JPH07118783A - Al alloy casting excellent in laser weldability, modifying method of al alloy casting joint made therefrom and of al alloy casting structural member made therefrom - Google Patents

Abstract

PURPOSE:To provide Al alloy casting excellent in laser weldability and to provide the modifying method to reform the mechanical property of joint of automobile frame using the Al alloy casting and Al alloy casting structural member made with the Al alloy casting. CONSTITUTION:This Al alloy casting contains, by weight, 3.5-12.0% Si, <=0.10% Fe, <=0.3cc/100g H, as necessary one or more kinds among 0.05-0.6% Mg, 0.1-0.6% Cu. While an inert gas or the mixed gas prepared by adding 1-7wt.% of hydrogen to the inert gas is blown on a structural member 1 consisting of the Al alloy casting, the casting is irradiated with laser beam to melt in a linear state and subsequently solidified so as to form melted/solidified region, thus the mechanical property of Al alloy casting structural member is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has excellent laser weldability,
And a technique for improving the strength, fatigue strength, ductility, etc. of the entire structural member by applying thermal processing (laser treatment) to only a part of the aluminum alloy casting and the aluminum alloy casting structural member with good strength and ductility of the joint portion Is.

[0002]

2. Description of the Related Art In recent years, in transportation equipment such as automobiles, railway vehicles, ships, etc., there has been a need for reduction of fuel consumption and higher speed, so that the structure itself has been made lighter in weight and the structural material used therefor. The weight is being actively reduced. In order to reduce the weight of this structural material, a lightweight aluminum alloy material has been used instead of a conventional steel material.

These aluminum alloy materials include rolled materials, extruded materials, castings, etc., depending on the manufacturing method. Of these, rolled materials and extruded materials have been used extensively in railway vehicles and ships. Among them, the rolled material is processed into a desired shape by pressing, bending and drawing, and the extruded material is processed into a product with a desired shape such as a hollow material by a die shape, and these processed materials are arc-welded. The structure is assembled by joining by main welding.

On the other hand, for aluminum alloy castings,
The base metal performance is generally inferior to that of the rolled material, and the welded part performance is also insufficient. Therefore, it is rarely applied to the welded structure except when it is used as a repair material. In addition, aluminum alloy castings have a concern that their reliability is uncertain because the mechanical performance of the products varies depending on their size, thickness and application site.

USP 4,618,163 discloses a technique for obtaining a chassis structure by connecting extrusion frames of light alloy with a joint of light alloy in order to reduce the weight of an automobile. As a material of this joint, it is described that die casting is used in addition to the forged material. However, this prior art does not describe at all what composition the light alloy die-cast product has, or which component has an alloy as a base material. Therefore, this prior art does not disclose a material that exceeds the properties of conventional light alloy die casting. As mentioned above,
Conventional aluminum alloy castings are inferior in welding performance and mechanical properties to rolled materials, extruded materials, and forged materials, and have variations in mechanical properties. It is difficult to use as a joint for chassis.

[0006]

However, the aluminum alloy casting has an advantage that it is easy to obtain an arbitrary three-dimensional shape, unlike the rolled plate material and the extruded material. Therefore, it is desired to develop a technique capable of improving the weldability and nonuniformity of mechanical performance of the aluminum alloy casting while making the most of this advantage.

That is, regarding the weldability of aluminum alloy castings, conventionally, the materials themselves have been improved such as the reduction of impurities in the casting material and the refinement of the structure, and the material of the wire to be supplied must be devised. By doing so, we are improving the arc welding method. However, even if these improvements or improvements are made, the weldability and mechanical performance are still insufficient in practical use. Therefore, when a conventional aluminum alloy casting is used for a welded joint, the ratio of the strength of the welded joint to the strength of the base metal (hereinafter referred to as joint efficiency) is 60 to 80.
%, The welded joint has the drawback of breaking at the weld metal.

[0008] Further, the arc welding method has a drawback that the sputter or the like is scattered during welding and the appearance of the joint product is deteriorated, so that the commercial value is lowered. For this reason, there is a drawback in that the cost becomes high when repairing the appearance, because it requires man-hours for post-welding treatment.

