KR19990009803A - Aluminum alloy containing impurities - Google Patents

Abstract

An alloy that improves the mechanical properties of castings by improving the shape of coarse acicular iron-based intermetallic compounds by adding an appropriate amount of Be to an Fe alloy containing Fe impurities, mainly producing high toughness and high strength automotive aluminum wheels. It is to.

In addition, the present invention includes a method of increasing the tensile strength and shortening the aging treatment time by adding Be to an aluminum alloy obtained by adding Na, Sr, or the like to improve the process Si or a precipitation hardening aluminum alloy containing Mg. .

Description

Aluminum alloy containing impurity iron

1 is a comparative example of the microstructure of the aluminum alloy of the present invention as it is cast and heat treated

Figure 2 shows the relationship between the Fe impurity content and the Be content added in the present invention divided by the microscopic structure.

3 is a correlation diagram showing the change in the maximum length of the β-phase according to the Fe impurity content and the presence or absence of Be in the present invention divided into Be and without Be

FIG. 4 shows the image analysis results of the cast as it is in FIG. 2 by the length (μm) of the β phase according to the Fe increase and Be increase.

5 is a correlation graph in which tensile strength and elongation change according to Be-Fe ratio change.

6 is a graph showing the effect of Be on the tensile strength of the sample heat-treated in the aluminum alloy.

7 is a graph in which the tensile strength and elongation change according to the Fe content in the alloy of the present invention.

8 is a graph showing the effect of Be on the shooting value in the heat-treated sample in the aluminum alloy.

9 shows the change in Mg content by cycle time when Be is added and when Be is not added.

10 is a result of analyzing Be content change for 5 hours immediately after Be addition.

11 is a result of a tensile test at the F − site of the test specimens with and without Be in the cast state.

12 and 13 show the tensile test results of the samples after the T6 heat treatment and the coating treatment of the present invention, respectively.

Figure 14 shows the results of Brinell hardness according to different heat treatment conditions at the F-site of the product of the present invention.

FIG. 15 shows the impact characteristics of the conventional products and the products according to the present invention to which Be is added in a heat treatment state, and compares them graphically.

Detailed description of the invention

The present invention relates to a method of improving the mechanical properties of an aluminum alloy casting by improving the shape of the coarse acicular iron-based intermetallic compound by adding an appropriate amount of Be to the aluminum alloy molten metal containing Fe impurities.

In general, in the case of aluminum alloys, the important mechanical properties are greatly changed by the microstructural factors such as the distribution, size and shape of the crystallized phases. The content of alloying elements and the cooling rate according to the casting process during solidification of castings.

However, when the castings are manufactured by one and the same casting process, since the cooling rate is maintained almost constant, the main factor that determines the mechanical properties may be the alloying elements and the content of these alloying elements.

In addition, the Fe-based intermetallic compound formed by Fe is not significantly affected by the addition of an improving treatment agent, and may cause more problems in mechanical properties because it does not become micronized or spherical like process Si even during heat treatment.

Therefore, it is essential to control the Fe content as a way to improve the mechanical properties of the aluminum alloy casting manufactured at a relatively slow cooling rate, such as low pressure casting. However, in the prior art, it is practically very difficult to suppress the increase in the Fe content which is present as an impurity or introduced upon remelting. The incorporation of Fe as an impurity component in these alloying elements is coarse when the Fe content increases at relatively slow cooling rates commonly found in the recycling and remelting of scrap and the use of steel tools in foundries during the preparation of alloys. To form intermetallic compounds, which have been found to have a weak bond with the matrix in the casting and are locally segregated, leading to degradation of mechanical properties such as tensile strength, elongation and impact strength. . In particular, for example, in the case of the A356 alloy, the allowable limit of the impurity Fe is much lower than that of other Al-Si alloys, so that the allowable limit of the impurity Fe should be less than 0.3 wt.%. Coarse Fe-based intermetallics are formed in a large amount in the A356 alloy. These coarse Fe-based intermetallics act as a cause of deterioration of all mechanical properties such as elongation, yield strength, toughness and fatigue properties. Because. In other words, it has been found that the small incorporation of impurity Fe provides the largest cause of the deterioration of the properties of the A356 alloy.

