JP3320145B2 - Aluminum alloy material for upset butt welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy material used for upset butt welding, such as a rim of a two-piece wheel for an automobile, and more particularly to an improved weldability of an upset butt weld. It relates to an aluminum alloy material.

[0002]

2. Description of the Related Art Conventionally, in the process of manufacturing a rim of a two-piece wheel for an automobile using an aluminum alloy,
It was usual to use flash butt welding,
Recently, upset butt welding has often been adopted.

[0003] In the former flash butt welding method, a flash (electric spark) is generated by electric discharge by applying a large current at a predetermined interval between the welding surfaces of a material to be welded, and the heat of the flash causes the welding surface to be welded. Is heated, and a large pressing force is applied in a state where a thin molten layer is formed on the surface of the welding surface to bring the welding surface into pressure contact.

[0004] On the other hand, the latter upset butt welding method differs from the flash butt welding method in that it does not utilize the heat of the flash due to the above-described discharge.
That is, in the upset butt welding method, the material to be welded is clamped with electrodes, the end faces of the material to be welded are abutted, a pressure is first applied at a predetermined pressure, and a voltage is applied between both electrodes while the pressing force is applied. In this welding method, a predetermined current is passed, the mating surface is heated and softened by Joule heat caused by the contact resistance of the mating surface and the specific resistance of the material, and the softened portion is pushed to the side by the pressing force to join.

[0005] Such an upset butt welding method can save a material for a flash allowance (a part which is scattered or gasified by a flash and disappears) as compared with a flash butt welding method which has been conventionally used, and also has a short processing time. In addition, there is an advantage that the operation is safe because there is no flash, there is no contamination of the working environment, and the inspection of the equipment becomes easy.

[0006]

Generally, when manufacturing a welded part using an aluminum alloy, further processing is often performed after welding, and the application of upset butt welding does not leak to this example.

For example, in the case of manufacturing a rim of a two-piece wheel for an automobile by applying upset butt welding, ends of aluminum alloy plates rolled into a short cylindrical shape are butted, and after the butted portion is upset butt welded, The burrs extruded by the upset butt welding are removed, and the final product is finished through flaring, roll forming, and expanding to determine the size. Since various processes are performed after upset butt welding in this way, the joints are elongated or bent by the processing, so if the joints are not sound, cracks will occur during processing and the product yield will decrease. Cause. Therefore, as for the aluminum alloy material used in the upset butt welding, a material which has good bondability in the upset butt welding and has less cracks at the joint is desired.

By the way, the upset butt welding method has been mainly applied to a hot-rolled steel sheet in the past, and has been rarely applied to an aluminum alloy. For this reason, the bondability of aluminum alloys in upset butt welding has not been sufficiently studied in the past, and the relationship between the properties of the joining surfaces and the bondability in upset butt welding has not yet been clarified. is there. Therefore, conventionally, when attempting to produce a welded part by upset butt welding using an aluminum alloy, a situation where cracks occur at the joints and the product yield is reduced,
It was difficult to reliably and sufficiently prevent it.

The present invention has been made in view of the above circumstances, and provides an aluminum alloy material for upset butt welding, which has good joining properties in upset butt welding and is less likely to crack at the joint. The purpose is to do so.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive and experimental studies on the welded portion of an aluminum alloy by upset butt welding, and as a result, have found that the amount of oxide film on the surface to be a butt surface during upset butt welding is determined. It has been found that by appropriately controlling the strength, the joining properties of upset butt welding can be improved without impairing the strength and formability, and the present invention has been accomplished.

More specifically, the aluminum alloy material for upset butt welding according to the present invention is characterized in that an oxide film on a surface to be a butt surface when performing upset butt welding has a thickness of 200 angstroms or less. It is a feature.

[0012]

[Function] In upset butt welding, the factors that influence the joining properties are the joining temperature and the upset length (the length obtained by subtracting the final interelectrode distance after pressurization from the initial interelectrode distance before pressurization; (A value that serves as an indicator of whether the surface has been processed), and the surface condition of the butted surface at the time of joining.

By the way, an aluminum alloy has a hard and brittle non-conductive oxide film on its surface, and in particular, an aluminum alloy containing a large amount of Mg has a strong oxide film. In the upset butt welding of such an aluminum alloy, first, the temperature near the joining interface rises due to the resistance of the butt surface, and after a certain degree of upsetting, the oxide film on the joining surface is destroyed.
The atoms are bonded to each other at the bonding interface to complete the bonding.
Therefore, in upset butt welding of an aluminum alloy, it is essential that the oxide film is destroyed, and the thickness of the oxide film has a great effect on the bondability.

Of course, the joining temperature and the upset length cannot be ignored. If the joining temperature is increased by increasing the current or the upset length is increased, the oxide film can be easily broken, but the upset length must be increased. For example, there is a problem that the amount of extruded burrs increases, and if the joining temperature is increased by increasing the current value, problems such as an increase in energy cost occur. On the other hand, if the thickness of the oxide film on the butt surface is reduced, the oxide film can be easily broken at a lower joining temperature and with less energy, and the joining property can be improved. As a result of repeated experiments and studies by the present inventors, it has been found that good bonding properties can be obtained particularly when the average thickness of the oxide film is 200 Å or less.

Further, the present invention will be described in detail.

The type and composition of the aluminum alloy to which the present invention is applied are not particularly limited, and are usually of the 1000 series (pure Al series), the 2000 series (Al-Cu-Mg series), and 3000 series. Series (Al-Mn
No. 4000 system (Al-Si system), No. 5000 system (Al-Mg system), No. 6000 system (Al-Mg-Si system)
7000 series (Al-Zn-Mg series, Al-Zn
-Mg-Cu type), No.8000 type (Al-Fe type, etc.)
And the like. However, when applied to the rim material of a two-piece wheel for automobiles, it is desirable to use a 5000-series Al-Mg-based alloy in consideration of formability, fatigue strength, strength, and the like. Even in the case of a system-based alloy, Mg 2.0 to 5.0% (weight%,
The same shall apply hereinafter), Fe as an impurity is regulated to 0.3% or less, and Si as an impurity is regulated to 0.3% or less, respectively, and Mn is 0.01 to 1.3 as required.
%, Cr 0.01 to 0.20%, Zr 0.01 to 0.2
5%, V 0.01 to 0.30%, Cu 0.01 to 0.8
0% or more, more preferably 0.0001 to 0.01% Be, and if necessary, 0.25% or less of Ti alone or 0.05%. It is desirable to use an alloy that is contained in combination with the following B and the balance is made of Al and other unavoidable impurities.

The reasons for adding the component elements in such an Al-Mg based alloy are as follows.

Mg: Mg is an essential element of an Al-Mg alloy used as a rim material of a two-piece wheel for automobiles, and is added for improving strength, formability and weldability. If the amount of Mg is less than 2.0%, sufficient strength and fatigue strength cannot be obtained, and the formability also becomes low. On the other hand, if the Mg content exceeds 5.0%, the weldability decreases and the stress corrosion cracking resistance also deteriorates. Therefore, Mg is preferably in the range of 2.0% to 5.0%.

Fe and Si: Fe and Si are impurity elements inevitably contained in ordinary aluminum alloys. However, Fe and Si are restricted to 0.3% or less, respectively, because they reduce the formability and corrosion resistance. It is desirable. In particular, considering the bondability of upset butt welding, if the Fe content exceeds 0.25%, the bondability in upset butt welding decreases, so the Fe content is preferably regulated to 0.25% or less. The optimum amount of Fe is 0.15% or less. Also S
Even if the i content exceeds 0.20%, the bondability in upset butt welding decreases, so the Si content is preferably regulated to 0.20% or less, and the more optimal Si content is 0.15%.
%, More preferably less than 0.10%.

Mn, Cr, Zr, V, Cu: These elements have the effect of further improving the strength of the aluminum alloy and further improving the formability through the refining of recrystallized grains, so that one or two of these elements can be used. It is preferred to add more than one species. If each is less than 0.01%, the above-mentioned effects cannot be sufficiently obtained, while Mn is 1.3% and Cr is 0.20%.
If Zr exceeds 0.25% and V exceeds 0.30%, a coarse intermetallic compound is generated at the time of casting, and the formability, toughness, and rollability decrease. On the other hand, if Cu exceeds 0.80%, ear cracks at the time of rolling are increased, and the corrosion resistance is significantly reduced. Therefore, Mn is 0.01 to 1.3.
%, Cr is 0.01 to 0.20%, and Zr is 0.01 to 0.2%.
0.25%, V is 0.01 to 0.30%, Cu is 0.0
It is preferable to be within the range of 1 to 0.80%.

Be: Be has an effect of reducing the thickness of the oxide film on the aluminum surface, and is effective in improving the joining property at the time of upset butt welding. Therefore, 0.0001 to 0.01% of Be is added. In particular, when Mg is contained at 3.0% or more, Be is used.
Is effective. Such an effect is obtained when the Be amount is 0.0
001% or more, and more than 0.01%
Even if e is added, these effects are saturated, which leads to an increase in cost and is not preferable in terms of toxicity during casting. Therefore, the addition amount of Be is 0.0001 to 0.0.
It is preferable to be within the range of 1%.

Ti, B: Ti is effective for refining ingot crystal grains, and B is Ti
The addition also contributes to the refinement of ingot crystal grains. If Ti exceeds 0.25%, and if B exceeds 0.05%, a coarse intermetallic compound is formed during casting, and the formability and the rollability are reduced.
Preferably, the content of B is 25% or less, and the content of B is 0.05% or less.

In addition to the above, Zn may be contained as an unavoidable impurity in an aluminum alloy. However, if Zn exceeds 0.30%, the corrosion resistance is reduced. It is desirable to suppress it.

Next, as described above, the thickness of the oxide film was set to 200
A method for restricting to angstrom or less will be described.

Aluminum alloy materials used for molding, such as rim materials for ordinary automobile wheels, are often used as a soft material (O material) after final annealing in order to obtain good formability. In such a case, the oxide film thickness can be adjusted by appropriately regulating the final annealing conditions.

The specific final annealing conditions for controlling the oxide film to 200 Å or less include, in the case of batch annealing, an annealing temperature in the range of 250 ° C. to 400 ° C. and an annealing holding time of 0.5 to 400 ° C. It is preferable to be within the range of 5 hours. If the annealing temperature is lower than 250 ° C., the recrystallization is not completed. On the other hand, if the annealing is performed at a high temperature exceeding 400 ° C., the thickness of the oxide film exceeds 200 angstroms. In some cases, annealing is not performed for more than 5 hours. Further, the annealing atmosphere at the time of final annealing is an inert atmosphere or a non-oxidizing atmosphere having a dew point of 20 ° C. or less, an oxygen concentration of 2% or less in a furnace, or a vacuum atmosphere (1 × 1).
0 ^-3 Torr or less).

When continuous annealing is applied as the final annealing, the annealing temperature is preferably set to 400 ° C. or more and 550 ° C. or less, and the holding time is preferably set to 3 minutes or less, more preferably 1 minute or less. In this case, the annealing atmosphere has a dew point of 20%.
It is preferable to use an inert atmosphere, a non-oxidizing atmosphere, or a vacuum atmosphere (1 × 10 ⁻³ Torr or less) at a temperature of not more than ° C. In this case, as a heating method, when the plate thickness is large, the heating speed is higher in the method using electromagnetic heating than in the heating method using gas, the time required for temperature rise is shorter, and the thinner oxide film is required. Is preferred for

On the other hand, regardless of the regulation of the final annealing conditions, it is also possible to regulate the thickness of the oxide film to 200 angstrom or less by another method. One way is to
Oxidation of the surface by applying mechanical removal means such as grinding, cutting, shear cutting, saw cutting, or the like, or performing chemical etching or electrochemical etching (electrolytic etching) on the surface to be the butt surface after final annealing There is a method of removing the film to 200 Å or less. In particular, in the production of rim materials for automobile wheels, a step of cutting the coil from the plate with a gap shear is provided as a step before the upset butt welding after the coil is delivered, and the upset is performed immediately after cutting (before oxidation progresses). When butt welding is performed, the effect of the oxide film is almost eliminated, and good joining properties can be obtained.

Here, the chemical etching method for removing the oxide film may be any of alkali etching and acid etching. In the case of an Al-Mg alloy such as a rim material for an automobile wheel, Mg is used. Since there are many system-based oxides, etching with an acid is more effective. Preferred examples of conditions for alkali etching and acid etching are shown below.

Alkali etching: immersion in a 0.5-20% aqueous NaOH solution at a bath temperature of room temperature or higher for an appropriate time of several seconds to several minutes, washing with water, and then 10% or more of HNO ₃
Remove the smut with an aqueous solution and wash with water.

Acid etching: 0.5 to 40% sulfuric acid aqueous solution, or 0.5 to 66% nitric acid aqueous solution, or 1 to 3
Immersed in a 10-30% nitric acid aqueous solution containing
Wash with water. However, for alloys having a high Mg content, 80 to 90
It is preferable to immerse in a 10 to 20% aqueous sulfuric acid solution at a temperature of 2 ° C. for 2 to 3 minutes, and further immerse in a 40 to 50% aqueous sulfuric acid solution for 5 to 10 seconds.

In the above description, the rim material of an automobile wheel is taken as an example and a plate material (rolled material) is mainly described. However, the present invention is not limited to the plate material but can be applied to various shapes, bars, wires, and the like. Of course.

[0033]

【Example】

Example 1 Alloy No. 1 in Table 1 was used. Rolled plate coils (temper H18) having a composition of A1 to A3 and a plate thickness of 5.0 mm were produced. After cutting each rolled sheet coil to a width of 200 mm and a length of 1600 mm with a gap shear, the annealing condition Nos. The final annealing was performed under the conditions 1 to 4 to obtain a soft material (tempered O). The heating rate of the final annealing was about 50 ° C./hr.

For each of the alloy sheets thus treated, the welding conditions No. Upset butt welding was performed under the conditions shown in 1-3. The application of stress during welding may be divided into two stages: squeezing and upsetting in which the final joint is pushed outward as burrs. The same stress may be applied during squeezing and upsetting. However, in general, the stress at the time of upsetting is often higher than that at the time of squeezing. Therefore, in this embodiment, welding was performed under both conditions.

After the upset butt welding, burrs were removed from the joint, and a 180 ° bending test was conducted around the joint at a bending radius of 7.0 mm, and the occurrence of cracks in the weld joint after the test was visually examined. Was. The number of tests was 100 under each condition. Table 4 shows the crack occurrence rate of the welded joint (100 x joint crack length / weld length). The thickness of the oxide film was also examined, and the results are also shown in Table 4. The thickness of the oxide film was defined as a sputtering distance to a position where the oxygen count in the GDS was reduced by half using a glow discharge spectrometer (GDS).

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

As apparent from Table 4, in the present invention example in which the thickness of the oxide film is 200 angstroms or less, 200
It can be seen that the cracking rate of the joint is significantly lower in each of the comparative examples than in the case of the comparative example exceeding Å, and that the jointability in upset butt welding is excellent.

Example 2 The alloys of Table 5 B1 to B4 and the alloy Nos. A2
A rolled plate coil (temper H18) having a composition shown in A3 and having a plate thickness of 5.0 mm was produced. For each rolled sheet coil, width 2
After cutting to a thickness of 00 mm and a length of 1600 mm with a gap shear, final annealing was performed at 350 ° C. for 2 hours using a batch furnace to obtain a soft material (tempered O). The heating rate of the final annealing was about 50 ° C./hr, and the atmosphere in the furnace was such that the oxygen concentration in the furnace was 1% or less and the dew point was 2 ° C. Then, for each plate, the treatment method No. The oxide film thickness was adjusted by various methods as shown in 0 to 7.

After the above treatment, the welding conditions No. 1-4
After the upset butt welding was performed under the conditions shown in Table 1 and the burrs of the joint were removed, a 180 ° bending test was performed around the joint with a bending radius of 7.0 mm. Investigation was performed in the same manner as in Example 1 to determine the crack occurrence rate. Table 8 shows the results.

[0043]

[Table 5]

[0044]

[Table 6]

[0045]

[Table 7]

[0046]

[Table 8]

As is clear from Table 8, it can be seen that good bondability can be obtained by setting the thickness of the oxide film to 200 Å or less regardless of the method of the oxide film adjustment treatment.

[0048]

As is clear from the above-described embodiment, the aluminum alloy material for upset butt welding according to the present invention has an oxide film thickness of 200 mm on the surface to be a butt surface when performing upset butt welding. By restricting to angstrom or less, it is possible to improve the jointability of the joint by upset butt welding without impairing the strength and formability, so cracks occur at the joint even when forming processing is performed after upset butt welding There is very little risk of doing this. Therefore, the aluminum alloy material for upset butt welding of the present invention is most suitable for welding parts and welding structural materials represented by the rim of a two-piece wheel for automobiles, and is also applicable to various mechanical parts and ERW pipes. Can be.

Continued on the front page (72) Inventor Yasunobu Miyazaki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Masahiro Ohara 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation (56) References JP-A-3-257183 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 11/02 B23K 11/16 B23K 11/18 C22C 21/06

Claims (1)

(57) [Claims] 1. An upset butt welding excellent in upset butt joining, characterized in that an oxide film on a surface to be a butt surface when performing upset butt welding has a thickness of 200 Å or less. Aluminum alloy material.