JP2705844B2 - Magnesium alloy for galvanic anode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnesium alloy for a galvanic anode suitable for electrical protection of steel structures.

2. Description of the Related Art Conventionally, as a method of preventing corrosion of a steel structure used in seawater, sea soil, or soil, an electrolytic protection method in which iron is kept in a stable region against corrosion by a corrosion protection current has been widely used. In this cathodic protection method, for example, a noble insoluble alloy having an anodic potential such as high silicon steel or platinum is used as an anode, the object to be protected is connected as a cathode, and a direct current power supply is arranged in the middle to forcibly forcibly. An external power supply method in which an anti-corrosion current is obtained by applying a current, and a flow in which a surplus electron generated by corrosion of the anode is used as an anti-corrosion current using a base alloy having a low anode potential such as an aluminum alloy, a zinc alloy, or a magnesium alloy. There are two types of electroanode methods. Of these, the external power supply method is apt to be large-scale and requires continuous energization during the period of anticorrosion, and the cost is high.

Among them, magnesium alloy galvanic anode shows the lowest potential compared to aluminum alloy or zinc alloy,
It is widely used in environments with high specific resistance, such as buried pipes and bridge foundations installed in or on the soil, because it has a large potential difference from the steel structure that is the anticorrosion body.

[Problems to be Solved by the Invention] As such a conventional magnesium alloy anode, JI
There are pure Mg (JIS Class 1) and AZ63 alloy (JIS Class 2 and Class 3) specified in SH6125, especially Al5.3 ~ 6.7, Zn2.5 ~
AZ63 alloy containing 3.5, Mn of 0.15 to 0.60% by weight and the balance of Mg and unavoidable impurities is the mainstream.

The characteristic values of the galvanic anode include the amount of generated electricity, efficiency, and anode potential. The amount of generated electricity is the amount of anticorrosive electricity per unit weight, and the larger this value is, the better the anode is. In addition, when the weight is the same, the larger the value, the longer the anticorrosion current can be obtained, that is, the longer the life. Efficiency is the amount of electricity generated and the theoretical amount of electricity generated by the composition of the alloy (the reciprocal of the electrochemical equivalent; aluminum is
2980 Ahr / kg, zinc is 820 Ahr / kg, and magnesium is 2205 Ahr / kg. It is. The anodic potential is the natural potential of the alloy, and indicates that the larger the difference from the natural potential of iron, the more widely the anticorrosion current can flow.

The above-mentioned AZ63 alloy is said to have an efficiency of about 50-55% (generated electricity of 1100-1250 Ahr / kg), which is not sufficient for recent demands for longer life of steel structures. Met.

An object of the present invention is to provide a magnesium alloy for a galvanic anode having a large amount of generated electricity, high efficiency and long life.

[Means for Solving the Problems] To achieve the above object, the alloy of the present invention is composed of Al5-16, Zn
It contains 0.5 to 10, Mn 0.1 to 1, Ti 0.005 to 0.1, and B 0.001 to 0.02% by weight, with the balance being magnesium and inevitable impurities.

[Operation] The reasons for limiting the component composition ranges of the alloy of the present invention as described above will be described below.

Al is an element that effectively acts to smooth the melting surface, but less than 5% by weight does not have sufficient effect.
On the other hand, if it exceeds 16% by weight, the anodic potential becomes noble, so its content needs to be 5 to 16% by weight.

Zn is an element that effectively acts to smooth the melting surface, but less than 0.5% by weight does not have sufficient effect.
On the other hand, when the content exceeds 10% by weight, the theoretical amount of generated electricity of Zn is small and the amount of generated electricity of the alloy is reduced.
It must be ~ 10% by weight.

Mn is the amount of iron contained as inevitable impurities in Mg ingots,
Although it is an effective element for reducing the adverse effect of reducing the amount of generated electricity, its effect is not sufficient if its content is less than 0.1% by weight, whereas if it exceeds 1% by weight, the amount of generated electricity is reduced. Therefore, its content needs to be 0.1 to 1% by weight.

When Ti and B are added, the crystal structure changes from coarse columnar crystals to fine granular crystals, whereby the dissolution of the alloy becomes uniform, thereby preventing pitting, groove corrosion and adhesion of corrosion products. As a result, the uniformity and smoothness of the dissolution surface are improved. If the content of Ti is less than 0.005% by weight and the content of B is less than 0.001% by weight, the effect is not sufficient. On the other hand, if the content exceeds 0.1% by weight and the content of B exceeds 0.02% by weight, the amount of generated electricity decreases. Should be 0.005 to 0.1% by weight, and B should be 0.001 to 0.02% by weight.

[Example] An example will be described below.

The additive elements were blended in the composition shown in Table 1, melted using a cast steel crucible, and cast into a round bar-shaped mold having a diameter of 20 mm and a length of 150 mm to obtain a test piece. This sample was carried out in accordance with the “electrostatic anode test method” established by the Association of Corrosion and Corrosion Prevention (“electrostatic anode test method and its description”, anti-corrosion technology, vol. 31, p612-620, 1982). . Briefly, these test pieces were polished surface until 240 No. roughness ultimately sandpaper to remove the influence of the oxide of the cast skin surface, leaving a test area 40 cm ² sides Others were insulated with vinyl tape. Further, a solution of artificial seawater saturated with magnesium hydroxide was filled in a 1-liter beaker, and this was used as a test solution. The test piece is placed in the center of the container and this is used as the anode,
A stainless steel cylindrical plate arranged along the side wall of the container was connected to a cathode with a distance between electrodes of 30 mm being used as a cathode and a DC stabilized power supply was interposed therebetween. This was energized under a constant current condition of an anode current density of 0.1 mA / cm ² for 240 hours, and the amount of generated electricity was calculated from the weight loss of the test piece. The anodic potential immediately before completion was measured using a silver-silver chloride electrode and converted to a saturated calomel electrode reference value (SCE).
The results are shown in Table 1.

Table 1 shows that the alloy of the present invention has a sufficiently low anode potential of about -1500 mV (vs. SCE) and a sufficiently low value of 1690 to 1720 A · hr / kg even when compared with the comparative alloy and the conventional AZ63 alloy. It can be seen that it has a high amount of generated electricity.

[Effects of the Invention] When the alloy of the present invention is used for electrolytic protection of a steel structure installed in soil or on the ground, it has a sufficiently low anode potential and generates 1690-1720 A · hr while having a sufficiently low anode potential. /kg
And raises the efficiency of the alloy from 50-55% to 76-78% from the conventional one, and it is possible to obtain a long-life current-carrying anode that can be used stably for a long period of time. To demonstrate.

Claims (1)

(57) [Claims] (1) Al5-16, Zn0.5-10, Mn0.1-1, Ti0.005
A magnesium alloy for a galvanic anode, characterized by containing 0.1% by weight and 0.001 to 0.02% by weight of B, with the balance being magnesium and unavoidable impurities.