KR100663236B1 - Method of producing alloys for melt forging - Google Patents

Abstract

Disclosed is a method for producing a molten metal forging alloy having physical or mechanical properties superior to that of conventional materials. According to the present invention, the Al-Fe-based alloy was selected as an alloy containing Fe composition in an amount of 1 to 7 wt%, the alloy was melt-treated at 850 to 900 ° C. in an electric resistance furnace, and commercial degassing was performed in the range of 0.2% of the melt weight. Gravity casting and forging were performed with the molten metal which had been degassed with the treatment agent, and the molten forging was prepared by using a vertically pressurized forging press to produce a Φ5 × 10 cm rod-shaped specimen, wherein the molten metal was injected at 750 ° C. The temperature is maintained, and the mold is preheated to 200 to 250 ° C. to apply the inside of the mold and the punch with an oil-based graphite release agent, and after the injection of the molten metal, the pressing force is 50 to 100 MPa, the pressing time is 60 sec, and the pressing speed is set at 20 mm / sec. do.

Description

Method of producing alloy for forging molten metal {Method of producing alloys for melt forging}

1 is a schematic diagram of a molten metal forging apparatus used in the present invention,

Figure 2 is a view showing a test specimen specification (ASTM E8M-85) used in the present invention,

3 is a gravity casting in which the amount of Fe added in the Al-Fe alloy is changed to 1 wt% (a, b), 3 wt% (c, d), 5 wt% (e, f), and 7 wt% (g, h). And macroscopic (macro) tissue photographs at the time of forging, and FIG. 3 (a, c, e, g) is a tissue photograph when gravity casting, and FIG. 3 (b, d, f, h) is forging. In one case,

4 and 5 show that the amount of Fe added in the Al-Fe alloy during gravity casting and forging molten metal is 1wt% (FIG. 4 (a, b)), 3wt% (FIG. 4 (c, d)), 5wt 5 (a, b) and 7wt% (Fig. 5 (c, d)) are microscopic (micro) microscopic photographs of the optical microscope during gravity casting and molten forging. a, c) is a tissue photograph when gravity casting, Figure 4, 5 (b, d) is a tissue photograph when molten forging,

FIG. 6 is a graph showing Brinell hardness (H _B ) values according to the Fe alloy amount in gravity casting and molten forged Al-Fe alloy.

FIG. 7 shows tensile strength (kg / mm ² ), yield strength (kg / mm ² ), and elongation (%) as tensile test results according to the Fe alloy amount change in the same Al-Fe alloy as that of FIG. 6. Is a graph,

8 and 9 are graphs showing Vickers hardness (H _V ) values of specimens after the isothermal heat treatment of Al-Fe alloys prepared by molten forging and gravity casting after furnace cooling.

FIG. 10 is a graph showing tensile strength, yield strength, and elongation as a result of tensile test when the amount of regenerated Al alloy is changed in AC4C alloy.

FIG. 11 is a scanning electron micrograph of an AC4C alloy to which a regenerated Al alloy is added in a commercial AC4C alloy. FIG. 11 (a) is a typical optical microscope microstructure (magnification: x 200) of an AC4C alloy to which a regenerated Al alloy is added. 11 (b) is an optical microscope microstructure (magnification: x 200) photograph when gas pores are observed, and FIG. 11 (c, d) is an enlarged optical microscope microstructure (magnification: x 500) photograph.

The present invention relates to a method for producing a molten metal forging alloy, and more particularly to a method for producing a molten metal forging alloy having superior physical properties and mechanical properties than conventional materials.

In general, the molten metal forging method is a process of manufacturing a sound product by continuously applying high pressure during solidification. As a mass production process of light alloy casting, it is used for commercialization of products such as automobile pistons and wheels and commercialization of high-quality parts. It is getting attention recently. As the molten metal forging material for this purpose, existing industrial casting materials such as AC4C and AC8A are mainly used.

Until now, studies on molten forging alloys have been limited to Al-Si and Al-Cu binary alloys and industrial alloys. In this case, the effects of alloying elements and pressing force on the mechanical properties of molten forging casting state are mainly studied. Investigations are being reported.

Many studies to date on the squeeze casting method have been carried out by direct pressurization or plunger pressurization. However, current commercialization and mass production forging methods are mainly indirect pressurization, and there are few reports on the structure and properties of castings according to these process differences. In addition, most of the data on indirect pressurization are confidential as the company's own technology. Therefore, the results of this indirect pressurization process can be analyzed to investigate the difference between the data on the conventional forging structure and mechanical properties and to investigate the influence of the manufacturing parameters of the indirect melt forging, that is, the pressure, sample thickness, and material. Data is one of the main variables of the process and is a research project that must be secured on the spot.

