Patent Application
20200248287
The present invention relates to a metal connection member and a method for a chemical conversion treatment of a metal connection member.
The present application claims a priority to Japanese Patent Application No. 2017 154826 filed on Aug. 9, 2017, which is incorporated herein by reference in its entirety.
One of the known chemical conversion treatment methods in which a chemical conversion treatment film is formed on the surface of an aluminum (Al) member is, for example, the surface pretreatment of aluminum described in NPL 1. NPL 1 discloses atechnique in which a chromium free chemical conversion treatment liquid that includes zirconium (Zr) as a principal component is used.
NPL 1: Kiyotada Yasuhara, “Surface pretreatment of aluminum for coatings”, light metals, The Japan Institute of Light Metals, 1990, Vol. 40, No. 10, p. 753 to 760
A metal connection member according to the present disclosure includes: a Mg alloy member composed principally of magnesium; a partner member connected to the Mg alloy member, the partner member being composed principally of a metal nobler than magnesium; and a chemical conversion treatment film that covers a surface of the Mg alloy member and a surface of the partner member with covering a boundary between the Mg alloy member and the partner member.
A method for a chemical conversion treatment of a metal connection member according to the present disclosure includes:
a preparation step of preparing a metal connection member, the metal connection member including a Mg alloy member composed principally of magnesium and a partner member connected to the Mg alloy member, the partner member being composed principally of a metal nobler than magnesium; and a chemical conversion treatment step of bringing both of the Mg alloy member and the partner member included in the metal connection member into contact with a chemical conversion treatment liquid in a collective manner to form a chemical conversion treatment film on a surface of the metal connection member,
wherein the electric conductivity y of the chemical conversion treatment liquid satisfies at least one of the relation formulae (a) and (b) below,
y≤0.0007 x1+14.0 (a)
y≤0.054 x2+14.2 (b)
Al members are commonly connected to iron (Fe) members particularly in the production of parts of automobiles or the like. Since subjecting an Al member and a Fe member individually to a chemical conversion treatment requires multiple lines for the chemical conversion treatments of the members, the chemical conversion treatment may be performed by bringing an Al member and a Fe member into contact with a common chemical conversion treatment liquid in a collective manner while the Al member is connected to the Fe member.
The application of magnesium (Mg) alloy members is being studied in order to achieve weight reduction. However, there has not been developed any specific method in which a chemical conversion treatment of a Mg alloy, which is more base than Al, and a Fe member is performed by bringing the Mg alloy and the Fe member into contact with a common chemical conversion treatment liquid in a collective manner as described above while the Mg alloy and the Fe member are connected to each other. Therefore, the development of such a chemical conversion treatment method is anticipated.
Accordingly, it is an object to provide a metal connection member that includes a Mg alloy member, a partner member connected to the Mg alloy member, and a chemical conversion treatment film that covers the Mg alloy member and the partner member, the chemical conversion treatment film having good adhesion and good corrosion resistance.
It is another object to provide a method for a chemical conversion treatment of a metal connection member, the method enabling the chemical conversion treatment film to be formed on the surface of the Mg alloy member and the surface of the partner member while the Mg alloy member and the partner member are connected to each other.
In the metal connection member according to the present disclosure, the Mg alloy member and the partner member can be covered with the chemical conversion treatment film having good adhesion and good corrosion resistance.
The method for a chemical conversion treatment of a metal connection member according to the present disclosure enables the chemical conversion treatment film to be formed on the surface of the Mg alloy member and the surface of the partner member while the Mg alloy member and the partner member are connected to each other.
First, the aspects of the present invention are listed below.
(1) A metal connection member according to an aspect of the present invention includes:
a Mg alloy member composed principally of magnesium;
a partner member connected to the Mg alloy member, the partner member being composed principally of a metal nobler than magnesium; and
a chemical conversion treatment film that covers a surface of the Mg alloy member and a surface of the partner member with covering a boundary between the Mg alloy member and the partner member.
In the above described metal connection member, the Mg alloy member and the partner member can be covered with the chemical conversion treatment film having good adhesion and good corrosion resistance.
(2) In the above described metal connection member, the charge transfer resistance of the Mg alloy member in 1M of Na2SO4 is 300 Ω or more and 1200 Ω or less.
In such a case, the above described chemical conversion treatment film can be formed.
(3) In the above described metal connection member, the content of aluminum in the Mg alloy member is 0.3% by mass or more and 12.0% by mass or less.
In such a case, the chemical conversion treatment film can be formed.
(4) A method for a chemical conversion treatment of a metal connection member according to another aspect of the present invention includes:
a preparation step of preparing a metal connection member, the metal connection member including a Mg alloy member composed principally of magnesium and a partner member connected to the Mg alloy member, the partner member being composed principally of a metal nobler than magnesium; and a chemical conversion treatment step of bringing both of the Mg alloy member and the partner member included in the metal connection member into contact with a chemical conversion treatment liquid in a collective manner to form a chemical conversion treatment film on a surface of the metal connection member,
wherein the electric conductivity y of the chemical conversion treatment liquid satisfies at least one of the relation formulae (a) and (b) below,
y≤0.0007 x1+14.0 (a)
y≤0.054 x2+14.2 (b)
where x1 (Ω) is the charge transfer resistance of the Mg alloy member in 1M of Na2SO4, x2 (mass %) is the content of aluminum in the Mg alloy member, and y (mS/cm) is the electric conductivity of the chemical conversion treatment liquid.
