JPS60128251A - Manufacture of heat-resistant aluminum alloy member - Google Patents

Abstract

PURPOSE:To manufacture a heat-resistant Al alloy member having superior dimensional stability at high temp. by subjecting Al alloy powder contg. an added element in a supersatd. state to hot extrusion, hot forging, rapid cooling and heat treatment at a specified temp. CONSTITUTION:An Al alloy such as Al-Si, Al-Si-Fe or Al-Fe is melted, and the molten alloy is rapidly cooled at >=10<3> deg.C/sec cooling rate to prepare Al alloy powder contg. said added element solubilized in a supersatd. state. The Al alloy powder is heated to 300-520 deg.C and hot extruded to form a blank for forging. This blank is hot forged at >=300 deg.C, and the forged article is rapidly cooled at >=100 deg.C/sec cooling rate. It is then held at <=550 deg.C for >=30min to improve the dimensional stability at high temp.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a heat-resistant aluminum alloy member having excellent hot dimensional stability.

Conventionally, when obtaining the above-mentioned member, hot forging is performed on a heat-resistant aluminum alloy body using drawing or a cast body obtained by continuous casting to form the member, and then in order to improve the hot dimensional stability and strength of the member. A solution aging treatment is performed on the steel.

In this case, unless the aging treatment is performed at a high temperature higher than the working temperature of the member, the structure will change due to the heating of the member during use, resulting in dimensional growth.

For example, in the case of a piston for an internal combustion engine, it is heated to about 280 C over the engine operating range, but aging treatment is generally performed below this temperature (approximately 230 tZ' in T7 treatment) due to constraints imposed by the alloy structure. There is a problem of dimensional growth. This is JISAC8A, AC8B, AC8C
The same applies to pistons obtained by die casting using casting aluminum alloys such as . To avoid this problem, a heat-resistant aluminum alloy that can withstand high-temperature stabilization treatment is required.

In view of the above, an object of the present invention is to provide a manufacturing method capable of obtaining a high-strength member with excellent hot dimensional stability using a heat-resistant aluminum alloy that can withstand high-temperature stabilization treatment, The cooling rate of the molten aluminum alloy is 103C/sec.

A powder manufacturing process for obtaining an aluminum alloy powder in which additive elements are supersaturated as a solid solution by performing a powdering process by rapid solidification; A forming step of manufacturing a material, then hot forging the forging material at a temperature of 300C or higher to form an aluminum alloy member, and then rapidly cooling the member at a cooling rate of 100C/sec or higher; forming the member at a temperature of 550C. It is characterized by comprising: a stabilization treatment step of holding for 30 minutes or more;

As aluminum alloys, Al-5t, Al-5i-
This includes Fe, Al-Fe alloys, and the like.

In the powder manufacturing process, the cooling rate is 1-03c/sec.
By setting the above value to less than 10'C/s'cc, it is possible to dissolve the additive element in the structure in a supersaturated manner and to obtain a powder with stable quality. Also, the cooling rate was set to 10'C.
/sec or more and '07C/sec or less, the supersaturated solid solubility of the added element improves, and Fc.

It becomes possible to significantly add elements that improve high-temperature strength, such as wi and cγ, and precipitate more of these added elements as intermetallic compounds, thereby further improving the high-temperature strength of the member.

When the cooling rate is less than 10" C/s g c, the additive elements precipitate as coarse intermetallic compounds, which tend to cause structural defects and cause strength deterioration. On the other hand, when the cooling rate is less than 10" C/s g c
If the value exceeds tl:'/Sec, the manufacturing process becomes complicated and mass productivity is impaired, and furthermore, it becomes difficult to obtain powder with uniform characteristics.

During hot extrusion in the forming process, the temperature of the shape-retaining material made of aluminum alloy powder is set to 300C or higher5.
By setting the temperature to 20C or less, the supersaturated solid solution additive elements can be uniformly and finely precipitated in the structure as intermetallic compounds that are stable at high temperatures, and the high-temperature strength of the particles can be improved. Workability is also extremely good. In the powder manufacturing process, if the cooling rate of the molten metal is set to 105C/sec or more to enable the addition of large amounts of elements such as 11e, Ni, and Cγ, the hardness of the resulting powder will be high, so extrusion processing is not possible. It is also necessary to raise the temperature of the material during the process. When the material temperature is less than 300C, the deformation resistance is too high, resulting in poor workability.On the other hand, when the material temperature is more than 520C, the crystal grains become coarse and the high temperature strength becomes low T. As a result of various studies, it is preferable that the material temperature is 330C or higher, especially 400C.
If it is in the range of C or more and 450C or less, the moldability will be good,
Moreover, high temperature strength can be improved.