Further, since aluminum has a high thermal conductivity and the like, a large heat input is required for welding, and therefore,
There are serious drawbacks in that excessive bulges are formed and welding deformation is increased.

On the other hand, the laser welding method is widely used for welding steel materials and the like by utilizing its high energy density, and is put into practical use as a welding method of high speed, high efficiency and low strain. However, with respect to the application of the laser welding method to an aluminum material, laser light is likely to be reflected in the case of an aluminum material, and defects such as blowholes are likely to occur in the welded portion, so that it has not been applied to a large scale.

Regarding the mechanical performance of aluminum alloy castings, the castings differ in strength and elongation depending on their components and heat treatment, but generally, when the strength is increased, the elongation is reduced, and when the elongation is increased, the strength cannot be secured. There are difficulties. Therefore, conventionally, due to these balances,
It was common to determine the composition and heat treatment conditions, and neither could be enhanced.

[0012] For example, as a technique for improving the non-uniformity of mechanical performance, there is a method of increasing the plate thickness of a structural member in order to secure performance such as strength, but an increase in plate thickness leads to an increase in weight. There is also a defect that mechanical performance varies in the plate thickness direction.

The heat treatment can improve the elongation and strength of the aluminum alloy casting, but the heat treatment of the entire structure often causes deformation of the structure during the heat treatment, and the cost is low. It has the disadvantage of being disadvantageous.

Further, in recent years, in order to ensure safety, not only a part of the structure is strengthened, but conversely, a part of the structure is made to have a low strength, and this low strength part is deformed at the time of impact, thereby The structure is adopted to absorb the shock and ensure the safety of the crew. In this case, it is necessary to form a part having good ductility in a part of the structure. That is, when an impact is applied, the low-strength portion needs to have excellent ductility so that the low-strength portion does not collapse and the deformation absorbs the impact. is there.

However, in the aluminum alloy casting, it has been difficult to accurately and highly ductile the desired portion. Incidentally, there is a method of irradiating a necessary portion of a small part such as a cylinder head made of an aluminum alloy casting with a laser to re-melt it to improve durability.
No. 73, etc., but for that purpose, further improvement was required in terms of alloy composition and the like.

The present invention has been made in view of the above problems, and has excellent laser weldability, improved mechanical properties, improved homogeneity of mechanical properties, and particularly excellent ductility. It is intended to provide a cast aluminum alloy casting.

Another object of the present invention is to provide an aluminum alloy casting suitable for use as a joint for automobile frames, thereby providing an aluminum alloy casting joint having excellent ductility and sufficient deformation upon impact.

Still another object of the present invention is to provide a method for reforming an aluminum alloy casting which can improve the mechanical performance of a structural material made of the aluminum alloy casting.

[0019]

The aluminum alloy casting excellent in laser weldability according to the present invention is an aluminum alloy casting containing Si: 3.5 to 12.0% by weight and having a hydrogen content of 100 g of the alloy. It is characterized by being regulated to 0.3 cc or less, preferably 0.15 cc or less.

The Fe content in this aluminum alloy casting is preferably regulated to 0.10% by weight or less. Further, this aluminum alloy casting preferably contains at least one selected from the group consisting of Mg: 0.05 to 0.6% by weight and Cu: 0.1 to 0.6% by weight.

The aluminum alloy casting having such a composition is linearly irradiated with a laser while being blown with an inert gas, and is once melted and then solidified to form a linear melt-solidified region. Improve its ductility,
The mechanical properties can be improved.

Instead of the above inert gas, a mixed gas obtained by adding 1 to 7% by volume of hydrogen to the inert gas may be used.

Since the aluminum alloy casting thus obtained has excellent ductility and laser weldability, it can be used as a joint for connecting automobile frames.

[0024]

In the aluminum alloy casting of the present invention, the hydrogen content in the base alloy is 0.3 cc or less, preferably 0.15 cc or less per 100 g of the alloy (hereinafter, the hydrogen content in 100 g of the alloy is represented by cc / 100 g). Since it is regulated to be low, there are few sources of air holes such as blow holes that are likely to occur during welding.

