KR810002072B1 - Aluminium alloys having improved mechanical properties and work-ability and method - Google Patents

Abstract

The Al alloy contains 8-15 wt.% Si, 1-4 wt.% Cu and 0.05-0.7 wt.% Mg. The diam. of the hypereutic Si is 50μm and av. width of eutectic is < 5μm. The cast alloy is cooled at > 10≰C/sec, worked at 350-430≰C and pptn. hardened. The tensile strength, elongation and adrasion of the Al alloy is 40 kg/mm2, 10% and < 8×10-9mm2/kg, resp.

Description

Manufacturing method of aluminum alloy for high toughness processing

12-1d is a representative schematic diagram showing silicon crystals in eutectic.

2 is a manufacturing process of ingot by the continuous casting process

3 shows typical cooling rates during continuous casting of aluminum-silicon alloys.

4 is a graph of the mechanical properties of the alloy according to the content of magnesium and copper

5a-5d show micrographs showing the structure of the ingot at various cooling rates.

6a-6b are micrographs of the alloy after aging.

7 is a graph showing the change in mechanical properties with cooling rate and plastic working

8 is a graph showing the relationship between the processing rate and the elongation

9 is a graph showing the relationship between the tensile strength and the temperature according to the compositional difference of the alloy

10 is a graph showing the relationship between silicon content and elongation.

Figure 11 is a graph showing the relationship between silicon content and non-wear amount

Figure 12 is a graph showing the relationship between the silicon content and the coefficient of thermal expansion.

13 is a graph showing the relationship between the heat treatment method and the tensile strength

14 is a graph showing the relationship between magnesium content and impact value

FIG. 15 is a graph showing the relationship between forging temperature and Vicker hardness.

Figure 16 is a graph showing the relationship between silicon content and elongation after forging.

The present invention relates to a method for producing an aluminum alloy suitable for building and structural materials having excellent mechanical properties including tensile strength, elongation and workability, in particular 8 to 15% by weight of silicon, 1 to 4.5% of copper and 0.05 to 0.7% Improved mechanical properties, processability and corrosion resistance by solidifying the melt of aluminum alloy containing magnesium, and maintaining a solid cooling rate of 10 ° C / sec to crystallize silicon having an average width of 5 μm or less in the eutectic of the aluminum substrate. It relates to a method for producing an aluminum-silicon alloy having a.

Various kinds of aluminum alloys have been known in the past, and in recent years, attempts have been made to use aluminum alloys in place of steel materials.

The use of aluminum alloys for this purpose requires a tensile strength of at least 40 kg / mm ^2, an elongation of 10%, a wear rate of 8 × 10 ⁻⁹ mm ² / kg or less, and good workability. These properties are sometimes referred to as `` essential mechanical properties '' since they are the minimum requirements when using aluminum alloys as structural materials.

However, conventional aluminum alloys do not satisfy these essential mechanical properties. For example, most of them have a tensile strength of 30 kg / mm ₂ or less and a market degree of several percent.

Among conventional aluminum alloys, corrosion-resistant aluminum alloys containing magnesium have good workability but have very low tensile strength. Aluminum alloys with high tensile strength, which contain copper and magnesium as aging hardening components, have high mechanical strength but poor workability and very low wear characteristics.

Accordingly, an object of the present invention is to provide an aluminum alloy having a tensile strength of at least 40 kg / mm ² elongation of 10% and a specific wear rate of 8 × 10 ^-9 mm ² / kg or less and having good workability.

The present invention provides excellent mechanical properties not found in conventional aluminum alloys when aluminum alloys of any chemical composition are cast under conditions in which silicon crystals in eutectic silicon crystals are fine and homogeneous in the aluminum matrix and then subjected to plastic working and age hardening. It has been found that having aluminum alloys can be produced.

The features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

The alloying components of the present invention are similar to known aluminum alloys used for casting or forging. However, the inventors have found that the desired composition of the new aluminum-silicon alloy should be chosen from a different perspective than in the conventional casting and forging composition (also casting conditions, heat treatment and plastic working methods, etc.).

