JP2003147470A - Aluminum alloy for casting having excellent toughness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-heattreated Al-Mg aluminum alloy for casting which has excellent castability, and high toughness. SOLUTION: The aluminum alloy has a composition containing, by mass, 2.0 to 9.0% Mg, 0.1 to 5.0% Si, 0.05 to 1.0% Bi, and <=1.0% Fe, and the balance substantially Al. The alloy can contain one or more kinds selected from 0.3 to 1.5% Mn, 0.01 to 0.2% Ti and 0.0005 to 0.05% B as well. Thus, Mg-Si based crystallized products crystallized out on casting are refined, and its toughness is increased while maintaining the castability thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy for casting which can obtain high strength and toughness without heat treatment after casting and is excellent in castability.

Aluminum alloy castings have come to be used for car body parts in order to reduce the weight of automobiles. As an aluminum alloy for casting, Al-S with excellent castability
i-based aluminum alloys have been used. By the way, when such an aluminum alloy is used, it is necessary to perform heat treatment such as solution treatment or quenching after casting in order to obtain strength. Therefore, in the case of thin-walled parts, the product may be deformed during quenching. Therefore, an Al—Mg-based aluminum alloy that can obtain high strength without heat treatment has come to be used. The applicant of the present application also applied for a patent application 200
No. 1-238947 proposes an Al-Mg-based aluminum alloy having excellent castability.

[0003]

In recent years, in order to ensure the safety in the event of a collision accident, high toughness is required of the component materials in order to allow the body parts of automobiles to have a shock absorbing capability. However, in the case of an Al-Si-based aluminum alloy, a Si-based compound that reduces toughness is likely to be crystallized, so there is a limit to improving toughness. In addition, it is effective to add Si to a non-heat treatment type Al-Mg-based aluminum alloy when casting a product having a complicated shape. However, the addition of Si has a limit in improving the toughness. Thus, it was difficult to increase the toughness while maintaining the castability. Therefore, an object of the present invention is to provide a non-heat treatment type Al-Mg-based aluminum alloy, which is excellent in castability and has high toughness.

[0004]

The aluminum alloy for casting which is excellent in toughness of the present invention has the following object.
g: 2.0 to 9.0% by mass, Si: 0.1 to 5.0% by mass, Bi: 0.05 to 1.0% by mass, Fe: 1.0% by mass or less, the balance being substantially It is characteristically Al. Further, Mn: 0.3 to 1.5 mass%, Ti: 0.
01-0.2 mass% and B: 0.0005-0.05
It is also possible to include any one or more of the components by mass%.

[0005]

The present inventors investigated the cause of the decrease in toughness of the Al-Mg based aluminum alloy for casting. as a result,
This is due to the fact that the Mg-Si-based crystallized product that crystallizes during casting is likely to coarsen, and to improve the toughness, this Mg
It has been found that the -Si-based crystallized substance may be refined. As a result of further studies, the present inventors have confirmed that the addition of Bi can make the Mg-Si-based crystallized substance finer. 1 and 2, Al-5% Mg-1.6% Si
The casting structure of a -0.8% Mn alloy is shown. FIG. 1 shows the case where Bi is not added, and FIG. 2 shows the case where Bi is added by 0.1%.
Although there is no difference for the α phase, it can be seen that the eutectic structure crystallized at the α phase grain boundary is completely different depending on whether Bi is contained or not. That is, a needle-free large eutectic structure is observed in the case where Bi is not added, but a fine eutectic structure is obtained when Bi is contained. It is presumed that this increased the toughness.

In the present invention, the following alloy design is adopted from the viewpoint of castability, strength and toughness. Mg: 2.0 to 9.0 mass% Mg is an element that forms a solid solution in the matrix of the aluminum alloy and forms MgSi-based crystallized substances with coexisting Si to improve the strength. If the content is less than 2.0%, the effect of improving the strength is small, and if it exceeds 9.0%, stress corrosion cracking tends to occur.

Si: 0.1 to 5.0 mass% Si improves castability. Further, it is an alloy component that improves the strength by forming MgSi-based crystallized substances, and
When the content is 1% or more, those effects become remarkable. However, if an excess amount of Si exceeding 5.0% is included, Si
Since a large amount of the system compound can be formed, the toughness is significantly reduced.

Bi: 0.05 to 1.0% by mass Bi has a function of refining MgSi-based crystallized substances and improving the toughness of the alloy. If the content is less than 0.05%, the effect is not sufficient, and even if it is contained up to 1.0%, it has a toughness improving action. However, with respect to the improvement of toughness, it is saturated at about 0.5%, and further effects cannot be expected even if it is contained more than that. If the Bi content is high, a Bi-based compound is formed and the corrosion resistance and the alumite property are deteriorated. Therefore, it is preferable to keep the content to 0.5% or less.

Fe: 1.0% by mass or less It is an alloy component effective for improving strength by preventing seizure in a mold, forming a solid solution in a matrix phase and forming a crystallized product. In particular, at the time of die casting, the content of Fe has the effect of preventing seizure in the mold, so it is preferable to contain 0.1% or more. However, a large content causes crystallization of the Fe-based crystallized product and leads to a decrease in toughness, so the content is made 1.0% or less when it is contained.