The above described chemical conversion treatment method enables the chemical conversion treatment film to be formed on the surfaces of the Mg alloy member and the partner member as a single piece with covering the boundary between the two members while the two members are connected to each other. This is because, when at least one of the relation formulae (a) and (b) above is satisfied, the rate of formation of the chemical conversion treatment film is not excessively high.
(5) In the method for a chemical conversion treatment of a metal connection member, the charge transfer resistance xi is 300 Ω or more and 1200 Ω or less.
When the charge transfer resistance xi is 300 Ω or more, an excessive reaction between the chemical conversion treatment liquid and the Mg alloy member can be suppressed and, consequently, the above described chemical conversion treatment film can be readily formed. When the charge transfer resistance x1 is 1200 Ω or less, the chemical conversion treatment film can be formed without consuming an excessive amount of time.
(6) In the method for a chemical conversion treatment of a metal connection member, the content of aluminum x2 is 0.3% by mass or more and 12.0% by mass or less.
In such a case, the chemical conversion treatment film can be readily formed.
(7) In the method for a chemical conversion treatment of a metal connection member, the electric conductivity y of the chemical conversion treatment liquid satisfies 0.1 mS/cm≤y.
In such a case, the chemical conversion treatment film can be readily formed without consuming an excessive amount of time.
(8) In the method for a chemical conversion treatment of a metal connection member, the content of zinc in the Mg alloy member is 0.5% by mass or more and 6.2% by mass or less.
In such a case, the chemical conversion treatment film can be readily formed.
(9) In the method for a chemical conversion treatment of a metal connection member, the pH of the chemical conversion treatment liquid is 2.0 or more and 7.0 or less.
When the pH of the chemical conversion treatment liquid is 2.0 or more, an excessive reaction between the chemical conversion treatment liquid and the Mg alloy member can be suppressed and, consequently, the chemical conversion treatment film can be readily formed. When the pH of the chemical conversion treatment liquid is 7.0 or less, an excessive reaction between the chemical conversion treatment liquid and the partner member can be suppressed and, consequently, the degradation of the stability of the chemical conversion treatment liquid can be suppressed. This can reduce the likelihood of troubles occurring during a continuous operation.
(10) In the method for a chemical conversion treatment of a metal connection member, the pH and the electric conductivity y of the chemical conversion treatment liquid is adjusted using at least one acid or salt selected from nitric acid, sulfuric acid, hydrofluoric acid, hydrofluosilicic acid, bromic acid, manganic acid, permanganic acid, vanadic acid, hydrogen peroxide, an organic acid, and salts of these acids.
In such a case, the pH and the electric conductivity y (mS/cm) of the chemical conversion treatment liquid can be readily adjusted.
(11) In the method for a chemical conversion treatment of a metal connection member, the chemical conversion treatment liquid includes a metal element belonging to Group 4 of the periodic table.
In such a case, the chemical conversion treatment film can be readily formed.
(12) In the method for a chemical conversion treatment of a metal connection member, the temperature of the chemical conversion treatment liquid is 5° C. or more and 70° C. or less.
When the chemical conversion treatment temperature is 5° C. or more, the formation of the chemical conversion treatment film can be readily accelerated and the chemical conversion treatment film can be formed without consuming an excessive amount of time. When the chemical conversion treatment temperature is 70° C. or less, the temperature is not excessively high and the components of the chemical conversion treatment liquid can readily become stabilized. As a result, the chemical conversion treatment film can be readily formed.
(13) In the method for a chemical conversion treatment of a metal connection member, the Mg alloy member and the partner member is electrically connected to each other.
In such a case, the chemical conversion treatment film can be formed on the surfaces of the Mg alloy member and the partner member as a single piece with covering the boundary between the two members. Details of the mechanisms are described below.
Details of an embodiment of the present invention are described below. The metal connection member and the method for a chemical conversion treatment of the metal connection member are described below in this order.
A metal connection member 1 according to the embodiment is described below with reference to
Details thereof are described below.
The Mg alloy member 2 is composed of a Mg alloy that includes the Mg element as a principal component. The term “principal component” used herein refers to one of the elements constituting the Mg alloy member 2 the mass proportion of which is the largest. Examples of the Mg alloy include Mg alloys having various compositions (balance: Mg and inevitable impurities) containing Mg and additive elements. Typical examples of the Mg alloy include a Mg—Al base alloy. Other examples thereof include a Mg—Zn based alloy, a Mg RE (rare earth element) based alloy, and an Y containing alloy.
The Mg Al based alloy contains at least Al as an additive element. The higher the Al content, the higher the corrosion resistance and the better the mechanical properties, such as strength and plastic deformation resistance. However, if the Al content is excessively high, plastic formability may become degraded. Accordingly, the Al content is preferably 0.3% by mass or more and 12.0% by mass or less, is further preferably 5.6% by mass or more and 9.5% by mass or less, and is particularly preferably 8.3% by mass or more and 9.5% by mass or less. Examples of the additive elements other than Al include one or more elements selected from Zn, Mn, Si, Be, Ca, Sr, Y, Cu, Ag, Sn, Ni, Au, Li, Zr, Ce, and rare earth elements (except Y and Ce). In the case where the Mg Al based alloy contains the above elements, the total content of the elements is, for example, 0.01% by mass or more and 10% by mass or less and is preferably 0.1% by mass or more and 5% by mass or less. Examples of the impurities include Fe.
