JPS599622B2 - Surface hardening method for aluminum alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface hardening aluminum alloys used for pistons and other sliding members.

Conventionally, this type of sliding member is known to be made of aluminum alloy to reduce weight and improve thermal conductivity, but in this case, the surface of the aluminum alloy is Desired to be hardened.

As a hardening method, a method is known in which a hard dissimilar metal such as chromium is plated on the surface of the aluminum alloy to form a coating layer, but chrome has a low cathode current efficiency, so plating takes a long time. Moreover, the waste liquid treatment is dangerous and requires a large amount of equipment. It is also possible to use iron or its alloy, which is relatively easy to form, as the coating layer, but in this case, sufficient hardness cannot be obtained unless the coating layer is subjected to surface hardening treatment such as carburizing. In order to increase its strength, the general method is to perform solution treatment beforehand and then form the coating layer, and applying further surface hardening treatment to the coating layer is problematic both in terms of time and economy. Furthermore, if a surface hardening treatment such as carburizing treatment is carried out at a high temperature, even if the surface of the coating layer can be hardened, it is accompanied by the disadvantage of deterioration of the aluminum alloy.

The object of the present invention is to provide a surface hardening method that eliminates such disadvantages, and after forming a coating layer made of iron or its alloy on the surface of a bare metal made of an aluminum alloy, A method for surface hardening an aluminum alloy, comprising performing a nitriding treatment on the coating layer at a solution temperature, and then an aging treatment at an aging temperature of the aluminum alloy.

The drawings show a product obtained according to the present invention, and numeral 1 indicates a base metal made of an aluminum alloy, 2 a coating layer formed on the surface of the base metal made of iron or its alloy, and 3 a nitrided layer on the surface of the coating layer 2.

According to the present invention, first, the surface of the cast aluminum alloy base metal 1 is chemically activated by anodizing, shot blasting, etc., and then iron or its alloy is electroplated, or the surface of the base metal 1 is electroplated with iron or its alloy. A coating layer 2 is formed by thermally spraying iron or its alloy on the surface using plasma or the like, and then this is treated with ammonia gas or cyanide heated to a temperature (for example, 500 to 520°C for JISAC8A material or JISAC8B material) for solution treatment of aluminum alloy. The surface of the coating layer 2 is nitrided in a nitriding atmosphere such as a salt bath.

According to this, unlike carburizing treatment performed at a high treatment temperature of about 1000°C, a hard nitrided layer 3 can be reliably formed on the surface of the coating layer 2 even at a relatively low temperature of about the solution temperature. , and the solution treatment of the base metal 1 can be performed at the same time, and thereafter the aging temperature of the aluminum alloy (for example, JISA
1505-220℃ for C8A material, 1 for JISAC8B material
If the aging treatment is performed at a temperature of 50 to 200° C.), aging hardening of the base metal 1 and removal of strain generated in the coating layer 2 during the nitriding treatment are performed at the same time, and thus a high-quality product can be obtained.

Furthermore, according to the solution treatment of the base metal 1, the components of the coating layer 2 are the base metal 1.
is diffused into the aluminum matrix 1a, and thus the bonding strength between the base metal 1 and the coating layer 2 is also significantly enhanced. In the drawing, 1b is a eutectic crystal precipitated in the aluminum matrix 1a, which is spheroidized due to solution treatment.

As described above, according to the present invention, the coating layer made of iron or its alloy is nitrided at the solution temperature of the aluminum alloy, and the surface of the coating layer can be hardened without causing deterioration of the base metal. In addition, it is also possible to perform solution treatment of the base metal in conjunction with nitriding treatment, which eliminates the need to perform both separately, significantly improving work efficiency, and aging treatment after solution treatment ensures age hardening of the base metal. At the same time, distortions occurring in the coating layer are reliably removed, and the bonding strength between the base metal and the coating layer is also enhanced, resulting in the effect that high-quality products can be obtained at low cost.

Examples will be described below.

Example 1 An iron coating layer with a thickness of 20μ was formed on the surface of a base metal made of aluminum alloy (JISAC8A material), and this was
After being nitrided for 5 hours by immersing it in a molten cyanide salt bath at 0°C, it was quenched in hot water at 85°C and further heated to 180°C.
Aging treatment was performed for 5 hours in an air atmosphere at ℃.

As a result, the hardness of the surface of the coating layer was HV, 3O, and the hardness of the aluminum matrix of the base metal was HRB7O, and it was possible to harden the surface without impairing the mechanical properties of the base metal.

The hardness of the untreated aluminum matrix is HRB
The hardness of the 2Ol coating layer is HV23O.

Example 2 An iron coating layer with a thickness of 0.3 Tm was formed on the surface of the same base metal as in Example 1, and this was nitrided for 20 hours in ammonia gas at 500°C, and then heated at 50°C. After quenching in oil and then aging for 10 hours in an air atmosphere at 200°C, the surface hardness of the coating layer was HV7.
The hardness of the 8Ol aluminum matrix was HRB6O.

Example 3 The same coating layer as in Example 2 was formed on the same base metal as in Example 1, and this was placed in a low-pressure nitrogen gas atmosphere to generate ion discharge to perform ion nitriding treatment for 30 minutes. .

The atmospheric pressure at this time is approximately 2.5 Pa (Pa is 2×10-
2T0rr), and the treatment temperature was 510°C. after that,
When this was subjected to an aging treatment for 10 hours in an air atmosphere at 200°C, the surface hardness of the coating layer was HV. The hardness of the 58Ol aluminum matrix was HRB57. Example 4 0.5 on the surface of aluminum alloy (JISAC8B material)
An iron coating layer with a thickness of Trm is formed, and this is coated with KCNO,
It was immersed in a molten salt containing KCN and Na2CO3 in a ratio of 3:5:2, and heated at 520°C while blowing air.
After being subjected to soft nitriding treatment for an hour, it is quenched in cold water for 20 hours.
After being aged for 10 hours in an air atmosphere at 0°C,
The surface hardness of the coating layer was HV52, and the hardness of the aluminum matrix was HRB72.

[Brief explanation of the drawing]

The drawing is an enlarged cross-sectional view of a product obtained according to the invention. 1... Base metal, 2... Covering layer, 3... Nitriding layer.

Claims (1)

[Claims] 1 After forming a coating layer made of iron or its alloy on the surface of an aluminum alloy base metal, nitriding the coating layer at the solution temperature of the aluminum alloy, and then aging treatment at the aging temperature of the aluminum alloy. A method for surface hardening aluminum alloys, characterized by carrying out the following steps.