Currently applied pressure casting methods are vacuum casting, gravity casting, low pressure casting (2 -3kgf / cm ² ) and high pressure casting (500-1,000kgf / cm ² ), etc. are established as a stable casting method. Casting precision as the pressing force increases. Productivity and diversity are improving, but the cost is increasing due to the increase in the cost of managing and controlling the equipment, the difficult manufacturing conditions, the difficulty of small quantities of various kinds, and the high cost of molds.

Recently, a high pressure casting machine having a pressing force of about 200 kgf / cm ² has been developed and put into practical use in the European series. This applies to the manufacture of conventional aluminum engine blocks and die casting products. When the pressure is less, the device becomes simpler, so it is possible to mass-produce large castings even in a small casting machine, so that the development value is sufficient as long as there is no problem in the product. That is, as a basis for the research and development of casting machines using 5-200 kgf / cm ² pressing force and a new medium pressure casting method, investigation and analysis of basic characteristics such as solidification structure, mechanical properties, and solidification cooling rate should be preceded under such pressing force.

The present invention has been made to solve the conventional problems as described above, an object of the present invention is to provide a method for producing a molten metal forging alloy having superior physical properties or mechanical properties than conventional materials.

In order to achieve the above object, the present invention,

In the Al-Fe alloy, an alloy containing Fe of 1 to 7 wt% was selected as a starting alloy, and the alloy was melt-treated at 850 to 900 ° C. in an electric resistance furnace, and commercial degassing was performed at 0.2% of the melt weight. Gravity casting and molten forging are performed with the degassed molten metal, and the molten forging is made of a specimen of Φ5 × 10 cm rod shape by using a vertical pressure forging press, wherein the molten metal is injected at 750 ° C. Maintaining the temperature, the mold is preheated to 200-250 ° C, and the inside of the mold and the punch are applied with oil-based graphite release agent (7 wt% graphite, 85 wt% mineral oil and synthetic oil, 5 wt% dispersant and 3 wt% other oil additives). The pressing force after the injection of the molten metal is 50 to 100 MPa, the pressurization time is 60 sec, and the pressurization speed is set to 20 mm / sec.

Hereinafter, with reference to the accompanying drawings will be described in more detail with respect to the manufacturing method of the molten forging alloy according to the present invention.

In the present invention, the casting properties of molten forging and the industrial applicability and characteristics of the Al-based alloys according to the addition of transition elements were investigated for the alloys in which impurities (Fe, etc.) were added to the Al-based alloys. Al-Fe-based alloys strengthen the material by producing thermally stable fine particles inside the particles. When Al-Fe alloy is quenched at a high solubility range in a high temperature or liquid state, Fe having a low solubility with respect to Al has a low solubility. The possibility of being a high temperature structural material is attracting attention because it can be increased to obtain a new reinforcement phase which cannot be obtained in equilibrium solidification.

Al-Fe alloys have various metastable phases and stable phases depending on the composition and cooling rate of the alloy, and are generally metastable Al ₆ Fe phase at high solidification rate and A1 _{3 which} is stable at low solidification rate. Formation of intermetallic compounds in the Fe phase has been reported. In addition to these phases, metastable phases such as an icosahedral phase, a decagonal phase, Al _m Fe, and Al _x Fe have been reported. Therefore, the phase change such as crystallographic analysis of the intermetallic compounds and superstructure interaction by super-cold solidification is important for improving the characteristics of the Al-Fe alloy.

<Influence of alloying element addition>

end. Experiment method

Material and test piece manufacture

In order to investigate the effect of the composition of the molten forging Al-Fe alloy in this experiment, Fe alloys of about 1, 3, 5 and 7 wt% were added and commercial AC4C alloys were selected as experimental alloys. The alloy samples were Al (99.99% Al), commercial Al-40wt% Fe master alloy and commercial AC4C alloy. The alloy was melt-treated at 850 ~ 900 ℃ in the electric resistance furnace for quantitatively blended base materials, and degassing was performed by using a commercial degassing agent and degassing in the range of 0.2% of the weight of the melt. And molten metal forging.

The molten metal forging operation was performed using a 30 ton vertical pressure molten metal forging press, and a specimen of Φ5 × 10 cm rod form was prepared. In the molten forging test condition, the injection temperature was maintained at about 750 ° C., and the mold temperature was preheated to 200-250 ° C., and the inside of the mold and the punch were coated with an oil-based graphite release agent. After injection of the molten metal, the pressing pressure was 50-100 MPa, pressurization time 60sec, pressurization speed 20mm / sec, and the manufacturing conditions were identified.

