JPS5832222B2 - Fin material for cathodic protection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fin material for vacuum brazing that has excellent cathodic protection effects.

Generally, heat exchangers such as automobile radiators, condensers for heaters and coolers, and evaporators are made by vacuum brazing (brazing) by combining a tarling tube whose surface is clad with aluminum solder and an aluminum line for heat radiation. Manufactured by.

If a heat exchanger made in this way is used in a harsh corrosive environment, such as a salty coastal area or a place where road antifreeze is sprayed in the winter, corrosion will cause through holes in the tubes to form in a short period of time. This may occur.

Corrosion of the heat exchanger, even if it occurs on the fins on the air side, does not pose much of a problem in use, but if a through hole is formed in the tube through which the refrigerant passes, the heat exchanger becomes unusable.

For this reason, one possible method for preventing corrosion of the tube is to perform a surface treatment such as chemical conversion treatment or painting, but it is impossible to protect the tube for a long period of time with such measures.

In other words, it is said that surface treatment only has the effect of delaying the onset of corrosion by about one year.

As a second method, a method has been proposed in which the potential of the fins constituting the heat exchanger is appropriately lowered than that of the tubes to take advantage of the cathodic protection effect, and this method is quite effective. be.

In other words, the cathodic protection fin material is usually used with a thickness of 0.2M or less, and this is formed into a corrugated heat dissipation fin, which is alternately stacked with a cooling tube whose outer surface is clad with brazing filler metal. It is assembled as a heat exchanger by the phrasing method, and the electric potential of the fins is lowered than the electric potential of the brazing material cladding on the outer surface of the tube, so that it functions as a sacrificial anode and exhibits a cathodic corrosion protection effect.

For example, one example is a method in which fins are formed from an aluminum alloy containing Zn, which has been put to practical use as a caloric element in cathodic protection materials.

Aluminum alloy doped with Zn, e.g. Al-0
, 8 to 1.3 wt% Zn alloy (hereinafter wt% is simply written as 迤) (AA7072) is a 5φ NaC11 at 25°C.
In solution, the potential of the saturated calomel electrode is about -950 mV, whereas the potential of the tube clad with brazing material is about -950 mV.
It is 700mV.

Since the minimum potential difference normally required to exhibit cathodic protection is 50 mV, this fin made of Zn-added aluminum alloy serves as a sacrificial anode and sufficiently protects the tube from cathodic corrosion.

By the way, when vacuum brazing is performed using these Zn-added materials, the Zn in the surface layer is damaged due to the high vapor pressure of Zn.
is easily evaporated, and the Zn concentration in the surface layer becomes almost zero, and the cathodic protection effect described above is lost.

Furthermore, depending on the vacuum brazing conditions, more than 60% of Zn vaporizes, which poses a problem of contamination of the furnace.

In view of this, as a result of various studies, the present invention has shown that by adding Ca, the potential of aluminum is lowered, and by vacuum brazing, it has a cathodic protection effect without evaporating and contaminating the furnace.Furthermore, by making Ca and Zn coexist, We have developed a cathodic protection fin material that greatly suppresses Zn evaporation during vacuum brazing and exhibits excellent cathodic protection effects.
CaO, 02-3.0% or CaO, 02-3.0%
and Zn3.0% or less, and Mn1.5% or less, M
It is characterized by containing one or more types of sagging within the range of g1.3% or less, Si1.0% or less, Fe1.0% or less, Cu0.4% or less, and Zr0.2% or less, and the remainder is made of aluminum. shall be.

That is, when Ca is alloyed with aluminum, it lowers its potential like Zn and exhibits an effect as a sacrificial anode material, and does not evaporate during vacuum brazing and contaminate the furnace, and when Ca coexists with Zn, Ca is formed in the surface layer. Creates an oxide layer of Zn
It also has the effect of suppressing evaporation.

In other words, since Ca has a lower vapor pressure than Zn, the vacuum brazing conditions (600°C, 5 minutes, 5X10-5 Tor
r), there is almost no evaporation.

Furthermore, during vacuum phrasing, an oxidized layer of Ca is generated on the surface, which has the effect of greatly suppressing the evaporation of Zn.

Unlike Zn, Ca is an element that is difficult to form a solid solution in aluminum, so the cathodic protection effect is better when Zn coexists.

The reason for limiting the Ca content to the above range of 0.02 to 3.0 wt% is that below 0.02 wt%, the potential does not become low enough to exhibit the cathodic protection effect;
This is because when coexisting with Zn, evaporation of Zn is not sufficiently suppressed.

Furthermore, if the diameter exceeds 3φ, the effect will be saturated, and at the same time, cracks will occur during casting, workability will deteriorate, and other problems will occur in the manufacturing process.

Zn has the effect of lowering the potential of the aluminum alloy due to its additive, and is most suitable as a sacrificial anode material used for cathodic protection.

By coexisting with Ca, it exhibits a more stable cathodic protection effect than Ca alone, and the reason why its content was limited to the above range of 3.0 wt% or less is that 3.0 wt%
Even if the amount of Zn added exceeds
This is because it evaporates and contaminates the furnace.

Furthermore, when the amount of Zn added increases, the melting point of the aluminum alloy decreases, and the strength decreases during vacuum brazing, making buckling of the fins more likely.

Furthermore, the addition of Mn, Mg, Si, Fe, Cu, and Zr is to increase the strength of the aluminum alloy, and since vacuum brazing is heated to about 600'C, corrugated fins tend to buckle. A certain degree of strength is also required for the heat exchanger.

Therefore, it goes without saying that it is preferable to add appropriate amounts of these elements.

However, the content of these should be reduced to 1.5 wt% or less, Mn
g 1.3 wt% or less, Si 1.0 wt% or less, Fe
1. Owt% or less, Cu0.4wt% or less and Zr
The reason for limiting the amount to 0.2 wt% or less is that even if Mn and Fe are added above the upper limit, the strength increasing effect will be saturated and at the same time, the plastic workability will be extremely poor.

This is because if Si and Cu are added in amounts exceeding the upper limit, the melting point of the aluminum alloy will be lowered, making buckling of the fins more likely to occur during vacuum brazing.

Further, if Zr is added in an amount exceeding the upper limit, the effect will be saturated and at the same time, the cost will increase as it is an expensive element.

Next, examples of the present invention will be described, and comparative examples will also be described in order to confirm the effects of the present invention.

Example 1 An aluminum alloy having the composition shown in Table 1 was cast in a mold, homogenized at 550°C for 3 hours, and then both surfaces were faceted to form a mold with a thickness of 401J, a width of 180mm, and a length of 200M. It was made into an ingot.

Next, after heating to 500℃, immediately roll the
It was rolled to the desired thickness and further rolled to 0.21W with a cold roll.

After annealing this at 400℃ for 2 hours, it was cold-rolled to 0.16
The material was rolled to a black color, and then slitted into a strip with a width of 3211 gIl.

The thus obtained cathodic protection fin materials of the present invention (Arashi 1 to &5) and comparative fin materials (A6 to A7) were placed at a height of 207 mm.
1gl11 Pitch 4 #(1)] /I/ Force the gate fin, plate thickness 0.47#! praising sheet (core material: AA3003, brazing material Al-10Si-1
, 5Mg clad on both sides by 10%) and the first
As shown in the figure, praising sheets 1 and corrugated fins 2 were stacked in several stages and fixed using a jig.

This simulated core was
Brazing was performed by vigorously heating at 0°C for 3 minutes.

At this time, in order to examine the buckling state of the fins and at the same time confirm the cathodic protection effect of the fins, we conducted a 5% salt/water spray test (JIS Z 2371) for about 6 months. The depth of pitting corrosion that occurred in the plating sheet was investigated.

For reference, the potential of the fins after vacuum brazing was measured in a 5% NaCl solution (25° C.) using a saturated calomel electrode as a reference.

The results of these measurements are shown in Table 2.

In addition, if the value of the maximum pitting corrosion depth in the mating plating sheet was 0.1 layer or less, it was evaluated that cathodic protection was sufficiently achieved.

The results in Table 1 show that in the simulated core using the fin materials &1 to A5 according to the present invention, the surface potential of the fins is sufficiently lower than that of the mating plating sheet, and the depth of pitting corrosion caused in the mating plating sheet in the corrosion test is also low. Maximum 0.1
The cathodic protection effect is sufficiently exhibited below M.

The buckling resistance of the fins was also good.

In comparison, the simulated cores using comparative fin materials A, 6 to Arashi 8 having compositions outside the scope of the present invention were inferior in either the cathodic protection effect or the buckling resistance of the fins.

In particular, when Ca was added in excess of 3.0 wt%, many problems occurred in No. 7 during the manufacturing process, such as cracking during casting and cracking during rolling.

Example 2 Aluminum alloy fin materials having the composition shown in Table 2 were used as cathodic protection fin materials of the present invention (Gan 9 to &15) in the same manner as in Example 1.
A conventional fin material containing Zn and Zn was prepared.

However, the final plate thickness was 0.137#'. The test strip thus obtained was corrugated in the same manner as in Example 1 to prepare a simulated core, and the cathodic protection effect and fin buckling resistance were confirmed.

The residual rate of Zn after vacuum brazing was also confirmed by chemical analysis.

These results are shown in Table 2.

The results in Table 2 show that the fin material according to the present invention has a large amount of residual Zn after vacuum brazing and is effective in preventing furnace contamination, and at the same time, the coexistence of Zn has a better cathodic protection effect than Ca alone. It is clear that the pitting corrosion occurring on the opposing plating sheet is shallower.

Further, as shown in the conventional example, it is understood that if Ca is not added, a large amount of Zn evaporates, which contaminates the furnace and at the same time deteriorates the cathodic protection effect.

As explained above, the fin material of the present invention to which Ca element is added alone or together with Zn lowers the potential and exhibits a cathodic protection effect, and especially when coexisting with Zn, it also suppresses the evaporation of Zn and exhibits an excellent cathodic protection effect. It has remarkable effects as a cathodic protection fin material.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a simulated core in an embodiment of the present invention. 1... Placing sheet, 2... Col/7'-tuffin.

Claims (1)

[Claims] I Ca O, 02-3. Owt% and Mn i, 5w
t% or less, Mg i,: 3 wt% or less, 5110wt
% or less, Fe 1.0wt% or less, Cu 0.4w
Does it fall within the range of t% or less and Zr0.2wt% or less?1
A fin material for cathodic protection consisting of aluminum with the remainder being aluminum. 'l Ca O, 02-3.0 wt%, Zn 3.
0 wt% or less, Mn 1.5 wt% or less, Mg
1.3 wt% or less, Si1.0wt% or less, Fe
1. Owt% or less, Cu0.4wt% or less and Zr
Includes one or more types of collapse within the range of 0.2wtφ or less,
Cathodic protection fin material made of aluminum.