Further, since the Si content is set to be appropriate, the flowability of the molten metal is appropriate, so that holes and the like generated during welding are quickly discharged to the outside of the welding site. Therefore, there are no vacancy defects in the weld metal. Further, since the iron content in the weld metal is low, the ductility of the weld is excellent and the elongation of the weld is large. In addition, by adding Mg and Cu to the weld metal, it is possible to increase the strength of the welded portion.

First, the reasons for limiting the component composition in the present invention will be described in detail.

Si (Si) Si is an element that greatly affects the fluidity of molten metal at the time of welding, and if its content exceeds 12.0% by weight, the molten metal is disturbed and a huge cavity is formed in the weld metal. Occurs.
On the other hand, if it is less than 3.5% by weight, the fluidity in the molten metal is poor, and it becomes difficult for the holes in the molten metal to be discharged outside the welded portion
As a result, blowholes remain in the weld metal. Therefore,
The amount of Si is 3.5 to 12.0% by weight.

Since H (hydrogen) H causes blowhole defects in the weld metal, it is preferable to suppress it as little as possible. Hydrogen amount is 0.3cc /
If it exceeds 100 g, the number of blowhole defects in the weld metal will increase, and the strength of the welded joint will decrease, and other problems will occur. Therefore, the amount of hydrogen is 0.3 cc or less in 100 g of the alloy, that is, 0.3 cc / 100 g or less. It is preferably 0.15 cc / 100 g or less.

As a method for measuring the amount of hydrogen, there is a vacuum heating constant volume pressure measuring method (standard analysis method for metal materials: edited by the Titanium Association of Japan: published by Maruzen Co., Ltd. on January 30, 1974).
According to this method, the sample whose hydrogen content is to be measured is heated in vacuum, the hydrogen gas in the sample is extracted together with other gases (nitrogen, oxygen, hydrocarbon gas, etc.), and these gases are placed in a fixed volume. Collect and measure the pressure. The collected gas is oxidized with heated copper oxide to make hydrogen in the collected gas water, and the water is absorbed by phosphorus pentoxide, and then the pressure is measured. The amount of hydrogen existing in the sample is measured by this pressure difference.

Instead of extracting hydrogen in the sample into a vacuum, it is also possible to extract into an inert gas. This time is faster. Further, the amount of hydrogen in the sample can also be measured by measuring the electrical conductivity of the sample.

Void defects such as blowholes in the Fe (iron) weld metal can be reduced by optimizing the amounts of H and Si described above. Fe deteriorates the strength and ductility of the welded joint. Therefore, Fe is regulated to a predetermined amount or less in order to secure the strength and ductility of the aluminum alloy casting. In particular, it is extremely effective to regulate the amount of Fe in order to secure ductility. That is, if the Fe content exceeds 0.10% by weight, the ductility of the welded joint cannot be maintained at the same level as that of the base metal, so the Fe content is 0.10%.
Control to less than or equal to weight%.

Further, the following components may be contained if necessary.

Mg (Magnesium) Since Mg has the effect of improving the strength of the weld metal, it is added if necessary. In order to obtain the effect of improving the strength, it is necessary to add 0.05% by weight or more of Mg. However, if the Mg content exceeds 0.6% by weight, the ductility decreases although the strength increases. Therefore, the amount of Mg is 0.0
5 to 0.6% by weight.

Cu (copper) Cu also has an action of improving the strength of the weld metal similarly to Mg, and for this purpose, addition of 0.1% by weight or more is necessary. However, if the amount of Cu exceeds 0.6% by weight, the weld metal is cracked and cannot be used. Therefore, the Cu content is 0.1 to 0.6% by weight.

Laser Weldability The welding conditions of laser welding applied to the welding of aluminum alloy castings are not particularly limited. For example, an additive material such as a wire may not be supplied at the time of laser welding, but an additive material such as a wire is preferably supplied when extra reinforcement is required.
As the additive material, not only the aluminum alloy having the component composition according to the present invention but also the aluminum material having another component composition may be used. The laser welding can be applied not only to the laser welding of the aluminum alloy castings, but also to the laser welding of the aluminum alloy castings and the aluminum plate material or the aluminum extruded material.