Since the solubility of Fe and other alloying elements in aluminum is very low, the liquid phase in the interdendritic region during solidification has a large amount of coal elements, and Fe is a complex intermetallic compound with Al, Si, Mn, Mg, etc. To form. These compounds are not re-dissolved in the matrix by the diffusion reaction, and as the Fe content increases, the volume fraction of the intermetallic compound increases significantly. Such Fe compounds are fragile and have a low binding force to the matrix. When the Fe-based intermetallic compound is present in the form of a very long needle-like Fe-based intermetallic compound (β-phase), it is known that the mechanical properties are further reduced. In particular, as the Fe content increases, It is also reported that castings are more vulnerable due to the increase in size than the increase in the number of Fe-based intermetallic compounds (β-phase). In addition, when the Fe content is 0.7 wt.% Or more, the Fe-based intermetallic compound (β-phase) such as Al ₅ FeSi tends to crystallize into a very large plate.

As the Fe content increases and the cooling rate is slow, the amount and length of the β phase tend to increase gradually. As such, there is a need to control Fe, which has a bad effect when it is introduced into the aluminum molten metal. First, a method of reducing the Fe content in the molten metal as much as possible and second, a β-phase having a high Fe content by using any element. -rich β phase) can be said to change the shape. In addition, as Fe content increases, the characteristics of elongation, impact value, etc., rather than tensile strength and yield strength are remarkably lowered. This is characterized by coarse needle-like intermetallic compounds, such as β-AlFeSi, which are defined. This is considered to be due to weakening due to local stress concentration. The quality of the casting can be improved by preventing or improving the production of such a Fe-based metal compound, and the harmful effects of Fe can be minimized by the following three methods. The methods to reduce the solution of Fe include ① rapid solidification method, ② melt superheating method, ③ addition methods such as Be, Mn, Cr, etc. Among these methods, ① and ② methods are found to be ineffective. In the method of ③, when Mn or Cr is added, it is combined with Fe to form a sludge. When it is formed in the liquid state, if the molten metal is maintained for a long time, the sludge density is larger than that of molten aluminum, and thus tends to settle at the bottom of the crucible. As other additive elements, elements such as Mo, Ni and the like have been used but are less successful.

Therefore, in the present invention, beryllium (Be) having excellent characteristics is selected. A small amount of Be is added to the molten aluminum, but in the present invention, 0.05 to 0.30 wt.% Of Be is added to the aluminum molten metal. The reason is that when it is 0.05 wt.% Or less, the desired effect cannot be obtained, and when 0.30 wt.% Or more is added, the effect becomes a limit value and gradually decreases.

In addition, in this range, the strength and toughness are increased by improvement through the shape change of the fragile and coarse plate- or needle-like Fe-based intermetallic compound; Removal of oxygen or nitrogen from the melt; Increased strength and toughness of the product due to improved cleanliness of the melt due to the formation of beryllium oxide (BeO) on the melt surface; Allow high Fe content (reuse of scrap) by reducing formation of fragile phases; An effect of improving the process Si with the improving treatment agent; It is possible to obtain the dispersion strengthening effect of Be itself.

