JPS62124263A - Heat treatment of aluminum casting - Google Patents

Abstract

PURPOSE:To improve mechanical properties of aluminum castings by subjecting aluminum castings containing silicon and copper to heating to a specific temp., to holding, and to cooling down to room temp. CONSTITUTION:An Al alloy casting is composed of an Al alloy material containing, by weight, 4-12% Si and 0.25-4.5% Cu. This Al alloy material is melted, and the molten alloy is poured into a silica-sand shell mold and solidified to form the Al casting. Subsequently, as heat treatment, the Al casting is heated and held at 300-400 deg.C for 30min-5hr and then cooled to room temp. In this way, heat treating time is shortened and workability is improved and, simultaneously, mechanical properties such as impact value, elongation, etc., can also be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for heat treating aluminum castings.

[Conventional technology]

Casting aluminum alloys are widely used in the production of mechanical parts and structural materials, and a variety of methods are used to improve their mechanical properties, including the addition of various ingredients and heat treatment.

For example, aluminum castings made of aluminum-silicon (St) alloys are subjected to heat treatment (JISTb) as shown in Figure 4.
By performing this treatment, it is possible to not only control the state of solid solution and extraction of the alloy component elements, but also to improve the toughness by making the eutectic Si spheroidal.

[Problem that the invention seeks to solve]

However, for example, JISTb treatment requires solution treatment and tempering treatment, so the heat treatment time is long, resulting in poor workability (and also being disadvantageous in terms of cost as it consumes a large amount of energy. In the field, a process without solution treatment is desired.Heat treatments without solution treatment include JI8Ts, T@ treatment, and annealing treatment, but these 'r, , T, and treatment are all treatments. I have not found any studies that have investigated the strength or dimensional stability of objects that have focused on toughness.

10,000, When AJ gold alloy containing @ (Cu) is used in Tb treatment to make, for example, automobile engine parts and used in an environment subject to heat load, the precipitation state of solute elements, which are added components, changes with time. . Among these, toughness decreases in a state where an intermediate phase is precipitated. Therefore, embrittlement caused by tempering is an important problem in parts subjected to heat loads.

The present invention is intended to solve the above-mentioned problems in the conventional technology, and its purpose is to have structural stability and good dimensional stability even in a convenient environment where heat load is applied, and to prevent embrittlement. It is an object of the present invention to provide a low-cost and simple heat treatment method that does not require solution treatment, in order to obtain an aluminum casting having good toughness.

[Means for solving problems]

That is, the method for heat treating aluminum castings of the present invention involves heating a casting material made of an aluminum alloy containing silicon and copper to 30%
The special mission is to heat it to 0°C to 400°C, hold it for 50 minutes to 5 hours, and then cool it to room temperature.

It is said that the toughness of castings made of aluminum alloys varies depending on the shape, size, distribution, etc. of crystallized substances, but it also largely depends on the state of precipitation of solute elements in the matrix. Therefore, it is important to create a precipitation state that is structurally stable and exhibits toughness through heat treatment. In aluminum alloys containing coarse elements, the precipitation state of solute elements obtained differs depending on the heat treatment conditions.The toughness of the material changes accordingly.In particular, when the intermediate phase is precipitated, the toughness decreases significantly. Therefore, it is necessary to precipitate the solute element as a stable phase in order to avoid embrittlement due to precipitation of the intermediate phase and to maintain structural stability even under thermal load.

Silicon and steel are preferred as solute elements. In particular, silicon 4% to 12% in weight ratio to aluminum base material, steel α25
It is preferable to use a cast material made of an aluminum alloy containing ~4.5%.

Further, the processing temperature is set to 300° C. to 400° C. because this is a preferable temperature range for precipitating the solute elements that are supersaturated in solid solution during casting as a stable phase. That is, 4
When heated above 00℃, solute elements re-dissolve,
There is a risk that tissue changes may occur due to heat load in the usage environment. In addition, heating at 500° C. or lower requires heating for a long time to precipitate the desired stable phase, resulting in poor working efficiency.

〔Example〕

The invention will be explained in further detail in the following examples. Note that the present invention is not limited to the following examples.

[Example 1] 6% Si, 55% Cu, and M2 as impurities by weight
AC2B alloy containing 3% LL and 25% Fe (7)
Melt at 50℃ and pour into a silica sand shell mold at 100℃ for about 5 minutes.
Figure 1 shows the relationship between the impact bending strength of a casting solidified in 0 seconds and the treatment temperature. The test piece had a 110×10×55 shape with a 2-diameter pannotch and the cast surface was intact. For the impact test, a &-m Charpy** testing machine was used. When heated at a temperature of 300°C to 400°C for 5 hours using the method of the present invention, the impact value is larger than that of as-cast material,
Especially when heated to 550℃ (A in the figure), the as-cast material (81 in the figure)
and about twice the value of T6 treated material (B2), 152 ki? −
1%,' was obtained. Although the impact value when heated to 450℃ (C in the figure) is higher than that of as-cast material,
It can be seen that the temperature tends to be lower than that of heating at 0°C and 400°C.

FIG. 2 shows the relationship between impact bending strength and heating time for castings having the same composition as FIG. 1. 300℃ and 5
In the heat treatment at 50° C., the OfI impact value increased with the treatment time. On the other hand, at 400°C, treatment was carried out for 2 hours (D in the figure).
A maximum value α of 54 kg-m/.2" was obtained. Even when the heating time was further increased to 5 hours, the impact value remained the same as that for 2 hours.

[Example 2] A plate-shaped test piece (JIS
A tensile test was conducted using an autograph using a No. 7 test piece. The relationship between elongation and treatment temperature at that time is shown in FIG. When treated by the method of the present invention at a temperature of 500°C to 400°C for 5 hours, all as-cast materials (E1 in the figure)
The elongation was larger than that of the T6-treated material (B2), and especially when treated at 350°C (F in the figure) and 400°C (G in the figure), an elongation of 6%, which is 1.5 times that of the as-cast material, was obtained.

(Effects of the Invention) As described above, the method for heat treating aluminum castings of the present invention heat-treats a casting material made of an aluminum alloy containing silicon and copper at 300°C to 400°C for 50 minutes to 5 hours, so it is different from the conventional method. Compared to other heat treatment methods, the heat treatment time is shorter, workability is improved, and no solution treatment is required.
It also reduces energy consumption and is advantageous in terms of cost.

Furthermore, aluminum castings heat-treated by the method of the present invention have improved mechanical properties such as impact value and elongation compared to as-cast materials and T6-treated materials that are not heat-treated. When used in parts used in heat-loaded environments such as automobile engines, it is structurally more stable and less likely to form cells than conventional products.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between heating temperature and (1-stroke bending strength) of as-cast aluminum alloy casting materials used in the method of the present invention, T6-treated materials, and heat-treated materials using the method of the present invention. In the figure, people are cast metals heat treated to 350℃, B1 is as-cast material, B2 is T6 treated material, C is 450℃
Fig. 2 is a graph showing the relationship between the heating time and the impact bending strength at various heating temperatures of the aluminum alloy casting material for casting used in the method of the present invention. ℃2
Fig. 3 is a graph showing the relationship between heating temperature and elongation in a tensile test of an aluminum alloy having the same composition as that shown in Fig. 1, in which E1 is an as-cast material and B2 is a T6 treated materials,
F is a casting material heat-treated to 350°C, G is a casting material heat-treated to 400°C, and Figure 4 is a graph showing the relationship between heating time and heating temperature for an example of a conventional heat treatment method for aluminum alloys for casting. be. Patent applicant Toyota Central Research Institute Co., Ltd. Fang 3 figure; l fi (@C) Fang 4 figure time opening (hr)

Claims (2)

[Claims] (1) A method for heat treating aluminum castings, which comprises heating a casting material made of an aluminum alloy containing silicon and copper to 300°C to 400°C, holding it for 30 minutes to 5 hours, and then cooling it to room temperature. (2) Aluminum alloy contains 4% to 12% silicon by weight,
A method according to claim 1, characterized in that it contains 0.25% to 4.5% copper.