KR0121569B1 - Method of manufacturing aluminium sheet - Google Patents

Abstract

Boards for aluminium-alloy utensils having superior strength and surface hardness are manufactured by hot and cold rolling of an alloy cast body which is comprised of iron, silicon, etc. After preparing an alloy cast consisted of iron of 1.67% by weight, silicon of 0.05% by weight, titanium of 0.03% by weight and aluminium, the alloy cast is maintained at 580 deg C for 12 hours and preheated at 450deg.C. Then, a square-shaped material is prepared by hot extraction and a final board material is obtained by cool rolling. After the final board material is maintained at 400 deg C for 1 hour, the final board material is subject to annealing and recrystallizing, and an aluminium alloy board material is finally manufactured.

Description

Manufacturing method of plate for aluminum alloy material to obtain milky white anodized film

1 is a photograph of the observation of the orange peel at the surface grain structure of the final annealing plate in Example 1 and very severely bent (90 ° or more) after the molding,

(A) is a photograph showing the structure after the Tucker etching of the annealing plate

(B) is a picture of observing the orange peel after molding.

2 is a photograph showing the effect of mechanical polishing on the surface grain structure of Example 4.

(A) Tucker etching structure

(B) Tucker etching structure after normal mechanical polishing

(C) is a photograph of orange peel after molding

3 is a photograph of the observation of the orange peel at the surface grain structure of the final annealed sheet material and the severely bent portion (90 ° or more) in Comparative Example 1,

(A) is a photograph showing the structure after the Tucker etching of the annealing plate

(B) is an image of orange peel after molding

4 is a photograph showing the change of the surface dispersion structure according to the change of Si content,

(A) Example 1

(B) Comparative Example 1

Figure 5 is a photograph showing the observation of the orange peel at the surface grain structure of the final annealed sheet material and Comparative Example 2 very severely bent after the molding (more than 90 °),

(A) Tucker etching organization chart of annealing plate

(B) is an image of orange peel after molding

The present invention relates to the production of aluminum alloy plate material for a material having a milky white anodized film, and more particularly to the production of a plate material with excellent moldability and excellent hardness and surface hardness than the conventional manufacturing process. In general, in producing a base aluminum alloy sheet having a milky white anodized film, an Al alloy containing a small amount (1.0-2.5 wt.%) Of Fe is homogenized at a temperature higher than the usual homogeneous temperature at 550 ° C. or higher and is usually used. It was first known in Japanese Patent Application No. 49-16341 that anodized in sulfuric acid solution of ethylene can give an elegant milky white anodized film.

Later, Japanese Patent Application Laid-Open No. 60-103164 has used this fact to optimize the alloy composition and to define homogeneous and hot working conditions to propose a method for producing an aluminum alloy for milky natural color-developing materials with dense microstructure and uniform color tone.

The core technology of this technology is whether the process of heat treatment at high temperature of 550 ℃ or higher is included in the entire board manufacturing process.

This is because the metastable Al ₆ Fe phase, which is crystallized during casting, is colored gray black during anodization in sulfuric acid solution, and the Al ₃ Fe phase, which is stable, is colored milky white.

When heat-treated at a high temperature more than 550 ℃ Al ₆ Fe phase castings that were colored with hoeheuksaek because the phase transformation into a stable Al ₆ Fe is set to indicate a positive electrode oxide film having a translucent white as the heat-treated at a high temperature.

In view of the characteristics of the Japanese process, it is mainly applied to hot rolling, and complete the phase transformation of the Al ₆ Fe → Al ₃ Fe phase for milky color with homogeneity by heat treatment for a long time at high temperature (at 560 ℃ or more) during homogeneous treatment After heat processing, normal low temperature annealing (400-460 degreeC) is performed, It is characterized by the above-mentioned.

Recently, a domestic patent (notice 93-7949) proposed a method for producing a milky white anodized film using hot extrusion instead of hot rolling using the phase transformation principle.

In the case of hot extrusion, it is said that the temperature of the extruded material rises rapidly due to the generation of a large amount of deformation heat, so that the existing Japanese hot working process (Japanese Patent Application No. 60-103164) cannot be used.

