JPH0830259B2 - Method for generating Zn vapor for surface Zn concentration of Al member - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for generating Zn vapor for surface Zn concentration of an Al member, which is particularly applied to brazing of a heat exchanger for automobiles, and Al member at the same time as brazing. It is suitable for forming a Zn diffusion layer having excellent pitting corrosion resistance on the surface of.

[Conventional technology]

A special feature is to spray Zn vapor on the surface of the Al extruded material to form a Zn coating layer, which is then diffused to the surface of the Al extruded material by heating such as brazing to improve the corrosion resistance by the sacrificial effect of the surface layer. It is disclosed in Japanese Patent Publication No. 59-31588. In this case, Zn vapor is generated by inserting a gas introduction pipe into the molten Zn held at 550 ° C., supplying N ₂ gas and bubbling to disperse Zn vapor in N ₂ gas serving as a carrier,
Zn vapor is sprayed onto the surface of the Al extruded material through the heat-retaining passage to form a Zn coating layer on the surface of the Al extruded material. The thickness of the Zn coating layer is adjusted by the extrusion rate of the Al extrusion mold material and the gas supply amount.

[Problems to be solved by the invention]

Zn in the material is used to form an Al surface with pitting resistance.
When coating treatment and heat treatment for Zn diffusion are required, and considering improvement of pitting corrosion resistance of Al heat exchanger, Zn
Since the coating material is brazed and heated, the cost becomes high. Also, with Al extruded material, it is easy to spray Zn vapor inside the extruded material, but Zn vapor blows outside to the outside,
Furthermore, it is difficult to form a uniform Zn layer in a short time because oxidation proceeds in the atmosphere. Further, in an Al heat exchanger using a brazing sheet, it is difficult to spray Zn vapor at the time of manufacturing a brazing sheet material due to its wide plate width, which is not applicable. Still Zn steam generation method, a high pressure for bubbling N ₂ gas N ₂
A gas supply facility, a Zn melt holding furnace and piping are required.

[Means for solving problems]

As a result of various investigations in view of this, the present invention brazes using a non-corrosive fluoride-based flux (hereinafter abbreviated as NB brazing) in order to perform Zn vapor coating treatment and Zn diffusion treatment simultaneously with brazing. In addition, we have developed a Zn vapor generation method for surface Zn concentration of Al members that can efficiently generate Zn vapor.

That is, the present invention is a method of placing Zn in a heating furnace that passes N ₂ gas as a carrier gas, melting Zn by heating the Zn and furnace atmosphere temperature to 430 ° C. or higher, and generating Zn vapor from the molten Zn. If the internal volume of the heating furnace is Vl, the amount of Zn melt is 1
To 10 g / l, the surface area of 0.05~2.5cm ² / l of Zn melt, and flow rate 0.05V~Vl / min of N ₂ gas, -20 ° C. The dew point of the atmosphere in the heating furnace at about atmospheric pressure, oxygen The feature is that Zn vapor is generated from the molten Zn while maintaining the concentration at 1000 ppm or less.

[Action]

In the present invention, heating the temperature of Zn and the atmosphere in the furnace to 430 ° C. or higher is to evaporate Zn in the N ₂ atmosphere at atmospheric pressure, to heat Zn to 430 ° C. or higher and hold Zn in a molten state. This is because it is necessary. The evaporation amount of Zn increases as the temperature increases, but it is desirable to maintain the Zn and furnace atmosphere temperatures at 430 to 600 ° C. in order to perform Zn concentration treatment on the surface of the Al member simultaneously with NB brazing.

Next, assuming that the internal volume of the heating furnace used for steam generation is Vl, the amount of Zn molten metal is set to 1 to 10 g / l because the amount of Zn molten metal is 1 g / l.
If the amount is less than 10%, the inside of the furnace cannot be filled with Zn vapor, the contact between Zn vapor and aluminum material is insufficient, and proper Zn diffusion cannot be obtained.If it exceeds 10 g / l, Zn vapor is saturated and the Al member This is because when Zn vapor treatment is performed, an excessive diffusion pattern comes to be exhibited. Further to that the surface area of the Zn melt and 0.05~2.5cm ² / l can not be filled the furnace in Zn vapor is less than 0.05 cm ² / l, the consumption of Zn vapor exceeds 2.5 cm ² / l However, the efficiency becomes poor for continuous generation of Zn vapor.

Furthermore, the N ₂ gas flow rate of 0.05 V to Vl / min is 0.05 V / m
This is because if it is less than in, the evaporation of Zn will be insufficient, and if it exceeds 1 Vl / min, the consumption of Zn will increase. N ₂ when brazing NB
Flow rate is 30-60 m ³ / hr (500 in continuous furnace with internal volume of about 2000 l
There is no problem even if it flows up to about 1000 l / min). This not only allows Zn vapor to be generated in another furnace, but it is also possible to place Zn molten metal in the NB brazing furnace to generate Zn vapor.
The -20 ° C. The dew point of the atmosphere in the heating furnace at about atmospheric pressure or less, the oxygen concentration of 1000ppm or less, to prevent oxidation of the Zn melt surface, N ₂ gas in order to efficiently generate Zn vapor For this purpose, liquid N ₂ is vaporized and used. Considering that N ₂ gas is also used in NB brazing, the use of N ₂ gas is optimal. Even when Zn is placed in the NB brazing furnace, the atmosphere conditions necessary for NB brazing are as follows: dew point -30 ° C or lower, oxygen concentration 1000 pp
Since it is m or less, Zn can be evaporated without being oxidized.

