WO2024181286A1 - AL-SI ALLOY FOR CASTING, AL-Si ALLOY CASTING AND METHOD FOR PRODUCING AL-Si ALLOY CASTING - Google Patents

Abstract

The present invention provides: an Al-Si alloy casting which exhibits excellent mechanical joining properties of rivets or the like, and has excellent impact resistance; a production method for obtaining said Al-Si alloy casting; and an Al-Si alloy for casting. An Al-Si alloy for casting according to the present invention is characterized in that the Ti content is no more than 0.05 mass%. The Al-Si alloy for casting preferably has an Si content of 5.0-12.0 mass%, and preferably has an Mn content of 0.4-1.5 mass%, an Mg content of 0.05-0.6 mass%, a Cr content of 0.1-0.5 mass%, and an Fe content greater than 0 and no greater than 0.6 mass%, with the remainder comprising Al and inevitable impurities.

Description

Al-Si alloy for casting, Al-Si alloy casting, and method for producing Al-Si alloy casting

The present invention relates to an Al-Si alloy that can be suitably used for casting, particularly die casting, and Al-Si alloy castings cast with this Al-Si alloy are suitable for mechanical joining using rivets (particularly self-piercing rivets) etc.

Al-Si alloys have excellent castability and are therefore used as casting alloys. Casting here refers to known casting methods such as sand casting, metal mold casting, low pressure casting and die casting, and is not limited to any particular casting method.

Aluminum materials are joined using methods such as brazing, adhesive bonding, welding, friction stir welding, and friction welding, but in recent years, mechanical joining using self-piercing rivets has attracted attention as a simpler joining method.

Self-piercing riveting is a joining method in which the materials to be joined are overlapped, a receiving die is placed on the underside of the lower material, and a self-piercing rivet is driven from above the upper material to be joined; the shank of the self-piercing rivet expands when driven into the materials, achieving the joining.

For example, Patent Document 1 (JP Patent Publication No. 2020-66751) describes a plastically processed material to be used for self-pierce riveting, containing Si: 0.95% to 1.25% by mass, Mg: 0.80% to 1.05% by mass, Cu: 0.30% to 0.50% by mass, Mn: 0.40% to 0.60% by mass, Fe: 0.15% to 0.30% by mass, Cr: 0.09% to 0.21% by mass, B: 0.0001% to 0.03% by mass, and Zn content The aluminum alloy plastically processed material is characterized in that the content of Zr is 0.25 mass% or less, the content of Zr is 0.05 mass% or less, the content of Ti is 0.10 mass% or less, and the balance is Al and unavoidable impurities, and that the maximum shear tensile load measured in accordance with JIS Z3136-1999 for a self-pierce riveted joint between the aluminum alloy plastically processed materials is 8.5 kN or more.

The plastically worked Al-Mg-Si aluminum alloy material described in Patent Document 1 above is said to be able to provide an Al-Mg-Si aluminum alloy plastically worked material with excellent joining strength for self-pierce riveting by optimizing the composition.

Furthermore, Patent Document 2 (JP 2002-121635 A) discloses an aluminum alloy extrusion material for automobile frames having excellent self-pierce riveting joinability, which is made of an Al-Mg-Si-based aluminum alloy extrusion material containing 0.30 to 0.70% (mass%, the same applies hereinafter) Mg, 0.40 to 0.80% Si, 0.05 to 0.40% Cu, 0.05 to 0.30% Mn, 0.05 to 0.20% Zr, with the balance being Al and unavoidable impurities, and which is subjected to press quenching by air cooling followed by aging treatment to have a proof stress of 200 N/mm2 ^or more and a local elongation of 3.5% or more.

In the aluminum alloy extrusion material for automobile frames described in Patent Document 2, it is said that by performing aging treatment after press quenching by air cooling, which is advantageous in terms of dimensional accuracy and cost, an aluminum alloy extrusion material with the necessary strength (yield strength) for automobile frames and excellent self-pierce riveting jointability can be obtained.

JP 2020-66751 A JP 2002-121635 A

However, the subject of the above Patent Document 1 is a plastically processed Al-Mg-Si aluminum alloy material, while the subject of the above Patent Document 2 is an extruded aluminum alloy material, and in both cases, the subject is an aluminum alloy material whose microstructure and mechanical properties are controlled by plastic processing.

