JPS62130234A - Method for homogeneously mixing al-pb alloy - Google Patents

Abstract

PURPOSE:To obtain an Al-Pb alloy having high homogeneity by agitating a vacuum-melted Al-Pb alloy by rotation until solidification is nearly completed. CONSTITUTION:While being cooled, a vacuum-melted Al-Pb alloy is agitated by rotation at a low speed with a rotator. When the alloy begins to solidify, the speed of rotation of the rotator is increased simultaneously with the beginning, and agitation is continued by rotation at a high speed under continuous cooling. The rotator is pulled out of the alloy immediately before solidification is completed. Thus, an Al-Pb alloy having extremely high homogeneity is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a method for homogeneously mixing Al--Pb alloys mainly used for wear-resistant materials such as bearing alloys.

[Prior Art] Recently, the potential for practical application of Al-Pb alloys has been pointed out due to their excellent bearing properties and material costs that are much lower than Sn-based alloys, and they are particularly popular in the automobile industry. I,% started to be in the spotlight.

However, there is a problem that PB hardly dissolves in solid solution in the A1 matrix, and gravitational segregation of PB tends to occur due to the large density difference between the two. To overcome this problem, several types of manufacturing methods have been experimentally attempted. It is being

Among these methods, the powder metallurgy method, in which AI and PB powders are uniformly mixed and sintered, and the space metallurgy method, in which solidification is performed under microgravity, have high material manufacturing costs, and the conventional rapid solidification method A problem arises in that the solidification structures of the surface layer and the center of the ingot are different.

On the other hand, Pathak et al. have proposed an inexpensive manufacturing method for Al-Pb alloys, in which the alloy is completely molten at 700 to 900°C and is heated to a rotary blade at a rotational speed of 600 to 1400 rpm.
, we proposed a method in which the mixture was stirred and mixed, and then immediately poured into a #8 mold using the bottom pouring method and rapidly cooled (J, P, Patha).
k, S, N.

Tiwariand S, L, Malhotra
: Metals Technology, 8 (197
3), 442. ).

However, although this method can be used to produce Al-Pb alloys with a Pb content of up to 50 wt%,
If the Pb content exceeds this, there is a problem and it is difficult to achieve homogeneous mixing throughout.

[Problems to be Solved by the Invention] As described above, the purpose of the present invention is to
Homogenizing the microstructure in the l-Pb alloy,
Moreover, it is an object of the present invention to provide a method that enables OJ production of the Al-Pb alloy at low cost.

[Means and effects for solving the problem] In order to achieve the above object, the method of the present invention involves adding low-speed rotational stirring using a rotor to the vacuum-melted Al-Pb alloy before cooling it to initiate solidification. At the same time, the rotational speed of the rotor is increased, and high-speed rotational stirring is continued while being continuously cooled to obtain a highly homogeneous AI-Pb alloy.

To explain more specifically, in the method of the present invention, in 'F3, the Al-Pb alloy melted in vacuum is first subjected to low-speed rotational stirring using a rotor under rapid cooling conditions, but the rotational speed in this case is Since it is necessary to prevent the alloy in a molten state from scattering due to stirring, it is set within this range to an extent that can suppress separation of A1 and pb from each other. Furthermore, it is appropriate that the shape of the single rotor is a shape that does not generate splashes relatively easily, such as an octagonal cross section, as used in the experimental apparatus described below.

Rotate and stir as described above under the specified cooling conditions! ! Then, when solidification of the alloy starts, the rotational speed of the rotor is increased at the same time as solidification of the alloy starts, and high-speed rotational stirring is continued while continuously cooling. The rotation speed of the rotor in this case is
Since the alloy becomes semi-molten and its scattering is suppressed,
It is possible to increase the speed relatively, and in order to homogenize the alloy, it is desirable to increase the speed within a range that does not cause any other problems. This high-speed rotational stirring is preferably continued until just before the completion of solidification, at which point the rotor is pulled out from the sample sample to prevent welding between the rotor and the sample sample, thereby forming an extremely highly homogeneous Al-Pb. Obtain a series alloy.

This method can not only be effectively used to produce Al-Pb alloys with high Pb content, but also achieve homogeneous microstructures in Al-Pb alloys that are prone to gravitational segregation by achieving homogeneous mixing throughout. Moreover, it is possible to create an Al-Pb alloy at low cost.

[Example] Examples of the present invention will be described below.

Table 1 shows the composition of the Al-Pb alloy used in the experiment.

These alloy materials are 99.99% At, 99.99%
Pb, 99.99%Cu, 88%Si, 88.9%M
H or 99.97% Ni is precisely blended using an electronic precision balance.