Examples of the more specific composition of the Mg—Al based alloy include an AZ based alloy (Mg—Al—Zn based alloy, Zn: 0.2% by mass or more and 1.5% by mass or less), an AM based alloy (Mg—Al—Mn based alloy, Mn: 0.05% by mass or more and 0.5% by mass or less), an AS based alloy (Mg—Al—Si based alloy, Si: 0.3% by mass or more and 4.0% by mass or less), a Mg—Al-RE (rare earth element) based alloy, an AX based alloy (Mg—Al—Ca based alloy, Ca: 0.2% by mass or more and 6.0% by mass or less), an AZX based alloy (Mg—Al—Zn—Ca based alloy, Zn: 0.2% by mass or more and 1.5% by mass or less, Ca: 0.1% by mass or more and 4.0% by mass or less), and an AJ based alloy (Mg—Al—Sr based alloy, Sr: 0.2% by mass or more and 7.0% by mass or less) defined by the ASTM standard.
Typical examples thereof include an AZ31 alloy (Al: 2.5% by mass or more and 3.5% by mass or less, Zn: 0.6% by mass or more and 1.4% by mass or less) and an AZ91 alloy (Al: 8.3% by mass or more and 9.5% by mass or less, Zn: 0.5% by mass or more and 1.5% by mass or less), which are the AZ based alloys. Typical examples thereof also include an AM60 alloy (Al: 5.6% by mass or more and 6.4% by mass or less, Mn: 0.15% by mass or more and 0.50% by mass or less), which is the AM based alloy. Other examples of the AZ based alloy include AZ10, AZ61, AZ63, AZ80, and AZ81. Other examples of the AM based alloy include AM100.
The Mg—Zn based alloy contains at least Zn as an additive element. The Zn content is preferably 0.5% by mass or more and 6.2% by mass or less and is particularly preferably 1.5% by mass or more and 4.0% by mass or less. The additive elements other than Zn, the content of the additive elements, and the impurities are the same as the additive elements contained in the Mg—Al based alloy, the content of the additive elements, and the impurities contained in the Mg—Al based alloy, respectively, which are described above.
Examples of the more specific composition of the Mg Zn based alloy include a ZX based alloy (Mg—Zn Ca based alloy, Zn: 0.5% by mass or more and 6.2% by mass or less, Ca: 0.05% by mass or more and 0.3% by mass or less) and a ZE based alloy (Mg—Zn-RE based alloy, Zn: 0.5% by mass or more and 6.2% by mass or less, rare earth elements: 0.05% by mass or more and 0.5% by mass or less). Other examples thereof include a Mg—Zn—Sr based alloy, a Mg—Zn—Ba based alloy, a Mg—Zn—Ca-RE based alloy, a Mg—Zn—RE-Mn based alloy, a Mg—Zn—Sr-RE based alloy, and a Mg—Zn—Ba-RE based alloy. Typical examples thereof include ZX10, which is a ZX based alloy.
The corrosion resistance of a Mg alloy varies with the composition thereof. Since the state of formation of the chemical conversion treatment film 4 and the rate of formation of the chemical conversion treatment film 4 vary with corrosion resistance, it is preferable to specify the corrosion resistance of the Mg alloy. On the basis of a Tafel distribution curve, a corrosion current density in the standard state can be used as an index. The charge transfer resistance of the Mg alloy measured using 1M of Na2SO4 as a solvent and a silver electrode as a counter electrode is preferably 300 Ω or more and 1200 Ω or less. The unit “M” used herein refers to volume molar concentration: mol/L (dm3). When the charge transfer resistance is 300 Ω or more, an excessive reaction between the chemical conversion treatment liquid and the Mg alloy member 2 can be suppressed and, consequently, the chemical conversion treatment film 4l can be readily formed on the surfaces of the members 2 and 3 as a single piece with covering the boundary between the members 2 and 3. When the charge transfer resistance is 1200 Ω or less, the above described chemical conversion treatment film 4 can be formed without consuming an excessive amount of time. The charge transfer resistance is further preferably 400 Ω or more and 1100 Ω or less and is particularly preferably 800 Ω or more and 1050 Ω or less.
Examples of the type of the Mg alloy member 2 include a cast material prepared by casting, such as twin roll or die casting; a rolled material prepared by rolling the cast material; a processed material prepared by subjecting the rolled material to a heat treatment, a leveling process, polishing processing, or the like; and a plastic formed material prepared by subjecting the rolled material or the processed material to plastic forming. The Mg alloy member 2 can be subjected to a solution treatment prior to the rolling. The shape of the Mg alloy member 2 may be selected appropriately. Typical examples thereof include a plate like shape. Although the size of the Mg alloy member 2 can be selected appropriately, it is preferable that the surface area ratio described below be satisfied.
The partner member 3 is formed of a material composed principally of a metal nobler than the Mg alloy. The metal nobler than the Mg alloy is a metal having a lower ionization tendency than the Mg alloy. Specific examples of the partner member 3 include an Fe member composed of an Fe based material and an Al member composed of an Al based material. The term “Fe based material” used herein refers to pure Fe or an Fe alloy composed principally of the Fe element. The meaning of the term “principally” is the same as for the Mg alloy described above. Examples of the iron alloy include a steel, a stainless steel alloy, and a carbon steel. The partner member 3 is, for example, a steel member composed of a steel. The term “Al based material” used herein refers to pure Al or an Al alloy composed principally of the Al element. The meaning of the term “principally” is the same as for the Mg alloy described above. Examples of the Al alloy include an Al—Mg based alloy (5000 series alloy) and an Al—Mg—Si based alloy (6000 series alloy).
The number of the partner members 3 may be one or two or more. In the case where the number of the partner members 3 is two or more, at least one of the partner members 3 may be one of the Fe member and the Al member, and the other partner members 3 may be members formed of a material composed principally of a metal that is nobler than the Mg element and is other than the principal element (Fe or Al) of the at least one partner member 3. For example, the other partner members 3 may be Zn members composed of a Zn based material. That is, the partner members 3 may be the Fe member and the Al member only or may be at least one of the Fe member and the Al member and the Zn member.
The shape of the partner member 3 can be selected appropriately. Typical examples thereof include a plate like shape, as for the Mg alloy member 2. Although the size of the partner member 3 may be selected appropriately, it is preferable that the surface area ratio described below be satisfied.
(Surface Area Ratio)
Although the surface area ratio between the surface area of the Mg alloy member 2 and the surface area of the partner member 3 (Surface area of Mg alloy member 2 Entire surface area) may be selected appropriately, the surface area ratio is preferably 0.1% or more and 50% or less, is further preferably 0.1% or more and 10% or less, and is particularly preferably 0.1% or more and 3% or less. The current that flows in the Mg alloy member 2 and the partner member 3 varies with the above surface area ratio. When the surface area ratio is 0.1% or more, a homogeneous chemical conversion treatment film 4 can be readily formed on the surfaces of the members 2 and 3 as a single piece with covering the boundary between the members 2 and 3. When the surface area ratio is 50% or less, the amount of time required by the chemical conversion treatment can be readily reduced. The entire surface area used for calculating the surface area ratio does not include the contact surface at which the Mg alloy member 2 and the partner member 3 come into contact with each other.
The mode of connection between the Mg alloy member 2 and the partner member 3 may be selected appropriately in accordance with, for example, the type of the material constituting the partner member 3. The connection between the Mg alloy member 2 and the partner member 3 can be established by, for example, clamping with bolts and nuts, clamping using rivets, welding, or friction stir welding. In the case where bolts are used, for example, through holes into which the bolts are to be inserted are formed in the members 2 and 3. In the case where rivets are used, for example, rivets are formed in one of the members 2 and 3 and holes into which the rivets are to be inserted are formed in the other member.
The chemical conversion treatment film 4 covers the surface of the Mg alloy member 2 and the surface of the partner member 3 with covering the boundary therebetween. That is, the chemical conversion treatment film 4 is arranged to cover the boundary between the Mg alloy member 2 and the partner member 3 so as to extend from one of the members 2 and 3 to the other member. The region covered with the chemical conversion treatment film 4 varies with the mode of connection between the Mg alloy member 2 and the partner member 3 and is, for example, a region other than the contact surface at which the Mg alloy member 2 and the partner member 3 come into contact with each other.
The chemical conversion treatment film 4 includes an oxide of an element belonging to Group 4 of the periodic table as a principal component. The Group 4 element is zirconium (Zr), titanium (Ti), or hafnium (Hf). The oxide thereof varies with the components of the chemical conversion treatment liquid and may be, for example, zirconium oxide (ZrO2), zirconium nitrate (Zr(NO3)4), or zirconium fluorophosphate (ZrFPO4). The chemical conversion treatment film 4 may further include a fluoride of the Group 4 element (e.g., ZrF4), a fluoride that does not include the Group 4 element (e.g., HF, NH4HF2, NH4F, NaHF2, or NaF), or the like. A chemical conversion treatment film 4 formed on the surface of the Mg alloy member 2 may further include an oxide or hydroxide of Mg. A chemical conversion treatment film 4 formed on the surface of the partner member 3 may further include an oxide or hydroxide of the principal element (Fe or Al) of the partner member 3, a fluoride of the principal element, or a compound containing the principal element, the oxygen element, and the fluorine element. The materials constituting the chemical conversion treatment film 4 and the contents of the materials may be determined by X ray fluorescence analysis (XRF).
The thickness of a region of the chemical conversion treatment film 4 which covers the Mg alloy member 2 and the thickness of a region of the chemical conversion treatment film 4 which covers the partner member 3 are preferably, for example, 10 nm or more and 300 nm or less. When the thicknesses of these regions are 10 nm or more, corrosion resistance can be readily enhanced. When the thicknesses of these regions are 300 nm or less, the thicknesses of these regions are not excessively large.
The thicknesses of the above regions are further preferably 20 nm or more and 250 nm or less and are particularly preferably 50 nm or more and 200 nm or less. The thickness of a region of the chemical conversion treatment film 4 which covers the Mg alloy member 2 and the thickness of a region of the chemical conversion treatment film 4 which covers the partner member 3 may be equal to or different from each other. The thickness of the above regions can be measured by observing a cross section with a scanning electron microscope (SEM). Specifically, the thickness of the chemical conversion treatment film 4 is measured at plural (e.g., five or more) positions in a cross section of each region, and the average thereof is considered the thickness of the region of the chemical conversion treatment film 4 which covers the member.