Accordingly, the newly designed process is characterized by homogeneous treatment at a relatively low temperature (550-570 ° C.) for a short time to suppress phase transformation of Al ₆ Fe → Al ₃ Fe phase during homogeneous treatment, and then lower the temperature than the normal hot working temperature. After preheating to the temperature and hot-extruded to form a sheet by cold rolling, and then subjected to a long time at a very high temperature of more than 580 ℃ in the annealing process to complete the Al ₆ Fe → Al ₃ Fe phase transformation for the milky color with annealing treatment It features.

The method of manufacturing a milky white aluminum alloy sheet using the hot extrusion is performed in a milky white color (Al ₆ Fe → Al ₃ Fe phase transformation) by maintaining a long time (7-11 hours) at a high temperature (580-620 ℃) during the annealing process in contrast to the Japanese process There was a problem in that the crystal grains recrystallized in relation to the treatment is excessively grown to lower the strength and surface hardness of the final plate.

In addition, the homogeneous treatment tended to be incomplete due to the relatively short time (5-7 hours) at 550-570 ° C. during homogeneous treatment (to prevent Al ₆ Fe → Al ₃ Fe phase transformation as much as possible).

As a result, the orange peel phenomenon tended to occur at the place where the material was sharply deformed, such as a sharp bending part of the product.

The present invention is a method of manufacturing a plate using extrusion to improve the disadvantages, unlike the domestic process (notice 93-7949), while maintaining a long time at high temperature during homogeneous treatment to sufficiently homogeneous and at the same time phase transformation for complete milky color development ( Al ₆ Fe → Al ₃ Fe).

In addition, the purpose is to improve the material of the plate material by performing a normal low temperature annealing (350-450 ℃) to completely solve the orange peel problem and to improve the strength and surface hardness.

This series of processes is rather similar to the Japanese process, which mainly uses hot rolling.

However, when hot extrusion is used, unlike hot rolling (as already pointed out in Korean Patent Publication 93-7949), the surface temperature of the extruded material is greatly increased during extrusion due to the severe deformation difference.

As a result, excessive coarsening of grains occurs, resulting in coarsening of the product and causing defects.

The present invention newly discovers that the grain coarsening problem is largely dependent on the Si content of the alloy, and as a result, by adjusting the Si content, the grain coarsening problem is completely solved while the extrusion for the extrusion utilizing the characteristics of high temperature homogeneity and low temperature annealing. A new process has been developed.

Hereinafter, the present invention will be described in detail.

The alloy composition of the present invention is: Fe: 1.0-2.5wt.%; Si: 0.10 wt.% Or less; Ti: 0.0l-0.08wt.% And the rest is composed of an alloy of impurities and Al.

Fe is an essential element for obtaining a milky white anodized film.

Fe 1.0wt.% Or less of Al ₃ Fe particles as a milky color development is small, the color development effect is not sufficient, at 2.5wt.% Or more it is easy to form coarse crystals such as Al ₃ Fe → Al ₆ Fe during casting The uniformity and formability of crystal grains fall. Si plays a very important role in this process and its effect is newly discovered in the present invention.

That is, Si greatly improves the growth rate of dispersions (Al ₆ Fe, Al _m Fe, Al ₃ Fe) formed during casting during homogeneous treatment, and this effect tends to increase with increasing Si content.

As a result, in the case of homogeneous treatment at a high temperature for a long time like this process, when the Si content is more than 0.10 wt.%, The dispersions are excessively coarsened, resulting in excessive grain growth during hot extrusion, and thus the microstructure of the final plate is excessive. It is coarsened so that the quality of the product is greatly reduced.

This problem does not occur during hot rolling (Japanese Patent Laid-Open No. 60-103164). This is because during hot extrusion, the temperature of the extruded material rises momentarily due to many deformations occurring during extrusion.

Such rapid temperature rise easily causes excessive coarsening of partial grains during hot working.

Ti plays a role of miniaturizing the grain size of the cast body, thereby improving drawing formability and suppressing orange peel generation.

At 0.01 wt.% Or less of Ti, there is little effect, and coarse crystallization may be formed at 0.08 wt.% Or more to inhibit hot workability and drawing formability.

Unlike the conventional process (domestic patent publication 93-7949), the billet of the alloy casting is homogenized for a long time (more than 10 hours-16 hours) at a high temperature of 560-620 ℃.

Its purpose is to completely remove the orange peel that may be present in severely deformed areas, such as edge breaks, by sufficient homogeneous treatment.

The second is to completely transform the black gray color factor Al ₆ Fe to the milky color factor Al ₃ Fe phase during anodization during casting. This is completely different from the purpose of the existing process.

