JPS63250498A - Magnesium alloy member with corrosion-resistant structure - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A8 Object of the Invention (1) Field of Industrial Application The present invention relates to a magnesium alloy member having a corrosion-resistant structure.

(2) Conventional technology Conventionally, this type of member has been made of a base material made of a magnesium alloy, an oxide film formed on the entire surface of the base material by anodizing treatment to improve corrosion resistance, and a base material of the oxide film. It is known to have a synthetic resin coating formed by general painting such as spray painting on the parts other than the contact surface with a dissimilar metal member attached to the material.

(3) Problems to be solved by the invention However, conventional magnesium alloys, and thus base materials, are still insufficient in terms of corrosion resistance, and the oxide film has poor adhesion to synthetic resin coatings formed by general painting. Since it is not so good, there is a risk of the synthetic resin coating peeling off.Furthermore, since the oxide film has countless micropores on the contact surface with the dissimilar metal component, the oxide film alone is not enough to prevent the base material and the dissimilar metal component from coming into contact with each other. There are problems in that it is not possible to reliably avoid the electrolytic corrosion that occurs during the process, and in addition, anodizing the entire base material is expensive, which increases the manufacturing cost of the member.

An object of the present invention is to provide a magnesium alloy member having the above-mentioned corrosion-resistant structure, which can solve the above-mentioned problems.

B0 Structure of the Invention (11 Means for Solving the Problems) The present invention provides a base material made of a corrosion-resistant magnesium alloy, a chemical conversion film formed on the surface of the base material by film chemical conversion treatment, and a chemical conversion film formed on the surface of the base material. The magnesium alloy has a synthetic resin coating film formed on the surface by electrodeposition coating, and the magnesium alloy is made of aluminum.
5.7-6.3% by weight, MnO, 15-0.45% by weight
, and Mg containing unavoidable impurities. Among the unavoidable impurities, for Fes Cu and Ni, Mg
The weight ratio of n/Fe is 20 or more, the Cu content is 0.025% by weight or less, and the Ni content is 0.
．． 0.004% by weight or less.

The present invention also provides a base material made of a corrosion-resistant magnesium alloy, an oxide film formed by anodizing on the contact surface of the base material with a dissimilar metal member attached to the base material,
and a synthetic resin coating film formed by electrodeposition on the surface of the oxide film, and the magnesium alloy has /l! 5.7
6.3% by weight, Mn 0.15-0.45% by weight, and Mg containing unavoidable impurities, and among the unavoidable impurities, for Fe, Cu, and Ni, M n /
The weight ratio of Fe is set to 20 or more, and the content of Cu is set to 0.
025% by weight or less; Ni content is 0.0
04% by weight or less for the first time.

(2) Effect In the first invention, the magnesium alloy of the above composition, and therefore the base material, has excellent tensile strength and relatively high yield strength, and also has suitable elongation, impact value and hardness, and Has excellent corrosion resistance.

In the alloy, At' has the effect of improving tensile strength and yield strength. However, when its content is less than 5.7% by weight, the elongation properties are improved, but the tensile strength and yield strength are reduced, resulting in lower stiffness;
If it exceeds , the elongation will drop significantly and the impact value will also be low.

Mn also has the effect of improving corrosion resistance. TAX゛shi,
When the content is less than 0.15% by weight, the effect of improving corrosion resistance is small, while when it exceeds 0.45% by weight, the elongation rate decreases.

Furthermore, Fe is a chemical component that affects corrosion resistance in relation to Mn, and CU and Ni are chemical components that each independently affect corrosion resistance, and when the weight ratio of M n / p' e is less than 20,
Further, the content of Cu and Ni is 0.025% by weight and 0.025% by weight.
If the content exceeds 0.004% by weight, corrosion resistance deteriorates.

The chemical conversion film formed on the surface of the base material has good adhesion to the base material and the synthetic resin coating film, and since the synthetic resin coating film is formed by electrical action, it cannot be used on parts with complex shapes. The corrosion-resistant protective film can be reliably hidden with a uniform thickness, thereby forming a corrosion-resistant protective film with strong adhesion. Moreover, since the film chemical conversion treatment is relatively inexpensive, the manufacturing cost of the member can be reduced.

