JPH0745913B2 - Aluminum pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum pipe having excellent pitting corrosion resistance, and is particularly suitable for automobile radiators, heater cores, air conditioners and the like.

[Prior Art] An all-aluminum radiator or heater core has fins (3) between a number of flat tubes (4) as shown in FIG.
, And the pipes (1) and (1 ') are brazed to the tank (2) provided at the end of the tube (4), and a rubber hose is connected, though not shown in the figure. As shown in FIG. 3, the serpentine type evaporator has fins (3) attached between the extruded tubes (6) bent in a meandering shape, and the pipe (1) is brazed to the end of the extruded tube (6). Although not shown in the figure, an Al pipe is connected through the union (5). Further, in the air conditioner, as shown in FIG. 4, one end of a serpentine type evaporator (12) and one end of a condenser (10) are connected to a liquid tank (11) by using a pipe (1), a union (5) and a connector (13). And the other end of the evaporator (12) and the condenser (1
The flex hose (9) is attached to the pipe (1) attached to the other end of the pipe (1) using the union (5) and the connector (13) and is connected to the compressor (8). In the figure, (7) indicates an engine.

The above pipes include those that are used after being heat treated at the same time as brazing of the heat exchanger, and those that are used without being heat treated.Generally, JIS 1050, 1100, 3003, 6063 etc. Al or Al alloy drawn tubes Or JIS clad with JIS 7072 alloy
3003 alloy pipe (hereinafter abbreviated as Alclad pipe) is used,
Normally, the pipe wall thickness is 0.8 to 1.6 mm and the pipe outer diameter is 8 to 16 mm.

The air conditioner piping is generally attached to the engine room, and is attached under the floor in large vehicles such as trucks and buses.
Therefore, in order to satisfy the corrosion resistance life against the corrosion due to the rolling up of water and mud from the outside and the collision of earth and sand, and to withstand the internal pressure.
JIS 3003 alloy tubes and alclad tubes clad with JIS 7072 alloy to a thickness of 5 to 20% are used. When the pitting corrosion peculiar to aluminum reaches the core material, the alclad tube preferentially corrodes the JIS 7072 alloy layer which is the sacrificial layer as the sacrificial layer, and prevents the pitting corrosion of the JIS 3003 alloy which is the core material.

[Problems to be solved by the invention]

Alclad pipes have excellent pitting corrosion resistance against atmospheric corrosion, but when JIS 7072 alloy is used as a skin material and clad on the inner or inner surface to be used for radiator or heater core piping, it will not work as an inner surface or rubber hose. JIS 7072, which is a sacrificial layer, is rapidly formed by the cooling liquid in the outer surface contact area.
Not only the alloy is consumed, the pitting corrosion resistance life is shortened, but also the flat tubes of the radiator and the heater core are clogged, which deteriorates the heat exchange function.

This is especially a skin material when the Alclad tube is used without being heat treated at the same time as brazing JIS 7072
This is because the Zn concentration changes rapidly at the interface between the alloy and the JIS 3003 alloy that is the core material, and the sacrificial layer is consumed more heavily.

[Means for solving problems]

As a result of various investigations in view of this, the present invention develops not only JIS 7072 alloy but also a sacrificial layer containing Zn as an inner surface of the pipe, an outer surface, or an aluminum pipe with improved pitting corrosion resistance of the pipe clad on the inner and outer surfaces. It was done.

That is, the pipe of the present invention, a base Al alloy containing Zn as a skin material, the inner surface of the tubular body having a noble Al or Al alloy as a core material, a pipe in which a skin material is clad on the outer or inner surface, Zn, The maximum Zn concentration in the diffusion pattern is 0.2 to 1.5 wt%, the distance from the depth showing the maximum Zn concentration to the boundary part of the core material and the skin material is 20 μm or more, from the depth showing the maximum Zn concentration to the deepest Zn diffusion part. Is 30 μm or more, and the Zn diffusion depth is
It is characterized by being 40% or less.

[Work]

In the present invention, a base Al alloy containing Zn which is a skin material, and Al or an Al alloy which is a noble core material, it is necessary to combine an alloy having a potential difference of 30 mV or more, By setting the maximum Zn concentration of the skin material (sacrificial layer) to 0.2 to 1.5 wt%, the potential difference between the skin material and the core material can be set to 30 mV or more. However, if the maximum Zn concentration is less than 0.2 wt%, the sacrificial action does not work, and if it exceeds 1.5 wt%, the self-corrosion of the sacrificial layer becomes large, causing clogging of the flat tubes of the radiator and the heater core, which hinders liquid circulation. Come here.