In contrast, it is often necessary to join aluminum alloy castings such as die-cast materials to other structural components using mechanical joining methods such as self-piercing rivets, and when mechanical joining is applied to aluminum alloy castings, suppressing cracks that occur during joining becomes a more serious issue.

In view of the problems with the conventional technology described above, the object of the present invention is to provide an Al-Si alloy casting that has excellent impact resistance and excellent mechanical joinability with rivets, a manufacturing method for obtaining said Al-Si alloy casting, and an Al-Si alloy for casting.

In order to achieve the above objective, the inventors conducted extensive research into the relationship between the composition, microstructure, and mechanical properties of Al-Si alloy castings and cracking during mechanical joining, and discovered that cracking during mechanical joining is strongly correlated not with total elongation or uniform elongation, but with the limit bending angle (or local elongation) in the VDA bending test.

Furthermore, as a result of further research, it was discovered that there is a strong correlation between the Ti content of Al-Si alloy castings and the limit bending angle in the VDA bending test, and that reducing the Ti content increases the limit bending angle in the VDA bending test, leading to the invention.

That is, the present invention provides:
The Ti content is 0.05 mass% or less;
The present invention provides an Al-Si alloy for casting, characterized by:

By setting the Ti content to 0.05 mass% or less, it is possible to effectively suppress the coarsening of the structure of the Al-Si alloy casting. More specifically, by setting the Ti content to 0.05 mass% or less, it is possible to refine the dendrite cell size and increase the limit bending angle in the VDA bending test. The Ti content is preferably set to 0.03 mass% or less, more preferably set to 0.02 mass% or less, and most preferably set to 0.01 mass% or less.

In addition, in the Al-Si alloy for casting of the present invention, it is preferable that the Si content is 5.0 to 12.0 mass%. Al-Si alloys have a wide solid-liquid coexistence region and excellent fluidity, making them suitable for casting. This effect is remarkable when the Si content is 5.0 mass% or more.

In addition, the Al-Si alloy for casting of the present invention preferably further contains Mn: 0.4-1.5 mass%, Mg: 0.05-0.60 mass%, Cr: 0.1-0.5 mass%, Fe: more than 0.6 mass%, and the remainder is Al and unavoidable impurities.

By adding 0.4 mass% or more of Mn to Al-Si alloys for casting, it is possible to prevent seizing onto the mold, suppress the needle-like formation of Al-Si-Fe crystals, and suppress the decrease in elongation of Al-Si alloy castings. In addition, by keeping the amount of Mn added to 1.5 mass% or less, it is possible to suppress the decrease in elongation of Al-Si alloy castings due to the coarsening of Al-Si-(Fe, Mn) crystals.

In addition, adding 0.05 mass% or more of Mg can improve the mechanical properties of Al-Si alloy castings through solid solution strengthening of Mg and precipitation strengthening of Mg-Si compounds. Furthermore, by limiting the amount of Mg added to 0.60 mass% or less, excessive increases in deformation resistance can be suppressed, and the occurrence of cracks during mechanical joining can be suppressed.

In addition, the Al-Si alloy for casting of the present invention preferably contains one or more of the following: Cu: 0.05-0.50 mass%, Ca: 0.005-0.030 mass%, B: 0.001-0.020 mass%, Sr: 0.005-0.030 mass%, Sb: 0.01-0.20 mass%, and Na: 0.002-0.020 mass%.

By further adding these elements, it is possible to adjust the microstructure and mechanical properties of the Al-Si alloy casting, and further enhance the crack suppression effect. It is also possible to impart the desired yield strength to the Al-Si alloy casting.

The addition of Cu can increase the strength and yield strength of Al-Si alloy castings, and the addition of B can improve the local elongation of Al-Si alloy castings. In addition, Ca, Sr, Sb, and Na have the effect of refining and granulating eutectic Si, which can improve the elongation of Al-Si alloy castings.

The present invention also provides an Al-Si alloy casting made of the Al-Si alloy for casting of the present invention, characterized in that the limit bending angle in the VDA bending test specified in VDA238-100 is 33° or more. The limit bending angle in the VDA bending test is preferably 34° or more, and more preferably 35° or more.