1 is a schematic diagram of a molten metal forging apparatus used in the present invention. The Al-Fe alloys prepared by molten forging and gravity casting were cooled by isothermal heat treatment for 1 hour at room temperature, 250 ° C, 350 ° C, 450 ° C, 550 ° C and 650 ° C, respectively. In addition, the mechanical properties were evaluated after fabrication of the specimens by adjusting the ratio of regenerated Al in order to reduce the cost of adding regenerated Al (secondary Al).

Organizational observation

The prepared specimens and heat treated specimens were visually inspected for blisters and macro defects on the surface. For the observation of the eye tissue was observed defects such as shrinkage cavity seats side by the etching using the reagent Tucker _{(45㎖ HCl, 15㎖ HNO 3.} 15㎖ HF, 125㎖ H 2 0). The microstructure was etched with a Keller reagent by cutting the central portion of the specimen, and microstructure observation and component analysis were performed using a scanning electron microscope (SEM / EDS) equipped with an optical microscope and an X-ray spectrometer.

Mechanical characterization

Hardness test was carried out five times from the center of the specimen to the surface using a Micro Hardness Testing Machine (Model FM7, Capa 1000kg) of Future-tech, the average value was taken as Brinell hardness value, and compared with the Vickers hardness value. Tensile test (INSTRON 20,000kg Model 4485) was tested by making a specimen with a proportional specimen standard of ASTM E8M-85 as shown in Figure 2 in the vertical cut in the longitudinal direction of the specimen.

 I. Research Results and Discussion

Organizational observation

3 is a macroscopic (macro) macroscopic photograph of gravity casting and forging with varying amounts of Fe at 1 wt%, 3 wt%, 5 wt% and 7 wt%. In the case of gravity casting, the higher the amount of Fe added, the poorer the castability. In the forging of the molten metal, the castability was improved due to the pressing effect. This casting structure is a solidification of the solidification structure, that is, the first time near the mold wall or the mold wall, the solid nucleus increases over time to form an outer isometric axis, wherein the heat dissipation direction and anti-parallel Dendritic in the outer isometric region, which can grow, advances very quickly.

The competition between the crystals inhibits growth in the other direction, forming a columnar zone. After some stages of columnar dendrite growth, the arms may fall off the columnar column and grow independently. These fallen branches are equiaxed because they radiate latent heat through the supercooled melt. This coagulation zone is called the inner exquiaxed zone, and the change from columnar to equiaxed growth is greatly affected by the degree of convection in the liquid.

The well-developed columnar and equiaxed tissues can be observed with the gravity casting and molten forging tissues of FIG. 3. 4 and 5 are the microstructures during gravity casting and molten forging, and the Al-Fe-based resin and the narrow plate-like A1 ₃ Fe branch when 1wt% Fe is added in Fig. 4 (a, b) in Al-Fe system. It can be observed that it is formed on the dendritic phase of Al matrix in the shape of). As illustrated in FIG. 4 (c, d), needle-like A1 ₃ Fe primary tablets were generated at ₃ wt% Fe or more, and the addition of a large amount of coarse primary tablets could be observed to form sharply.

In the microstructure of molten forging, it was observed that the microcrystallization and spheroidization of some α resin phases were promoted, but the refinement of the primary and overall tissues due to the pressurization and quenching effect of the molten forging was not greatly promoted. That is, the Al-Fe alloy shows no difference in size and dispersion of A1 ₃ Fe phase during gravity casting and forging. This is considered as not contributing to the miniaturization of the high pressure to act in the solid-liquid co-exist in which a Primary coagulation during squeeze casting is already in progress A1 ₃ Fe phase that is crystallized segment A1 ₃ Fe. This result is considered as the same result as the report that there is no difference in the size of primary Si when solidified in solid phase in hypereutectic Al-Si alloy.

Mechanical property

6 is a Brinell hardness value according to the Fe alloy amount in the gravity casting and molten forged Al-Fe alloy system. As the amount of Fe alloy increased from 1 wt% to 3, 5 and 7 wt%, the Brinell hardness value increased from 36 to 40 at gravity casting and from 43 to 49 at hot casting. That is, it was difficult to observe a large difference in the microstructure, but the Brinell hardness value was improved by about 18% to 26% compared to the gravity casting during the forging of molten metal.