The metal connection member 1 can further include a coating film (not illustrated in the drawings) that covers the surface of the chemical conversion treatment film 4. The structure of the coating film may be a single layer structure or a multilayer structure. Examples of the material constituting the coating film include an acrylic resin. Examples of the coating material constituting the coating film include MG Net T (MG Net is a registered trademark) produced by Origin Co., Ltd. and RYLCON BB20 (RYLCON is a registered trademark) and ARMOR TOP AT20 (product name) produced by Musashi Paint Holdings Co., Ltd. The coating film may have, for example, a single layer structure consisting of the above coating material or a multilayer structure that includes a lower layer that is disposed immediately on the chemical conversion treatment film 4 and composed of an electrodeposition coating material and one or more upper layers that are disposed immediately on the lower layer and composed of the above coating material.
[Applications]
The metal connection member 1 according to the embodiment can be suitably used as a part of automobiles.
In the metal connection member 1 according to the embodiment, the Mg alloy member 2 and the partner member 3 can be covered with the chemical conversion treatment film 4 as a single piece.
A method for a chemical conversion treatment of the metal connection member according to the embodiment is described below. The method for a chemical conversion treatment of the metal connection member according to the embodiment includes a preparation step of preparing a metal connection member that includes a magnesium (Mg) alloy member 2 and a partner member 3 that is connected to the Mg alloy member 2 and composed of a specific material; and a chemical conversion treatment step of subjecting the metal connection member to a chemical conversion treatment. One of the features of the method for a chemical conversion treatment of the metal connection member is that the Mg alloy member 2 and the partner member 3 included in the metal connection member are brought into contact with a specific chemical conversion treatment liquid in a collective manner. Details of the above steps are described below.
In the preparation step, a metal connection member that includes the above described Mg alloy member 2 and the above described partner member 3 that are connected to each other, which is the member that is to be subjected to a chemical conversion treatment, is prepared.
In the chemical conversion treatment step, the metal connection member is subjected to a chemical conversion treatment in order to form a chemical conversion treatment film 4 on the surfaces of the Mg alloy member 2 and the partner member 3 included in the metal connection member. In the chemical conversion treatment, the Mg alloy member 2 and the partner member 3 included in the metal connection member are brought into contact with a common chemical conversion treatment liquid in a collective manner. Specifically, for example, an immersion method in which the metal connection member is immersed in the chemical conversion treatment liquid and a coating method in which the chemical conversion treatment liquid is applied to the metal connection member by spraying or the like can be suitably used. In the coating method, the chemical conversion treatment liquid is applied onto the surfaces of the Mg alloy member 2 and the partner member 3 so as to form a coating film that covers the boundary between the members 2 and 3 as a single piece.
Upon the metal connection member being brought into contact with the chemical conversion treatment liquid, a current flows from the chemical conversion treatment liquid to each of the Mg alloy member 2 and the partner member 3. Since the partner member 3 is composed of a metal nobler than that constituting the Mg alloy member 2, a galvanic current flows from the partner member 3 to the Mg alloy member 2. In the case where the metals are not electrically connected to each other, the current flows through the coating liquid. The galvanic current that occurs in the early stage of the contact between the metal connection member and the chemical conversion treatment liquid is larger than the current that flows from the chemical conversion treatment liquid to the partner member 3. While this relationship is satisfied, the chemical conversion treatment film 4 is more likely to be formed on the surface of the Mg alloy member 2 than on the surface of the partner member 3. This is because the galvanic current accelerates the formation of the chemical conversion treatment film 4 on the Mg alloy member 2. When the formation of the chemical conversion treatment film 4 on the surface of the Mg alloy member 2 starts, the electric resistance of the Mg alloy member 2 increases and the current that flows from the chemical conversion treatment liquid to the partner member 3 becomes larger than the galvanic current. In this stage, the chemical conversion treatment film 4 is formed on the surface of the partner member 3. As a result, the chemical conversion treatment film 4 can be formed, as a single piece, on the surfaces of the Mg alloy member 2 and the partner member 3 that are connected to each other, with covering the boundary between the members 2 and 3.
The chemical conversion treatment liquid is a coating liquid used for forming the chemical conversion treatment film 4 on the surfaces of the Mg alloy member 2 and the partner member 3 of the metal connection member. The chemical conversion treatment liquid preferably contains an element belonging to Group 4 of the periodic table.
In such a case, a chemical conversion treatment film 4 including an oxide of the Group 4 element can be formed on the surfaces of the Mg alloy member 2 and the partner member 3 of the metal connection member. The Group 4 element may be included in the chemical conversion treatment liquid, for example, in the form of a fluoride. For example, examples of a fluoride of Zr include H2ZrF6 (fluorozirconic acid) and (NH4)2ZrF6 (ammonium hexafluorozirconate), which is an ammonium salt of fluorozirconic acid.
