JP7419983B2 - Mold surface treatment method - Google Patents

Description

The present invention relates to a surface treatment method for a mold for producing aluminum die-cast members.

BACKGROUND ART Conventionally, as described in Patent Document 1, for example, a mold apparatus has been known that is used in a die casting method for producing a member of a desired shape by supplying molten metal to a mold and pressurizing it.

In the mold device described in Patent Document 1, the surface layer portion, which is the surface forming the cavity of the mold, contains 20% by weight or more of chromium as a countermeasure against aluminum welding and corrosion damage to the mold. This makes it possible to form a dichromium trioxide film on the cavity side surface of the surface layer portion. The dichromium trioxide film is a dense passive film that is non-wetting to molten aluminum and has corrosion resistance. This was said to be able to prevent welding of the base of the mold and the molten aluminum when the cavity is filled with the molten aluminum.

Japanese Patent Application Publication No. 2019-147179

However, in the mold device described in Patent Document 1, the outermost layer on the cavity side is a mixed layer of chromium oxide and iron oxide, and since the chromium concentration is not high, it is not a chromium oxide film with good aluminum resistance, but an aluminum oxide film. The ability to prevent welding was insufficient. Other mold surface treatments include nitriding and multilayer coating with heat-resistant ceramic layers, but none of these treatments were sufficient to suppress aluminum welding.

The present invention was created in view of these points, and its purpose is to improve the mold surface by suppressing welding of molten aluminum and suppressing mold breakage, thereby improving the mold life. The purpose is to provide a processing method.

The mold surface treatment method of the present invention is a method of performing surface treatment on the surface forming the cavity (100) of a mold (10) used for manufacturing aluminum die-casting members, and is based on a predetermined test evaluation. Crack-free is defined as a state in which there are no cracks on the surface in terms of appearance, and includes a chrome plating step (S3) and a heating step (S4).

In the chromium plating step (S3), a chromium plating layer (113) is formed on the base (111) made of iron.
In the heating step (S4), after the chromium plating step, by heating in the air atmosphere, a dichromium trioxide layer (115) is formed on the cavity side of the chromium plating layer, and a base layer is formed on the interface between the base and the chromium plating layer. A side diffusion layer (112) is formed, and an oxidized side diffusion layer (114) is formed at the interface between the chromium plating layer and the dichromium trioxide layer.
The crack-free chrome plating layer has a thickness of 10 μm or more and 30 μm or less.
In the heating step, the heating temperature is 600° C., and the heating time is 1 hour or more and 10 hours or less in an air atmosphere.

According to this configuration, the base side diffusion layer and the oxidation side diffusion layer are formed by performing the heating step. That is, the heating step forms a base-side diffusion layer and increases the adhesion between the base and the chromium plating layer .

FIG. 1 is a schematic diagram of a mold device according to a first embodiment. 2 is an enlarged view of part II in FIG. 1. FIG. It is a figure which shows the process in the surface treatment method of a metal mold|die in a flowchart. It is a figure for explaining processing conditions in a heating process. It is a figure which shows the component composition change by a heating process in a sample, (a) shows the sample before heating, (b) shows the sample after heating. FIG. 3 is a diagram showing the relationship between the thickness of a crack-free chromium plating layer and the occurrence of cracks.

Embodiments of the present invention will be described below based on the drawings.
<First embodiment>
[Configuration of mold device 1]

The mold apparatus 1 and the surface treatment method for a mold according to the first embodiment will be explained based on the figures in FIGS. 1 to 6. The mold device 1 is used to die-cast an aluminum die-cast member made of aluminum. The mold apparatus 1 includes a mold 10 and a molten metal supply section 20, as shown in FIG.

The mold 10 has a movable mold 11 and a fixed mold 12. The mold 10 includes a movable mold 11 and a fixed mold 12 to form a cavity 100 that can be filled with molten aluminum.

The movable mold 11 is made of metal, for example, steel. The movable mold 11 is provided so as to be movable relative to the fixed mold 12 as shown by an outline arrow F0. As shown in FIG. 1, the movable mold 11 has a first space 110 having an opening on the fixed mold 12 side. The first space 110 becomes a part of the cavity 100.