Here, VDA stands for the German Association of the Automotive Industry (Verband der Automobilindustrie), and VDA238-100 is prescribed as a plate bending test aimed at evaluating the cracking behavior when a component is crushed.

In addition, in the Al-Si alloy casting of the present invention, it is preferable that the average dendrite cell size is 7.1 μm or less. As a result of the inventor's intensive research, it has become clear that the limit bending angle in the VDA bending test of Al-Si alloy castings is very sensitive to the dendrite cell size, and that by setting the average dendrite cell size to 7.1 μm or less, the occurrence and propagation of cracks when stress is applied to the Al-Si alloy casting can be extremely effectively suppressed, and excellent local elongation can be imparted to the Al-Si alloy casting. As a result, in the Al-Si alloy casting of the present invention, the occurrence of cracks during mechanical fastening is effectively suppressed. It is more preferable that the average dendrite cell size is 6.9 μm or less, and most preferably 5.9 μm or less.

Furthermore, the present invention provides
A Ti removal process in which B is added to a molten Al-Si alloy, Ti in the molten Al-Si alloy is converted to _TiB2 , and then the _TiB2 is removed;
A casting step of performing casting using the molten metal from which the Ti removal step has been performed to obtain an Al-Si alloy casting,
The Ti removal step reduces the Ti content of the Al-Si alloy casting to 0.05 mass% or less,
The limit bending angle of the Al-Si alloy casting in the VDA bending test specified in VDA238-100 is 33° or more.
Also provided is a method for producing an Al-Si alloy casting, characterized by:

Ti is often added to Al-Si alloy castings because adding Ti during casting serves as a nucleus for the crystallization of the α phase and improves castability. However, as a result of extensive research by the inventors into the relationship between the composition and microstructure of Al-Si alloy castings, it has become clear that when Ti exceeds 0.05 mass%, the dendrite size in Al-Si alloy castings increases. In contrast, in the manufacturing method of Al-Si alloy castings of the present invention, Ti is actively removed from the molten Al-Si alloy by adding B, which effectively reduces the dendrite size and makes it possible to set the limit bending angle of the VDA bending test specified in VDA238-100 to 33° or more.

The method of removing _TiB2 from the molten metal is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known methods can be used. For example, _TiB2 that has settled in the molten metal may be removed by an appropriate method, or may be removed using a filter. By removing _TiB2 , the Ti content of the molten metal can be reduced to 0.05 mass% or less. The Ti content of the molten metal is preferably 0.03 mass% or less, more preferably 0.02 mass% or less, and most preferably 0.01 mass% or less.

Furthermore, in the manufacturing method of the Al-Si alloy casting of the present invention, by reducing the Ti content, it is preferable to set the limit bending angle of the VDA bending test specified in VDA238-100 to 34° or more, and more preferably 35° or more. Here, if the limit bending angle of the VDA bending test is lower than the desired value, the Ti content can be further reduced.

In addition, in the manufacturing method of the Al-Si alloy casting of the present invention, it is preferable that the molten metal used in the casting has the composition of the Al-Si alloy for casting of the present invention. By making the composition of the molten metal the composition of the Al-Si alloy for casting of the present invention, it is possible to reliably obtain an Al-Si alloy casting that has excellent impact resistance and also has excellent mechanical joinability with rivets, etc.

The present invention provides an Al-Si alloy casting that has excellent impact resistance and mechanical joinability with rivets, a manufacturing method for obtaining the Al-Si alloy casting, and an Al-Si alloy for casting.

1 is a photograph of the structure of an Al—Si alloy sheet material having the composition of Example 1. 1 is a photograph of the structure of an Al—Si alloy sheet material having the composition of Example 2.

The Al-Si alloy for casting and the Al-Si alloy castings of the present invention, as well as the manufacturing method of the Al-Si alloy castings, are described in detail below, but the present invention is not limited to these.

1. Al-Si alloy for casting The Al-Si alloy for casting of the present invention is characterized in that the Ti content is 0.05 mass % or less. Each component will be described in detail below.

