initial temperature above the liquidus temperature to sufficiently melt the alloy;
Reducing the temperature of the alloy from a high temperature of the initial metal alloy to a semi-solid temperature below the liquidus temperature and above the solidus temperature;
Maintaining the alloy at the semi-solid temperature for a time sufficient to produce a semi-solid structure in the alloy in which a spherical solid phase is dispersed in the liquid phase, the semi-solid temperature comprising: The solid structure comprises a solid phase of less than about 50% by weight,
Removing at least some but not all of the liquid phase present in the semi-solid structure of the metal alloy to produce a solid-rich semi-solid structure of the alloy comprising the steps of: A removing step comprising removing the liquid phase until the solid rich semi-solid structure comprises about 35 to about 55 wt% solid phase; and the solid rich semi-solid structure Forming the alloy having a predetermined shape,
A method comprising the steps of: