KR101405813B1 - Aluminium alloy trailing arm and manufacturing method thereof - Google Patents

Abstract

More particularly, the present invention relates to a trailing arm using an aluminum alloy tube and a method of manufacturing the same.
The present invention relates to a method for manufacturing an aluminum alloy pipe, comprising the steps of: A preforming step of bending the alloy tube in a shape corresponding to the shape of the trailing arm; And a hydroforming step of placing the preliminarily molded article in a mold having a molding groove corresponding to the shape of a trail arm and then expanding and forming the interior of the preliminarily molded article by water pressure.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy tube,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a trailing arm that is a suspension unit of a vehicle, and more particularly, to a trailing arm using an aluminum alloy tube and a method of manufacturing the same.

In the automotive industry, the rear suspension system is being changed from rear-torsion beam axle type to sub-mid-range vehicles in order to lighten the vehicles, improve the fuel economy, and manufacture cars with price competitiveness. In conventional vehicles, the multi-link type suspension is used for various parts such as rear axle, trailing arm, low arm, upper arm, stabilizing bar, etc. The two parts using the torsion beam and trailing arm can be used for existing parts Instead of the performance of these. Therefore, the material to be used must be made stronger and thicker in order to withstand the roll stiffness, torsional moment generated from the rear of the vehicle, and shocks transmitted from the wheels. Although the torsion beam axle type has been made lighter than the existing system, there is still a lot of need for weight reduction due to the overweight of the component itself.

Until now, these parts have been manufactured by hydroforming a steel pipe material.

The present invention is to provide an aluminum alloy tube capable of manufacturing such components by hydroforming and a method of manufacturing the same.

Related Prior Art Korean Patent Publication No. 10-2005-0101899 (published on October 25, 2005) entitled 'Coupled Torsion Beam Axis for Vehicles'.

An object of the present invention is to enable the production of a trail arm using an aluminum alloy pipe.

Another object of the present invention is to reduce the number of parts and reduce the number of welded parts by manufacturing an aluminum alloy tube of a vehicle by a hydroforming method to manufacture a trailing arm.

The present invention relates to a method for manufacturing an aluminum alloy pipe, comprising the steps of: A preforming step of bending the alloy tube in a shape corresponding to the shape of the trailing arm; And a hydroforming step of placing the preliminarily molded article in a mold having a molding groove corresponding to the shape of a trail arm and then expanding and forming the interior of the preliminarily molded article by water pressure.

Wherein the aluminum alloy pipe material in the alloy tube preparing step comprises 0.09 to 0.45 wt% of Si, 0.11 to 0.24 wt% of Fe, 0.02 to 0.2 wt% of Cu, 0.02 to 0.76 wt% of Mn, 2.7 to 4.1 wt% (Al) and inevitable impurities, the steel comprising 0.11 to 0.25% by weight of Cr, 0.003 to 0.014% by weight of Zn, and 0.021 to 0.0031% by weight of Ti. do.

The aluminum alloy pipe material preferably has a tensile strength of 260 to 275 MPa and an elongation of 20 to 27%.

At this time, it is preferable that the hydroforming step is performed such that the expansion ratio of the maximum expanded portion is 26% or less.

In addition, after the hydroforming step, the hole forming step may be further performed to perforate the product. The hole machining step may use laser machining, or a hydro-piercing method.

The present invention also provides a ferritic steel comprising 0.09 to 0.45 wt% of Si, 0.11 to 0.24 wt% of Fe, 0.02 wt% or less of Cu, 0.02 to 0.76 wt% of Mn, 2.7 to 4.1 wt% of Mg, 0.11 to 0.25 wt% (Al) and unavoidable impurities, the balance being aluminum (Al) in an amount of 0.003 to 0.014 wt%, Zn: 0.003 to 0.014 wt%, and Ti: 0.021 to 0.0031 wt%.

The above-mentioned trailing rock is more preferably produced by hydroforming using an aluminum alloy pipe having a tensile strength of 260 to 275 MPa and an elongation of 20 to 27%.

The trailing arm according to the present invention uses an aluminum alloy material, which brings about an effect of reducing the weight of the parts compared with the conventional steel material.

The trailing arm according to the present invention is manufactured by a hydroforming method using an aluminum alloy tube, and there is no welded portion. Therefore, the durability and reliability of the parts can be ensured.

1 is a flow chart showing a process for producing an aluminum alloy tube according to the present invention,
2 is a photograph showing the structure of the aluminum alloy before the homogenization treatment,
3 is a photograph showing the structure of the aluminum alloy after the homogenization treatment,
4 is a view showing a structure of a torsion beam axle included in a trailing arm,
5 is a flow chart showing a process for producing a trailing rock according to the present invention.

Hereinafter, a trailing arm using an aluminum alloy tube according to an embodiment of the present invention and a manufacturing method thereof will be described.

The present invention relates to a steel sheet comprising 0.09 to 0.45 wt% of Si, 0.11 to 0.24 wt% of Fe, 0.02 wt% or less of Cu, 0.02 to 0.76 wt% of Mn, 2.7 to 4.1 wt% of Mg, 0.11 to 0.25 wt% (Al) and unavoidable impurities, which contains 0.003 to 0.014% by weight of Zn and 0.021 to 0.0031% by weight of Ti, and which is produced through an extrusion processing method and has a tensile strength of 260 - 275 MPa, yield strength 110 to 125 MPa and elongation 20 to 27%.

First, a method of manufacturing an aluminum alloy tube will be described.

Composition of aluminum alloy

The aluminum alloy tube used in the present invention is composed of 0.09 to 0.45 wt% of Si, 0.11 to 0.24 wt% of Fe, 0.02 wt% or less of Cu, 0.02 to 0.76 wt% of Mn, 2.7 to 4.1 wt% of Mg, : 0.11 to 0.25 wt%, Zn: 0.003 to 0.014 wt%, and Ti: 0.021 to 0.0031 wt%, and is composed of aluminum (Al) and unavoidable impurities.

Aluminum (Al)

Aluminum (Al, Al) is the most abundant element on earth after silicon. The specific gravity is 2.7, which is the lightest metal of practical metals except Mg (1.74) and Be (1.85). It is easy to cast, alloy well with other metals, and easy to process at room temperature and high temperature.

Aluminum (Al, Al) is the most abundant element on earth after silicon. The specific gravity is 2.7, which is the lightest metal of practical metals except Mg (1.74) and Be (1.85). It is easy to cast, alloy well with other metals, and easy to process at room temperature and high temperature.

Al has a specific gravity of 2.7, which is about 3/1 of that of 8.87 of Fe 7.87 Cu. Al also reacts with atmospheric oxygen to form a thin and dense oxide film on the surface, which is excellent in corrosion resistance and can be extruded, rolled, It is easy to perform plastic working such as molding.

Hereinafter, the composition of the additive elements and the characteristics of the respective elements will be examined.

Silicon (Si: 0.09 to 0.45% by weight)

Silicon can be added to improve the fluidity of molten aluminum and to improve the castability during solidification. In addition, in the case of aluminum-silicon alloy (Al-Si alloy), it is possible to show the mixed structure of primary α-aluminum phase and process silicon during casting, and it is possible to refine the structure of silicon- The mechanical strength can be remarkably improved.

Iron (Fe: 0.11 to 0.24% by weight)

Since iron is an unavoidable impurity, there is a risk of lowering the pitting resistance of aluminum even in the presence of a trace amount of aluminum.

Copper (Cu: 0.02 wt% or less)

The objective of the present invention is to improve the SCC characteristics by avoiding the rapid decrease of solid solution of Zn and Mg in the vicinity of grain boundaries by retarding the phase transformation rate at the initial stage of precipitation by adding Cu to the Al-Zn-Mg alloy.

When Cu is added to this alloy system, it reacts with Mg to form MgCu ₂ and Mg ₂ Cu, and forms a zone. The addition of only 0.5% Cu has a sufficient effect on the initial transformation process, so that the rate of zone formation is slower than that of the Al-Mg-Zn ternary system, the density of the zone is reduced to about 1/4, . Once η 'is generated, the initial zones disappear abruptly and the rapid decrease of Mg-Zn around the grain boundary is mitigated. On the other hand, Cu inhibits the formation of zones in the Al-Zn-Mg-Cu system, while it accelerates the precipitation of Al ₇ Cr in the Cr-added alloy, which also has the opposite effect of weakening the grain boundary.

In general, there is a restriction on the Cu content, which tends to lower the material strength according to the cooling rate and is effective in preventing stress corrosion.