Table 1 (·t%) Figure 1 shows the configuration of the experimental equipment in which the test metals having the above composition were homogeneously mixed. With this experimental apparatus, even if the sample gold is melted in a vacuum, the emission of PB can be ignored. ),
The rotor inserted into the same alloy was solidified during the solidification process under continuous cooling.
By rotating at a high speed of 000 rpm or higher, the PB element can be uniformly dispersed.

To explain the device shown in the same figure, a Chanpachi main body 1 with an opening/closing door on the front constitutes a vacuum container, and the inside is divided into upper and lower parts by a molybdenum shutter 2 that is opened and closed by an air cylinder 3. A molybdenum resistance heating furnace 5 is installed and placed in the heating chamber 4 of the
A water-cooled outer cylinder 7 made of US304 stainless steel EW and a rotor 8 hanging down from above are arranged inside the cooling outer cylinder 7, and this rotor 9 is driven to rotate by a torque motor 10.

The rotor has an octagonal pyramid shape with a long sleeve of 38 mm and a short axis of 30 mm in cross section at the upper end, a long sleeve of 32 mm at the lower end, a short axis of 25 mm, and a length of 120 mm.

In this apparatus, the inside of the chamber body 1 is connected to a vacuum source (not shown), and after evacuation, the test gold is heated and melted in a graphite crucible 12 in the furnace.
The support rod 1 which penetrates the lower surface of the chamber body 1 by opening the
1 is a crucible lifting mechanism capable of lifting and lowering the graphite crucible 12.
By raising the rotor 9 into the water-cooled outer cylinder 7, the rotor 9 is inserted into the crucible 12, and during the rapid cooling process 1 in the cooling chamber 5, the seventh rotor 8 is The rotation stirs the semi-molten alloy. The crucible has an outer diameter of 78 mm, an inner diameter of 550 mm on the upper surface, 50 mm on the lower surface, and a depth of 130 mm.

The torque motor 10 that rotates the rotor 9 is provided with a torque detector and a rotation detector on its rotation shaft, and these are connected to a digital display and a digital printer.

As for the experimental operations in the above apparatus, the chamber body 1 was evacuated to below IX 1O-5 Torr, and then the AI-P'c-based sample metal was placed in a graphite crucible in a molybdenum resistance heating furnace at the bottom of the heating chamber. After heating approximately 0.5kgt-710 and confirming that the alloy has melted, the molten metal was held at 827°C for 30 minutes, and then the shutter on the furnace belly was opened.
The molten metal was raised at a speed of 25 mm/s by the crucible lifting mechanism, a rotor was inserted into the molten metal, and the lowest end of the rotor was stopped at a position just 10 cm above the inner bottom of the crucible.

Immediately after that, the rotor is rotated at a rotation speed of 540 and 11080 rpm.
PB during the molten metal quenching process by rotating at low speed in two stages.
Efforts were made to prevent gravitational segregation of elements until solidification begins. During this time, the onset of solidification was monitored by the cooling curve during continuous recording on the temperature recorder attached to the above device, and when the temperature drop suddenly became gradual, the rotation speed of the rotor was started to increase, and the rotation speed was increased for 10 seconds. The speed was maintained at a constant speed of 420 rpm. At this time, the rate of increase in the number of rotations was kept constant in order to prevent as much as possible the scattering of the semi-molten alloy to the outside of the crucible due to the rapid increase in the speed of rotational stirring.

Thereafter, rotational stirring was continued at the above constant speed for 120 to 240 seconds while continuously cooling the sample metal, and until solidification was completed, the crucible was lowered by 20 cm using the crucible lifting mechanism.
Prevented lava from rotor and test metal.

Set a of alloy ingots thus obtained! The observation was carried out using a scanning electron microscope and an optical wJ microscope. In addition, samples were taken from the cross sections of the head, center, and bottom of these alloy ingots.
Chemical analysis was conducted to examine the degree of gravitational segregation of the PB element.

The results of the experiment will be explained below.

First, when homogeneously mixing a sample metal using the experimental equipment 2 shown in FIG. 1, changes in torque during the rotational agitation solidification process were investigated. As a result, FIG. 2 shows the torque variation during high-speed rotation stir solidification for the G-J alloy, with the rotor rotating at a speed of 420 Orpm. Here, the solidification start temperature (high speed stirring start temperature) of G, H, I and J alloys is BO
B, 599.593 and 588°C, and the high speed stirring end temperature is 555.546, 551 and 551'
It is O. The solid phase ratio at the end of these rotary stirrings is about 80%.