Aluminum alloys of any composition have sufficient processing and heat treatment properties and the metallographic structure is important. In order for the ingot to have workability, the silicon crystal in the eutectic and the silicon crystal in the ingot must have a specific shape and size. As a result of the research of the present invention, the silicon crystal in the eutectic is long and flat or flaky crystallized in the ingot as shown in FIG. 1a, and the narrower the width of the flat and flaky silicon crystal in the eutectic, the better the processing effect. In particular, when the average width of silicon crystals in the eutectic is less than 5 µm, good workability is obtained. Here, the term “average width” is required to ensure that the ingot has sufficient workability. The maximum value of the silicon crystal width of the interface should be 5 μm or less not only in one part but also in the cross section.

Therefore, it is not usually possible to obtain sufficient workability only by trimming the surface of the ingot with a permanent mold.

By the plastic working, the silicon crystal in the eutectic body is divided in the longitudinal direction as shown in Fig. 1b, and then becomes a rounded crystal solid as shown in Fig. 1d due to the heat treatment. This is called a three-dimensional crystal and the ratio between the longest and the shortest is less than two. The aluminum-silicon alloy thus obtained has excellent mechanical properties, processability and large elongation (10% or more) in any case.

Supercrystalline silicon, on the other hand, has an effect on the plasticity of the ingot but has a greater effect on the mechanical properties of the aluminum-silicon alloy. Since the size or shape of the supercrystalline silicon plastic working or heat treatment hardly changes, certain conditions must be provided in the casting process. In crystal eutectic, supercrystalline silicon does not crystallize in the usual amount, while in the excess eutectic containing silicon at an amount exceeding the eutectic point, a large amount crystallizes. When primary silicon crystals have an area ratio of 6% or less of the substrate and a maximum particle size of 50μ or less, there is no adverse effect on the plastic workability of the ingot and the mechanical properties of the aluminum-silicon alloy.

The area ratio in the arrangement is determined by microscopic studies of alloy cross sections. Crystallization of silicon and crystallization of silicon in eutectic depends on the method of preparation and post-treatment of ingot. In conventional molds where silicon crystals in the eutectic crystallize in an aluminum-silicon alloy, silicon was added primarily to improve the flowability of the melt and the template contains crude supercrystalline silicon of eutectic silicon crystals and char- eutectic alloys.

The crude silicon crystal once crystallized cannot be made homogeneous even by plastic working or heat treatment. As a result, satisfactory mechanical properties and mass productivity of conventional castings could not be obtained due to coarse supercrystalline silicon and eutectic silicon crystals. Continuous casting methods, on the other hand, are generally used for the production of aluminum-silicon alloys, which are used as single alloys, and casting has been handled by switching the continuous casting methods used for the production of aluminum alloys containing silicon in impurities.

Therefore, supercrystalline silicon and silicon crystal in eutectic are also coarse.

Especially in the case of high-strength aluminum alloys containing strength-promoting components such as magnesium and magnesium, the homogeneous treatment method or similar heat treatment method may be used after casting to remove the agglomeration occurring when the molten metal solidifies. There is a need.

In the present invention, in the case of the aluminum-silicon alloy containing the above-mentioned components when the casting is processed by a method in which the maximum solid cooling rate is 10 ° C./sec or more after the solidification of the molten metal is completed, It has been found that supercrystalline silicon is finely dispersed in an array. Since the average width of the silicon crystal in the eutectic is 5 μm or less, the effect of eutectic silicon easily separated in the longitudinal direction by plastic working is obtained.

When the maximum grain size of supercrystalline silicon is 50μm or more, stress is concentrated in this area, which reduces the mechanical properties of aluminum.

However, when the ingot is formed under the above-mentioned solid cooling rate of more than 10 DEG C / sec, the supercrystalline silicon is not larger than 50 mu m and averages 5 mu m. The term `` solid cooling rate '' is used to mean: In other words, the silicon crystal and the supercrystalline silicon of the eutectic change depending on the cooling rate of the ingot. Determination of the cooling rate can be made by various methods.

According to the experiments of the present inventors, the cooling rate of the ingot having the lowest cooling rate is applied as the standard cooling rate so that the size of the silicon crystal falls within the required range. For example, in the case of continuous casting, in Figure 2 the solid cooling rate is the cooling rate after solidification. The parts with the lowest cooling rate on both sides of the continuous casting and the casting by water-cooled metal forming can be known by casting together by heat bonds located at predetermined positions.

Typical changes in temperature upon solidification are shown in FIG. The molten metal here is cooled to the maximum cooling rate m ° C./sec, solidification starts at point M, ends at point S, and the maximum cooling rate after completion of solidification is S ° C./sec.