The stationary mold 12 is made of metal, for example steel. The fixed mold 12 is fixed immovably, and has a second space 120 having an opening on the movable mold 11 side and a communication hole 121, as shown in FIG. The second space 120 becomes a part of the cavity 100. That is, the cavity 100 includes a first space 110 and a second space 120. The communication hole 121 communicates the second space 120 with the outside of the fixed mold 12 .

The molten metal supply section 20 is configured to be able to supply molten aluminum to the cavity 100 that the mold 10 has. The molten metal supply unit 20 supplies molten aluminum to the second space 120 through the communication hole 121 of the fixed mold 12 .

FIG. 2 shows an enlarged view of the surface layer of the movable mold 11 on the side that comes into contact with the molten aluminum. The lower side of FIG. 2 is the deep side, and the upper side is the surface side. As shown in FIG. 2, the surface layer of the movable mold 11 includes, in order from the deep part, a base 111, a base-side diffusion layer 112, a crack-free chrome plating layer 113 (hereinafter also simply referred to as a "chromium plating layer"), and an oxidation side diffusion layer. It has a layer 114 and a dichromium trioxide layer (hereinafter referred to as "Cr ₂ O ₃ ") 115. The base 111 and each layer 112, 113, 114, 115 are integrally formed.

The base 111 is a part that forms the skeleton of the movable mold 11. The base 111 is provided at a relatively distant position from the first space 110, as shown in FIG. In this embodiment, the base 111 is made of iron with a carbon concentration of 0.07% by weight or less.

The crack-free chrome plating layer 113 is provided on the cavity 100 side of the base 111, and is a crack-free chrome plating layer formed by a chrome plating process to be described later. In FIG. 2, the chromium plating layer 113 is a portion shown from broken line CL1 to broken line CL2. The chromium plating layer 113 has a thickness T1 of 10 μm or more and 30 μm or less, and is formed so that the internal stress with the compression side being negative is 800 MPa or less. Note that, in FIG. 2, the formation of each layer is schematically illustrated so that it is easy to understand, and the scale is changed.

The Cr ₂ O ₃ layer 115 is formed closest to the first space 110 in the surface layer portion. The Cr ₂ O ₃ layer 115 has a heat resistance temperature of 1350° C., which is higher than the aluminum casting temperature of 680° C., and is characterized by having no defects. In FIG. 2, the Cr ₂ O ₃ layer is a portion shown from broken line CL2 to solid line L5. A solid line L5 is an interface between the surface layer portion and the first space 110. In this embodiment, the Cr ₂ O ₃ layer 115 is formed to have a thickness T2 of 50 nm or more. The metal component of the Cr ₂ O ₃ layer is 100% chromium. Note that metal components such as carbon and other unintended impurities are excluded.

The base side diffusion layer 112 is a diffusion layer of iron and chromium, and is formed at the interface between the base 111 and the chromium plating layer 113. The base side diffusion layer 112 is a portion shown from the two-dot chain line L1 to the two-dot chain line L2 in FIG. Formation of the base-side diffusion layer 112 increases the adhesion between the base 111 and the chromium plating layer 113. In addition, the approximate intermediate position between the two-dot chain line L1 and the two-dot chain line L2 coincides with the broken line CL1. The deep side of the base side diffusion layer 112 overlaps with a part of the surface side of the base part 111, and the cavity 100 side of the base side diffusion layer 112 overlaps with a part of the deep side of the chrome plating layer 113.

The oxidation side diffusion layer 114 is a diffusion layer in which oxygen is diffused into the chromium plating layer 113, and is formed at the interface between the Cr ₂ O ₃ layer and the chromium plating layer 113. The oxidation-side diffusion layer 114 is a portion shown from a two-dot chain line L3 to a two-dot chain line L4 in FIG. 2, and its thickness T3 is approximately 10 nm. The oxygen concentration in the Cr ₂ O ₃ layer gradually decreases in the depth direction. Note that the approximate midpoint between the two-dot chain line L3 and the two-dot chain line L4 coincides with the broken line CL2. The deep side of the oxidation side diffusion layer 114 overlaps with a part of the surface side of the chromium plating layer 113.