(1) Essential additive elements Si: 5.0 to 12.0 mass%
The present invention is directed to an Al-Si alloy, and Si is an essential additive element. The Si content is preferably 5.0 to 12.0 mass%. Si has the effect of improving the castability of the aluminum alloy, and also has the effect of improving mechanical properties such as tensile strength. This effect is significant when the content is 5.0 mass% or more, but when the content exceeds 12.0 mass%, eutectic Si and primary crystal Si tend to become coarse, local elongation decreases, and cracks tend to occur when mechanical joining is performed. The amount of Si added is more preferably 6.0 to 9.0 mass%, and most preferably 6.0 to 7.0 mass%.

(2) Optional Added Elements Mn: 0.4 to 1.5 mass%
Mn has the effect of preventing seizure to a mold and the effect of suppressing the needle-like formation of Al-Si-Fe crystals and suppressing the decrease in elongation. This effect becomes remarkable at 0.4 mass% or more, but conversely, at more than 1.5 mass%, Al-Si-(Fe, Mn) crystals tend to become coarse, which causes the decrease in elongation. The Mn content is preferably 0.5 to 0.7 mass%.

Mg: 0.05 to 0.60% by mass
Mg has the effect of improving the mechanical properties by dissolving in Al, and when aging treatment is performed, it precipitates together with Si as an Mg-Si compound, improving the mechanical properties. This effect is The effect is significant when the amount of Mg added is 0.05% or more by mass, but on the other hand, when the amount of Mg added exceeds 0.60% by mass, the deformation resistance increases and cracks are likely to occur when mechanically joining. The content is preferably up to 0.30 mass %, and more preferably 0.05 to 0.14 mass %.

Cr: 0.1 to 0.5% by mass
Cr has the effect of preventing seizure to the mold and improving corrosion resistance. This effect is remarkable at 0.1 mass% or more. On the other hand, if it exceeds 0.5 mass%, it becomes easy to form coarse compounds. , elongation tends to decrease.

Fe: more than 0 and 0.6% by mass or less Fe has the effect of improving mechanical properties such as tensile strength and preventing seizure of a mold. However, if the content exceeds 0.6% by mass, elongation decreases and cracks are likely to occur when mechanical joining is performed.

Cu: 0.05 to 0.50% by mass
Cu has the effect of improving mechanical properties, and this effect becomes significant when the Cu content is 0.05 mass% or more. Conversely, when the Cu content exceeds 0.50 mass%, the corrosion resistance decreases. It is preferable that the content is 0.20 to 0.40 mass %.

B: 0.001 to 0.020% by mass
B has the effect of improving local elongation and mechanical joinability. This effect is remarkable when the content is 0.001 mass% or more. On the other hand, when the content exceeds 0.020 mass%, it is a factor of increasing production costs. It becomes.

Ca: 0.005 to 0.030% by mass
By adding 0.005 to 0.030 mass % of Ca, the eutectic silicon can be made fine and granular. When the eutectic silicon is made fine and granular, elongation is improved, and when mechanical joining is performed, This can suppress the occurrence of cracks in the steel sheet.

Sr: 0.005 to 0.030% by mass
By adding 0.005 to 0.030 mass % of Sr, the eutectic silicon can be made fine and granular. When the eutectic silicon is made fine and granular, elongation is improved, and when mechanical joining is performed, This can suppress the occurrence of cracks in the steel sheet.

Sb: 0.01 to 0.20% by mass
By adding 0.01 to 0.20 mass % of Sb, the eutectic silicon can be made fine and granular. When the eutectic silicon is made fine and granular, elongation is improved, and when mechanical joining is performed, This can suppress the occurrence of cracks in the steel sheet.

Na: 0.002 to 0.020% by mass
By adding 0.002 to 0.020 mass % of Na, the eutectic silicon can be made fine and granular. When the eutectic silicon is made fine and granular, the elongation is improved, and when mechanical joining is performed, This can suppress the occurrence of cracks in the steel sheet.

(3) Inevitable impurities Among the inevitable impurities, the content of Ti must be strictly controlled to 0.05 mass% or less. The Ti content is preferably 0.03 mass% or less, more preferably 0.02 mass% or less, and most preferably 0.01 mass% or less. The contents of V and Zr are also reduced as much as possible, preferably 0.05 mass% or less, more preferably 0.03 mass% or less, even more preferably 0.02 mass% or less, and most preferably 0.01 mass% or less.