Bubbles, particles, and impurities in the ingot make it difficult to process and heat-treat the ingot.

Therefore, when the ingot solidifies in any direction, no defects occur in the ingot and a uniform structure can be obtained. In this regard, ingots with very low internal defects and high uniformity are obtained by using the method according to the solution pool formed at the top such as continuous casting or casting by water-cooled metal casting. Heat treatments such as aging yield excellent aluminum-silicon alloys that were not expected in all properties.

The aluminum-silicon alloy of the present invention thus obtained has almost the same mechanical properties as 10% elongation and tensile strength of 40 kg / mm ² and duralumin of JIS 2017.

However, the aluminum-silicon alloy of the present invention does not have cracking property due to stress corrosion, which is the biggest drawback of duralumin, and is superior in corrosion resistance. Furthermore, the aging treatment of duralumin is required only about 5 hours in the aluminum alloy of the present invention as compared with requiring 15 hours at 170 ° C., thus having a great effect on saving thermal energy.

Such high strength and ease of aging are obtained depending on the grain size of the silicon crystal and the content of magnesium and copper.

The aluminum alloy of the present invention has high toughness, stress corrosion resistance, corrosion resistance, impact resistance, bending resistance, abrasion resistance and low thermal expansion coefficient, excellent machinability, good plastic workability, and easy precipitation due to high uniformity in the structure and magnesium and copper strengthening action. It combines curability and mass productivity simultaneously.

The composition range of the alloy of the present invention is as follows. The amount of silicon is 8-15% by weight, preferably 9-14% by weight, and even more preferably in the range of eutectic point sites (about 11 ± 1% by weight).

In alloys with an amount of silicon of 8% or less, the proportion of eutectic in the alloy is 68% or less, resulting in insufficient dispersion and reinforcement of silicon crystals in the eutectic, and a predetermined wear resistance and hardness are not obtained.

When it reaches 9%, the proportion of eutectic exceeds 75%, so that even if there is slight component variation, the predetermined property can be obtained stably. In the component system of aluminum-silicon, the eutectic point of silicon is 11.7% by weight, but when the third element is added or the cooling state changes, the eutectic point is actually transferred. In the super eutectic region containing silicon at or above the eutectic point, primary crystals of silicon first crystallize at the time of solidification, but when silicon weight is 14% or less, solidification is initiated and crystallized by supercooling by rapid cooling. It is possible to increase the tension by suppressing the size of the supercrystalline silicon. If the amount is more than 15% by weight, the amount and distribution of supercrystalline silicon increases, so that the machinability, strength, etc. are lowered, and the production of alloy ingot becomes difficult.

Magnesium forms precipitates such as Mg ₂ Si and shows remarkable effects on tensile strengthening by heat treatment.

The range of 0.05-0.7 weight% especially 0.2-0.4% is suitable also with respect to the copper content mentioned later.

At 0.05% by weight or less, the amount of formation of metal compounds such as Mg ₂ Si is small, other precipitation strengthening is insufficient, and the machinability is lowered again. As the added amount increases, the tensile strength and hardness increase, but the impact value starts to decrease from a certain value, and drops sharply especially when it exceeds 0.6% by weight. In addition, when the amount of magnesium is large, it is related to the contents of copper, iron and the like described later, but the flow of the solution at the time of casting becomes bad and scratches occur. In the case of mass production for the purpose of the present invention, scratching of the ingot is a major drawback in view of workability and the like.

Copper is useful for improving mechanical properties and abrasion resistance and has an effect of more than 0.5% by weight. In the case of containing 0.3% by weight of magnesium, the highest strength is shown at the point of 3% by weight. If the content exceeds 4.5% by weight, there is no cracking or the like in forming the ingot, and the stress corrosion splitting sensitivity is increased, and the strength and elongation also gradually decrease, so the maximum is 4.5% by weight.

In the alloy of the present invention, the above-described content ratio and processing ratio of Mg and Cu are particularly important, and as shown in FIG. 4, good mechanical properties are determined by the addition ratio of these two elements. 4 is a strength curve in the case where T6 is treated after 80% processing is applied to the ingot having the fine homogeneous structure described above.

In Fig. 4, I is a strength curve of 20 kg / mm ² , II is 30 kg / mm ² , III and VI are 40 kg / mm ² , IV is 45 kg / mm, and V is 48 kg / mm. The lower area of dotted line V1 in the figure is more than 10% elongation.