In addition, when a small amount of Be (0.005 ~ 0.05%) is added to the molten aluminum it was found that the following characteristics can be obtained. Namely, formation of an oxide film; Increased recovery of the melt due to the formation of a coating; Anodization reduces the amount of dross; Formation of an oxide film maintains the cleanliness of the molten metal; Clean melt has better fluidity; Clean molten metal produces high quality castings with excellent surface and strength and tensile properties; In the case of an alloy containing Mg, prevention of oxidation of Mg: easy management of molten metal of Mg: prevention of coarsening of crystal grains, etc. Accordingly, the present invention is directed to aluminum alloy of Be in order to obtain an optimal aluminum alloy casting having the above-described characteristics and effects. The addition amount of is maintained so that the ratio (Fe; Fe impurity) to the Fe impurity content is about 0.2 to 0.4: 1. The reason is that coarse needle coexists at Be: Fe less than 0.2: 1, and the structure becomes brittle, and when Be: Fe is more than 0.4: 1, an appropriate amount of Be is applied to A1 alloy molten alloy such as A356 aluminum alloy containing Fe impurities. By adding, it is possible to draw high toughness and high strength aluminum wheels for automobiles, and by adding Be, to Al alloy which has improved Si by adding Na, Sr, etc., the effect of M improvement treatment agent is maintained, and Mg is contained. By adding Be to the precipitation hardening Al alloy, the amount of Mg ₂ Si produced was increased to increase the precipitation hardness and shorten the aging treatment time. This will be described in more detail by one embodiment as follows.

Example 1

After melting the A356 aluminum alloy ingot and changing the Fe content to 0.09, 0.12, 0.21, 0.33, 0.50, 0.68 wt. According to the Fe content change conditions, the Be was changed to each of five conditions to prepare a test piece.

The casting temperature was generally 750 to 800 ° C. during the manufacture of the test pieces, and the temperature of the mold was preheated to 300 ° C. in order to minimize the variation in mechanical properties according to the cooling rate of each test piece.

Each sample was classified as A-F according to the Fe content change, and the content of Be was changed and the component analysis after the test piece production was shown in [Table 1]. In the case of A test piece manufacturing conditions, 0.32 ~ 0.34wt.% Mg content was shown, and B-F test pieces showed Mg content of 4 ~ 4.5wt.%. However, in the case of specimens with the same Fe content, the Mg content tends to increase gradually, which is considered to be due to the fact that the Mg content was supplemented little by little to compensate for the decrease in the Mg content due to long-term maintenance of the molten metal during the test piece preparation. .

In the case of Be, according to the Fe content conditions, the test specimens were prepared from no addition condition to 0.5 wt.% Added condition. In addition, Ti-B added as a grain refining agent was charged at a target of 0.17 wt.%, And the result was measured at a level between about 0.15 to 0.20 wt.%.

In the present embodiment, the following four phases were observed when the microstructure was observed by varying the Fe and Be contents. According to the addition of Be, the shape of the Fe-based intermetallic compound is changed from a weak needle shape to a script shape, and when a large amount of Be is added, a beryllium-rich phase (Be-rich phase) is formed. . Considering these changes comprehensively based on various literatures, they are as follows.

Needle Morphology (Al ₅ FeSi):

Reaction is produced as an intermetallic compound that appears coarser and longer with increasing Fe content.

The temperature was generally 575 ℃ and because of the high fish temperature, it is not easily dissolved even by heat treatment. Intermetallic compounds of this shape appeared to act as factors that directly affect the stretching properties.

Thick thick (Al ₈ Si ₆ Mg ₃ Fe): This thick phase is optically pale gray in colour, round and blunt. The production temperature is generally 567 ° C. to 554 ° C., and since it is dissolved during heat treatment, it does not cause a big problem when the heat treatment is performed. However, since the formation of the intermetallic compound contains Mg in the composition of the compound, it is characterized by a decrease in Mg ₂ Si generation which contributes to the strength characteristics when it is not dissolved during heat treatment.

Letterpress shape (Al ₁₀ Si ₄ Mg ₄ Fe):

It is also reported that the number is reduced when Be is added as a compound produced when Mg is contained or when Be, Mn, and Co are added. It is reported that such a compound has a round shape and is formed inside aluminum dendrites, and thus does not significantly affect the stretching characteristics.

Be-Rich Phase

It is reported to be formed when a large amount of Be is added, and the composition and properties of the compound are not known precisely, but there is also a literature reporting BeFeSiAl ₅ . Since this beryllium phase (be-rich phase) is formed inside the dendrite (dendrite) is not considered to affect the stretching characteristics.

