JPH086159B2 - Heat treatment method for aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present method is widely used for automobile parts, marine prime mover parts and their safety parts, for example, pressurization such as die casting and molten metal casting (high pressure casting). The present invention relates to a heat treatment method for an aluminum alloy after being formed by a casting method.

[Prior Art] Aluminum alloys can be roughly classified into wrought alloys and casting alloys. However, according to the characteristics of aluminum alloys, non-heat treatment type alloys and heat treatment type alloys can be roughly divided. it can. Heat-treatable alloys are age-hardenable alloys that are heated to a temperature above the solid solubility limit and then rapidly cooled to bring the homogeneous state to room temperature, that is, after quenching, let them stand for normal temperature at room temperature. And then hardened by natural aging (T4 treatment)
In addition, there are those that obtain high strength by tempering at a suitable temperature of 100 to 200 ° C for a suitable time (T6 treatment).

Then, in order to obtain high strength and toughness of the alloy in the production of cast aluminum alloy, it is required to subject the cast product after the solution treatment to a solution treatment, then perform quenching, and then carry out artificial aging. Exactly the same, for castings obtained by the pressure casting method, solution heat treatment at a temperature of 500 to 550 ° C for several hours, artificial aging treatment at a temperature of 100 to 200 ° C for several hours,
Each was needed.

[Problems to be Solved by the Invention] A general heat treatment method for a casting made of a pressure cast aluminum alloy is as follows:
After holding it in an air circulation type heating furnace at a temperature of ~ 550 ° C for 3 ~ 6 hours, quench it in cold water or warm water, and then leave it at room temperature for an appropriate time, and again in an air circulation type heating furnace to 100 ~ 200 ° C.
After maintaining at the temperature of 2 to 8 hours, it is air-cooled (hereinafter referred to as a conventional method).

In such a conventional heat treatment method, if the temperature rise time and the like are added to the net treatment time, the total heat treatment step requires at least 20 hours, and in the long case, 40 hours. It was not preferable in terms of heat economy.

[Means for Solving Problems] In order to solve the above problems, according to the present invention, a molded product taken out of the mold does not cool down to 300 ° C. after the molten aluminum alloy is pressure-cast into the mold. At 400-550
After immersing in the melt at ℃ for about 5 to 30 minutes,
It has been found that a heat treatment method of immersing in cold water or warm water and quenching (hereinafter referred to as rapid solution heat treatment method) is beneficial.

And, after the treatment of this rapid solution treatment method, the molded article that has been subjected to the usual artificial aging treatment can secure a quality that is sufficiently comparable to the mechanical properties of the casting obtained by the conventional heat treatment method.
The processing time is short.

[Operation] The reason why the rapid solution treatment method of the present invention is that the time required for the heat treatment step for an aluminum alloy molded product is extremely short, and the quality is equivalent to or higher than that of the conventional product. Since the molded product obtained by the pressure casting method is of high quality, it has significantly less casting defects than the conventional gravity casting method and low pressure casting method, and its solidification structure is fine, so it is necessary for solution treatment. It is considered that the time can be significantly shortened.

Moreover, the reason why the solution temperature range is 400 to 550 ° C.
The average solution temperature of Al-Mg and Al-Mg-Zn alloys is 42
The temperature is 0 to 430 ° C., and the temperature of the Al--Si--Mg alloy is 52
Since the temperature was 0 to 540 ° C, the temperature range for solution treatment was set to 400 to 550 ° C from those temperature ranges.

When solution treatment is carried out in a melt such as a salt bath, the heat capacity of the melt is large, which facilitates rapid heating of the molded product, and the temperature before liquefaction is always 300 ° C.
The above is also what makes rapid heating of the molded product easy and smooth.

[Example] Aluminum alloy casting (JIS standard AC4CH, chemical composition Si7.
05%, Mg0.30%, Ti0.15%, Fe0.11%)
After pressure casting in a cup-shaped mold of 10 mm, outer diameter of about 100 mm, and height of 120 mm at an injection pressure of 1000 Kg / cm ² , the rapid solution treatment of the present invention (using a salt bath) is applied, The mechanical properties of the cast product that has been tempered at an appropriate temperature and the cast product that has been subjected to the conventional heat treatment method are investigated, and the results are shown in FIG. 1 (a),
It is shown in (b).

FIG. 1 (a) shows a comparison between the method according to the invention and the conventional method in terms of tensile strength and yield point, FIG. 1 (b).
Shows a comparison between the two regarding elongation. As is clear from this graph, there is a large difference in strength due to the difference in the heat treatment method, and in the heat treatment method according to the present invention, the solution treatment time is 5
Despite the extremely short time of ~ 30 minutes, the tensile strength is 30
Kg / mm ^2, yield point can hold about 22 Kg / mm ^2. On the other hand, in the conventional method, solutionizing for about 2 hours is required to reach the same strength as those. Therefore, when the rapid solution treatment method according to the present invention is applied, the treatment time can be greatly shortened, and mechanical properties comparable to those of the conventional method can be obtained by solution treatment for about 5 minutes.