Next, cross sections of the head, center, and bottom of the Al--Pb alloy ingot solidified by high-speed rotation stirring in the above apparatus were observed using a scanning electron microscope. As an example, scanning micrographs of alloy D are shown in FIGS. 3(a) to 3(c). The same figure (a
) is a compositional image of the head, (b) is a compositional image of the central part, and (c) is a cross-sectional image of the bottom. According to this, the crystal structure of an Al-Pb alloy solidified by rotational stirring at 4,200 rpm differs from the fine PB particles scattered in the normal rapidly solidified structure of the same alloy, and contains crushed dendrite crystals. It is observed that the irregularly shaped pb phase (white area in the figure), which exists between the primary crystal particles and the gaps between them, is uniformly dispersed throughout the ingot.

In addition, in order to clarify the difference in crystal structure due to increase or decrease in the amount of Pb element, 15% Pb (E alloy) is included in Figure 4 (a) and 35% Pb (F alloy) is included in Figure 4 (b). Al-Cu-
This is a scanning electron micrograph of a Mg-Pb quaternary clay cast alloy ingot. In this structure, in the 15% PB alloy, the PB phase (
In the 35% PB alloy, the PB phase coexists with the eutectic so that the white area in the figure is sandwiched between them, but in the 15% PB alloy, the PB phase is not seen in the narrow spaces between the primary crystal grains, but rather in the narrow spaces between the primary crystal grains. It is observed that it accumulates in a wide area.

Additionally, the tentolite structure that generally crystallizes during alloy casting has a solid phase ratio of approximately 87% and is in a closed form, which prevents the fluid flow of the remaining liquid phase and prevents sufficient hot water from being supplied at the final stage of solidification. is the main cause of casting defects. However, by applying high-speed rotational stirring to an Al-Pb alloy in a solid-liquid coexistence state, the present inventors destroyed the dendrite morphology and produced a material without casting defects, while at the same time dispersing the Pb element homogeneously. It was confirmed that the mechanical properties were improved.

Furthermore, we compared the high-speed rotation stirring solidification and the low-speed rotation stirring solidification of the Al--Pb alloy, and conducted the following study in order to prove the practicality of the former.

That is, after melting the sample metal in vacuum, a rotor was inserted into the molten metal, and while the molten metal was being cooled at a cooling rate of about 1°C/s, one rotor was rotated at a low speed of 54 Orpm. Even after the match metal reached the solidification start temperature, rotational stirring was continued at the same speed, and the solid phase content was drawn out while rotating the rotor until the solid phase ratio was around 80%.

As an example of the results, the E composition alloy in Table 1 is 54Or
Figures 5(a) and 5(b) show the solidified structure of the cross section of the top and bottom of an ingot that was solidified by rotational stirring at a rotational speed of pm. Here, the chemical analysis value of pb of the cross section of the head of the same alloy ingot is 6,
4 ± 0.2 wt%, and the pb value of the bottom cross section was 42
．． 5±0.3 wt%. Therefore, in low-speed rotation stirring solidification with a rotor rotation speed of 54 Orpm, it is impossible to trap the PB liquid phase in the gaps between primary crystal particles generated by crushing dendrite crystals, and ultimately prevents gravitational segregation. I can't.

On the other hand, the chemical analysis values of the head of the solidified alloy ingot by rotation stirring at 3600 and 420 Orpm are 33.2±0.4 and 35.0
±0.2%. In addition, the analysis value at the bottom is 35.5±
0.3 and 35.0±0.3%. As a result, A
It was confirmed that high-speed rotation stirring solidification of l-Pb alloys is effective in preventing gravitational segregation of Pb elements.

[Effects of the Invention] As detailed above, according to the method of the present invention, Al-
It is possible to achieve homogenization of the microstructure and improvement of mechanical properties of the Pb-based alloy, and to reduce the cost of wear-resistant materials such as bearing alloys.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the experimental apparatus used to experimentally implement the method of the present invention, Fig. 2 is a graph showing torque changes during high-speed rotation stirring solidification according to the method of the present invention, and Fig. 3 (a )
~(c) and FIGS. 4(a) and (b) are micrographs substituted for drawings of the alloy obtained by the present invention, and FIGS. 5(a) and (b).
) is a photomicrograph substituted for a drawing of an alloy obtained by solidifying with low-speed rotational stirring as a comparative example. 9 fists/rotors, 12...crucibles. Figure 3 Figure 5

Claims (1)

[Claims] 1. While cooling the vacuum melted Al-Pb alloy, add low-speed rotational stirring using a rotor, increase the rotational speed of the rotor at the same time as solidification begins, and continue high-speed rotational stirring while continuously cooling. A method for homogeneous mixing of Al-Pb alloys, which is characterized by obtaining highly homogeneous Al-Pb alloys.