By generating Zn vapor from the molten Zn while maintaining the above conditions, it is possible to perform efficient Zn diffusion treatment on the surface of the Al member. In order to remove the initial oxide film of the molten Zn, it is effective to wash the Zn base metal with an acid and then dissolve it in an atmosphere furnace. Further, mechanically removing the film on the surface of the molten Zn in the heating furnace is also effective in increasing the Zn vapor generation rate. When Zn vapor is generated in the NB brazing furnace, it is desirable to stir the Zn vapor for uniform Zn diffusion.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail.

Example 1 An Al plate having a thickness of 1 mm, a width of 50 mm, and a length of 100 mm was brazed in an NB brazing furnace, and at the same time, the surface of the Al plate was subjected to Zn concentration treatment. The NB brazing furnace has a muffle type with a preheating chamber and a heating chamber, height 400 mm, width 600 mm, length 2000 mm,
Using a furnace with a volume of 480 l, apply a non-corrosive fluoride fluoride flux to the Al plate at a concentration of 5%, hang all 10 of them together in a jig, put them in a drying furnace heated to 200 ° C, and evaporate the water content. Let This is put in the preheating chamber heated to 550 ° C of the NB brazing furnace and held for 5 minutes, then moved to the heating chamber heated to 600 ° C and held for 15 minutes to braze at 600 ° C for 3 minutes at the actual temperature. I did. After heating, it was quickly taken out into the atmosphere through the preheating chamber and allowed to cool.

In the NB brazing furnace, 240 l / min of N ₂ gas was introduced into the heating chamber and discharged outside the furnace through the preheating chamber, and the atmosphere inside the furnace was dewed to −
The oxygen concentration was kept at 100 ppm at 35 ° C. On the other hand, Zn is 200m high
Place in a Zn steam generation furnace with m, width 300 mm, length 500 mm, volume 30 l, N ₂ gas is flowed, the furnace atmosphere is dew point −40 to −30 ° C., oxygen concentration is 100 to 300 ppm and heated and melted to 500 ° C. , Zn vapor was generated. The Zn vapor generated in this way was introduced into the preheating chamber of the NB brazing furnace through a pipe kept at 550 ° C,
At the same time as NB brazing, the surface of the Al plate was subjected to Zn concentration treatment,
Zn diffusion behavior of Al surface (surface concentration, diffusion depth) when changing N ₂ flow rate, amount of Zn melt, and surface area of Zn melt in steam generator
Was examined by EPMA analysis. The results are shown in Table 1.

For EPMA analysis, 5 points were measured for each of 10 Al plates,
The average value of 50 points was calculated.

As is clear from Table 1, according to the method Nos. 1 to 11 of the present invention.
Those that generated Zn vapor show a Zn diffusion pattern with a surface Zn concentration of 2 to 10% and a diffusion depth of about 100 μ, and it is clear that pitting corrosion resistance equivalent to that of flux brazed products with excellent corrosion resistance can be obtained.

On the other hand, in the comparative method out of the conditions specified in the present invention, it is not possible to obtain a Zn diffusion pattern having excellent pitting corrosion resistance,
Alternatively, there is a problem that the Zn diffusion depth is deep and the consumption amount of Zn increases. For example, Comparative Methods No. 12, 14, 16, and 18 did not generate sufficient Zn vapor and did not show a Zn diffusion pattern with excellent pitting corrosion resistance. Further, in Comparative Methods No. 13, 15, and 17, there are problems that Zn vapor is often generated, the diffusion depth is deep, Zn consumption is large, and pitting depth is deep.

Example 2 NB brazing was performed in the same manner as in Example 1. At that time, Z in the preheating chamber (height 400 mm, width 600 mm, length 900 mm, volume 216 l)
Place n to melt and evaporate, and in the preheating chamber, preheat the Al plate and
The surface of the plate was subjected to a Zn concentration treatment, and Z was applied in the same manner as in Example 1.
We investigated the diffusion situation. As a result, as shown in Table 2, all of the method Nos. 19 to 22 of the present invention provided a good Zn diffusion pattern.

Example 3 NB brazing was performed in the same manner as in Example 1. At that time, in the heating chamber (height 400 mm, width 600 mm, length 1100 mm, volume 246 l)
Zn was left to melt and evaporate, and the surface of the Al plate was subjected to Zn concentration treatment at the same time as NB brazing of the Al plate in a heating chamber, and the Zn diffusion state was examined in the same manner as in Example 1. As a result, as shown in Table 3, in the method Nos. 23 to 24 of the present invention, good Zn diffusion patterns were obtained.

(Effect of the invention) As described above, according to the present invention, the generation of Zn vapor for the surface Zn concentration treatment of the Al member is facilitated, and in NB brazing using a fluoride-based non-corrosive flux, brazing At the same time, Zn diffusion treatment is possible, and industrially significant effects such as improvement of pitting corrosion resistance of the heat exchanger at low cost are achieved.

Claims (1)

[Claims] 1. A method in which Zn is placed in a heating furnace through which N ₂ gas is passed as a carrier gas, Zn and the atmosphere in the furnace are heated to 430 ° C. or higher to melt Zn and generate Zn vapor from the molten Zn. , If the inner volume of the heating furnace is Vl,
10 g / l, the surface area of Zn molten metal was 0.05 to 2.5 cm ² / l, the flow rate of N ₂ gas was 0.05 V to Vl / min, and the dew point was -20 ° C or less in the atmosphere of the heating furnace near atmospheric pressure and oxygen. The feature is that Zn vapor is generated from the molten Zn while maintaining the concentration below 1000 ppm.
Zn vapor generation method for surface Zn concentration of Al member