However, by decreasing the extrusion speed and extrusion ratio and increasing the extrusion pressure, it is possible to perform extrusion processing at a lower temperature. In this case, it is defined as, and generally an extrusion ratio of about 5 or more and 20 or less is considered to be a practical range. When the extrusion ratio exceeds 20, huge extrusion equipment is required and industrial efficiency deteriorates.

On the other hand, if the extrusion ratio is less than 5, there will be large variations in performance such as hardness 2 strength between the 6 parts and the outer periphery of the product after extrusion, but when performing secondary plastic working such as forging after extrusion, Since the forging makes the crystal grains uniform and fine, there is no practical problem even if the extrusion ratio is about 2.

Also, during forging, by setting the forging material temperature to 300C or higher, the forging formability of the material will be good, and the resulting parts will not suffer from cracks or forging cracks, but if the material temperature is below 3000C, the forging process will not occur. Formability deteriorates, causing cracks and forging cracks in the component.

In the powder manufacturing process, in the case of a forging material made of the powder obtained at a cooling rate of 10''C/sec or more, it is desirable to increase the material temperature as the hardness increases.

Furthermore, by setting the cooling rate after forging to 10 oC,,'s Cc or more, coarsening of crystal grains can be suppressed and high-temperature strength and hardness can be improved. When the temperature is lower than 100%, the structure recovers and recrystallization occurs, which leads to coarsening of crystal grains and a decrease in high-temperature strength. This cooling operation is generally performed by water cooling, but in the powder manufacturing process, the cooling rate is 10'7:J:I
In the case of a material made of the powder obtained above, a large amount of intermetallic compounds with excellent high temperature stability are precipitated due to the addition of a large amount of additive elements, and these intermetallic compounds cause recovery of the structure after forging. Since recrystallization is prevented, the above cooling operation does not necessarily have to be carried out by water cooling.

In the stabilization process, the member is heated to a temperature of 550C or less for 3
By holding it for 0 minutes or more, its hot dimensional stability can be improved. In short, the stabilization treatment temperature must be higher than the working temperature of the part; if the stabilization treatment temperature is lower than the working temperature, the member will undergo dimensional growth and the hot dimensional stability will deteriorate. When the temperature exceeds 550C, the high temperature strength of the aluminum alloy deteriorates, and the processing time:
If the heating time is less than 30 minutes, homogenization of the tissue cannot be achieved and a product of stable quality cannot be obtained.

Next, an embodiment in which the present invention is applied to the manufacture of a piston for an internal combustion engine will be described.

<Example I> Table (1,) shows heat-resistant aluminum alloys A-D used in the present invention and J Is ACsC as a comparative example.
The composition of the moon E is shown.

Table (I) When using the above alloys A-D, the cooling rate is 103C/s
Atomization is applied under conditions of ec or more and less than 105 C/''' to produce four types of alloy powder, and each alloy powder is molded into an extrusion material having a shape retention property of 225 mm in diameter.Each extrusion process The material for extrusion is placed in a soaking furnace with an internal temperature of 370C and held for 10 hours, and then the extrusion material is subjected to extrusion processing to produce a round bar-shaped forging material with a diameter of 70 squares.

Thereafter, each forging material is hot forged to form a piston material. In this case, the material made of alloy A is 450C
Then, the materials made of alloys B and C are heated to 550C, and the material made of alloys is heated to 470C. After forging, each piston element is water-cooled at a cooling rate of 660 C/sec.

When Alloy E is used as a comparative example, a piston material is cast using a mold.

Figure 1 shows the change in hardness (HRB) when each piston material was subjected to stabilization treatment, and each hardness was measured at room temperature after holding each piston material at each temperature for 48 hours. a and -e indicate piston materials made of alloys A to E, respectively.

Since the operating temperature of the piston is approximately 280C, the stabilization treatment is preferably performed at a higher temperature, for example, 300C or higher. As is clear from Fig. 1, in the case of piston materials a, to d made of alloys A and D, the stabilization treatment temperature is 3.
Even at 00C or higher, no significant decrease in hardness is observed, and it is fully possible to set the HRB to 60 or higher in order to maintain the durability of the ring groove. On the other hand, the piston material e,
In this case, if the stabilization treatment temperature is 300C or higher, the hardness may decrease significantly and the piston may no longer function as a piston.

In Fig. 2, each piston material a1 to d is 410tZ'.

After 3 hours of stabilization treatment, the pistons a2 to d with a head outer diameter of 73.55711711 were machined.
2 is removed and the dimensional growth change is shown when it is held at 300C for a predetermined period of time.

The dimensional growth change in this case is shown as the change in the outer diameter of the head portion, and is expressed as follows. Furthermore, with the reference value zero as the boundary, the positive side is the case of permanent deformation due to expansion, and the negative side is the case of permanent deformation due to contraction.