Moreover, in the second invention, the base material has the same physical properties as described above. Further, since the oxide film has not only corrosion resistance but also relatively high strength, it is possible to strengthen the contact surface of the base material with a dissimilar metal member. Furthermore, the synthetic resin coating film formed by electrical action covers the surface of the oxide film with a uniform thickness and seals the countless micropores in the oxide film, so the anchoring effect of these micropores creates a synthetic resin coating. It is possible to strengthen the adhesion of the resin coating, thereby forming an excellent corrosion-resistant protective film, and reliably avoiding electrolytic corrosion that occurs between the base material and dissimilar metal parts over a long period of time. Can be done. Furthermore, since a part of the base material is subjected to anodization treatment, an increase in the manufacturing cost of the member can be suppressed.

(3) Examples 1 to 3 show a vehicle wheel l as a magnesium alloy member having a corrosion-resistant structure.
An annular mounting portion 5 of a cast iron brake disc 4 and a mounting flange portion 7 of a cast iron hub 6, which are dissimilar metal members, are superimposed in this order on the outer surface of an end wall 3 of a boss portion 2 protruding inwardly from the vehicle body at the center of the hub. The wheel 1, the brake disc 4, and the hub 6 are integrally coupled by screwing naphts 9 onto a plurality of bolts 8 that protrude from the mounting flange portion 7 and pass through the mounting portion 5 and the end wall 3.

A bushing 11 is screwed into each bolt insertion hole 10 of the end wall 3,
This is designed to prevent the bolt insertion holes 10 from being worn out. S is a sealing agent that seals the gap between the bushing 11 and the bolt insertion hole 10.

The wheel 1 has a base material 12 having the same shape as the wheel 1, which is made of a corrosion-resistant magnesium alloy by applying a casting method, and a corrosion-resistant protective film, which will be described later, is provided on the surface of the base material 12.

Corrosion-resistant aluminum alloy contains 5.7 to 6.3% by weight of Al.
, Mn 0.15 to 0.45% by weight, and Mg containing unavoidable impurities. Among the unavoidable impurities, F
For Cu and Ni, the weight ratio of Mn/Fe is 20 or more, the Cu content is 0.0.25% by weight or less, and the Ni content is 0, 0% by weight or less, respectively. Set.

FIG. 4 shows the case where the Al content is variously changed in a magnesium alloy containing 0.22% Mn and the above-mentioned unavoidable impurities, and the Ae content is 5.7 to 6.3%.
% by weight, the alloy, and therefore the substrate 12, has excellent tensile strength and relatively high yield strength;
The elongation, impact value and hardness will also be appropriate.

As clearly shown in FIG. 5, the outer surface of the end wall 3 of the wheel 1, that is, the surface of the base material 12 excluding the contact surface 13 (FIG. 6) with the brake disc 4 of the base material 12 and its vicinity, is subjected to a film chemical conversion treatment. A synthetic resin coating 15 is formed on the surface of the chemical conversion coating 14 by electrodeposition coating.If necessary, a synthetic resin coating 15') is coated on the surface of the synthetic resin coating 15'. Intermediate coating layer 16I made of massafacer etc., top coating layer 162 made of metallic paint etc., and J? made of transparent paint etc. 516. Decorative coating film 1 with
6 is formed.

In the case of magnesium alloy, when the base material 12 begins to corrode,
Since the corroded portion becomes alkaline, the electrodeposition coating is preferably an epoxy-based cationic electrodeposition coating which has good alkali resistance.

The chemical conversion film 15 formed on the surface of the base material 12 has good adhesion to the base material 12 and the synthetic resin coating film 15, and in addition, the synthetic resin coating film 15 is formed by electrical action. Even complex-shaped parts can be reliably hidden with a uniform thickness, thereby making it possible to construct a corrosion-resistant protective film with strong adhesion.

Moreover, since the film chemical conversion treatment is relatively inexpensive, the manufacturing cost of the wheel 1 can be reduced.

Further, as clearly shown in FIG. 6, on the contact surface 13 of the base material 12 with the brake disc 4 and in the vicinity thereof, there is an oxide film 17 formed by anodic oxidation treatment, and its oxidation degree I
A synthetic resin coating film 15 formed by electrodeposition is provided on the surface of I*17.

As mentioned above, when the oxide film 17 is formed on the contact surface 13 of the base material 12, the oxide film 17 not only has corrosion resistance but also has higher strength than the chemical conversion film 15. 3
can be strengthened.

Furthermore, the synthetic resin coating film 15 formed by electrical action covers the surface of the oxide film F and fills and seals the countless micropores 18 of the oxide film 17, so that these micropores I
The anchoring effect of 8 can strengthen the adhesion of the synthetic resin coating 15, thereby forming an excellent corrosion-resistant protective film and preventing electrolytic corrosion occurring between the base material 12 and the brake disc 4 over a long period of time. can be reliably avoided.

