JPS63290677A - Production of aluminum alloy casting - Google Patents

Abstract

PURPOSE:To prevent pitting on an aluminum alloy base material by arranging zinc coated layer on surface of a mold forming exposed part to corrosion atmosphere, casting by pouring the molten aluminum alloy into the mold and forming the aluminum-zinc alloy layer. CONSTITUTION:A core for forming cooling water passage as the mold forming the exposing part to the corrosion atmosphere in a cylinder head, forms the coated layer by making solution of silica sand with alcohol after forming by using zircon sand and forming the coated layer by dipping in this solution, to form a core body 1A. Next, Zn powder is made to solution with the alcohol and the core body 1A is dipped and the coated layer 1B of scaly Zn is formed on the circumferential surface. This core 1 is inserted in a cavity in the mold 2 for the cylinder head and the low pressure casting is executed by pouring molten Al alloy from the sprue 2A. Next, after solution heat treatment is executed, the quenching and tempering treatments are executed. By this method, the Al-Zn alloy layer 5 is formed on the surface of the base material 4 for forming cooling water passage 3 and the pitting of the Al alloy base material is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing aluminum alloy castings, and particularly to a manufacturing method suitable for aluminum alloy castings exposed to corrosive environments.

(Prior art and its problems) In recent years, A-type alloy castings have been used for cylinder blocks and cylinder heads in order to make engines lighter 3+E.

However, when Au alloy castings are applied to items with cooling water passages that are exposed to corrosive environments, such as the cylinder head or cylinder block of a water-cooled engine, depending on the cooling water or antifreeze Mll&, the surface of the cooling water passage may be damaged. Corroded.

The form of corrosion is called pitting corrosion, and is the most feared type of corrosion in A1 alloys.

In the neutral region, the surface of A1 alloy generally becomes passivated and has good corrosion resistance, but when the concentration of C1- ions in cooling water or antifreeze is high, localized corrosion occurs due to the presence of dissolved oxygen, which acts as an oxidizing agent. do. This corrosion progresses inward at a high speed, so it becomes a thank-you note and is called pitting corrosion, which occurs in a relatively short period of time.
() This leads to perforation, which causes cooling water leakage.

In order to prevent such pitting corrosion, appropriate surface treatment may be applied to the surface of the cooling water passage, but this is extremely difficult because the cooling water passage generally has a complicated shape. Therefore, countermeasures have been taken so far by restricting the composition of cooling water or antifreeze, but there is a problem that sufficient control cannot be carried out in the market.

(Object 1 of the Invention) In view of the above-mentioned circumstances, the present invention provides an anti-corrosion treatment for the surface of the part exposed to the corrosive environment during casting of A alloy castings exposed to the corrosive environment such as engine parts. The purpose is to provide a method for manufacturing alloy castings.

(Structure of the Invention) Therefore, the method for producing a casting made of A alloy according to the present invention is to provide a coating layer of zinc on the pI type surface that forms the part exposed to a corrosive environment, and assemble it in the mold cavity. It is characterized by pouring molten alloy into a mold and casting, and forming an A-Zn alloy layer on the surface of the part exposed to a corrosive environment.

In the A alloy casting formed in this way, A! ;
The L-Zn alloy layer acts as a sacrificial anode against the base material A-type alloy, providing a so-called cathodic corrosion protection effect.
As the Zn alloy layer is preferentially corroded, the A of the base metal
! Corrosion of Q alloy is suppressed.

(Embodiment of the Invention) The case of a cylinder head will be described below as an embodiment of the unexploded 11J.

First, the core for forming the cooling water passage, which is a mold that forms the part exposed to the corrosive environment, which is a feature of the present invention, is molded into a predetermined shape using zircon sand (1, Owt% resin), and then the particle size is Silica sand weighing less than 50 liters is dissolved in alcohol, immersed in this solution to form a coating layer of approximately 300 gm, and molded into the core body IA in Fig. 1. Next, Zn powder (
The core body IA was immersed in a solution of 20 μLm (particle size: 20 μLm) in alcohol, and a coating layer IB of scaly Zn of about 200 ALm was formed on the circumferential surface of the core body IA to form a core I.

