JPH0266140A - Heat treatment for aluminum die-cast product in pressurized atmosphere - Google Patents

Abstract

PURPOSE:To carry out heat treatment without causing blistering defect to the surface of the title aluminum die-cast product and to improve mechanical properties by subjecting an Al die-cast product to heating and quenching under pressurized atmosphere. CONSTITUTION:A pallet 5 on which Al die-cast products A are piled up is placed on a stand 4, and a heating unit 2 is electrified. A pressure device 6 is operated to feed a pressurized gas of the prescribed pressure in a pressure accumulation tank 9 into a furnace body 1. A fan 3 is operated to agitate the heated atmospheric gas, and the die-cast products A are heated under the prescribed pressure for the prescribed length of time. Subsequently, a refrigerant gas for hardening in a pressure accumulation tank 13 is substituted for the above atmosphere, and the above die-cast products A are quenched. By the above heat treatment in the pressurized atmosphere, mechanical properties can be improved by about 50%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a pressurized atmosphere heat treatment method for aluminum die-cast products (hereinafter referred to as die-cast products).

[Conventional technology]

Conventionally, in die-casting products, molten metal is injected into a mold at high speed and high pressure, so gas such as air in the cavity cannot completely replace the molten metal, and gets caught up inside the thick wall of the die-casting product, causing microporosity. remain.

For die-cast products with residual microporosity,
If heat treatment such as solution treatment is performed to remove residual stress or improve mechanical properties, the surface of the die-cast product will locally blister after the heat treatment, resulting in loss of commercial value.
Furthermore, heat treatment is not applied to conventional die-cast products.

On the other hand, in recent years, the drawbacks of the conventional die casting method as described above have been improved, and methods such as non-porous die casting method, in which the mold cavity is filled with oxygen for casting, and vacuum die casting method, in which casting is performed by evacuating the inside of the mold cavity, have been developed. laws etc. were developed,
Die-cast products manufactured by this improved die-casting method are heat-treated to reduce microporosity, but die-cast products manufactured by this method are inferior to die-cast products manufactured by conventional methods. In comparison, it has not yet been widely adopted because of the high cost due to the need for incidental equipment, the complicated mold structure, and the need for oxygen gas.

[Problem to be solved by the invention]

Therefore, the present inventors conducted intensive research to make it possible to heat-treat die-cast products manufactured by this method by taking advantage of the high productivity, which is one of the features of the conventional die-casting method. The phenomenon of blistering on the surface of a die-cast product is caused by the pressure of gas trapped within the microporosity of the die-cast product, which is usually about 100 to 200 kgf.
In addition to this, the pressure during heat treatment is increased to approximately 500 to 600 Kgf/cm, and the actual strength of the die-cast product is approximately 20 Kgf/cm" at room temperature.
ms" (2000Kgf/cm2) becomes about 5Kgf/mn+" (500Kgf/cm2) due to heating during heat treatment.
It is inferred that this is because the thickness strength from the microporosity to the surface cannot fully resist the gas pressure within the microporosity and bulges outward from the surface in a state balanced by the gas pressure. As a result of repeated experiments based on this reasoning, we were able to invent a heat treatment method for die-cast products that allows the thickness strength from the microporosity to the surface to withstand the gas pressure within the microporosity during heat treatment. be.

[Means to solve the problem]

The gist of the present invention developed as described above is a pressurized atmosphere heat treatment method for heat treating an aluminum die-cast product under a pressurized atmosphere.

[Function] By heat-treating an aluminum die-cast product in a pressurized atmosphere, the mechanical properties are improved by about 50%.

The pressure of this pressurized atmosphere is 500 to 600 kg.
f/am" is desirable; if it is less than 500 Kgf/cm", it will not be possible to completely prevent the occurrence of blistering;
This is because if it exceeds 00 Kgf/cm'', the effect of preventing the occurrence of blisters will be saturated and the cost will increase.

〔Example〕

Examples related to the present invention will be described below.