Alloys within the range enclosed by lines connected to points A, B, C, D, E and A satisfy both strength and other characteristics of at least 40 kg / mm ² . Points A (Cu 4.5%, Mg 0.05%), B (Cu 3%, Mg 0.05%), C (Cu 1%, Mg 0.3%), D (Cu 1%, Mg 0.6%), E (Cu 4 %, Mg 0.7%) and components within the range surrounded by the line connected to point A are obtained. The elongation is more than 10% and the toughness of 45kg / mm ² or more is a (Cu 3%, Mg 0.15%), b (Cu 2%, Mg 0.3%), c (Cu 2%, Mg 0.5%) Range surrounded by d (Cu 2.5%, Mg 0.6%), e (Cu 3.0%, Mg 0.65%), f (Cu 3.5%, Mg 0.6%), g (Cu 3.9%, Mg 0.3%) and point a Is obtained within.

Iron is an unavoidable impurity, which has the effect of strengthening the base, but when the amount is excessive, iron tends to form acicular crystals such as Al 4 FeSi, which impairs the strength of the alloy and is therefore limited to the range of 0.05-0.7% by weight.

In addition to the above-mentioned components, the alloy of the present invention can add other component elements as necessary. For example, small amounts of chromium, manganese, and nickel were found to increase the stress corrosion susceptibility and increase mechanical strength in high temperature areas. However, when the addition of these alloys deteriorates the tensile force of the alloy of the present invention, and this is particularly a problem, it is preferable to suppress it to about 0.15% by weight or less.

Addition of various inoculants such as strontium, natrium, and phosphorus can inhibit the growth of common silicon or silicon primary crystals, which is effective in the refinement of crystals and mechanical properties of cast materials. In particular, in the case of solidifying the alloy for slow cooling at a slow cooling rate, it is necessary to add an inoculum.

In the present invention, the solid cooling rate is defined as at least 10 ℃ / sec and according to the cooling rate the average width of the eutectic flake silicon crystal can be made less than 5μm and the maximum particle size of supercrystalline silicon can be made less than 50μm have.

Continuous casting processes are most suitable as casting processes for the practice of the present invention. In other words, according to the continuous casting process, the ingot is made into a liquid phase that is converted only in one direction upon solidification. Therefore, less gas is formed and less impurity cavities are formed, so there is less difference between the surface and the interior. Moreover, this process is suitable for mass production.

The plastic working of the ingot according to the present invention is carried out in order to obtain the required metal body, and may also be performed in two ways, cold and heat by a combination of processing and heat treatment.

By plastic working, the silicon crystal and α-aluminum crystal of the eutectic body are separated and refined. In this way, the silicon crystals of the eutectic are uniformly dispersed in the aluminum substrate.

A typical silicon crystal shape of the eutectic is shown in FIGS. 1A-1B. FIG. 1a shows the eutectic silicon crystal in the eutectic crystallized with a sufficiently narrow width and FIG. 1b shows the silicon of FIG. 1a separated by plastic working. When uniform heat treatment is performed without plastic working, the silicon crystals appear as agglomerates as in Fig. 1c.

This mass is not separated or refined by plastic working. Therefore, the aluminum alloy having such silicon crystals cannot be sufficiently improved. On the other hand, in the silicon crystal of the eutectic separated by plastic working, the coagulation accelerator component is solidified by suitable heat treatment to form particles as shown in FIG. 1d. If the eutectic silicon particles are separated as shown in Fig. 1b, most of the separated silicon crystals do not become agglomerated again by heat treatment such as forging.

Plastic working is processed by various means, such as melting, rolling, and extrusion.

The processing effect can be found by measuring the percent elongation of the alloy.

Elongation% begins to increase at 15% machining rate and reaches saturation of about 30%. Therefore, the processing rate of plastic working is required at least 30%. When the alloy is subjected to a suitable heat treatment at a temperature of at least 2000 ° C. after plastic working, the separated silicon crystals are rounded and coagulation is accelerated. The flexibility of the alloy improved by plastic working is hardened because it is hardly lost by heat treatment.

The promotion of the solidification of the alloy according to the invention can be accomplished by the treatment of T4, T5 and T6. T4, T5, and T6 treatments as aluminium ageing treatments are well known in the art. T4 treatment includes solid melting treatment and natural aging, T5 treatment includes thermal aging treatment, and T6 treatment includes solid dissolution treatment and aging heat treatment.