However, the laser irradiation applied to the improvement of the structural member using the aluminum alloy casting must be performed under the following conditions.

Since the aluminum alloy is a metal which is active at high temperature, it is preferable to spray an inert gas such as argon or helium as a shield gas to the target site during laser irradiation. As a result, the strength of the molten portion is improved, and the strength and thickness of the entire structure can be increased.

Instead of the inert gas, a mixed gas obtained by adding 1 to 7% by volume of hydrogen to the inert gas may be used as the shield gas. By mixing hydrogen, it is possible to form fine spherical pores uniformly in the molten metal. This method improves the strength of the molten part and increases the ductility (elongation).
Can also be improved. Even if the amount of hydrogen in the aluminum alloy casting is increased, spherical vacancies can be formed in the molten metal, but with this method, vacancies of huge and non-uniform shape are formed, and improvement of ductility is expected. Can not.

Performance Improvement of Aluminum Alloy Castings by Laser Irradiation Laser irradiation can improve the mechanical properties of the structural material made of aluminum alloy castings. This aluminum alloy casting is irradiated with a laser to locally locally melt it once and then solidify.

As shown in FIGS. 2 to 4, with respect to structural materials 1 to 3 of an aluminum alloy casting having an arbitrary cross-sectional shape such as a box shape and a pipe shape, a part of the structural material is linear in the longitudinal direction, for example. By irradiating the laser along the longitudinal direction (FIG. 2), along the longitudinal direction along the spiral (FIG. 3), or in the circumferential direction (FIG. 4),
This portion is melted in a linear shape (straight or curved shape) and then solidified to form a linear melt-solidified region 5. As a result, the strength, fatigue strength, ductility, etc. of the required parts can be improved, and the mechanical performance of the entire structural member can be improved.

Other laser irradiation conditions are not particularly limited.
For example, in selecting the laser itself, in order to melt the aluminum alloy, it is desirable that the carbon dioxide laser has an output of about 3 kW or more, and the YAG laser has an output of about 500 W or more. The processing conditions such as the laser output and the processing speed may be selected based on the type of laser used, the thickness and shape of the portion to be processed, and the like. An additive material such as a wire can be used if necessary.

[0042]

EXAMPLES Next, the effects of Examples of the present invention will be described in comparison with Comparative Examples.

Example 1 As shown in Table 1, the plate thickness is 2.5 mm with the composition changed.
Laser casting test (CO ₂ laser, output 3.0 kW, welding speed 300 cm)
/ Min) and the laser weldability was investigated. The results are shown in Table 1. The laser weldability was evaluated based on the hole condition of the welded portion according to JIS Z 3105.

As is clear from Table 1, the amount of hydrogen is 0.3
It can be seen that the generation of vacancy defects in the welded portion can be prevented by suppressing the amount to cc / 100 g or less and by optimizing the amount of Si to be in the range of 3.5 to 12.0 wt%. In addition, FIG. 1 is a diagram showing the relationship between the amount of hydrogen and the amount of Si and the vacancy generation state in the welded portion, with the amount of Si on the horizontal axis and the amount of hydrogen (cc / 100 g) on the vertical axis. The numbers in the figure indicate the grades in the radiation transmission test. As is clear from FIG. 1, the Si content is 3.5 to 12.0% by weight,
By setting the amount of hydrogen to 0.3 cc or less in 100 g of the alloy, good laser weldability can be obtained.

[0045]

[Table 1]

Example 2 As shown in Table 2, an aluminum alloy casting having a plate thickness of 2.5 mm in which the composition (Fe) was changed was manufactured, and a laser welding test (CO ₂ laser, output 4.0 kW, welding speed) was performed. Four
00 cm / min), the elongation of the welded joint was investigated. The results are shown in Table 2. Elongation from the weld to JIS
Two Z 2210 No. 5 test pieces were collected and evaluated by a tensile test.

It can be seen from Table 2 that the reduction of the elongation (ductility) of the welded joint can be prevented by suppressing the Fe content to 0.10% by weight or less.