Further, as shown in FIG. 1, by setting the distance (a) from the depth showing the maximum Zn concentration (Max Zn concentration) to the boundary portion to 20 μm or more, it becomes possible to suppress the consumption of the sacrificial layer.
However, if the distance is less than 20 μm, pitting of the core material occurs immediately following the consumption of the sacrificial layer. That is, by reducing the Zn concentration of the sacrificial layer near the boundary with the core material, it is possible to reliably prevent pitting corrosion in the core material by utilizing the potential difference between the core material and the sacrificial layer base alloy excluding Zn. .

Further, by setting the distance (b) from the depth showing the Max Zn concentration to the deepest Zn diffusion portion to 30 μm or more, the sacrificial action can be maintained for a long period of time. Furthermore, the Zn diffusion depth (c) from the surface is
By setting the content to 40% or less, it is possible to suppress the decrease in material strength due to the decrease in plate thickness due to corrosion and reduce the influence on the pressure resistance strength.

〔Example〕

The core alloys and skin alloys shown in Table 1 were cast respectively, the core material was a hollow billet with an outer diameter of 9inch and an inner diameter of 7inch, and the skin material was an extruded tube with an outer diameter of 7inch and a wall thickness of 2.5mm. It was subjected to an experiment.

First, insert the extruded tube for skin material inside the hollow billet for core material, hot extrude at 500 ° C, and then draw the pipe with the skin material clad on the inner surface (outer diameter 16 mm, wall thickness 1.0 mm, endothelial clad rate). 10%). In the manufacturing process of piping,
The heating hold time at 500 ° C before hot extrusion was changed to change the Zn diffusion pattern of the final cladding tube.

With respect to these pipes, city water containing 10 ppm Cu ²⁺ ions was used as a corrosive liquid, and a cycle circulation test was performed at room temperature for 16 hours and at 88 ° C for 8 hours to determine the corrosion depth of the inner clad layer in 3 months. It was measured. The results are shown in Table 2. The flow rate of the corrosive liquid was 10 / min. The Zn diffusion pattern of the clad leather was obtained by EPMA line analysis of the cross section.

As is clear from Table 2, in the pipes Nos. 1 to 11 of the present invention, the corrosion depth was 0.2 mm or less in the circulation test for 3 months, and only the general corrosion of the sacrificial layer was found. On the other hand, in comparative pipe No. 12 having a Max Zn concentration of 0.1 wt%, the sacrificial layer did not act and deep pitting corrosion occurred. Further, in the comparative pipe No. 15 having a Max Zn concentration of 2.9 wt%, pit-like corrosion occurred, and the pitting corrosion sometimes reached the core material. Further, the distance (a) from the depth showing the Max Zn concentration to the boundary is smaller than 20 μm, and the distance (b) from the depth showing the Max Zn concentration to the deepest Zn diffusion part is smaller than 30 μm. The sacrificial layer was completely removed, and pitting of the core material occurred. In comparison pipe No. 14 where the Zn diffusion depth (c) from the surface is greater than 40% of the plate thickness, the diffusion layer is deep and corrosion stops at the diffusion layer, but the pipe wall thickness decreases greatly, The decrease is remarkable.

〔The invention's effect〕

According to the present invention, the pitting corrosion resistance of the pipe provided with the sacrificial layer is improved, the corrosion weight loss can be reduced as much as possible, and the duration of the action of the sacrificial layer can be prolonged. The aluminum elution is reduced, the corrosion products do not cause clogging of the heat exchanger and the like, and the problem of deterioration of the characteristics thereof is eliminated.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a Zn diffusion pattern of the pipe of the present invention, FIG. 2 is a perspective view showing an example of a heater core pipe attachment, and FIG. 3 is a perspective view showing an example of an evaporator pipe attachment. FIG. 4 is a piping diagram showing an example of piping of an air conditioner. 1,1 '…… Piping 2 …… Tank 3 …… Fin 4 …… Flat tube 5 …… Union 6 …… Extrusion tube 7 …… Engine 8 …… Compressor 9 …… Flex hose 10 …… Condenser 11 …… Liquid Tank 12 …… Evaporator 13 …… Connector

Claims (1)

[Claims] Claim: What is claimed is: 1. A pipe containing a base Al alloy containing Zn as a skin material, and a noble Al or Al alloy as a core material and clad with a skin material on the inner surface, outer surface or inner / outer surface of the tubular body. The maximum Zn concentration in the pattern is 0.2 to 1.5 wt%, and the distance from the depth showing the maximum Zn concentration to the boundary between the core material and the skin material is 20μ.
An aluminum pipe characterized in that the distance from the depth showing the maximum Zn concentration to the deepest Zn diffusion portion is 30 μm or more, and the Zn diffusion depth is 40% or less of the wall thickness.