JP2002146463A - Aluminum alloy for die casting - Google Patents

Abstract

(57) [Summary] [Object] To provide an aluminum alloy which has both high yield strength and elongation, and which can maintain its mechanical properties permanently as cast without requiring a stabilizing heat treatment, and has good die castability. [Structure] 3.0% to less than 4.0% by mass of magnesium, 1.0% to 1.5% by mass of manganese, 0.5% to 1.5% by mass of silicon, and 0% by mass. 0.5% by mass or less of iron, the balance substantially consisting of aluminum, and a ratio of magnesium to silicon of Mg / S
It is an aluminum alloy for die casting in which i is 2.7 or more. If necessary, copper may be contained in an amount of 0.5% by mass or less.

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 die casting which is suitable for manufacturing a thin and large vehicle body part for an automobile which requires an impact energy absorbing property by using a die casting machine.

[0002]

2. Description of the Related Art Aluminum die-cast parts are used for joints and center pillars of an aluminum frame body structure. Die-cast parts used in the body structure of automobiles are required to have impact energy absorption properties at the time of automobile collision, but they have mechanical properties that are not sufficient with conventional die-casting alloys, that is, they have both high yield strength and elongation This is necessary. As such die-cast alloys for aluminum frame body structures, developed alloys from Reinfelden, Germany and Alcoa, USA are known. These alloy compositions are Al-5% Mg-2% Si-Mn (Mags
m59), Al-3% Mg-Mn-Co (Magsm22) @cf: Diecasting Wor
ld, March 2000｝, Al-4% Mg-1% Mn ｛JP-A-11-808
No. 75 gazette｝.

[0003] Alloys of these compositions are satisfactory in that they have both high yield strength and elongation as material properties.
There are problems for each practical alloy. That is, Al-5
% After Mg-2% Si-Mn alloy casting to proceed at room temperature precipitation phenomenon of Mg ₂ Si phase rapidly, there is a disadvantage that the elongation with time decreases significantly. Castings with low elongation break immediately when impact energy is applied, and cannot absorb impact energy beyond the energy used for fracture. On the other hand, a casting with large elongation deforms without breaking when impact energy is applied, and absorbs the impact energy as deformation energy. Therefore, when used for automobiles, it does not break even when collision energy is applied due to an automobile accident, thereby avoiding an increase in damage. Therefore, in practical use, it is more advantageous as the elongation is increased permanently. In the Al-5% Mg-2% Si-Mn alloy, in order to secure elongation for many years, 300 to 40 after casting
A structure stabilizing heat treatment at 0 ° C. is indispensable. In addition, Si
Al-3% Mg-Mn (Co) alloys that do not contain manganese have a problem with castability, cracking defects are likely to occur during die casting, and are not applicable to the die-casting method, in which castings with complex shapes are integrally formed. hard.

[0004]

As described above, when an attempt is made to apply aluminum die-casting technology to the production of automobile body structural components, the castability is high so that mass production is possible, and the mechanical material properties required for the vehicle body are required. And an alloy which does not change in properties such as proof stress and elongation even when it is maintained as cast for a long time is required. The present invention has been devised to solve such a problem, has both high yield strength and elongation, and can permanently maintain mechanical properties as cast without the need for stabilizing heat treatment. An object of the present invention is to provide an aluminum alloy having good die castability.

[0005]

The aluminum alloy for die casting of the present invention is based on aluminum-magnesium-silicon-manganese having the following composition in order to achieve the object. That is, the alloy of the present invention is 3.0
Magnesium in an amount of not less than 4.0% by mass and less than 4.0% by mass, manganese in an amount of not less than 1.0% by mass and not more than 1.5% by mass, silicon in an amount of not less than 0.5% by mass and not more than 1.5% by mass, and iron in an amount of not more than 0.5% by mass And the balance substantially consists of aluminum, and the ratio Mg / Si of magnesium to silicon is 2.7 or more. If necessary, copper may be contained in an amount of 0.5% by mass or less. Further, the content of other elements is 0.1.
It is desirable that the content be 1% by mass or less.