The surface layer part of the fixed mold 12 has the same structure as the movable mold 11, and includes a base 111, a base side diffusion layer 112, a crack-free chromium plating layer 113, an oxidation side diffusion layer 114, and a Cr ₂ O ₃ layer. 115. The base 111 and each layer 112, 113, 114, 115 of the fixed mold 12 have the same configuration and characteristics as the base 111 and each layer 112, 113, 114, 115 of the movable mold 11, so a description thereof will be omitted. .

[Surface treatment method for mold 10]
Next, a method for surface treatment of the mold 10 will be explained. As shown in FIG. 3, the surface treatment method of this embodiment mainly includes a degreasing step S1, an etching step S2, a chrome plating step S3, and a heating step S4.

In the degreasing step S1, acid-alkali cleaning is performed before plating. After removing dirt such as oil and fat on the surface of the base portion 111 with an alkali or the like, oxides on the surface are removed with hydrochloric acid at room temperature. Next, in the etching step S2, the surface is etched by reverse electrolytic treatment. The mold 10 to be plated is connected to + and the electrode is connected to -, and a direct current of about 30 A/dm ² is applied to further clean the surface.

After passing through the degreasing step S1 and the etching step S2, in the chromium plating step S3, a so-called crack-free chromium plating treatment is performed in which stress is controlled to prevent cracks from occurring. The mold 10 is connected to - and the electrode is connected to +, and in this embodiment, a direct current of approximately 30 A/dm ² is passed for several tens of minutes to grow plating on the surface of the mold 10. The plating solution composition includes, for example, 400 g/L of chromic anhydride, 4 g/L of sulfuric acid, and small amounts of other additives. After that, wash off the chemicals on the surface with tap water, and then dry it with air.

After the chromium plating step S3, a heating step S4 is performed. In the heating step S4 of this embodiment, the heating temperature is 600° C. and the heating time is 10 hours in an air atmosphere. Although the heat treatment conditions can be changed as appropriate, the minimum conditions are that the heating temperature is 400° C. or more and 600° C. or less, and the heating time is 1 hour or more. As shown in FIG. 4, if the heat treatment conditions are lower than 400°C, the formation of the Cr ₂ O ₃ layer 115 will be insufficient, and if the heat treatment conditions are higher than 600°C, the base material will soften due to tempering.

By performing the heating step S4, a Cr ₂ O ₃ layer 115 is formed on the outermost surface of the mold 10. FIG. 5 is a diagram showing a change in the composition of a sample due to heat treatment after chromium plating. As shown in FIGS. 5(a) and 5(b), the outermost surface after the heat treatment has a decreased secondary ion strength of chromium and an increased oxygen concentration compared to before the heat treatment. This means that a Cr ₂ O ₃ layer was formed on the outermost surface. By performing the heat treatment under the conditions of this embodiment, a Cr ₂ O ₃ layer having a thickness of approximately 50 μm is formed.

Further, by performing this heating step S4, the base side diffusion layer 112 and the oxidation side diffusion layer 114 are formed. That is, the heating step S4 forms the base-side diffusion layer 112 and increases the adhesion between the base 111 and the chromium plating layer 113.

Next, the operation of the mold device 1 will be explained. First, the movable mold 11 and the fixed mold 12 are combined to form the cavity 100. Molten aluminum is supplied from a molten metal supply section 20 to a mold 10 in which a cavity 100 is formed. The molten aluminum supplied by the molten metal supply section 20 is press-fitted into the cavity 100 and filled into the cavity 100 . The movable mold 11 and the fixed mold 12 are in contact with the molten aluminum through the Cr ₂ O ₃ layer 115 . The molten aluminum filled in the cavity 100 solidifies to form a member. Once the member is molded, the movable mold 11 and the fixed mold 12 are separated by moving the movable mold 11, and the molded member is taken out from the mold 10.

[effect]
(1) In the mold apparatus 1 of the above embodiment, the surface layer of the mold 10 on the side of the cavity 100 includes, in order from the deep part, the base 111, the base side diffusion layer 112, the crack-free chromium plating layer 113, and the oxidation side diffusion layer 114. And a Cr ₂ O ₃ layer 115 is integrally formed. The Cr ₂ O ₃ layer 115, which is located on the crack-free chromium plating layer 113 and is formed by heat treatment after the chromium plating process, has a high chromium concentration with a metal component of 100% chromium. Further, the thickness of the Cr ₂ O ₃ layer 115 is 50 nm or more, which is a sufficient thickness.