In addition to this aging treatment, there is a forging treatment method that includes maintaining the alloy at 350-430 ° C. for at least one hour and then gradually cooling the flexibility to improve the characteristics of the alloy according to the present invention.

The alloy can be hardened by subjecting T4, T5 and T6 after cold working but sufficient strength can be obtained by hardening by cold working. Thus, the aging treatment may be omitted.

As used herein, the processing rate means the reduction of the cutting plane in the case of extrusion, suction and the like and also the reduction of thickness or height upon rolling or melting.

The required product can be produced by the process described above, but the product can be completed by cutting, extrusion, pressing, welding, surface treatment and the like.

The following describes an embodiment.

Example 1

10.91 Si-2.4 Cu-0.48 Mg-0.02 Fe-Remaining solidification rate of 90 ° C / sec, 25 ° C / sec, 15 ° C / sec and 5 ° C / sec after melting by high frequency furnace Ingot of 30-200mm was prepared). Next, the ingot was preheated to 400 ° C, subjected to back extrusion under a condition of 60% working rate, and then tensile test pieces were taken. 5a-5d show microscopic tissue of the ingot. The cooling rate at the time of solidification greatly changes the shape of the silicon crystals in the tissue, and thus the silicon crystals are rapidly cooled and thus finely crystallized. In particular, there is a peculiar characteristic between 15 ° C / sec and 5 ° C / sec, and the cooling rate of 5 ° C / sec or less increases the width of the eutectic silicon crystal, resulting in high abundance of 5 μm or more, and crystallization of bulk supercrystalline silicon. do.

FIG. 6A is a microscopic organization diagram when the ingot cooled to 15 ° C / sec and 5 ° C / sec is subjected to T6 treatment after hot working. Finely crystallized eutectic silicon crystals are finely divided and uniformly dispersed by hot working, and are subsequently granulated by T6 treatment. However, when the width of the silicon crystal is crystallized to 5 탆, the particles are not divided but become large flat particles, and the dispersion state is also nonuniform.

On the other hand, although not shown, it has been confirmed that supercrystalline silicon does not divide by a raw material. 7 shows the tensile test results at room temperature. The greater the cooling rate during solidification, the greater the rate of increase in tensile strength elongation by machining. This causes stress concentration to be avoided by segmented microparticles of hard eutectic silicon crystals. The silicon crystals are also granulated by prolonged heat treatment instead of processing, but in this case, there is little increase in tensile strength and the increase in elongation is about 1/2 of that by plastic processing.

Two processes are essential for toughening eutectic alloys. That is, (1) the cooling rate at the time of solidification is increased to finely crystallize the eutectic silicon crystals, and (2) the eutectic silicon crystals are finely divided, granulated and uniformly dispersed by processing. On the other hand, the processing rate greatly affects the dispersion by the division of silicon. There is a tensile test performed by preheating a lump of 15 deg. C / sec to 400 deg. C and performing hot working with a cross-sectional reduction rate of 10, 20, 30, 60, 85%. In the case where the processing rate is around 40%, when the processing rate rises, the elongation rate increases rapidly, and above that, the rate increases. As a result, it is known that the processing rate is preferably 30% or more.

Example 2

Ingots having a diameter of 150 mm were produced by the continuous casting method under the condition that the cooling rate at the time of solidification was 15 ° C./sec or more after the aluminum alloy constituting the predetermined component was dissolved in a high frequency melting furnace.

The chemical composition (analytical value) of the ingot is shown in the first table.

TABLE 1

Next, the ingot was preheated to 450 ° C. and back extruded at a processing rate of 80% to prepare a cup-shaped cylindrical product. Various test pieces were taken from the cylindrical part and the affinity test was done. Now, the test piece was subjected to T4, T5 and T6 treatment. 9 shows the results of a tensile test after varying the temperature from room temperature to 300 ° C. and holding at that temperature for 1 hour.

The most eutectic alloy No. close to the eutectic component. 1 has a large number of dispersed particles and high strength. No. of silicon in particular 2 shows a tendency for high temperature strength to fall. FIG. 10 shows the relationship between the amount of silicone and elongation (as casting and after T6 treatment after 80% hot processing) at room temperature.