In addition, addition of a small amount of Be to the casting Al-Si alloy is known to affect the shape of the Fe-based intermetallic compound and the process Si, it was observed as shown in FIG.

Here, A is a microstructure in a cast state without process Si improvement and Be addition, and can observe coarse needle-like Fe-based intermetallic compound (Needle) and needle-like process Si not improved. However, B is a case in which 0.75 wt.% Of Be is added to A, and the Fe-based intermetallic compound which is changed into a fine process Si and a script shape can be observed. From this, the improvement of the process Si and the shape change of the Fe-based intermetallic compound may be referred to as the effect of Be addition, which is also a major effect of the well-known Be.

In the figure, C is the result of T6 heat treatment of the A test piece, and the process Si was spheroidized during the solution treatment, but the shape of the Fe-based intermetallic compound was not changed by the heat treatment. These Fe-based intermetallic compounds are expected to act as a major cause of elongation and toughness reduction in tensile and impact tests. In addition, in the case of D (appropriate amount of Be, heat treatment), it is possible to obtain the finest microstructure (improved process Si, change in the shape of Fe-based compound), thereby obtaining mechanical properties with greatly increased elongation and fracture toughness. It seems to be possible.

Next, the shape change of the Fe-based intermetallic compound according to the ratio of Be and Fe was examined. The results of the study on the microstructural changes are summarized in FIG. 3. The chart is only considered in terms of the shape change among the microstructural change factors of the Fe compound. As Be is added, the microstructure is characterized by script morphology, ie, type and beryllium subtypes in the shape of a long needle. (Be-rich phase) has been shown to change. In addition, when the Be: Fe ratio was 0.4 or more: 1, the shape of the short needle was partially present.

The shape change of the Fe-based intermetallic compound can be divided into five steps according to the Be: Fe ratio.

① Long needle (Be: Fe is 0.2 or less: 1)

It is characterized by coexistence with a short needle as a coarse needle (Al ₅ FeSi). In addition, it corresponds to a region in which a thick thick phase or a script type coexists in part by containing Mg. However, the thick or type intermetallic compound generated by containing Mg during heat treatment is dissolved and is a region where only coarse acicular intermetallic compound exists. These β phases become coarse in size with increasing Fe content, and have a decisive influence on the mechanical properties even after heat treatment.

② Single needle (0.4 or more: 1)

Coarse acicular Fe-based intermetallics are found in the area of 0.4 or more: 1, which is fragmented or hardly grown during coagulation. This phenomenon is more frequent especially when the Fe content is more than 0.5wt.%. In the case of single needle, it dissolves or exists more finely during heat treatment and has less influence on the mechanical properties than the long needle, but the influence on the mechanical properties may be somewhat different depending on the location of formation.

③ type (0.2∼0.4: 1)

It is reported that the addition of Be reduces the elements such as stress concentration rather than the long needle shape as the first shape change caused by the change of the shape of the Fe-based intermetallic compound. In this region, a needle bed which cannot be partially changed in the high Fe content region may be observed.

④ type and small Be-rich phase (0.4 ~ 1: 1)

It is a region where a type of print and a small beryllium sub-image coexist. It is an intermediate process from the shape of a trace to a small beryllium sub-image. In this area, the needles and the magnesium-containing phases partially segregated toward the high Fe content can be observed.

⑤ Large and small beryllium sub burns (1 or more: 1)

In the case where the Be: Fe ratio was 1 or more: 1, only a beryllium image was observed in all regions, and no other needle and magnesium-containing phases were observed. The beryllium sub-image does not change even in the heat treatment and is formed inside the dendrite, so it is considered that the beryllium sub-image does not significantly affect the elongation. It was also observed that as the amount of Be was increased, the growth was increased from the soberyllium sub-image to the large beryllium sub-image.

Change in maximum length of β-phase:

In order to determine the change in the maximum length of β-phase according to the increase of Fe content, the results of image analysis are shown in FIG. 3 compared with previously published data.