The Al-Si alloy casting of the present invention is made of the Al-Si alloy for casting of the present invention, and has a major feature that the limit bending angle in the VDA bending test specified in VDA238-100 is 33° or more. The microstructure and mechanical properties will be described in detail below.

(1) Metal structure In the Al-Si alloy casting of the present invention, the average dendrite size is 7.1 μm or less, and the occurrence and propagation of cracks when stress is applied to the Al-Si alloy casting is extremely effectively suppressed, and the Al-Si alloy casting is provided with excellent local elongation. As a result, in the Al-Si alloy casting of the present invention, the occurrence of cracks during mechanical joining is effectively suppressed. The average dendrite size is more preferably 6.9 μm or less, and most preferably 5.9 μm or less.

The method for confirming the average dendrite size is not particularly limited, and any of the various conventionally known microstructural observation methods may be used. For example, the cross section of a mirror-polished Al-Si alloy casting can be observed with an optical microscope or a scanning electron microscope (SEM).

Here, for example, the average dendrite size can be measured by the intersection method according to the procedure of the DAS measurement method (dendrite arm spacing measurement method). In this case, it is preferable to measure at a position that avoids eutectic structures as much as possible.

(2) Mechanical Properties The Al-Si alloy casting of the present invention has excellent tensile properties including high strength, proof stress and ductility. In addition, the occurrence of cracks during mechanical joining is effectively suppressed.

The mechanism by which cracks occur when mechanically joining is complex, and it is difficult to evaluate it solely from measurements of the mechanical properties of Al-Si alloy castings, such as tensile properties and hardness. However, as a result of extensive research by the inventors, it has become clear that there is a strong correlation between the limit bending angle in the VDA bending test specified in VDA238-100 and the presence or absence of cracks when mechanically joining.

More specifically, to prevent cracking during mechanical joining, the limit bend angle in the VDA bend test specified in VDA238-100 must be 33° or greater. A preferred limit bend angle is 34° or greater, and a more preferred limit bend angle is 35° or greater.

3. Manufacturing method of Al-Si alloy casting The manufacturing method of Al-Si alloy casting of the present invention includes a Ti removal step of removing Ti contained as an inevitable impurity in the molten Al-Si alloy, and a casting step of casting the molten Al-Si alloy from which Ti has been removed. Each step will be described in detail below.

(1) Ti Removal Step The Ti removal step is a step for reducing the Ti content in the molten metal as much as possible by adding B to the molten metal of an Al-Si alloy, converting Ti in the molten metal to _TiB2 , and then removing the _TiB2 . The Ti content must be 0.05 mass% or less.

The method of removing _TiB2 from the molten metal is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known methods can be used. For example, _TiB2 that has settled in the molten metal may be removed by an appropriate method, or may be removed using a filter. By removing _TiB2 , the Ti content of the molten metal can be reduced to 0.05 mass% or less. The Ti content of the molten metal is preferably 0.03 mass% or less, more preferably 0.02 mass% or less, and most preferably 0.01 mass% or less.

The molten Al-Si alloy to be subjected to the Ti removal process is preferably made to have the composition of the Al-Si alloy for casting of the present invention. By making the composition of the molten metal the composition of the Al-Si alloy for casting of the present invention, it is possible to reliably obtain an Al-Si alloy casting that has excellent impact resistance and excellent mechanical joinability with rivets, etc.

(2) Casting process The casting method in the casting process is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known casting methods (sand casting, metal mold casting, gravity casting, low pressure casting, die casting, etc.) can be used. That is, the aluminum alloy casting of the present invention is not limited to one cast by a specific casting method.

In addition, the casting conditions are not particularly limited as long as they do not impair the effects of the present invention, and various casting conditions that are conventionally known can be used.

The above describes typical embodiments of the present invention, but the present invention is not limited to these, and various design modifications are possible, all of which are within the technical scope of the present invention.

Example
Raw materials mixed to obtain the compositions (mass%) shown in Table 1 as Examples 1 to 6 were melted at 750°C, deslag treatment was performed using a molten metal cleaning flux, and degassing treatment was performed by blowing in Ar gas. Then, an Al-Si alloy plate material, which is an embodiment of the Al-Si alloy casting of the present invention, was obtained by PF die casting under the conditions of a high-speed injection speed of 2.0 mm/s, a casting pressure of 80±5 MPa, a casting temperature of 730±10°C, and a mold temperature of 100 to 150°C. The size of the Al-Si alloy plate material was 110×110×3 mm.