The chemical conversion treatment liquid may further contain one or more substances selected from nitric acid, a nitrate, an organic acid, an organic acid salt, boric acid (e.g., HBF4 (tetrafluoroboric acid)), a borate, phosphoric acid, a phosphate, sulfuric acid, a sulfate, hydrofluoric acid, a hydrofluoride, hydrofluosilicic acid, a hydrofluosilicate, bromic acid, a bromate, manganic acid, a manganate, permanganic acid, a permanganate, vanadic acid, a vanadate, hydrogen peroxide, and a hydrogen peroxide salt. The above acids and salts adjust the electric conductivity y and pH of the chemical conversion treatment liquid which are described below. Specifically, the higher the contents of the above acids and salts, the higher the electric conductivity y and pH of the chemical conversion treatment liquid. Among these, the phosphoric acid and the phosphate are preferably used in amounts at which they do not affect the main reaction of the chemical conversion treatment (are not formed as the chemical conversion treatment film 4). The chemical conversion treatment liquid may further contain vanadium or sodium gluconate. Specifically, the chemical conversion treatment liquid may contain, for example, as a principal component, a substance prepared by adding the above described fluoride of Zr and hydrofluoric acid to water used as a solvent. In the present disclosure, pH refers to hydrogen ion exponent.
The chemical conversion treatment liquid may contain ions of one or more elements selected from Mg, Al, Si, P, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Sr, Sn, Y, La, rare earth elements (except Y and La), and the like. The total content thereof may be, for example, by mass, more than 0 ppm and 10000 ppm or less, is further preferably 5000 ppm or less, and is particularly preferably 200 ppm or less. The above ions substantially do not change the electric conductivity y (mS/cm), pH, and treatment temperature of the chemical conversion treatment liquid.
The electric conductivity y (mS/cm) of the chemical conversion treatment liquid may be selected appropriately in accordance with the composition of the Mg alloy member 2 and the material constituting the joint member. At least one of the relation formulae (a) and (b) below is satisfied, where x1 (Ω) is the charge transfer resistance of the Mg alloy member 2, and x2 (mass %) is the aluminum content in the Mg alloy member 2. Note that, the electric conductivity y of the chemical conversion treatment liquid is an approximate value obtained by rounding the calculated value to the first decimal place. When at least one of the relation formulae (a) and (b) below is satisfied, the chemical conversion treatment film 4 can be formed on the surfaces of the Mg alloy member 2 composed principally of Mg, which is a metal more base than Al relative to Fe, and the partner member 3 as a single piece with covering the boundary between the members 2 and 3 while the members 2 and 3 are connected to each other. This is because the rate of precipitation of the components of the chemical conversion treatment film 4 is not excessively high (e.g., 1.2 mg/m2·s or less) and, accordingly, the rate of formation of the chemical conversion treatment film 4 is not excessively high. It is needless to say that both formulae (a) and (b) below are preferably satisfied.
y≤0.0007 x1+14.0 (a)
y≤0.054 x2+14.2 (b)
The electric conductivity y of the chemical conversion treatment liquid preferably satisfies 0.1 mS/cm≤y. When the electric conductivity y is 0.1 mS/cm or more, the certain pH and the certain ion concentration adequate for forming the chemical conversion treatment film 4 can be maintained. This enables the above described chemical conversion treatment film to be readily formed without consuming an excessive amount of time. Although the chemical conversion treatment film 4 can be formed by performing the chemical conversion treatment for a long period of time even in the case where the electric conductivity y satisfies y<0.1 mS/cm (e.g., y=about 0.01 mS/cm), it is preferable to satisfy 0.1 mS/cm≤y as described above in consideration of a realistic chemical conversion treatment time.
For example, the electric conductivity y of the chemical conversion treatment liquid is preferably 0.2 mS/cm or more and 12 mS/cm or less, is further preferably 7.0 mS/cm or less, and is particularly preferably 5.0 mS/cm or more and 6.0 mS/cm or less.
The pH of the chemical conversion treatment liquid is preferably 2.0 or more and 7.0 or less. When the pH of the chemical conversion treatment liquid is 2.0 or more, an excessive reaction between the chemical conversion treatment liquid and the Mg alloy member 2 can be suppressed and, consequently, the chemical conversion treatment film 4 can be readily formed. When the pH of the chemical conversion treatment liquid is 7.0 or less, an excessive reaction between the chemical conversion treatment liquid and the partner member 3 can be suppressed and, consequently, the degradation of the stability of the chemical conversion treatment liquid can be suppressed. This can reduce the likelihood of troubles occurring during a continuous operation. The pH of the chemical conversion treatment liquid is further preferably 2.0 or more and 6.0 or less and is particularly preferably 2.5 or more and 4.5 or less.
The temperature of the chemical conversion treatment liquid can be selected appropriately in accordance with the material constituting the partner member 3, the type of the chemical conversion treatment liquid, and the like and is, for example, 5° C. or more and 70° C. or less. When the temperature of the chemical conversion treatment liquid is 5° C. or more, the formation of the chemical conversion treatment film 4 can be readily accelerated and, consequently, the chemical conversion treatment film 4 can be formed without consuming an excessive amount of time. When the temperature of the chemical conversion treatment liquid is 70° C. or less, the temperature is not excessively high and the components of the chemical conversion treatment liquid can readily become stabilized. As a result, a homogeneous chemical conversion treatment film 4 can be readily formed. The temperature of the chemical conversion treatment liquid may be, for example, 10° C. or more and 60° C. or less and, in particular, 30° C. or more and 60° C. or less.
The amount of time during which the chemical conversion treatment is performed is not limited and is preferably 30 minutes or less. In such a case, the amount of treatment time is not excessively large. The above chemical conversion treatment time is preferably 1 minute or more. In such a case, a homogeneous chemical conversion treatment film 4 can be readily formed. The chemical conversion treatment time is further preferably 1 minute or more and 3 minutes or less and is particularly preferably about 2 minutes.