First, the maximum length change of β-phase showed a maximum length of less than 60 ㎛ below 0.3wt.% Fe, but the length of β-phase was increased exponentially under the Fe content of 0.3wt.% Or more. have.

Comparing the results published in 1984 with data published by Borren et al., Which were studied under the same alloy composition and cooling rate conditions, the change in length of the maximum β-phase plate is similar. have. In addition, the length of β-phase plate was measured around 10㎛ when Be: Fe ratio was added to about 1: 1, and about 20 ~ 30㎛ for D and E in the figure. This is a case where the addition amount of Be to Fe is small, and it is considered that the β-top plate of about 10 μm can be obtained by increasing the addition amount of Be to the level of Be: Fe to 1 or more: 1.

Quantitative change of β-phase:

In order to investigate the effect of the β-phase plate on the mechanical properties in detail, the image analysis results of the length and frequency of the β-phase plate are shown in FIG. 4 according to the Fe content and the Be content.

Observation results show that the amount and length of β-phase intermetallic compounds are increasing with increasing Fe content.

In the case of 0.09 wt.% Fe, the maximum acicular intermetallic compound has a length of about 30 μm and the average frequency is around 10. However, in the case of 0.68wt.% Fe content, the intermetallic compound of up to 190㎛ was partially observed, and the frequency of the intermetallic compound was found to be very large. It can be seen that the frequency of the intermetallic compound becomes very large as the Fe content increases. This indicates that the amount and size of the intermetallic compound gradually increases with increasing Fe content, and the mechanical properties are expected to decrease significantly. However, it can be seen that the amount of acicular Fe-based intermetallic compound decreases significantly as Be is added. This means that the shape change of the acicular Fe-based intermetallic compound by Be in the same Fe content range is considered to be able to prevent the decrease in elongation due to the acicular Fe-based intermetallic compound.

Example 2

In order to make β-addition as described above according to the present invention and to measure the change in mechanical properties accordingly, the following test was carried out.

First, in the tensile test, the tensile strength, yield strength, and elongation were measured at a crosshead speed of 2 mm / min using a 50-ton capacity INSTRON 1342 model.

Next, the hardness test was carried out in the same part (F-part) using a Brinell hardness tester, the test conditions were tested by holding a 500kg load, 10mm diameter ball for 30 seconds.

In addition, the test piece was divided into small size and precision processed, and the Charpy impact tester was used.

In order to investigate the tensile properties of the casting state, the tensile test results of the test specimens prepared under different Fe and Be content conditions are shown in FIG.

The change in tensile strength and elongation in FIG. 5 (A) shows that the addition of 0.7 at Be slightly improved the tensile strength and elongation compared to the condition (0) without adding Be. It was found to be improved. The elongation was greatly improved from Be addition conditions of 0.6 (B), 0.3 for (C), 0.13 for (D), 0.08 for (E), and 0.2 for (F). There was no big change. In addition, it can be seen that the width of the elongation increase due to the addition of Be is more remarkable as the Fe content is increased.

Considering the fact that not only the Fe-based intermetallic compound but also the shape (improvement) of the process Si significantly affects the elongation in the casting state, the cause of the elongation increase is due to the improvement of the process Si of Be. Treatment effect ② Melt cleaning effect ③ Fe-based intermetallic compound is considered to be due to improvement.

On the other hand, in order to see the change in the mechanical properties of low-pressure castings, the results of the tensile test in Fe (F-part) of the test specimen without Be and the added specimen in the casting state is shown in FIG.

The tensile properties of casted specimens showed that the maximum tensile strength was 185.9 MPa, yield strength 107 MPa, and elongation 9.52% for A3 specimen without Be, and maximum tensile strength 190 MPa, yield strength 111 MPa , Elongation was over 12%. This is due to the effects of Be addition, such as the shape change of Fe-based intermetallic compound by Be addition, the reduction of fragile intermetallic compound, improvement of process Si as well as long-term maintenance of improvement treatment effect and cleaning effect of molten metal. Judging. In addition, the excellent effects of Be also appeared during heat treatment and coating treatment, and the tensile test results after T6 heat treatment and coating treatment of the product are shown in FIGS. 12 and 13.