The elongation of the T6 treatment (the eutectic silicon is not segmented) in the casting state is higher than 10% for 6% silicon (No. 2) with a small amount of silicon, but decreases as the amount of eutectic increases. 5%. After 80% of hot working, the effect of breaking up silicon is remarkable above 8% silicon. FIG. 11 shows an example of the results of the overwhelming wear test. The test in the figure was carried out under the conditions of 18.9 kg final load, 600 m friction distance, wear rate 2 m / sec, and state object (rotating body) JISFc 30. Wear resistance improves as more silicon is added. If the silicon is less than 8%, the wear resistance is low.

Many aluminum materials are often used in combination with steel materials. In this case, the conventional aluminum alloy has a problem that the coefficient of thermal expansion is higher than that of steel. As the structural aluminum ash, a thermally expandable material is preferable. Figure 12 shows the amount of silicon and the coefficient of thermal expansion (room temperature 100 ℃).

The coefficient of thermal expansion decreases with the amount of silicon.

As an aluminum alloy with a low thermal expansion coefficient, 8% or more of silicon whose thermal expansion coefficient becomes ^21x10 <^-6> or less is preferable. Next, one of the effects of the present alloy is excellent in heat treatment.

13 is No. (1) The tensile test results of T4, T5 and T6 after preheating the alloy to 400 ° C and hot working at a processing rate of 80% (No. 3, No. 4 and No. 5, which have a large amount of silicon, are omitted as similar ones. ).

This alloy has improved heat treatment properties by precipitation on silicon, and strengths of 40 kg / mm ² or more are obtained even in T4 and T5 treatments.

In this alloy system, it has been said that the distribution of silicon crystals greatly influences the strength and elongation.

To quantify No. Four alloys were solidified at a cooling rate of 5-200 ° C./sec to prepare ingots having different sizes of supercrystalline silicon, and then preheated to a temperature of 400 ° C., followed by back extrusion at a reduction ratio of 80%. Tensile test pieces were taken from the extrusion, subjected to T6 treatment, and subjected to tensile test at room temperature. As the cooling rate during solidification increases, supercrystalline silicon becomes finer and elongation increases with it.

In particular, when silicon crystals are 5 μm or less, elongation is rapidly increasing. As for the cooling rate at the time of solidification, 15 degreeC / sec or more in which elongation rapidly rises is preferable. Next to No. Inoculants based on Na, P, Ca, and K were added to a solution of the same component as 4 to form ingots as described above at the cooling rates of 5 ° C./sec and 15 ° C./sec. The microscopic observation of the cross section of the ingot showed that the amount of supercrystalline silicon decreased compared to the case where no inoculant was added and the size of the ingot became 5 μm or less even at 5 ° C / sec. .

Example 3

After the alloy was dissolved in a component of Table 2 by a high frequency furnace, a continuous casting was performed at a casting temperature of 750 ° C. and a solid cooling rate of 15 ° C./sec to prepare an ingot having a diameter of 150 mm.

TABLE 2

No. 9 and No. In 10, the depth of the wrinkles is 2 mm or more, and the continuous castability is deteriorated. The ingot is thens at 400 ° C. and cold extrusion is carried out to a processing rate of 60-80%. Thereafter, the T6 treatment was performed.

The machinability test and the Charpy impact test were performed using this. Machinability is evaluated in terms of cutting tool level, cutting resistance, cutting surface accuracy, cutting type, and the like.

The third table shows the machinability at a cutting depth of 1 mm, a feed rate of 0.15 mm / rotation and a cutting speed of 120 m / min.

TABLE 3

The amount of magnesium has a great influence on the machinability, and more than 0.05% of magnesium is required.

Next, the charpy impact value is shown in FIG.

The impact value decreases as the amount of magnesium increases, and is constant at 0.72% or more of magnesium.

The stress corrosion splitting test was then conducted under constant stresses of 15 and 20 kg / mm ² in a solution of CrO ₃ : 36 g, K ₂ Cr ₂ O ₇ : 30 g saline: 3 g, pure water: 11, and Duralumin (JIS 2017) Cracking was also observed in all samples, but sample No. 7 did not occur at all. In this way, it became clear that it can use as an aluminum alloy.

Example 4

Alloys containing the components shown in Table 4 were melted and cast by the continuous casting process at a cooling rate of 75 ° C./sec to obtain an ingot of 100 mm Φ.