Furthermore, since a part of the base material 12 is subjected to anodizing treatment, an increase in manufacturing cost of the wheel 1 can be suppressed.

The wheel 1 is manufactured through the following steps.

That is, a vacuum die-casting process for the base material I2 (removal of the casting surface if necessary) - a degreasing process for the base material 12 -> a film chemical conversion process performed by masking the contact surface 13 of the base material I2 and its vicinity - masking An anodizing process performed by removing the anodizing process - an electrodeposition coating process which also serves as a sealing process for the oxide film 17 obtained by the anodizing process - a process for forming the decorative coating film 1G.

The vacuum die casting is performed at a pouring temperature of 700°C and a pressure.
It is carried out under the conditions of 750 kg/cJl and mold preheating temperature of 150°C.

For film conversion treatment, dichromate 150-200 g
The substrate 12 is soaked for 30 to 60 seconds in a room temperature treatment solution containing 150 to 200 g/l of nitrate, 10 to 20 g/1 of ammonium salt, and the like.

Anodizing treatment is performed using NaOH (or KOH) 100~
200 g/i, l salt 20-50 g/j! The base material 12 is immersed in a treatment solution at room temperature containing 10 to 30 g/l of Cr salt, 20 to 60 g/l of carboxylate, etc., and the current density is 1.
The test is carried out under the conditions of ~3 A/d and a voltage of 20 V.

In the electrodeposition process, the base material 12 is immersed in a weakly acidic bath at about 26°C containing 19% epoxy resin, and the electrodeposition voltage is 200%.
It is carried out under the conditions of V.

If the sealing treatment of the oxide film 17 is performed in the electrodeposition coating process as described above, the number of work steps can be halved compared to the case where sealing and painting are performed in separate processes, and since the coating film is continuous, corrosion resistance is improved. It is effective in improving

Next, we will discuss the corrosivity of the base material 12, and therefore the magnesium alloy, and the unavoidable impurities contained in the alloy, such as Fe and C.
The relationship between u and the Ni content will be explained. Note that since Fe affects the corrosivity of the alloy in relation to Mn, it will be considered as a weight ratio of Mn/Fe.

The test pieces used were cast bodies obtained by vacuum die-casting using various magnesium alloys, on which the chemical conversion coating 14 and the synthetic resin coating 15 were sequentially formed.

The corrosion test is performed by making cross-cut scratches on the synthetic resin coating 15 of the test piece and spraying salt water on the cross-cut scratches in an atmosphere at a temperature of 35°C (JIS 2237).
1).

Figure 7 shows 1,11!5.9% by weight, Ni 0.001
When the contents of Mn and Fe are changed, Mn and F
The case where the content of e is changed is shown. As is clear from FIG. 7, good corrosion resistance can be obtained by setting the weight ratio of M n /Fe to 20 or more.

In the corrosion test, the time taken for corrosion to progress from the cross-cut scratch to the position of the second crane was determined, and in Figure 7, it was 216 hours at point a, 456 to 768 hours at point C, and 768 to 960 hours at point C. , it has been found that at point d it is 1008 hours or more and at point e it is 792 to 1080 hours.

Figure 8 shows 1.15.9% by weight, Mn 0.22% by weight, F
The graph shows the case where the Cu content is changed in a magnesium alloy containing e O,005% by weight (M n /F e weight ratio 44), Ni O,001, and CU. As is clear from Fig. 8, Cu
By setting the content to 0.025% by weight or less, good corrosion resistance can be obtained.

Figure 9 shows AIl 5.9% by weight and Mn 0.22% by weight.
, Fe3 0.003 weight ratio Mn/Fe approximately 73.3), Cu O, 015% by weight or less and N
In the magnesium alloy containing i, the case where the Ni content is changed is shown. As is clear from Figure 9,
Good corrosion resistance can be obtained by setting the Ni content to 0.004% by weight or less.

In the electrodeposition coating and anodizing treatment, the synthetic resin coating film 15 and the oxide film 17 tend to be thinner at the edge portions of the base material 12. This is the radius R of the arc surface of the edge part
Therefore, after various studies, we found that by setting the radius R to 0.5 or more, preferably 0.8 or more, a synthetic resin coating with a thickness that can ensure corrosion resistance [1
5 and an oxide film 17 can be formed.

FIG. 10 shows the relationship between the radius R of the circular arc surface at the edge and the thickness of the synthetic resin coating 15, where the radius R is 0.5 t.
m or more, it is possible to obtain a synthetic resin coating film 15 having a thickness substantially equivalent to that of the flat surface portion of the base material 12. However, when the radius R is less than 0.5 am, the thickness of the synthetic resin coating 15 becomes thinner, corrosion of the base material 12 progresses, and many cracks occur due to the alkalinity of the corroded part. do.