This is because the purpose of the existing process is to perform homogeneous treatment but to suppress Al ₆ Fe → Al ₃ Fe phase transformation as much as possible (see Patent Publication 93-7949).

At low temperatures, a relatively long time (˜16 hours) of heat treatment is required, and at high temperatures, a relatively short time (˜10 hours) of heat treatment time is required.

If the temperature is lower than the air temperature range or the heat treatment time is shorter than this, the phase transformation is incomplete and the final plate tends to be colored gray during coating. If the temperature is higher than the temperature range or longer, the grains of the final board tend to be excessively coarsened.

Next, the homogenized billet is preheated at 400-460 ° C and hot-extruded to obtain a rectangular shape.

Below 400 ° C., deformation is difficult, and a lot of energy is consumed during extrusion, and the material of the plate may be degraded due to difficulty in uniform extrusion.

Above 460 ° C, the surface temperature of the extruded material rapidly rises due to a lot of deformation heat generated during extrusion, resulting in excessive coarsening of the surface grains, resulting in coarsening of the surface structure of the final plate.

This process uses a higher extrusion preheating temperature than the existing domestic process, which seems to be possible because of the different homogeneous conditions.

Next, cold rolled extruded extruded material is made of a plate having a desired thickness.

The substrate is then annealed and recrystallized at 350-500 ° C. for 0.5-5 hours.

The purpose of this process is for pure annealing and recrystallization, and it is difficult to obtain sufficient recrystallization at 350 ° C. or lower, and coarsening of recrystallized grains may occur at 500 ° C. or higher to lower mechanical strength.

This process is completely different from the existing process (Guns 93-7949).

Existing processes are simultaneously subjected to phase transformation treatment for milky white color during annealing, so that they are heat treated at a high temperature of 560 ° C. or more for a long time.

Rather, this process is very similar to the process of Japanese Patent Application Laid-Open No. 60-103164 mainly using hot rolling.

As a result of the mechanical test of the plate thus manufactured, it was possible to obtain a plate having excellent formability and excellent strength and surface hardness than that produced by the conventional process.

The substrate was molded into a desired shape and then subjected to a conventional anodizing film in a sulfuric acid bath to obtain a uniform and dense elegant milky white material.

In addition, the problem of orange peel occurrence, which frequently occurs in severely deformed parts such as severely bent parts of the body, has been completely eliminated.

Next, the Example by this process and the comparative example by the existing process are demonstrated.

Example 1:

The composition Fe: 1.67 wt.%; Si: 0.05 wt.%; An alloy consisting of Ti and 0.03 wt.% And the remainder of impurities and Al is cast into a 178 mm diameter billet.

The billet is kept homogenized at 580 ° C. for 12 hours.

It is pre-heated at 450 degreeC, and then hot-extruded and the square extruded material of 160 mm x 10.5 mm is obtained.

This was cold rolled to obtain a final sheet having a thickness of 2 mm, and then maintained at 400 ° C. for 1 hour to be annealed and recrystallized.

As a result of observing the plate material prepared in this way with an optical microscope after etching with a Tucker solution, most of the structure was significantly superior to the density produced by the conventional extrusion process (Fig. 1 (a)). However, sometimes areas that appear to be Cho Dae Jung were observed, and the problem is explained in detail in FIG. As a result of testing the mechanical properties (Table 1), the elongation was superior to the plate manufactured by the existing process, but the strength and surface hardness were excellent.

As a result of molding to the desired shape, it was possible to obtain an excellent product without any orange peel even in a very severely bent portion (90 ° or more) (Fig. 1 (b)).

Anodized for 30 minutes in a 15% sulfuric acid solution with a current density of 2A / dm ² showed an elegant milky white anodized film, and its texture and color tone were very dense and uniform.

Example 2:

The composition Fe: 1.67 wt.%; Si: 0.05 wt.%; Ti: 0.03wt.% And the remainder is cast alloy of impurity and Al with 178mm straight billet, homogeneous treatment at 600 ℃ for 10 hours, and other processes are the same as in Example 1 to prepare a plate of 2mm thick Prepared. As a result of anodizing in the same manner as in Example 1, similar to Example 1, the milky white color tone was very uniform and dense, thereby obtaining an elegant milky white substance having no orange peel.