That is, the Cr ₂ O ₃ layer 115 of this embodiment has very good aluminum resistance, and when molten aluminum is supplied to the mold 10 , the Cr ₂ O ₃ layer 115 prevents the molten aluminum from being welded to the mold 10 . is effectively suppressed, and the life of the mold device 1 can be improved.

(2) In addition, the mold 10 of the above embodiment has a base side diffusion layer 112 and an oxidation side diffusion layer 114 formed in the heating step S4 after the chromium plating step S3, and the mold 10 of the above embodiment has high adhesion between each layer. , damage to the mold 10 can be suppressed and the durability of the mold 10 can be improved.

(3) The crack-free chromium plating layer 113 of the above embodiment has a thickness T1 of 10 μm or more and 30 μm or less. If the chrome plating layer is too thin, its lifespan will be short; if it is too thick, it will crack. FIG. 6 is a diagram schematically showing the film thickness on the horizontal axis and the state of crack occurrence on the vertical axis. As shown in FIG. 6, no cracks were observed when the film thickness was 30 μm or less. At a film thickness of 35 μm, cracks were sometimes observed and sometimes not depending on the part of the sample observed. When the film thickness was 40 μm or more, cracks were found in most places when observed. That is, a good thickness without cracks is 30 μm or less. In this embodiment, the crack-free chromium plating layer 113 is free from cracks and has a long life.

(4) In the heating step S4 of the above embodiment, the heating temperature is 600° C. and the heating time is 10 hours in an air atmosphere. Under these conditions, it is possible to form a Cr ₂ O ₃ layer with an appropriate thickness of approximately 50 μm. Since the Cr ₂ O ₃ layer 115 has a sufficient thickness of about 50 μm, the Cr ₂ O ₃ layer 115 is not easily peeled off during repeated molding and can exhibit durability.

<Other embodiments>
In the above embodiment, the crack-free chromium plating layer 113 has a thickness T1 of 10 μm or more and 30 μm or less, and an internal stress of 800 MPa or less, but the thickness and internal stress are not limited thereto.

In the embodiment described above, the thickness T2 of the Cr ₂ O ₃ layer 115 is 50 μm or more, but the thickness is not limited to this.

In the above embodiment, the heating temperature was 600° C. and the heating time was 10 hours in the air atmosphere, but other conditions may be used as long as a good Cr ₂ O ₃ layer 115 and each diffusion layer 112, 114 are formed. . In general, it is sufficient that the heating temperature is 400° C. to 600° C. and the heating time is 1 hour or more in an air atmosphere.

The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention.

1... Mold device 10... Mold 20... Molten metal supply section 100... Cavity 111... Base 112... Base side diffusion layer 113... Crack-free chrome plating layer 114... - Oxidation side diffusion layer 115 ... dichromium trioxide layer

Claims (1)

A mold surface treatment method that performs surface treatment on the surface forming a cavity (100) of a mold (10) used for manufacturing an aluminum die-cast member, and the surface treatment method involves performing a surface treatment on the surface forming a cavity (100) of a mold (10) used for manufacturing an aluminum die-casting member. If we define crack-free as the state without
a chromium plating step (S3) of forming a crack-free chrome plating layer (113) on a base (111) made of iron;
After the chromium plating step, by heating in the air atmosphere, a dichromium trioxide layer (115) is formed on the cavity side of the crack-free chromium plating layer, and the interface between the base and the crack-free chromium plating layer is formed. a heating step (S4) of forming a base side diffusion layer (112) on the substrate, and forming an oxidation side diffusion layer (114) on the interface between the crack-free chromium plating layer and the dichromium trioxide layer;
including;
The crack-free chrome plating layer has a thickness of 10 μm or more and 30 μm or less,
In the heating step, the heating temperature is 600° C., and the heating time is 1 hour or more and 10 hours or less in an air atmosphere .

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