The method for a chemical conversion treatment of the metal connection member can further include a coating step. In the coating step, a coating film is formed on the surface of the chemical conversion treatment film 4. The formation of the coating film can be done by electrodeposition coating or the like.
The method for a chemical conversion treatment of the metal connection member according to the embodiment can be used as a chemical conversion treatment method in which a chemical conversion treatment film is formed on the surfaces of the Mg alloy member and the partner member connected to each other.
The method for a chemical conversion treatment of the metal connection member according to the embodiment enables the chemical conversion treatment film 4 to be formed on the surfaces of the Mg alloy member 2 and the partner member 3 as a single piece with covering the boundary between the members 2 and 3 while the members 2 and 3 are connected to each other.
Metal connection members including the Mg alloy member and the partner member connected to each other were subjected to a chemical conversion treatment and a coating treatment. The state of formation of a chemical conversion treatment film on the surfaces of the two members was evaluated.
(Sample Nos. 1-1 to 1-34)
Each of the metal connection members prepared in Sample Nos. 1-1 to 1-34 included a rectangular sheet composed of a specific one of the alloys described in Table 1, which served as the Mg alloy member, and a rectangular SPCC (cold rolled steel sheet) conforming to “Cold reduced carbon steel sheet and strip, JIS G 3141 (2017)”, which served as the partner member, the two members being connected to each other. The size of the Mg alloy member and the partner member used for measuring the galvanic current was 10 mm×40 mm×1.0 mm thick. The Mg alloy member and the partner member were connected to a zero shunt ammeter (HM 103A produced by HOKUTO DENKO CORPORATION) with a copper wire in order to simulate a state electrically equivalent to the state in which the Mg alloy member and the partner member are directly connected to each other. The size of the Mg alloy member and the partner member used for evaluating the state of formation of the chemical conversion treatment film was 30 mm×100 mm×1.0 mm thick. The two members were connected to each other by superimposing the members on each other such that the members partially overlap each other and then clamping the members with bolts and nuts. The holes into which the bolts were inserted were formed in the portions of the two members which overlap each other. The size of the Mg alloy member and the partner member was set such that the surface area ratio of Mg alloy member Entirety was a corresponding one of the values described in Tables 2 to 7. The metal connection members of Sample Nos. 1-1 to 1-34 were not pickled prior to the chemical conversion treatment.
(Sample Nos. 2-1 to 2-18)
Each of the metal connection members prepared in Sample Nos. 2-1 to 2-18 included a rectangular sheet composed of a specific one of the alloys described in Table 1, which served as the Mg alloy member, and a rectangular 5000 series Al alloy A5052, which served as the partner member, the two members being connected to each other. The size of the Mg alloy member and the partner member used for measuring the galvanic current was the same as in Sample No. 1-1, etc. The size of the Mg alloy member and the partner member used for evaluating the state of formation of the chemical conversion treatment film was 60 mm×100 mm×1.0 mm thick. The two members were connected to each other in the same manner as in Sample No. 1-1, etc. The size of the Mg alloy member and the partner member was set such that the surface area ratio of Mg alloy member Entirety was a corresponding one of the values described in Table 8. The metal connection members of Sample Nos. 2-1 to 1-18 were not pickled prior to the chemical conversion treatment.
The metal connection members were subjected to a chemical conversion treatment. In the chemical conversion treatment, three types of chemical conversion treatment liquids A to C were used. The chemical conversion treatment liquids A to C were prepared by adding nitric acid and ammonia to a chemical conversion treatment liquid containing Zr (Grander AL80 produced by MILLION CHEMICALS CO., LTD.). The chemical conversion treatment liquids A to C contain, in addition to a Mg ion, Fe and Al ions in different combinations as described below. The contents of the Fe and Al ions were adjusted to be trace such that electric conductivity and pH were not changed. Specifically, the contents of the Fe and Al ions were adjusted to be about 100 ppm by mass. The above adjustment was made by immersing the SPCC or the A5052 in the chemical conversion treatment liquids before the samples were immersed in the chemical conversion treatment liquids. The electric conductivity and pH of each of the chemical conversion treatment liquids were set to the values described in Tables 2 to 8 by adjusting the amounts of nitric acid and ammonia added. Electric conductivity and pH were determined using a commercial multi function water quality meter (MM 60R produced by DKK TOA CORPORATION).
Chemical conversion treatment liquid A: contains Fe ion (102 ppm) and Mg ion
Chemical conversion treatment liquid B: contains Al ion (108 ppm) and Mg ion
Chemical conversion treatment liquid C: contains Fe ion (107 ppm), Al ion (99 ppm), and Mg ion
The Mg alloy member and the partner member connected to each other were immersed in a specific one of the chemical conversion treatment liquids A to C in a collective manner. The temperature and treatment time of the chemical conversion treatment liquid were set as described in Tables 2 to 8. Subsequently, the amount of Zr precipitated (mg/m2) and the galvanic current (mA) were measured. Tables 2 to 8 summarize the results. Tables 2 and 3 summarize the results obtained when the metal connection members of Sample Nos. 1-1 to 1-34 were immersed in the chemical conversion treatment liquid A. Tables 4 and 5 summarize the results obtained when the metal connection members of Sample Nos. 1-1 to 1-34 were immersed in the chemical conversion treatment liquid B. Tables 6 and 7 summarize the results obtained when the metal connection members of Sample Nos. 1-1 to 1-34 were immersed in the chemical conversion treatment liquid C. Table 8 summarizes the results obtained when the metal connection members of Sample Nos. 2-1 to 2-18 were immersed in the chemical conversion treatment liquid C. Galvanic current was measured using the above zero shunt ammeter. The amount of Zr precipitated was determined from the galvanic current on the basis of the Faraday's second law.