Example 3:

The composition Fe: 1.67 wt.%; Si: 0.05 wt.%; An alloy consisting of Ti: 0.03 wt.% And the remainder of impurities and Al was cast and homogenized in the same manner as in Example 1, followed by preheating at 420 ° C., hot extrusion and cold rolling to prepare a plate having a thickness of 2 mm. In this case the microstructure of the sale was similar to Example 1 overall. Testing of the mechanical properties of the sheet showed that the strength tended to decrease slightly, but generally showed similar strength and elongation.

Example 4:

The composition Fe: 1.67 wt.%; Si: 0.05 wt.%; Ti: 0.03wt.% And the remainder of the alloy consisting of impurities and Al in the same manner as in Example 1, homogeneous treatment at 620 ℃ for 10 hours, preheated to 440 ℃ hot-extruded and cold rolled to a plate of 2 mm thick Prepared.

After etching this in the Tucker solution, the surface texture was observed. Some coarse grains were observed on the surface (Fig. 2 (a)). The tissue was observed ((b) of FIG. 2). As a result, no surface roughness was found. This shows that Cho Jung-jung exists extremely limited to the surface. Therefore, the presence of such surface roughness does not affect the beauty of the final product. As a result, orange peel was not observed at all when the surface polished sheet was molded into a base ((c) of FIG. 2), and similar to Example 1, the color of the anodized film was very uniform and dense.

Comparative Example 1:

The composition Fe: 1.67 wt.%; Si: 0.15 wt.%; Ti: 0.03wt.% And the rest of the alloy consisting of impurities and Al in the same manner as in Example 1 to prepare a plate of 2mm thickness. After etching this with a Tucker solution, the surface structure was observed (FIG. 3 (A)). As a result, the crystal grains were very coarse. As a result of molding to the desired shape, the orange peel phenomenon was severely generated (Fig. 3 (b)). This difference is due to the Si content. As shown in FIG. 4, FIG. 4 (a) of Example 1 shows a comparative example 1 in which the spacing of the dispersion is dense during homogeneous treatment, whereas the Si content is large. 4 (b) tended to significantly coarse the dispersion during homogeneous treatment. As a result, remarkable coarsening of recrystallized grains occurs during hot extrusion.

Comparative Example 2:

The composition Fe: 1.74 wt.%; Si: 0.05 wt.%; Ti: 0.03wt.% And the remainder was cast in the same manner as the alloy consisting of impurities and Al in the same manner as in Example 1 and the billet was homogenized at 570 ℃ for 7 hours.

After preheating this at 410 degreeC, the square extruded material of 160 mm x 10.5 mm is obtained. This was cold rolled to a sheet of 2 mm thick and then annealed by heating and holding at 600 ° C. for 10 hours.

This process can be seen that the surface texture observed after etching with a Tucker solution in the domestic patent (Gun 93-7949) shows a generally fine and uniform surface texture (Fig. 5 (a)). However, compared with the case of Example 1, the fineness tends to be inferior.

As a result of molding to the desired shape, the orange peel tends to be observed in a very sharply bent portion (90 ° or more), as shown in FIG. As a result of testing the mechanical properties of the plate, as shown in Table 1, the elongation tends to be less than or equal to Example 1, but the strength and surface hardness are relatively low.

Table 1

Claims (2)

The weight ratio of Fe: 1.0 to 2.5%, Si: 0.10% or less, Ti: 0.01 to 0.08%, and the remainder of the cast (billet) of the alloy consisting of impurities and Al in the temperature range of 560-620 ℃ over 10 hours to 16 hours It consists of a process of heating and preheating at a temperature range of 400-460 ° C., followed by hot extrusion, and a step of cold rolling the extruded material to sell a plate, and then heating it at a temperature range of 350-500 ° C. for 0.5-5 hours. Method for producing a plate for aluminum alloy substrates to obtain a milky white anodized film characterized in that. The weight ratio of Fe: 1.0 to 2.5%, Si: 0.10% or less, Ti: 0.01 to 0.08%, and the rest of the cast (billet) of the alloy consisting of impurities and Al in the temperature range of 560-620 ℃ over 10 hours to 16 hours Heating and preheating at a temperature range of 400-460 ° C. and hot extrusion, and extruding the surface of the extruded material after cold rolling to form a plate, and heating and maintaining the same at a temperature range of 350-500 ° C. for 0.5-5 hours. A method for producing a plate for aluminum alloy substrates to obtain a milky white anodized film, characterized in that the process is made.