Next, in the same manner, the injection pressure of 1000 Kg / c was applied to the cup-shaped mold.
After pressure casting at m ² , after the rapid solution treatment of the present invention, it is left at room temperature to be hardened by natural aging, so-called T4
2 (a) and 2 (b) show the results of examining the mechanical properties of the treated casting and the conventional heat treatment casting.

FIG. 2 (a) shows a comparison regarding tensile strength and yield point, and FIG. 2 (b) shows a comparison regarding elongation. From FIGS. 2 (a) and 2 (b), there is almost no difference in the strength due to the difference in the heat treatment method, and the strengths are almost the same, but the difference in elongation is clear, and the method according to the present invention is different from the conventional method. However, it is clear that the elongation can be greatly improved by the solution treatment in a much shorter time.

Figures 3 (a) and 3 (b) show the casting temperature and T6 immediately before solution heat treatment.
After treatment, it shows the correlation of tensile strength, yield point and elongation, and as is clear from this graph, the rapid solution treatment method of the present invention performs solution treatment on the casting after pressure casting. At this time, the reason why the temperature of the casting immediately before was set not to fall below 300 ° C was that all mechanical properties were affected by the casting temperature immediately before solution treatment, and to keep the tensile temperature and yield point high.
This is based on the fact that 300 ° C or higher and 200 ° C or higher are required for elongation.

The heat treatment conditions are shown in FIG.
0 ° C., artificial aging 170 ° C. × 2 Hr, solution temperature 520 ° C. in FIG. 2, then natural aging, solution temperature 520 ° C. × 5 min water cooling, artificial aging 170 ° C. × 2 Hr in FIG.

From the above results, the casting temperature immediately before solution heat treatment in the present invention was determined to be 300 ° C or higher.

The above are examples of aluminum alloy castings (JIS standard AC4CH), but aluminum alloy castings (JIS standard AC7B, chemical composition Si 0.3% or less, Mg9.5-11.0%, Fe0.4
%, The solution temperature was 430 ° C.), and good results were obtained almost in the same manner as above.

[Effects of the Invention] The castings that have been subjected to normal artificial aging after rapid solution treatment according to the present invention have mechanical properties sufficiently comparable to those of castings obtained by conventional methods.

In addition, if only the rapid solution treatment is applied and the subsequent artificial aging is omitted, the toughness is greatly improved, but the strength cannot be expected to increase. However, since the pressure casting has a certain strength even in the as-cast state, it can withstand sufficient use depending on the application, and the processing time is further shortened.

From the above, according to the present invention, the heat treatment time after pressure casting of the aluminum alloy can be greatly shortened, and thus it is possible to greatly improve the productivity and the thermoeconomical efficiency as compared with the conventional case.

Further, according to the rapid solution treatment of the present invention, the pressing time is extremely short, so that the deformation and strain due to the heat treatment are remarkably small, and blisters are unlikely to occur.

It should be noted that the method of maintaining the temperature in the heating furnace is simpler than the method of immersing the molten solution in the molten solution using a salt bath furnace, without restrictions on pollution control when installing the furnace.

[Brief description of drawings]

1 (a), (b) and 2 (a), (b),
FIG. 1 (a) and FIG. 2 (a) are diagrams showing the relationship between solution treatment time and mechanical properties of different aluminum alloy castings in the salt bath furnace method of the present invention and in the conventional method. Regarding tensile strength and yield point, Fig. 1 (b)
2 and FIG. 2 (b) show those relating to elongation. FIGS. 3 (a) and 3 (b) are diagrams showing the relationship between the temperature immediately before solution treatment and the mechanical properties after heat treatment of a cast aluminum alloy by the method using the salt bath furnace of the present invention. FIG. 3 (a) shows tensile strength and yield point, and FIG. 3 (b) shows elongation. FIGS. 4 (a) and (b) and FIGS. 5 (a) and (b) show different aluminum alloy castings in the method using the heating furnace of the present invention and the conventional method, respectively.
FIG. 4 is a diagram showing the relationship between solution treatment time and mechanical properties, FIGS. 4 (a) and 5 (a) relating to tensile strength and yield point, and FIGS. 4 (b) and 5 ( b) is related to elongation. FIGS. 6 (a) and 6 (b) are diagrams showing the relationship between the temperature immediately before the solution treatment and the mechanical properties after the heat treatment of the cast aluminum alloy by the method using the heating furnace of the present invention.
FIG. 6 (a) shows tensile strength and yield point, and FIG. 6 (b) shows elongation.

Claims (2)

[Claims] 1. A molded product obtained by press-casting a castable aluminum alloy melt in a mold and then taking it out of the mold is 300 pieces.
After immersing in the melt held at 400-500 ° C for 5-30 minutes before cooling to 400 ° C, or in a heating furnace at 400-550
A method for heat treating an aluminum alloy, which comprises holding at 5 ° C for 5 to 30 minutes and then quenching in water. 2. A molded product taken out of a mold after press-casting a castable aluminum alloy melt in a mold is 300 pieces.
After immersing in the melt held at 400-500 ° C for 5-30 minutes before cooling to 400 ° C, or in a heating furnace at 400-550
A method for heat treating an aluminum alloy, which comprises holding at 5 ° C for 5 to 30 minutes, further quenching in water, and then performing an artificial aging treatment.