As a result of the tensile test, the tensile strength, yield strength, and elongation increased significantly when Be was added, compared with the case where Be was not added, and the fracture toughness of the product was considered to be very high. In particular, increasing the elongation and increasing the yield strength is believed to improve the fatigue characteristics of low pressure cast aluminum wheels, which are subjected to continuous cyclic loads.

Next, after the solution was subjected to the solution treatment for 6 hours at 540 ℃ using the cast specimen prepared to determine the tensile properties by heat treatment, and then subjected to the precision test and tensile test after the test specimen subjected to aging treatment at 140 ℃ for 6 hours Is shown in FIG.

Analysis of the tensile test results shows that in the case of Fe content of 0.09 wt.% (A) in FIG. 4, the elongation is increased from 16.5% to 19.5% by adding Be ratio 1.1 compared to the condition without adding Be. have. In the case of the test piece containing a small amount of Fe, the frequency of β-phase formation is small and the degree of elongation due to the formation of such intermetallic compounds is small. Therefore, the increase in elongation is caused by the addition of Be. It is thought to be due to not only the effect, ② melt cleaning effect. In addition, the maximum tensile strength tends to increase gradually despite having similar Mg content (0.32 wt.%). This is believed to be due to the increase of Mg ₂ Si formation kinetic energy due to the decrease of Mg-containing phase formation of Fe-based metal compound by adding Be.

In case of FIG. 4 (B), by adding Be about 0.6: 1, a high elongation rate of 17% or more was obtained, and the tensile strength gradually increased as the Be content was increased. Compared with the results of the component analysis, the change of Mg content seems to have a significant influence on the tensile strength and elongation. In spite of the increase of Mg content, there is no decrease in elongation because the quality of cast product is improved by the melt cleaning effect by Be.

In the case of Fig. 4 (C) and (D), it can be seen that both tensile strength and elongation are simultaneously improved by adding Be. In addition, in the (E) and (F) diagrams where the Fe content is increased by more than 0.50 wt.%, The elongation is greatly reduced by 5% due to the formation of coarse needles. . In particular, in the case of (E), the elongation was decreased even when Be was added, which is based on the image analysis result (Fig. 4E). It is believed to be due to the increase of.

In particular, it is noteworthy that (C) the use of scrap under the conditions of 0.21wt.% Fe content, even if the Fe content increases to 0.2wt.% Level, the Be: Fe 0.3: 1 or less Be is enough to extend the elongation It could improve from 12% to 17%.

Next, the change of mechanical and physical properties according to the amount of Be added was observed. In the case of the addition amount of Be for manufacturing aluminum 흴 for automobiles, the optimum ratio of Be: Fe was around 0.2: 1 considering the properties and economics of the casting. Accordingly, the change in tensile properties according to the increase of the Fe content in the T ₆ heat treatment state is shown in FIG.

A curve of FIG. 7 is a case where Be is not added, and a B curve is a case where Be: Fe ratio is 0.2-0.3: 1. In the figure, the maximum tensile strength was over 300MPa by adding Be, and the Mg content was changed to 0.4 ~ 0.45wt.% By adding Be. In addition, in the case of elongation, it can be seen that the Fe decreases rapidly as the content of Fe increases, and when Be is added, the elongation increases significantly. This is believed to be due to the shape change and the decrease of the amount of Fe-based intermetallic compound due to the addition of Be. The fact that the elongation does not decrease significantly even at high Mg content shows a large decrease of elongation easily generated in high Mg alloy by adding Be. It is believed that this is due to the reduced production of Mg0 that results.

As a result of investigating this through various experiments and mechanical property tests, it was found that Mg is desirable to be limited to a certain range in relation to Be because Mg brings about a decrease in its mechanical properties, particularly elongation and yield strength.