In all examples, B was added to the molten raw material to generate _TiB2 , and after degassing, the material was allowed to settle for 1 hour to allow _TiB2 to settle and be removed (Ti removal process), and then PF die casting was performed. The composition shown in Table 1 is the value for the molten metal after the Ti removal process. As shown in Table 1, in all examples, the Ti content is 0.05 mass% or less.

　

The obtained Al-Si alloy plate material was subjected to a VDA bending test specified in VDA238-100 to evaluate the limit bending angle. Three measurements were performed on each Al-Si alloy plate material, and the average value was calculated. The obtained limit bending angles are shown in Table 1. As shown in Table 1, it can be seen that the limit bending angle in the VDA bending test was 33° or more in all examples.

Samples for microstructural observation were cut out from each Al-Si alloy plate material, and the cross sections were buffed and observed under an optical microscope. As representative examples, microstructural photographs of Al-Si alloy plate materials having the compositions of Examples 1 and 2 are shown in Figures 1 and 2, respectively. Comparing the microstructures in Figures 1 and 2, it can be seen that the dendrite cell size is finer in Example 1, which has a lower Ti content. In addition, the average dendrite cell size was calculated from each obtained microstructural photograph using the intersection method (number of intersections: 10) according to the procedure of the DAS measurement method. The obtained values are shown in Table 1. As shown in Table 1, it can be seen that the average dendrite cell size is 7.1 μm or less in all examples.

Comparative Example
An Al-Si alloy plate material, which is a comparative Al-Si alloy casting of the present invention, was obtained in the same manner as in the Examples, except that raw materials were used that were blended to obtain the composition (mass%) shown in Comparative Example 1 in Table 1.

In addition, the average values of the limit bending angle and the dendrite cell size in the VDA bending test of the Al-Si alloy sheet material were measured in the same manner as in the examples. The obtained values are shown in Table 1. It can be seen that in the comparative example, the Ti content exceeded 0.05 mass% to 0.110 mass%, and the dendrite cell size was 7.3 μm, resulting in a low limit bending angle of 32.6° in the VDA bending test.

Claims (8)

The Ti content is 0.05 mass% or less;
An Al-Si alloy for casting, characterized by: The Si content is 5.0 to 12.0 mass%;
The Al-Si alloy for casting according to claim 1, Furthermore,
Mn: 0.4 to 1.5% by mass,
Mg: 0.05 to 0.60% by mass,
Cr: 0.1 to 0.5% by mass,
Fe: more than 0 and 0.6 mass% or less;
the balance being Al and unavoidable impurities;
The Al-Si alloy for casting according to claim 1 or 2, Furthermore,
Cu: 0.05 to 0.50% by mass,
Ca: 0.005 to 0.030% by mass,
B: 0.001 to 0.020% by mass,
Sr: 0.005 to 0.030% by mass,
Sb: 0.01 to 0.20% by mass,
Na: 0.002 to 0.020 mass%.
The Al-Si alloy for casting according to claim 1 or 2, The Al-Si alloy for casting according to claim 1 or 2 is used.
The limit bending angle of the VDA bending test specified in VDA238-100 is 33° or more.
The Al-Si alloy casting is characterized by the above. The average dendrite cell size is 7.1 μm or less;
The Al-Si alloy casting according to claim 5, A Ti removal process in which B is added to a molten Al-Si alloy, Ti in the molten Al-Si alloy is converted to _TiB2 , and then the _TiB2 is removed;
A casting step of performing casting using the molten metal from which the Ti removal step has been performed to obtain an Al-Si alloy casting,
The Ti removal step reduces the Ti content of the Al-Si alloy casting to 0.05 mass% or less,
The limit bending angle of the Al-Si alloy casting in the VDA bending test specified in VDA238-100 is 33° or more.
The method for producing an Al-Si alloy casting is characterized by the above. The molten metal used in the casting has a composition of the Al-Si alloy for casting according to claim 1 or 2;
The method for producing an Al-Si alloy casting according to claim 7,