The chemical conversion treatment film of each of the samples was overcoated with ARMOR TOP AT20 produced by Musashi Paint Holdings Co., Ltd.
The appearance of each of the samples was visually inspected. The appearance of the sample was evaluated as Good when the surface of the sample was smooth. The appearance of the sample was evaluated as Bad when irregularities or air bubbles were confirmed. Tables 2 to 8 summarize the results.
The corrosion resistance of each of the samples was evaluated. This evaluation was conducted conforming to “Methods of salt spray testing, JIS Z 2371(2000)” and “JIS K5600 5 6:1999 (Testing methods for paints Mechanical property of film Adhesion test (Cross cut test)”. Specifically, for each of the samples, the coating films and the chemical conversion treatment films formed on the Mg alloy member and the partner member were cross cut, and the resulting samples were subjected to a salt spray test under the following test conditions. In the salt spray test, a salt spray test instrument (STP 90V produced by Suga Test Instruments Co., Ltd.) was used. After the test, the swelling and peeling of the coating film was observed on the surface of the Mg alloy member and on the surface of the partner member. Corrosion resistance was evaluated as Good when the maximum width of swelling or peeling of the coating film observed on the surfaces of the Mg alloy member and the partner member was 2.0 mm or less. Corrosion resistance was evaluated as Bad when the above maximum width was more than 2.0 mm. Tables 2 to 8 summarize the results.
Saltwater concentration: 5%
Testing temperature: 35° C.
Testing time: 960 h
The secondary adhesion of each of the samples was evaluated after the salt spray test. This evaluation was conducted by a cross cut test. In this test, notches that reached the Mg alloy member or the partner member were formed in the coating films and the chemical conversion treatment films disposed on the Mg alloy member and the partner member at intervals of 1 mm in the vertical and horizontal directions to create a 10×10 grid pattern. An adhesive tape was stuck onto the grid pattern and then removed in order to evaluate the adhesion of the coating film. Whether or not detachment (peeling) occurred in the cells of the grid was visually inspected and the number of cells in which peeling occurred was counted. The adhesion of the coating film was evaluated as Good when detachment did not occur in any of the cells (100 cells+100 cells). The adhesion of the coating film was evaluated as Bad when detachment occurred even in only one cell. Tables 2 to 8 summarize the results.
The surfaces of the Mg alloy member and the partner member included in each of the samples were observed with a field emission scanning electron microscope (FE-SEM). On the basis of the galvanic current, the amount of Zr precipitated, and the results of the observation, it was confirmed that, in the metal connection members of Sample Nos. 1-2 to 1-8, 1-11 to 1-14, 1-16, 1-17, 1-19 to 1-21, 1-23 to 1-25, 1-27 to 1-29, and 1-31 to 1-33, a chemical conversion treatment film was formed on the surfaces of the Mg alloy member and the partner member as a single piece with covering the boundary between the two members. It was also confirmed that, in the metal connection members of Sample Nos. 2-1 to 2-18, a chemical conversion treatment film was formed on the surfaces of the Mg alloy member and the partner member as a single piece with covering the boundary between the two members. In contrast, in the metal connection members of Sample Nos. 1-1, 1-9, 1-10, 1-15, 1-18, 1-22, 1-26, 1-30, and 1-34, a chemical conversion treatment film was not formed on the surfaces of the Mg alloy member and the partner member as a single piece with covering the boundary between the two members.
In particular, in Sample Nos. 1-5, 1-6, 1-12, 1-16, 1-20, 1-24, 2-3 to 2-5, 2-8, 2-11, 2-14, and 2-17, where the amount of Zr precipitated was 10 mg/m2 or more and 100 mg/m2 or less and the galvanic current was 200 mA or less, appearance after the coating step was evaluated as good.
The linear approximation formulae determined from the graphs illustrated in
In particular, it was also found that, when the electric conductivity y is 5.0 mS/cm or more and 6.0 mS/cm or less, the surface of the coating has good appearance. It was also found that a chemical conversion treatment film can be formed on the surfaces of the Mg alloy member and the partner member as a single piece with covering the boundary between the two members while the two members are connected to each other when the pH of the chemical conversion treatment liquid is 2 or more and 6 or less and, in particular, when the pH of the chemical conversion treatment liquid is 2.5 or more and 4.5 or less, the surface of the coating material has good appearance.
It is intended that the scope of the present invention is not limited by the above examples, is defined by the claims, and includes equivalents of the claims and all modifications within the scope of the claims.
1 METAL CONNECTION MEMBER
2 Mg ALLOY MEMBER
3 PARTNER MEMBER
4 CHEMICAL CONVERSION TREATMENT FILM
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-154826 | Aug 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/023785 | 6/22/2018 | WO | 00 |