Figure 7 shows the effect of the addition of Fe on the tensile strength, yield strength and elongation when the tensile test with the same sample as in FIG. As a result of the addition of Fe element, the tensile strength during gravity casting was about 9kg / mm ² for 1wt% Fe and 7kg / mm ² for 7wt% Fe. The tensile strength when the molten metal is forged by 10.4kg / mm ² when the case of the case of 1wt% Fe 12.1kg / mm ² was a case of ^{3wt% Fe 13.6kg / mm 2,} 5wt% Fe 10.8kg / mm 2 was 7wt% Fe Decreased.

At this time, the yield strength is 1wt% Fe in the case 6.4kg / mm ² was, when the 3wt% Fe 7.7kg / mm ^2, when the 5wt% Fe case of about 6.3kg / mm ² was 7wt% Fe 6.3kg / mm ² It was. The elongation was 23% for molten forging 1wt% Fe, 8.8% for 3wt% Fe, 3% for 5wt% Fe, and 4% for 7wt% Fe. That is, as in the Brinell hardness value, it was difficult to observe a large difference in the microstructure in the tensile test results, but the tensile strength value improved by about 30% compared to the gravity casting during the forging of the molten metal.

Considering the structure characteristics shown in Figs. 4 and 5, the Fe content is dispersed in a large number, and it is considered that the formation and propagation of the Al ₃ Fe phase facilitates crack generation and propagation, resulting in a decrease in elongation and a decrease in tensile strength. do. In the above, the mechanical strength of the Al-Fe alloy during the forging is generally low, and the quenching and pressurization effects due to the forging are not sufficient. It is believed that this resulted in the solidification during the forging of molten metal, so that high pressure acted in the solid-liquid coexistence section, which did not contribute significantly to the miniaturization of A1 ₃ Fe phases.

8 and 9 are Al-Fe-based alloys prepared by molten forging and gravity casting are for the furnace-cooled specimens after isothermal heat treatment at room temperature and 250 ° C, 350 ° C, 450 ° C, 550 ° C, and 650 ° C for 1 hour, respectively. The Vickers hardness value is shown. The molten forging shows a slightly higher hardness value from room temperature to 450 ° C. and does not show a big difference at 550 ° C. and 650 ° C.

All. conclusion

The microstructure and mechanical properties of gravity casting and molten forging of Al-Fe alloys were not significantly different from that of gravity casting in Al-Fe alloys. Due to the castability is good. In addition, it was observed that the microstructure and spheroidization of the α resin phase were promoted by the microstructure during the forging of the molten metal, but the refinement of the grains and the overall tissue due to the pressurization and quenching effect by the forging was not greatly promoted.

The mechanical properties of the molten forging resulted in an overall improvement of Brinell hardness and tensile strength by 20-30% compared to gravity casting. The mechanical properties of the Al-Fe alloy after molten forging facilitate the crack generation and propagation due to the crystallization of the coarse A1 ₃ Fe phase, and the mechanical strength such as lowering of elongation and tensile strength is generally low. It is judged that the quenching and pressurizing effects are not sufficient. It is believed that this resulted in the solidification during the forging of molten metal, which caused high pressure in the solid-liquid coexisting zone, which did not contribute significantly to the miniaturization of A1 ₃ Fe phases.

<Effect of Regenerated Al Alloy Addition>

The following table shows the tensile test results when regenerated Al alloy is added. Tensile test results by the addition of regenerated Al did not show a significant difference as shown in the following table, but some pores were found in the specimen by the scanning electron micrograph of FIG. 11. Using the EDS attached to the scanning electron microscope, the distribution of the fine inclusions in the pore area was not found. These results indicate that the molten metal was effectively managed.

As mentioned above, in the method of manufacturing the molten metal forging alloy according to the present invention, the castability is improved due to the pressurizing effect during the forging of the melt, and the tensile strength is generally increased due to the pressurization and quenching effect due to the forging. The effect of improving about -30% was obtained.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the present invention described in the claims I can understand that you can.

Claims (1)

In the Al-Fe alloy, an alloy containing Fe composition of 1 to 7 wt% was determined as a starting alloy, the alloy was melted at 850 to 900 ° C. in an electric resistance furnace, and degassed at 0.2% of the melt weight. Gravity casting and molten forging are performed with molten metal, and the molten forging is manufactured by using a vertically pressurized molten metal forging press to produce a Φ5 × 10 cm rod-shaped specimen, wherein the molten metal is maintained at an injection temperature of 750 ° C., and the mold is Preheating to 200 ~ 250 ℃ to apply the inner mold and the punch with an oil-based graphite release agent, after the injection of the molten metal, the pressing force is set to 50 ~ 100MPa, pressurization time is 60sec, pressurization speed is set to 20mm / sec Method for producing a crude alloy.

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