Manganese (Mn: 0.02 to 0.76% by weight)

Mn accelerates the precipitation of the η 'phase in the GP zone and does not produce a reactant that would otherwise interfere with the formation of MgZn ₂ (η') even if it reacts with Mg or Zn.

By adding Mn, G.P. The zones have been increasing in number with their spheres maintained.

In fact, the addition of Mn at a certain level (0.2 to 0.9% Mn, depending on the alloy, limited to 0.02 to 0.76% by weight in the case of the present invention) to commercial alloys does not completely overcome this problem, This prevents formation of recrystallized coarse particles in solution treatment of extruded material.

Magnesium (Mg: 2.7 to 4.1% by weight)

Magnesium is an element necessary to impart sufficient strength to aluminum. If the content is less than 2.7% by weight, the required strength for the automobile parts can not be obtained. If the content exceeds 4.1%, the possibility of edge damage increases and the productivity is lowered.

Chromium (Cr: 0.11 to 0.25% by weight)

Although Cr has a small atomic radius, it reacts with Zn rather than Mg and binds about 30% of Zn in solid state to make CrZn ₁₇ . And on the other hand it reacts with Al to form Al ₇ Cr which can solidify Mn. Generally, the solubility of Cr is only 0.015% even at 300 ° C.

Therefore, Al ₇ Cr precipitates around the grain boundaries long before the zone is formed in the Al-Zn-Mg-based alloy, and the distribution of the generated zones is uniformly generated in the grain or grain. Therefore, Al ₇ Cr precipitated in the grain boundaries is not solubilized in the solution treatment, and thus shows an effect of retarding recrystallization and sub-grain formation and growth.

Zinc (Zn: 0.003 to 0.014% by weight)

When zinc is added to aluminum, about 80% by weight is employed at 382 캜, but the degree of solubility is drastically reduced as the temperature is lowered. In the case of the aluminum alloy according to the present invention, about 18% Zinc is in a state of employment.

The excess zinc which is not solubilized at this time can be used to form an Al-Zn-Cu compound by reacting with aluminum or copper as described above. Therefore, it is necessary to add zinc to aluminum within the above range in order to obtain both of the effects of solid solution strengthening and compound formation of zinc.

Titanium (Ti: 0.021 to 0.0031% by weight)

There is almost no role of Ti in the phase transformation or precipitation process with respect to the Al-Zn-Mg alloy. However, Ti added during melt casting becomes a solidification nucleus of the tissue particles in the form of AlB ₂ or TiB ₂ together with the element B, thus exhibiting an effect of particle refinement.

Hereinafter, a method of manufacturing an aluminum alloy tube having the above composition will be described.

Aluminum alloy tube manufacturing method

1 is a process flow chart showing a method for manufacturing an aluminum alloy tube according to the present invention.

As shown in the figure, the aluminum alloy tube manufacturing method according to the present invention comprises: 0.09 to 0.45 wt% of Si, 0.11 to 0.24 wt% of Fe, 0.02 wt% or less of Cu, 0.02 to 0.76 wt% of Mn, 2.7 (Al) and inevitable impurities, which contains 0.1 to 4 wt% of Cr, 0.11 to 0.25 wt% of Cr, 0.003 to 0.014 wt% of Zn, and 0.021 to 0.0031 wt% of Ti, (S-12) for homogenizing the billet, a homogenizing step (S-14) for homogenizing the billet, an extrusion processing step (S-16) for extruding the billet into a tubular shape using a mold, And an annealing heat treatment step (S-18) for subjecting the extruded aluminum alloy pipe material to an annealing heat treatment.

Further, it may further include a stretching step of calibrating the shape of the aluminum alloy tube before or after the annealing heat treatment step (S-18).

The present invention is characterized in that an aluminum alloy tube without welds is manufactured by using an extrusion processing method.

The extrusion, forging, and casting methods can be used for producing aluminum alloy parts. The extrusion method is superior in productivity compared to other methods, is inexpensive, and is excellent in toughness because it is a stretched material.

In case of the forging method, it is difficult to form into a hollow shape, and in case of casting, the cost is high and the toughness is low.

Hereinafter, each step will be discussed.

Billet preparation stage

A melt casting method may be used as a method for producing an aluminum alloy billet having the above composition.

It is preferable to prepare a billet in an air slip type at a high temperature by adding a parent alloy in accordance with the above alloy composition.