In other words, when Mg: Fe: Be was set at a constant ratio without changing the content of Fe impurity, Mg: Fe: Be was found to be limited to a ratio of 1.1 to 1.5: 1: 0.1 to 0.5. For example, when the ratio of Mg is less than 1.1, the hardness and yield strength are insufficient. When the Mg ratio is 1.5 or more, the elongation is less than the increase of hardness. In the case of Be0.1 with the Mg ratio as it is, the needle-like Fe-based metal compound is not inhibited and determined, and the overall mechanical properties deteriorate. On the contrary, when Be≥0.1, the mechanical properties are not improved. It was found to be uneconomical because the expensive beryllium was excessively consumed as the sub-phase was settled.

In order to reconsider the microstructure change of the low pressure castings by the addition of Be, the microstructures were observed according to the heat treatment state at each site (F = site, S-site, H-site).

14 shows Brinell hardness results for different heat treatment conditions in the product F-section.

There was little change in hardness of cast state due to the addition of Be. The hardness of B5 specimen was higher than that of A5 specimen during heat treatment. This means that Mg ₂ Si is increased by Be addition. However, in the case of E5 and E6, the hardness was decreased by performing the coating treatment after T6 heat treatment.

On the other hand, using a cast specimen prepared in different Fe and Be content conditions to determine the impact characteristics after performing a solution treatment for 6 hours at 540 ℃ 6 days aging treatment at 140 ℃ 6 hours by precision processing The results of the impact test are shown in FIG.

As a result, it was found that the impact strength value increased significantly by adding Be. In addition, the impact value at the F-part of the wheel casting of the participating company was 0.65kg f · m / ㎠ in T ₆ heat treatment state, and the impact strength value after coating treatment was 0.62kg f · m / ㎠. When comparing these results with current Be addition conditions, it was found that the impact value was greatly improved due to the decrease of the β-phase and the melt cleaning effect due to the Be addition.

In addition, in order to investigate the impact characteristics of low-pressure castings, the tensile test results at the Fe-site of the test specimens without Be and the test specimens in the casting state are shown in FIG. Impact properties are more widely used as an index of toughness of cast aluminum alloys than in tensile tests because they are very sensitive to the micropores often observed in microstructures in tensile tests. Therefore, the Charpy impact test is often chosen as an indicator of the mechanical properties of cast aluminum alloys.

The impact characteristics of the conventional product and the product to which Be is added are shown in FIG.

As a result of the impact test of wheel castings without addition of Be (0.2wt.% Fe), 0.42kgf · m / ㎠ was found in the F-section of casted wheel castings, and 0.51kgf · m / ㎠ in the case of T6 heat treatment. The impact strength value after coating treatment was 0.52kgf · m / ㎠. In comparison, the wheel cast without Be (0.15wt.% Fe or less) showed 0.50kgf · m / ㎠ at F-section and 0.65kgf · m / ㎠ at T6 heat treatment. The impact strength value was 0.62 kgf · m / cm 2.

Compared with the present results, the overall impact strength was greatly improved. Especially, when Be was added, the impact strength of 1kgf · m / ㎠ or more was obtained, which was proportional to the increase in tensile strength and elongation at the time of tensile test. It can be seen that.

Claims (3)

In an aluminum alloy containing Fe impurities, Beryllium (Be) of 0.05 to 0.30 wt.% Is added, except that the amount of beryllium is correlated with the amount of Fe impurities, in which case the amount of Be added to the aluminum alloy is in proportion to the content of Fe impurities. In Addition amount of Be: Fe alloy content of 0.2 ~ 0.4: 1 to improve the shape of coarse acicular iron-based intermetallic compound The aluminum alloy according to claim 1, wherein when the aluminum alloy is A356, the allowable limit of impurity Fe is less than 0.3 wt.% Compared to other Al-Si alloys. The method according to claim 1, wherein when the aluminum alloy contains Mg, Be is added by limiting the ratio range of Mg at a ratio of Mg: Fe: Be = 1.1 to 1.5: 1: 0.1 to 0.5. Aluminum alloy