TABLE 4

After continuous casting, the ingot is maintained at 350-420 ° C. for 2 hours through plastic processing of about 50%, and then gradually cooled and completely hardened.

Specimens for tensile testing are taken from each alloy. The remaining alloys are subjected to cold compression at a processing rate of 30-50%. Tensile strength after cold working and surface roughness (working degree) by the neck side are shown in Table 5.

TABLE 5

In the last section of Table 5, the maximum surface roughness (workability) of the strength during extrusion of the JIS 2017 alloy is shown.

Compared with JIS 2017, it can be seen that the alloy according to the present invention is excellent in cold workability.

The ingot of alloy No. 12 was calcined at 50%, and maintained at 350-470 ° C. for 1 hour, and then gradually cooled.

So test the effect of forging temperature.

The result is shown in FIG. Hardness decreases at 350-420 ° C. forging temperatures, so this temperature range is optimal for forging. Next, the relationship between the silicon content, the size of the silicon crystal grains and the forging effect is shown in FIG.

Various aluminum alloys are provided containing up to 16% by weight of silicon, 0.3% by weight of magnesium and 0.7% by weight of copper. One of them is cast at 40-60 ° C./sec solid cooling within the casting conditions of the present invention and the other is cast at 2-5 ° C./sec solid cooling.

They are calcined by 70% by rolling and held in a forging furnace at 390 ± 5 ° C for one hour and then cooled slowly. Tensile test pieces are taken from this forged material and elongation is measured at room temperature. The forging effect is clearly shown by elongation. That is, in the case of an alloy containing large silicon crystals indicated by curve 2 of FIG.

On the other hand, when the eutectic silicon crystal and supercrystalline silicon are sufficiently fine, 5-15% by weight of silicon has a special forging effect and a remarkable improvement in elongation and flexibility. Elongation of at least 25% is good for use as a cold working material and alloys containing 8-11% by weight of silicon have such high flexibility. High flexibility is useful as a work material, and due to the high content of silicon, the work surface is also noticeably good.

Example 5

Mg 0.3%, Cu 3.4%, Si 11.7% The solution of the alloy containing the remaining Al was cast into a plate of 160 mmΦ by a continuous casting process at a solid cooling rate of 45 ℃ / sec and the ingot is thick by hot rolling at 350 ℃ It is machined into 22 mm plates, which are machined (machined) into pieces 200 mm long, 100 mm wide and 20 mm thick to obtain specimens. These pieces are longitudinally oriented and welded by joints, EBW (electromagnetic flux welding) and TIG welding and then subjected to T6 treatment. Specimens in this manner are subjected to tension testing at room temperature. Electromagnetic flux welding is performed under the following volume conditions.

In other words, I type inclination angle, input heat 3.6K Joul / cm, welding speed 0.5m / min, TIG welding rod having the same components as test specimen welded at V angle of 60 °, 200-250A and 18V AC current. Do using

The strength and flexibility of the weld are shown in Table 6.

TABLE 6

The welded surface is smooth and free from defects in processing and gaps.

In conventional aluminum alloys, there was a tendency for gaps to occur when the copper content is high, but the alloy of the present invention does not have any such problems and exhibits excellent weldability. Furthermore, the alloy of the present invention has excellent workability, making it easy to make a welding rod.

As described in detail above, the alloy of the present invention is obtained by combining selected components, suitable casting conditions, subsequent plastic working and suitable heat treatment, which at the same time have mechanical properties, wear resistance, corrosion resistance and excellent workability. Furthermore, the alloy of the present invention is excellent in adhesiveness by various organic adhesives and paints and can be anodized with chromic acid solution. Thus it is used for a wide range of applications.

Claims (1)

Mechanical properties, workability and stress corrosion resistance significantly improved by plastic working and heat treatment, essentially 8-15% by weight of silicon, 1-4.5% by weight of copper, 0.05-0.7% by weight of magnesium and the remainder It consists of condensing and cooling an alloy melt composed of aluminum in water-cooling molding and crystallizing plate or plate silicon having an average width of 5 μm or less in the eutectic of the aluminum matrix, and having a maximum particle size of 50 μm or less in the aluminum matrix. A method for producing a casting, wherein the solid cooling rate is maintained at 10 ° C./sec or higher after condensation of the melt in order to crystallize the silicon crystals, and an aluminum-silicon alloy having an area ratio of the primary silicon crystals crystallized in the aluminum matrix is 6% or less.

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