Homogenization step

The homogenization step is carried out by maintaining the temperature at 560 ° C ± 10 ° C for 9-11 hours, followed by air cooling.

The homogenization step is a treatment method in which the aluminum alloy billet produced through casting in the billet preparation step is maintained at a predetermined high temperature for a sufficient time to remove segregation by diffusion and obtain a homogeneous structure.

The homogenization step has the effect of removing micro-segregation, removing vertical supernatant, and eliminating internal residual stress.

Fig. 2 is a photograph showing the structure of the aluminum alloy before the homogenization treatment, and Fig. 3 is a photograph showing the structure of the aluminum alloy after the homogenization treatment.

2 and 3, it can be seen that a branch-like structure is observed before the homogenization treatment, but after the homogenization treatment, the dendritic structure disappears and the spheroidized uniform structure appears.

Extrusion processing step

The extrusion processing step is performed in a state where the billet is heated to 370 to 385 ° C, and the temperature of the mold is preferably maintained in the range of 405 to 425 ° C.

Heating the billet to the above-mentioned temperature range is for minimizing the friction between the billet and the mold during the extrusion, and for improving the extrudability. If the temperature of the billet is lower than the above range, an excessive extrusion pressure is required and the hardness of the final product may be insufficient.

When the temperature of the billet is higher than the above range, there is a problem that the surface of the billet ruptures and the structure of the aluminum alloy becomes large.

Heating of the billet can be performed using a gas heating furnace or a high-frequency heating furnace.

At this time, it is preferable that the extrusion processing step maintains the initial pressure for extruding the billet in the range of 23 to 25 MPa.

If the initial pressure of the billet extrusion is lower than the above range, the extrusion speed is too slow to reduce the productivity, and if it is excessively low, the extrusion is not performed.

On the other hand, when the initial pressure of the billet extrusion is higher than the above range, there is a possibility that a quality problem such as surface breakage or impingement may occur.

Annealing heat treatment step

The annealing heat treatment step is preferably performed at a temperature of 340 to 350 ° C. and then maintained for 2 to 3 hours, and the time required for the heating is preferably 1 to 2 hours.

The annealing heat treatment step is for imparting an appropriate strength to the extruded product and is carried out by keeping it at an appropriate temperature for a certain period of time.

The annealing heat treatment may be performed by a method in which a plurality of aluminum alloy tubes are spaced apart from each other by using an asbestos yarn and then charged into the heat treatment chamber all at once.

Wherein the time required for the temperature increase is 1 to 2 hours.

Stretching step

The stretching step is performed before or after the annealing heat treatment step, and is a step of pulling the aluminum alloy tube to remove the extrusion stress and to improve the strength.

In the stretching step, an aluminum alloy tube is fixed using a jaw, a certain amount of tension is applied, and the aluminum alloy tube is straightened.

Example

Aluminum alloy tubes having the compositions shown in Table 1 below were used to manufacture aluminum alloy tubes using the above-described manufacturing method, and the properties were evaluated.

Table 2 shows the results of physical property evaluation.

The results of Table 2 show that Examples 1 and 2 corresponding to the composition range of the present invention satisfied both the tensile strength of 260 to 275 MPa, the yield strength of 110 to 125 MPa, and the elongation of 20 to 27%

In Comparative Example 1, the tensile strength was inadequate and the elongation was insufficient. In Comparative Example 2, the tensile strength and the yield strength were too high and the elongation was insufficient.

4 is a view showing a structure of a torsion beam axle included in a trailing arm.

As shown in the figure, the torsion beam axle 400 includes a torsion beam 410 formed in the width direction of the vehicle and maintaining torsional rigidity, and a torsion beam 410 coupled to both ends of the torsion beam 410, one side connected to the wheel, A trailing arm mounting bush 430 and a spindle bracket 440 respectively coupled to both ends of the trailing arm 420 and a spindle bracket 440 and a spring seat 420 coupled to one side of the trailing arm 420, (450).

Among the components constituting the torsion beam axle, the spindle bracket 440 and the spring seat 450 are manufactured by press working in the form of plates, and the trailing arm 420 and the torsion beam 410, which are required to have rigidity and durability, ) Has a closed box form.

The present invention relates to a trailing arm (420) of these components and relates to a method for manufacturing the trailing arm (420) with the aluminum alloy tube described above.