[0048]

[Table 2]

Example 3 Laser butt welding of 3.0 mm thick aluminum alloy castings containing 7.0% by weight of Si and 0.1% by weight of Fe and having a hydrogen content of 0.2 cc / 100 g. It was carried out by a processing device, and the radiation transmission test of the welded joint and the joint strength and ductility were examined. The results are shown in Table 3. A carbon dioxide laser is used for laser welding, and output is 5.5k.
W and welding speed were 200 cm / min. 3 for each evaluation
A test piece of book was used.

As is clear from Table 3, in all cases, not only blowhole-like defects but also crack-like defects were not observed in the welded portion, which was good. In addition, the joint tensile test shows that all three test pieces fractured in the base metal and the joint had an elongation of 1
A high value of 0% or more was obtained.

[0051]

[Table 3]

Example 4 Si: 6.5% by weight, Fe: 0.08% by weight, hydrogen content: 0.2 cc / 100 g, Mg: 0.02-
Butt welding of aluminum alloy castings having a plate thickness of 2.5 mm containing 0.9% by weight was carried out by a laser processing apparatus, and joint strength and ductility of the welded joint were examined.

The results are shown in Table 4. A carbon dioxide laser was used for the laser welding, and the output was 5.0 kW and the welding speed was 250 cm / min.

As can be seen from Table 4, although the strength of the welded joint is improved by adding Mg, the elongation of the welded portion is decreased. 0.05% by weight to increase the strength of the weld
The above Mg addition is required, but the joint elongation is 10%
In order to achieve the above, it is necessary that the added amount of Mg be 0.6% by weight or less.

[0055]

[Table 4]

Example 5 Si: 6.5% by weight, Fe: 0.08% by weight,
Hydrogen content is 0.2 cc / 100 g, and Cu: 0.
Butt welding of aluminum alloy castings containing 02 to 0.8% by weight and having a plate thickness of 2.5 mm was carried out by a laser processing apparatus, and joint strength and ductility of the welded joint were examined. The results are summarized in Table 5. The laser welding conditions are the same as in Example 4.

From Table 5, it is understood that the strength of the welded joint is improved by adding Cu. To increase the strength of the welded joint, it is necessary to add 0.10% by weight or more of Cu,
If it exceeds 0.6% by weight, cracks occur in the weld metal.

[0058]

[Table 5]

Example 6 A rectangular pipe-shaped structure made of an aluminum alloy casting containing 6% by weight of Si and 0.05% by weight of Fe, having a hydrogen content of 0.05 cc / 100 g and a thickness of 2 mm,
CO ₂ laser at 4 locations in the longitudinal direction, output 5.0 kW,
Purity 99.999% under processing speed of 400 cm / min
A part of it was linearly melted by a laser while blowing the above argon gas (see FIG. 2), and the strength and resistance of the structure were compared with those of the untreated material.

As a result, as shown in Table 6, the strength of the material of the present invention is improved by 6% as compared with the untreated material without changing the plate thickness of the material. This means that the same strength can be obtained even if the plate thickness is reduced by about 6%, and the weight can be reduced by about 6%.

[0061]

[Table 6]

Example 7 Si: 7 wt% was included, and the amount of hydrogen was 0.05 cc / 100.
A pipe manufactured from an aluminum alloy casting having a thickness of 3 mm and a thickness of 3 mm was subjected to a spiral laser melting treatment (see FIG. 3), and its fatigue strength was evaluated in comparison with that of an untreated pipe. The laser melting processing conditions are the same as in Example 6. The results are shown in Table 7. As is clear from Table 7, the material of the present invention is
It was confirmed that the fatigue strength of the pipe was significantly improved as compared with the untreated material.

[0063]

[Table 7]

Example 8 Si: 6.5 wt% was contained, and the amount of hydrogen was 0.07 cc / 1.
A pipe-shaped structure manufactured from an aluminum alloy casting having a thickness of 00 g and a thickness of 2 mm was circumferentially subjected to laser melting treatment (see FIG. 4), and its strength was investigated. The laser melting process was performed under the conditions of a CO ₂ laser, an output of 5.0 kW, and a processing speed of 350 cm / min, using a mixed gas based on argon containing 0 to 15% by volume of hydrogen as a shield gas.