FIG. 1 is a schematic diagram of an apparatus used in the pressurized atmosphere heat treatment method for aluminum die-cast products according to the present invention, and 1 is an opening/closing device that can be closed when closed at the front (front in the figure). It is a furnace body with a door (not shown). 2 is
This is a heating element that is erected along the left and right side walls of the furnace body 1. 3
is a fan provided on the ceiling of the furnace body 1 for stirring the atmospheric gas inside the furnace. Reference numeral 4 denotes a stand provided in the furnace, on which a pallet 5 loaded with die-cast products A is placed. 6 is a pressurizing device for supplying atmospheric gas under pressure into the furnace during heating. A piping 7 has one end opened into the furnace and the other end connected to the pressurizing device 6, and an on-off valve 8 and a pressure accumulating tank 9 are disposed in the middle of the piping 7. 10
is a pressurizing device for supplying a quenching refrigerant atmosphere gas under pressure into the furnace. Reference numeral 11 denotes a pipe having one end opened into the furnace and the other end connected to the pressurizing device 10, and an on-off valve 12 and a pressure accumulating tank 13 for quenching refrigerant gas are disposed in the middle of the pipe 11. 14 is a pipe for releasing the gas in the furnace to the atmosphere via the on-off valve 15.

Pressurized atmosphere heat treatment of an aluminum die-cast product according to the present invention using a heat treatment furnace having such a configuration is performed in the following manner. First, pallet 5 loaded with die-cast products A
After charging through the entrance/exit of the furnace body 1 and placing it on the frame 4 in the furnace, the opening/closing door is closed to seal the entrance/exit. Next, the heating element 2 is energized to start heating, and the pressure accumulator tank 9 is charged.
The pressurizing device 6 is operated in advance to supply heated gas at a predetermined pressure, which has been stored inside the furnace body, by opening the on-off valve 8 and feeding it into the furnace body 1. At the same time, the fan 3 is operated to stir the heated atmospheric gas to perform die casting. After uniformly heating the product A at a predetermined temperature and under a predetermined pressure for a predetermined time, the on-off valve 12 is opened while the on-off valve 15 for venting to the atmosphere is opened.
The pressurizing device 10 is operated in advance to replace the pressure storage tank 13 with a quenching refrigerant gas of a predetermined pressure, and the die-cast product A is rapidly cooled and heat-treated. After that, the temperature of the gas in the furnace is lowered to a predetermined temperature, and the opening/closing door is opened to pull out the pallet 6 loaded with die-cast products A from inside the furnace.Fifteen pieces are manufactured by the conventional die-casting method using the above-mentioned heat treatment furnace and procedure. The heat treatment temperature was kept constant (500°C), and the pressurizing pressure of the atmosphere was set to ■atmospheric pressure, ■400Kgf/cm'', and ■550Kg.
Heat treatment was performed under three conditions of f/cm'.

As a result, the mechanical properties under the three conditions were approximately 30 kg in tensile strength.
f/m+w", 0.2% yield strength of approximately 20Kgf/ms", and elongation of approximately 5%, which was almost unchanged, but the surface condition was defective as all 5 pieces were blistered when the pressurization pressure was atmospheric pressure. Met. Two pieces with a pressurizing pressure of 400 Kgf/cm2 were good, but bulges were observed in three pieces. On the other hand, all the samples with a pressurizing pressure of 550 Kgf/cm" had no blisters and were in good condition.

〔Effect of the invention〕

As described above, according to the present invention, even die-cast products manufactured by conventional die-casting methods can be heat-treated without causing blistering defects on their surfaces, and their mechanical properties can be improved. It can be improved by about 50%.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a pressurized atmosphere heat treatment apparatus according to the present invention. 1 Furnace body 2 Heating element 3 Fan 4 Frame 5 Pallet 6.10 Pressure device 7, 11.14 Piping 15 Open/close valve pressure accumulator tank Die-cast product Patent applicant Kobe Steel, Ltd.

Claims (1)

[Claims] A pressurized atmosphere heat treatment method for aluminum die-cast products, the method comprising heat-treating the aluminum die-cast products in a pressurized atmosphere.