Conventionally, the trailing arm 420 is manufactured by connecting two press-processed products by welding to form a closed box. That is, although one trailing arm 420 is manufactured by welding two parts to each other by welding, the present invention does not require welding by using an aluminum alloy tube. Welded parts are always problematic in durability parts because of their inability to manage their physical properties.

The trailing arm 420 according to the present invention eliminates the welds, thereby solving the quality problem and reducing the weight of the parts. Further, by using an aluminum alloy material, the effect of lightening is further increased.

5 is a process flow chart showing a method for manufacturing a trailing rock according to the present invention.

(S-52) for preparing an aluminum alloy pipe, a pre-forming step (S-54) for bending the alloy pipe in a shape corresponding to the shape of a trailing arm, And a hydroforming step (S-54) of placing the preliminarily molded article in a mold having a forming groove corresponding to the shape of a trail arm, and then expanding the preliminarily molded article by water pressure.

The step (S-52) of preparing the alloy tube made of an aluminum alloy is the same as the above-mentioned description, so that the duplicate description will be omitted.

As shown in FIG. 4, the trailing rock has a bent shape in its entirety, and has a shape in which cross sectional areas on the respective sides are different from each other.

Therefore, before the hydroforming process, a preliminary molding step (S-54) is performed in which the entire curved shape is given in advance.

The pre-forming step (S-54) is carried out by cutting the prepared aluminum alloy pipe material to a predetermined length and then bending it.

In the hydroforming step (S-54), the preliminarily molded product after the preliminary molding step (S-52) is placed in a mold having a forming groove corresponding to the shape of the trailing arm, and then water pressure is applied to the interior of the preliminary molded product will be.

The water pressure is gradually increased and then applied in a form that is maintained at the maximum water pressure for a certain time.

It is also preferable that the expansion ratio of the maximum expanded portion (the portion having the largest internal cross-sectional area) at which the greatest amount is enlarged is 26% or less among the portions expanded due to the hydroforming. If the maximum expansion rate exceeds 26%, the incidence of failure such as tube rupture increases.

Since the tube material expands due to water pressure and is brought into close contact with the mold, the preform is shaped into a trailing ring shape corresponding to the shape of the mold by hydroforming.

The trailing arm must have various holes for assembling with other parts. For this purpose, a hole machining step (S-58) for machining holes in the parts subjected to the hydroforming step is performed.

The hole processing step (S-58) can utilize laser piercing or a hydro piercing method.

Since the trailing arm manufactured by this method is made of an aluminum alloy, it can be made lighter than conventional steel parts. In addition, since the tube is formed by hydroforming, it is not necessary to weld, and the quality problem caused in the weld can be solved. Also, the number of parts can be reduced.

S-12: Steps to build billet
S-14: homogenization step
S-16: Extrusion processing step
S-18: Annealing heat treatment step
S-52: Steps to prepare alloy tube
S-54: preforming step
S-56: Hydroforming step
S-58: Hole machining step

Claims (8)

0.04 to 0.45 wt% of Si, 0.11 to 0.24 wt% of Fe, 0.02 wt% or less of Cu, 0.02 to 0.76 wt% of Mn, 2.7 to 4.1 wt% of Mg, 0.11 to 0.25 wt% of Cr, 0.003 To 0.014% by weight of Ti, 0.021 to 0.0031% by weight of Ti, and a balance of aluminum (Al) and inevitable impurities; Maintaining the mold at a temperature of from 370 to 385 DEG C for 40 to 425 DEG C in a state where the billet is heated to 370 to 385 DEG C for a period of 9 to 11 hours, followed by air cooling to homogenize the billet, An annealing heat treatment step of subjecting the extruded aluminum alloy pipe material to an annealing heat treatment by raising the temperature to 340 to 350 ° C and holding the aluminum alloy pipe material for 2 to 3 hours; Thereafter, the aluminum alloy tube was fixed with the jaw A step of preparing an alloy tube having a tensile strength of 260 to 275 MPa and an elongation of 20 to 27%;
A preforming step of bending the alloy tube in a shape corresponding to the shape of the trailing arm;
A hydroforming step of placing the preliminarily molded product in a mold having a forming groove corresponding to the shape of a trail arm and then expanding the inside of the preliminarily molded product by water pressure so that the maximum expansion rate of the expanded portion is 26% ; And
A hole processing step of perforating the product using a laser processing, or a hydro-piercing method. delete delete delete delete delete delete delete

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