The results are shown in Table 8. As is clear from Table 8, it was confirmed that the ductility can be improved while the strength of the entire structure is kept high by using the mixed gas in which the argon gas is mixed with the hydrogen in the range of 1 to 7% by volume as the shield gas. Was done.

[0066]

[Table 8]

[0067]

According to the aluminum alloy casting of the present invention, defects such as holes are not generated during laser welding, and
A weld having high ductility and strength can be obtained. Thus, the aluminum alloy casting of the present invention is excellent in laser weldability, so not only laser welding of aluminum alloy castings, but by laser welding of aluminum alloy castings and aluminum plate materials or aluminum extruded shapes, high quality. Can be manufactured.

Further, since the joint has high strength and ductility, it is possible to reduce the plate thickness, which helps to reduce the weight, and it is also possible to repair defects that occur during casting by laser welding. It is also very useful for improving the yield of

In particular, when the aluminum alloy casting of the present invention is used as a joint for connecting automobile frames, since it is lightweight and has high ductility, it significantly contributes to improving the impact resistance of the automobile chassis.

Laser welding enables high-speed welding with less deformation and has good productivity. Further, unlike arc welding, addition of wires or the like is not always necessary, so that it is not necessary to delete the extra portion, which is economical.

Further, by performing a laser treatment on a part of the casting of the structure using the aluminum alloy casting by the method of the present invention, the mechanical properties such as strength, fatigue strength and ductility of the entire structure can be improved. it can. This allows
The material thickness can be minimized, and it can be processed after it is manufactured into a structure, which saves sample material and reduces the weight of transportation equipment such as automobiles, which greatly contributes to the reduction of fuel consumption. However, its production value is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of hydrogen and the amount of Si in an aluminum alloy casting obtained in an example of the present invention and the state of vacancy generation in a weld.

FIG. 2 is a diagram illustrating a procedure of linearly performing a laser melting process on a square pipe-shaped structure.

FIG. 3 is a diagram illustrating a procedure of spirally melting a pipe-shaped structure by laser melting.

FIG. 4 is a diagram illustrating a procedure for circumferentially performing laser melting processing on a pipe-shaped structure.

[Explanation of symbols]

 1-3: Structural material of cast aluminum alloy 5: Melt / solidification region

Claims (10)

[Claims] 1. An aluminum alloy casting containing Si: 3.5 to 12.0% by weight, wherein the amount of hydrogen is alloy 10.
An aluminum alloy casting excellent in laser weldability, which is regulated to 0.3 cc or less in 0 g. 2. The aluminum alloy casting according to claim 1, wherein the Fe content is regulated to 0.10% by weight or less. 3. Further, Mg: 0.05 to 0.6% by weight
And Cu: at least one selected from the group consisting of 0.1 to 0.6% by weight, the aluminum alloy casting according to claim 1 or 2. 4. The amount of hydrogen is 0.15 cc or less in 100 g of the alloy, according to any one of claims 1 to 3.
An aluminum alloy casting according to item. 5. Si: 3.5 to 12.0% by weight, Fe: 0.10% by weight or less, H: 0.3c
c / alloy 100 g or less, and the balance is aluminum and inevitable impurities, and an aluminum alloy casting having excellent laser weldability. 6. A joint for connecting an automobile frame, wherein the cast aluminum alloy according to any one of claims 1 to 5 is used. 7. The aluminum alloy casting joint according to claim 6, wherein the automobile frame is made of aluminum or an aluminum alloy. 8. The aluminum alloy casting joint according to claim 6, wherein the joint has a local portion that is once melted and solidified by irradiating a laser in an inert gas. 9. A structural member made of the aluminum alloy casting according to any one of claims 1 to 5 is linearly irradiated with a laser while being blown with an inert gas, is once melted, and is then solidified, A method for reforming an aluminum alloy cast structural material, which comprises forming a linear melt-solidified region. 10. The aluminum alloy casting structural material according to claim 9, wherein a mixed gas in which 1 to 7% by volume of hydrogen is added to the inert gas is used in place of the inert gas. Modification method.