JP2998760B2 - Manufacturing method of aluminum alloy casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Field of Industrial Application >> The present invention relates to a method for producing an aluminum alloy casting containing Si.

<< Prior Art >> For a method of manufacturing an Al-Si alloy casting, see, for example, FIG. 1-b of “Light Alloys” (1984) Vol. 34, No. 8, p477, and “Light Metals” (1988) Vol. 38 No. 7, p433, paragraphs 3.2 and 4. In the former example, the molten metal of Al-8Si alloy is pressurized and solidified under high pressure to improve the thermal conductivity with the mold (meaning an increase in cooling rate) and to reduce the Si particle size by ordinary gravity casting. It is shown that it can be reduced to 20 to 30% compared to wood.
(Thus, the solidification method of solidifying a molten metal under high pressure is generally called “molten forging”, and this term may be used hereinafter in the present specification.)
This document describes a so-called improvement treatment of a conventionally well-known Al-Si alloy, and shows that Si particles are refined to the same extent by Na, Sr, Sb, and the like, which are improvement elements.

It is known that the refining of Si grains as described above greatly affects the fatigue strength of Al-Si alloy castings. For example, see "Casting" Vol. 56 (1984), No. 7, p391, FIG. Indicates that the fatigue limit increases as the eutectic Si grain size decreases.

<< Problems to be Solved by the Invention >> Among the above-mentioned prior arts, the former aims to increase the cooling rate by high-pressure solidification (melt forging). However, it is difficult to increase the cooling rate up to the thick part. In the latter, the growth of Si crystal grains is controlled by an improvement treatment element (Na, Sr, Sb, Ca, etc.). The effect cannot be expected in the thick part. In both methods, it is difficult to achieve the refinement of the Si grains throughout the castings with different thicknesses.

The present invention has been made in view of the above-mentioned drawbacks of the conventional method, and has the object of reducing the Si grains throughout the entire Ai-Si alloy casting even when the thickness of the casting is complicatedly different, thereby increasing the fatigue strength of the casting. It is an object of the present invention to provide a manufacturing method which can be performed.

<< Means for Solving the Problems >> In order to achieve the above object, the method for producing an aluminum alloy braid according to the present invention improves the molten Al-Si alloy by a flux containing an improving element such as Na, Sr, Sb, and Ca. Process, and then
This improved Al-Si alloy melt is solidified under high pressure.

<< Operation >> According to the production method of the present invention having the above configuration, the effect of the improvement treatment by the improvement element is combined with the effect of the cooling rate increase by the high-pressure solidification (molten forging) of the molten metal, and the pressing force is relatively low (ie, (Since the cooling rate is slow), the remarkable effect of Si grain refinement appears, and the Si grain refinement proceeds sufficiently even in the thick part of the casting, and the crystal grains are refined over the entire grain, resulting in the fatigue strength of the casting. Is improved. In addition to the refinement of Si, the porosity of the casting is reduced by high-pressure solidification, and the mechanical properties are improved.

<< Examples >> A production test of an aluminum alloy casting was performed by the method of the present invention and a conventional method, and the results were compared.

As a test material, an AC8A material alloy having a chemical composition shown in Table 1 below was melted in a graphite crucible and cast by the method of the present invention and the conventional method.

FIG. 1 is a sectional view showing the shape and dimensions of a mold used in the present test. In the figure, 10 is a mold, 20 is a pressure punch, and 30 is a molten metal. The solidification temperature is measured from the bottom of the mold by 35
The measurement was performed at the positions 1, 2, and 3 shown in mm. 1 is mold 1
0 is a central portion, 3 is a portion near the side wall, and 2 is an intermediate portion of 1,3.

After dissolving the above test materials, the molten metal was treated with a Na-based flux, degassed with N ₂ gas for 30 minutes, calmed down for 30 minutes, and poured. In the Na improvement treatment, a float type additive was used, added immediately after sedation, kept for 30 minutes, and then poured. Na was added in an amount of 50 ppm. The melt temperature was 720 ± 15 ° C. and the mold temperature was 150 ± 5 ° C. Table 2 shows the casting conditions of each sample.

From the microstructure at the solidification temperature measurement position (see FIG. 1) of the sample cast under the above casting conditions, dendrite arm spacing (hereinafter referred to as DAS) was measured using an image analyzer. DAS has a correlation with cooling temperature, and FIG. 2 shows the relationship between the cooling rate of AC8A material and DAS.

FIG. 3 shows the relationship between the pressure applied during casting and the DAS. Figure (a) shows a sample without the Na improvement treatment (Sample No. 1 in Table 2).
4) and (b) are those obtained after the Na improvement treatment (5 to 15)
8). DAS with or without Na improvement treatment
It is constant at the applied pressure 500 kg / cm ^2, its value 10~22μ
m. In addition, the center (position 1) and the outside (3
The difference between the DAS values at the position () is smaller as the pressure is higher. This means that a difference in cooling rate due to a difference in location can be eliminated by increasing the pressure, which indicates that the structure can be made uniform in one casting.