The piston C2 made of alloy E is machined from a material C1 that has been subjected to T7 treatment so as to have the same outer diameter of the head portion as described above.

As is clear from Fig. 2, the rate of change in dimensional growth is extremely small in the case of pistons a2 to d2 made of alloys A to D, but the rate of change in dimensional growth increases over time in the case of piston C2 made of alloy E. .

In the case of the piston materials α, -d1 made of the alloys A-D, if the stabilization temperature is in the range of 300 to 500C, the same dimensional growth change rate as shown in FIG. 2 can be obtained.

The dimensional growth of the piston that occurs during engine operation is an irreversible change, so if the piston undergoes permanent deformation due to expansion, the frictional force of the piston against the cylinder sleeve will increase, resulting in a loss of power, and the deformation will increase. If the degree is too large, there is a risk of seizure occurring between the piston and the cylinder sleeve. On the other hand, if the piston undergoes permanent deformation due to contraction, problems such as an increase in the hitting noise caused by the piston, an increase in oil consumption, and an increase in blow-by gas occur.

In the pistons a2 to d2 made of the alloys Δ to D, the amount of permanent deformation caused by them during engine operation is extremely small, and therefore all of the above-mentioned problems caused by changes in the clearance between the piston and the cylinder sleeve can be eliminated. It is.

<Example ■> Table (II) shows the compositions of heat-resistant aluminum alloys F and -H used in the present invention, and these alloys F and Il
This is the same type of alloy as the coating (■), but the content of FC, which is an element that mainly improves high-temperature strength, is increased.

Table (n) When using the above alloys F and H, the cooling rate is 10''7:
Three types of alloy powders were produced by applying atomization under conditions of more than 22 mm in diameter.
A material for extrusion processing having a shape retention property of 5ya+n is molded. Each extrusion material is placed in a soaking furnace with an internal temperature of 420C and held for 10 hours, and then the extrusion material is extruded to produce a round bar-shaped forging material with a diameter of 70fi.

Thereafter, each forging material is hot forged to form a piston material. In this case, the materials made of alloy F-II are each heated to 470C. After hot forging, each piston material is water-cooled at a cooling rate of 6607:/sec.

Figure 3 shows the change in hardness (HRB) when each piston material was subjected to stabilization treatment, and each hardness was measured at room temperature after holding each piston material at each temperature for 48 hours. fI''h+ represents a piston material made of alloy F~, and CI represents the comparative example.

As is clear from FIG. 3, in the case of piston materials f1 to A1 made of alloys F and H, no significant decrease in hardness is observed even at a stabilization treatment temperature of 500C.

With the shift to diesel engines that employ direct injection types, the operating temperature of pistons tends to rise to 400 to 450 C, but even in such operating environments, the piston materials f1 to h1 have a sufficiently high temperature. It has strength, and in the powder manufacturing process, the cooling rate can be reduced to 1Q5C/s.
This can be achieved by setting it to ec or higher.

Each piston material JI-h1 was stabilized for 450C for 13 hours, and then machined to a head diameter of 7.
A piston of 3.55 order was ground, held at 400C for a predetermined time, and then the dimensional growth change rate was examined, and it was found that the value approximately corresponds to that of the piston d of Example 1. From this, it is clear that the pistons made of the alloys F and If have excellent hot dimensional stability.

As described above, according to the present invention, a high-strength heat-resistant aluminum alloy member with excellent hot dimensional stability can be obtained by using a specific heat-resistant aluminum alloy powder and undergoing a stabilization treatment process at high temperatures. I can do it.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between stabilization temperature and hardness for the piston material in the first example, and Figure 2 is the relationship between holding time and dimensional growth change rate when the piston is held at 300C in the first example. FIG. 3 is a graph showing the relationship between stabilization treatment temperature and hardness for the piston material in the second embodiment. Patent applicant: Honda Motor Co., Ltd. Figure 3 Figure 1

Claims (1)

[Claims] The molten aluminum alloy is cooled at a cooling rate of 1o3'I.
A powder manufacturing process of obtaining an aluminum alloy powder in which additive elements are supersaturated as a solid solution by performing a powdering process of rapid solidification at a temperature of 000 to 520 r. Extrusion processing is performed to produce a forging material, and then the forging material is heated to a temperature of 300°C.
The aluminum alloy member is formed by hot forging at C or above, and the rear limb member is cooled at a cooling rate of 100C/sec.
A method for manufacturing a heat-resistant aluminum alloy member having excellent hot dimensional stability, comprising: a forming step of rapidly cooling the member as described above; and a stabilizing treatment step of maintaining the member at a temperature of 550C or less for 30 minutes or more.