This core l is molded into a cylinder head mold 2 as shown in the second figure.
Assemble into the cavity of A! from sprue 2A! The molten metal of 1 alloy was injected and cast by low pressure casting (all materials JIS
AC4B).

Next, it is quenched after being liquefied at 525°C for 4 hours.
Thereafter, a tempering treatment was performed at 180° C. for 6 hours.

As a result, the forming portion i of the cooling water passage 3 as shown in the third figure.
k) An-Zn alloy layer 5 is formed on the surface of material 4. still,
FIGS. 4(A) to 4(D) show the metal compositions of the cooling water passage forming portions with different magnifications, respectively.

As is clear from this, the Au-Zn alloy layer is about 10
It is formed with a thickness of 0μ, and has good adhesion to the A1 alloy base material.

In this way, Sl! In the cooling water passage forming portion of the cylinder head, the electrode potential is lower than that of the A-patterned alloy in which the A-patterned Zn alloy layer is the base material.

In other words, the electrode potential of A or alloy castings varies slightly depending on the components, but approximately -0.7 to -0,81V (0 as a reference electrode).
．． 1μ or 12Xg electrode), whereas An-Zn
The alloy layer is in the range of -0.85 (pure A!;L) to -1.00 (pure Zn).

For this reason, it acts as a galvanic anode (sacrificial anode) for the base material A1 alloy, and the A1 alloy base material is corroded preferentially against the A1 alloy. It is possible to suppress pitting corrosion of itself.

In addition, since the core surface is covered with scaly Zn during casting,
It is difficult for the A1 alloy molten metal to enter the core, which is effective in preventing the molten metal from being inserted, and also reduces the entrapment of shell sand into the casting. Furthermore, during casting, the latent heat of fusion of Zn promotes the solidification of the molten A-type alloy, making it possible to improve the casting structure of the shell-core contact surface, which is disadvantageous in terms of cooling rate.

Note that in this example, the method was applied to manufacturing a cylinder head, but
A that is not necessarily limited to this, but is also applicable to other corrosive environments.
Needless to say, the present invention can be applied to the production of alloy castings.

(Effects of the Invention) According to the method for manufacturing a casting made of A alloy according to the present invention, AfL- Since the Zn alloy layer is formed, pitting corrosion of the Al alloy material can be reliably suppressed.

Furthermore, the Zn coating layer on the surface of the square mold that forms the TI in the part exposed to the corrosive environment can prevent molten metal from entering the mold during casting. Furthermore, since solidification of the molten metal is promoted by the latent heat of fusion of Zn, the total bending structure of the surface of the portion exposed to the corrosive environment is improved by tB.

[Brief explanation of drawings]

ftl Figure 1 is a sectional view of the core shown in one embodiment of the present invention, Figure 2 is a diagram of the core assembled into the mold, Figure 3 is a sectional view of the cooling water passage, and Figure 4 (A). -(D) are metallographic diagrams of the cooling water passage forming portion with different magnifications. 1... Core IA... Core body 1B...Z
n coating layer 2...mold 3...cooling water passage 4...A pattern alloy base material 5...A
M-Zn alloy layer Fig. 1 Fig. 2 2'A Fig. 3 5 (,)s, 1+117) Related Patent Applicant: Mazda Motor Corporation 4, 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture; Agent: 302-5 Asahi Kudan Mansion, 1-9-5 Kudankita, Chiyoda-ku, Tokyo 102; Date of Amendment Order: 7, 1988 June 28, 6, in the specification subject to amendment, in column 7 of "4 brief explanation of drawings", the contents of the amendment IJ ftE, old handwriting, line 14:

Claims (1)

[Claims] When manufacturing an aluminum alloy casting that is exposed to a corrosive environment, a coating layer of zinc is provided on the surface of the mold that forms the part exposed to the corrosive environment, and it is assembled in the mold cavity,
A method for manufacturing aluminum alloy castings, which comprises pouring molten aluminum alloy into a mold and casting, and forming an aluminum-zinc alloy layer on the surface of the portion exposed to a corrosive environment.