[0006]

The aluminum alloy for die casting according to the present invention can provide a material having productivity and mechanical properties suitable for the body structure of an automobile by combining the contents of magnesium, manganese and silicon in an optimum range. is there. The content of each alloy element will be described together with the operation.

[0007] Mg: 3.0% by mass or more and less than 4.0% by mass. Mg is the most important alloying element of the alloy of the present invention, and the material properties vary greatly depending on the magnesium content. Magnesium is an element that forms a solid solution in aluminum and increases the strength, but if its content is less than 3.0% by mass, the proof stress 140 MPa of the mechanical properties required for die-cast parts cannot be satisfied. If the content is 4.0% by mass or more, stress corrosion cracking is likely to occur, and Mg
_{The 2} Al ₃ phase precipitates at the grain boundaries, and the material becomes embrittled. Also,
In the case of an alloy for die casting, addition of silicon cannot be avoided in order to improve castability, but when silicon and magnesium coexist, if the magnesium content is 4.0% by mass or more, Mg ₂ Si precipitates much. In addition, since the material is also embrittled by Mg ₂ Si, the secular change becomes remarkable, and the elongation decreases with time. Therefore, the content of magnesium must be not less than 3.0% by mass and less than 4.0% by mass.

Mn: 1.0% by mass or more and 1.5% by mass or less of manganese has an effect of preventing seizure on a die casting mold and further improving the proof strength and high-temperature strength of the material. It also has the effect of preventing deformation of the casting at the time of removal of the casting after die casting. When the content is less than 1.0% by mass, when the iron content is low, it is easy to seize on the die casting mold, and when the cast product is taken out, the shape of the cast product is easily deformed. When the content exceeds 1.5% by mass, the solidification rate normally obtained by die casting exceeds the solid solution limit of manganese, and a huge crystallized substance is formed, which adversely affects the elongation in the material properties. Effect. Therefore, the manganese content that prevents seizure, secures the shape stability of the cast product at the time of removal, and does not reduce the elongation is 1.0% by mass or more and 1.5% by mass or less.

Si: 0.5% by mass or more and 1.5% by mass or less Silicon is a component necessary for improving the castability of an aluminum-magnesium alloy. The casting crack of the product can be prevented. However, if the content exceeds 1.5% by mass,
At the time of solidification of the alloy, the compound Mg ₂ Si with magnesium is crystallized, and the elongation of the alloy is reduced, and the elongation is further reduced by aging. Therefore, casting cracks are prevented, and the elongation of the material is not reduced.
% To ensure an elongation value of not less than 0.5% by mass.

Mg / Si: 2.7 or more Aluminum-magnesium having the above composition range
Even in a silicon-manganese-based alloy, when the ratio of Si to Mg is high, crystallization of Mg ₂ Si is prioritized during casting. Since the crystallized Mg ₂ Si tends to lower the elongation of the material, the magnesium content is larger than the silicon content, and the experimental result shows that the Mg / Si ratio is 2.7.
It is necessary to do above.

Fe: 0.5% by mass or less Iron has an effect of preventing seizure with a die casting mold during die casting, but hardly forms a solid solution in aluminum. When contained in large amounts, acicular Al-Fe-
It forms Si crystallization and sharply reduces the elongation of the material.
In order to keep the elongation value at 15% or more, its content must be 0.5% by mass or less.

Cu: 0.5% by mass or less Copper has an effect of improving the proof stress among the material properties, so that it is contained as necessary. However, since it reduces elongation and corrosion resistance depending on the content, even if it is contained,
It must be limited to 0.5% by weight or less. Other elements: 0.1% by mass or less In order to secure the elongation required for the material, it is necessary to minimize the mixing of other elements.
It is desirably set to not more than mass%.

By adjusting the components as described above, the aluminum alloy of the present invention does not cause casting cracks, does not cause seizure on a die casting mold, and does not cause the product to die even in the production of a die-cast casting having a complicated shape. The product does not deform when taken out from the product, and when cast by a high quality die casting method such as vacuum die casting method or oxygen die casting method, it secures sufficient elongation as it is cast without any heat treatment As a result, it is possible to manufacture a casting having a high impact energy absorbing ability that can be used as a vehicle body structural material of an automobile.