Mn: 0.3 to 1.5 mass% Mn crystallizes Al ₆ Mn during solidification to improve high temperature strength and suppress deformation of the product when the product is taken out after die casting, and at the same time gold It is an element that has the effect of preventing seizure on the mold. It also has the function of granulating the needle-shaped Fe-based crystallized substances and preventing a decrease in toughness. In order to exert these effects, the content of 0.3% is necessary, and conversely, if the content exceeds 1.5%, a coarse Mn-based crystallized substance is crystallized and the toughness is lowered. become. Therefore, when Mn is contained, 0.3 to
It should be in the range of 1.5% by weight.

Ti: 0.01 to 0.2% by mass, B: 0.
0005 to 0.05 mass% Ti, B or Ti and B are effective elements for refining the primary crystal α (Al) phase and improving the mechanical properties of the casting. Such an effect becomes remarkable when 0.01% or more of Ti or 0.0005% or more of B is added, but 0.2%
If more than Ti or more than 0.05% B is added, a coarse compound is formed and the toughness is lowered.

The aluminum alloy for casting of the present invention basically contains the alloy components listed above,
Trace amount of Zr, V, Mn, which is inevitably mixed in the manufacturing process
The inclusion of Cr, Zn, etc. is not excluded. The casting aluminum alloy of the present invention, by adopting the alloy design as described above, after casting while securing the castability,
Mechanical properties, especially toughness, can be enhanced without heat treatment. However, when higher strength is required or when the balance between strength and elongation is required to be improved, the alloy according to the present invention may be cast and then subjected to stabilization treatment or aging treatment.

[0013]

EXAMPLES Example 1 Al-5% Mg-2% Si-0.15% Fe alloy with Bi
Alloy was added by changing 0.1% in increments of 0.1
JIS 14A tensile test pieces were cut out from the cast article obtained by casting in a boat shape of S4 by gravity casting without subjecting it to heat treatment, and the mechanical strength and elongation were measured. The results are shown in Table 1.

[0014]

Example 2 Al-5% Mg-2% Si-0.15% Fe-0.8%
Cast article obtained by melting and alloying Mn-0.02% Ti-0.0007% B alloy with Bi changed by 0.1% and cast into a flat plate with a plate thickness of 3 mm by a die casting method. A tensile test piece of JIS14B was cut out without subjecting it to heat treatment, and its mechanical strength and elongation were measured. The results are shown in Table 2.

[0016]

As can be seen from the results of Tables 1 and 2 and FIGS.
Although the tensile strength and the 0.2% proof stress are hardly changed even if the added amount is increased, the elongation is improved as the Bi amount is increased. From this, it can be seen that in the Al-Mg based aluminum alloy for casting, the toughness is improved by adding Bi.

[0018]

As described above, the aluminum alloy for casting according to the present invention is M-crystallized during casting by adding Bi in the Al-Mg type aluminum alloy.
It was possible to refine the g-Si-based crystallized substance and enhance the toughness while maintaining the castability. According to the present invention, the toughness of an Al-Mg-based aluminum alloy casting that does not require heat treatment can also be improved, so that high-quality casting parts for automobiles required to have shock absorbing characteristics can be supplied at low cost. It became possible to do.

[Brief description of drawings]

FIG. 1 is a microscopic structure of a cross section of a Bi-free alloy casting,
(A) shows a cast structure, (b) shows an α-phase expanded structure, and (c) shows a eutectic expanded structure.

FIG. 2 is a microstructure of a cross section of a casting of a 0.1 mass% Bi-added alloy, (a) shows a cast structure, (b) shows an α-phase expanded structure, and (c) shows an expanded structure of a eutectic part. Indicates

FIG. 3 Al-5% Mg-2% Si-0.15% Fe
Graph showing the relationship between Bi addition amount and mechanical properties when Bi is added to alloy castings

FIG. 4 Al-5% Mg-2% Si-0.15% Fe
-0.8% Mn-0.02% Ti-0.0007% B alloy is a graph showing the relationship between the added amount of Bi and mechanical properties when Bi is added to the casting.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsuyoshi Minamida             1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture             Nippon Light Metal Co., Ltd. Group Technology Center             Within (72) Inventor Shinichiro Kaku             1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture             Nippon Light Metal Co., Ltd. Group Technology Center             Within (72) Inventor Haruno Hino             1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture             Nippon Light Metal Co., Ltd. Group Technology Center             Within

Claims (2)

[Claims] 1. Mg: 2.0 to 9.0 mass%, Si:
0.1 to 5.0% by mass, Bi: 0.05 to 1.0% by mass, Fe: 1.0% by mass or less, and the balance substantially A
An aluminum alloy for casting having excellent toughness, which is characterized in that it is 1. 2. Further, Mn: 0.3 to 1.5% by mass,
Ti: 0.01 to 0.2 mass% and B: 0.0005
The aluminum alloy for casting excellent in toughness according to claim 1, containing at least one of 0.05 to 0.05 mass%.