The cooling rates in gravity casting (non-pressure casting) and squeeze casting (pressure casting) were calculated from the obtained DAS values.
Shown in

It is recognized that the cooling rate in molten casting is 50 times faster at the center and 3 to 4 times faster at the outside than gravity casting. Naturally, the cooling rate (DAS
Was not significantly different.

FIG. 4 shows the relationship between casting pressure and Si grain size. As in the case of FIG. 3, FIG. (A) shows the case where the Na treatment was not performed (samples Nos. 1 to 4), and FIG. In those subjected to Na improving treatment, already particle size 10μ in applied pressure 200 kg / cm ²
m, and the difference in particle size depending on the location decreases as the pressure increases.
200 kg / cm, although it tends to decrease with increasing pressure
² is still relatively large at about 20 μm at the center. In other words, if the molten metal is cast after improving Na,
This means that Si grains can be refined from a lower pressure (that is, a slower cooling rate) than in the case of casting without processing. In addition, with only Na improvement treatment (pressurization pressure 0), the refining effect is a part where the cooling rate is high (position 3).
Limited to Thus, as in the case of DAS, in order to obtain a fine Si diameter regardless of the location, it is found that it is extremely effective to perform the Na improvement treatment of the method of the present invention and perform molten casting.

FIG. 5 shows the relationship between DAS and Si particle size. As shown in the figure, when DAS is 25 μm or less, the degree of miniaturization of Si by the Na improvement treatment is remarkable, and when it is 25 μm or more and 10 μm or less, the difference from non-treatment becomes small. DAS10 ~ 25μm
This is the range achieved by high pressure solidification. Therefore, the [Na improvement treatment + gravity forging] and the [Na improvement treatment + gravity casting] which are the conventional methods by the [Na improvement treatment + molten forging] of the method of the present invention.
It is known that Si is finer than that of [No treatment and molten metal forging].

As described above, it is known that the refinement of Si grains greatly affects the fatigue strength of a casting, and according to the method of the present invention,
It is presumed that the fatigue strength is greatly improved as compared with the conventional method. Table 4 shows the results of a fatigue test performed on the casting test samples (with a pressure of 20 kg / cm ² and 0) according to the method of the present invention and the conventional method. However, heat treatment is 510
After the solution treatment at 1.5 ° C. × 1.5Hr, aging treatment at 200 ° C. × 6Hr was performed.

Thus, according to the method of the present invention, it was demonstrated that the fatigue strength of the casting was greatly improved as compared with the conventional method.

Although the above proof describes the case where improvement processing is performed with Na, as described above, similar improvement effects can be obtained by performing similar improvement processing with other improvement elements such as Sr, Sb, Ca, etc. It is also possible to use these improving elements in the inventive method.

<< Effects of the Invention >> As is clear from the above description, the method for producing an aluminum alloy casting of the present invention employs a high pressure molten Al-Si alloy melt treated with a flux containing an improvement element such as Na, Sr, Sb, and Ca. Because it solidifies and refines Si particles, Si particles are refined even at relatively slow cooling speeds by the combined effect of improved treatment and high-pressure solidification, and a refinement effect is obtained over the entire casting. And the fatigue strength can be uniformly improved throughout the casting. Further, in addition to the refinement of the crystal, the porosity of the casting is reduced by the high-pressure solidification, and the effect of improving the mechanical properties of the casting is also obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the shape and dimensions of a mold used for a production test of an aluminum alloy casting according to the method of the present invention and a conventional method,
FIG. 2 is a diagram showing the relationship between the cooling rate of the AC8A material and DAS, FIG. 3 is a diagram showing the relationship between the pressure applied during casting and DAS, and FIG.
The figure shows a diagram showing the relationship between casting pressure and Si grain size.
FIG. 3 is a diagram showing the relationship between and Si grain size.

Continuation of the front page (56) References JP-A-57-185941 (JP, A) Fujii et al. "On the wall thickness sensitivity of Al-8% Si alloy solidified under high pressure", Light Metals (1984) Vol. 34 No. 8 P 446-453 Kitaoka et al., "Al-Si Light Alloy", Light Metal (1988), Vol. 38 No. 7 P 426-448 SAE TECHNICAL PAPER SERIES 910434 (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 1/02 B22D 18/02 B22D 21/04

Claims (1)

(57) [Claims] The present invention is characterized in that an Al-Si alloy melt is improved by a flux containing an improvement element such as Na, Sr, Sb, Ca, etc., and then the improved Al-Si alloy melt is solidified under high pressure. Aluminum alloy casting manufacturing method.