[0014]

EXAMPLE An aluminum alloy having the composition shown in Table 1 was melted, and then subjected to a degassing and deslagging treatment. The die casting metal held in a vacuum at a temperature of 720 to 750 ° C. and a mold temperature of 250 ° C. It was cast in a mold, and a flat casting having a thickness of 3 mm and a size of 150 mm × 200 mm was produced with a clamping force of 350 tons. Porosity in the die cast casting was controlled to a porosity of 2% or less. From this casting, three flat plate-shaped tensile test pieces with black scale were cut out from one plate-shaped casting, and nine test pieces per level were subjected to a tensile test. (In Table 1, the underline indicates that the value is out of the specified range.) The tensile test was performed on the as-cast sample without heat treatment, and after 3 days, 30 days, and 90 days after the die casting. It was performed later.

[0015]

Table 2 shows the results of a tensile test of each alloy.
The values in the table are the results of the average of nine tensile tests. Table 1
And Table 2 correspond to the alloy No. having the composition defined by the present invention. In 1-5, all alloys are 1
It had a yield strength of 40 MPa or more and an elongation of 15% or more. However, alloy No. 3 having a magnesium content of less than 3% by mass. In No. 6, the proof stress has not reached 140 Mpa.
Alloy No. No. 7 has a low elongation because the Mg / Si ratio is less than 2.7. Further, alloy No. In Nos. 8 and 9, since the magnesium content was 4.0% by mass or more, the tensile test after 3 days of casting maintained a considerably high elongation. However, in the tensile tests after 30 days or 90 days, 10 %.

[0017]

Next, using a practically usable die casting mold, the die castability and the mold release characteristics of the alloy were investigated. Die-casting conditions were the same as the tensile test sample, under the conditions of a molten metal temperature of 720 to 750 ° C. and a mold temperature of 250 ° C.
Cast into a box-shaped mold having a thickness of 2 mm and a flange with a width of 15 mm around the top, casting cracks generated at the bottom or flange of the box in this casting sample, and from the die at a sample temperature of 300 to 350 ° C after die casting. The state of occurrence of shape defects of the casting when the box-shaped casting sample was taken out was measured.

Table 3 shows the results. The results were organized by probability. As for casting cracks, even microscopically observed cracks were counted. In addition, the number in the table indicates the number of the 10 test pieces that had caused casting cracks. As shown in Table 3, 0.2% by mass of alloy No. 2 having a silicon content smaller than the range specified in the claims. 11,
In No. 12, casting cracks occur with a probability of 7 to 80% of the tested mold. Alloy N containing 0.4% by mass of Si
o. In the case of 13, cracking failure of about 20% still occurs. However, alloy N whose Si content exceeds 0.5% by mass
o. No casting cracks occurred in 14, 15, 16 and 17. The releasability of the casting from the mold was counted as defective if the test specimen taken out was applied to the surface plate and a deviation of 2 mm or more was observed. The number of defective products is shown in Table 3. Alloy No. having a manganese content of less than 1.0% by mass. In the case of alloy No. 14 in which deformation failure occurred, alloy No. 1
In 5, 16, and 17, the occurrence rate is zero.

[0020]

[0021]

As described above, the aluminum alloy for die-casting of the present invention can be obtained by adjusting the contents of magnesium, silicon and manganese to the optimum ranges.
It has excellent die-casting properties, and has material properties that have both high yield strength and elongation in an as-cast state, and is suitable for die-casting for automobile body structure.

Claims (2)

[Claims] 1. A mass of 3.0% to less than 4.0% by mass of magnesium, 1.0% to 1.5% by mass of manganese, 0.5% to 1.5% by mass of silicon, 0.
An aluminum alloy for die casting, comprising 5% by mass or less of iron, the balance substantially consisting of aluminum, and a magnesium / silicon ratio Mg / Si of 2.7 or more. 2. The aluminum alloy for die casting according to claim 1, further comprising 0.5% by mass or less of copper.