The arcuate surface is formed by attaching an arcuate surface to a mold, by machining, or by hand using Scotch prite, sandpaper, or the like.

In addition, in the said wheel, a dissimilar metal member may be a hub. Further, the present invention is applicable not only to wheels but also to other members.

Effects of the C6 Invention According to the first invention, a base material having excellent mechanical strength and corrosion resistance, and a corrosion-resistant protective film that reliably covers the surface of the base material and has strong adhesion, that is, a chemical conversion coating and a synthetic coating. It is possible to provide a magnesium alloy member having a corrosion-resistant structure and having a resin coating film. Furthermore, since the film conversion treatment is relatively inexpensive, the manufacturing cost of the member can be reduced.

According to the second invention, a base material having excellent mechanical strength and corrosion resistance as described above, and a corrosion-resistant protective film that reliably covers the surface of the base material and has strong adhesion, that is, an oxide film and a synthetic It is possible to provide a magnesium alloy member including a resin coating film and having a corrosion-resistant structure that can reliably avoid electrolytic corrosion occurring between a base material and a dissimilar metal member attached thereto. Further, since the anodizing treatment is performed only on a part of the base material, an increase in the manufacturing cost of the member can be suppressed.

[BRIEF DESCRIPTION OF THE DRAWINGS] Figures 1 to 3 show a vehicle wheel, where Figure 1 is a longitudinal sectional front view, Figure 2 is a view in the direction of Figure 1, and Figure 3 is an enlarged view of the main parts. Figure 4 is a graph showing the relationship between Al content and mechanical strength of magnesium alloys, Figure 5 is an enlarged view of the part indicated by the arrow in Figure 3, and Figure 6 is an enlarged view of the part indicated by the arrow in Figure 3. Figure 7 shows the Mn/F of a magnesium alloy with a corrosion-resistant protective film.
A graph showing the relationship between the weight ratio of e and the corrosion rate. Figure 8 is a graph showing the relationship between the Cu content and the corrosion rate of magnesium alloys with a corrosion-resistant protective film. Figure 9 is a graph showing the relationship between the Cu content and corrosion rate of magnesium alloys with a corrosion-resistant protective film. FIG. 10 is a graph showing the relationship between the Ni content and the corrosion rate, and FIG. 10 is a graph showing the relationship between the radius of the circular arc surface at the edge of the base material and the thickness of the synthetic resin coating film. 4...Brake disc as a dissimilar metal member, 12
... Base material, 13 ... Contact surface, 14 ... Chemical conversion film,
15... Synthetic resin coating film, 17... Oxide film Figure 2 Figure 3 = Figure 4 Ae content (weight %) Figure 6 Figure 5 Figure 7 Weight ratio of M n / Fe Figure 8 Cu content m<T11m%) Figure 9 Figure 10

Claims (4)

[Claims] (1) A base material made of a corrosion-resistant magnesium alloy,
The magnesium alloy includes a chemical conversion film formed on the surface of the base material by a film chemical conversion treatment, and a synthetic resin coating film formed on the surface of the chemical conversion film by electrodeposition coating, and the magnesium alloy is made of Al5.
7 to 6.3% by weight, Mn 0.15 to 0.45% by weight, and Mg containing unavoidable impurities.
The weight ratio of Cu is 20 or more, and the Cu content is 0.025.
% by weight or less, and further increase the Ni content to 0.004% by weight.
A magnesium alloy member having a corrosion-resistant structure characterized by the following settings. (2) The magnesium alloy member having a corrosion-resistant structure according to claim (1), wherein the magnesium alloy member is a vehicle wheel. (3) a base material made of a corrosion-resistant magnesium alloy;
The base material includes an oxide film formed by anodization treatment on the contact surface with a dissimilar metal member attached to the base material, and a synthetic resin coating film formed by electrodeposition coating on the surface of the oxide film, The magnesium alloy consists of 5.7 to 6.3% by weight of Al, 0.15 to 0.45% by weight of Mn, and Mg containing unavoidable impurities. Among the unavoidable impurities, F
For e, Cu and Ni, the weight ratio of Mn/Fe is 2.
A magnesium alloy member having a corrosion-resistant structure, characterized in that the content of Cu is set to 0.0 or more, the content of Cu is set to 0.025% by weight or less, and the content of Ni is set to 0.004% by weight or less. (4) The magnesium alloy member having a corrosion-resistant structure according to claim (3), wherein the magnesium alloy member is a vehicle wheel.