Aluminum alloy billet for extruded material, extruded material using same, and method for producing extruded material

Abstract

The purpose of the present invention is to provide an aluminum alloy billet for extruded material of which a wear-resistant aluminum alloy extruded material is obtainable, where a further purpose is to provide an extruded material having excellent wear resistance obtainable by the billet, and a method for producing the extruded material.　This billet is cast using an aluminum alloy that contains, in terms of mass percent, Si: 3.0-6.0%, Mg: 0.2-0.5%, Cu: 0.1-0.5%, Fe: 0.01 to 0.5%, Ti: 0.01 to 0.1%, and at least one of Mn, Cr, and Zr in a total amount of 0.01-0.6%, with the balance consisting of Al and inevitable impurities, and is characterized in that the average length of crystallized products in the metal composition is 100 μm or less, and the area ratio of the crystallized products therein is 6% or less.

Description

Aluminum alloy billet for extrusion material and extrusion material or method for manufacturing extrusion material using the same

[0001] The present invention relates to a wear-resistant aluminum alloy extrusion material having excellent caulking properties and fatigue strength, and is particularly effective in improving the utilization rate of recycled materials such as scrap materials.

[0002] In recent years, there has been an increasing need to recycle scrap materials generated in production processes and in the market in order to reduce environmental impact and energy consumption.

[0003] For example, Patent Document 1 discloses a method for producing aluminum casting alloys such as ADC12, which have improved recyclability by refining intermetallic compounds. Patent Document 2 discloses a plate material whose recyclability is improved by controlling second-phase particles in the metal structure to improve bending workability. However, these are applicable to casting aluminum alloys and plate materials, and are not applicable to wear-resistant aluminum alloy extrusions.

[0004] Japanese Patent Publication No. 2019-209362 Japanese Patent Publication No. 2010-116594

[0005] An object of the present invention is to provide an aluminum alloy billet for extrusion material from which a wear-resistant aluminum alloy extrusion material can be obtained, and to provide an extrusion material having excellent wear resistance obtained thereby, and a method for producing the same.

[0006] Automotive parts include sliding components and housing components incorporating sliding components. To apply aluminum alloy extrusions to these applications, wear resistance is required, so aluminum alloys containing a certain amount of Si are used. However, if Si particles in the metal structure are not controlled, cracks and other defects are likely to occur from these Si particles, resulting in reduced fatigue strength and reduced caulking properties. Furthermore, the use of scrap material can increase the amount of impurities in the alloy, leading to larger or more abundant crystallized particles in the metal structure, which can act as crack initiation sites and cause reduced tensile strength, fatigue strength, caulking properties, and other issues. Therefore, the present invention was developed as a result of investigations into aluminum alloy compositions and billets, as well as extrusions and manufacturing methods using such extrusions, that can contribute to improving the utilization rate of scrap material.

[0007] The aluminum alloy billet for extrusion material according to the present invention is a billet cast using an aluminum alloy containing, in mass %, Si: 3.0 to 6.0%, Mg: 0.2 to 0.5%, Cu: 0.1 to 0.5%, Fe: 0.01 to 0.5%, Ti: 0.01 to 0.1%, and one or more of Mn, Cr, and Zr, with a total of 0.01 to 0.6%, and the balance being Al and unavoidable impurities, and is characterized in that the average length of crystallized particles in the metal structure is 100 μm or less, and the area ratio of the crystallized particles is 6% or less.

[0008] The aluminum alloy extrusion material according to the present invention is produced using the aluminum alloy billet for extrusion material according to claim 1, and is characterized in that the average length of the crystallized particles in the metal structure of the extrusion material is 20 μm or less, and the area ratio of the crystallized particles is 6% or less.

[0009] Such an aluminum alloy extrusion material can be obtained by extruding the aluminum alloy billet for extrusion material described in claim 1 at an extrusion ratio of 8 or more, cooling the extruded material from a temperature of 400 to 550°C at a rate of 50 to 750°C / min, and then subjecting it to artificial aging treatment. Here, the extrusion ratio refers to the ratio of the cross-sectional area of ​​the billet to the cross-sectional area of ​​the extruded material.

[0010] The aluminum alloy extrusion material manufactured as described above has a tensile strength of 250 MPa or more, a 0.2% yield strength of 200 MPa or more, a wear amount of 10 μm or less in a predetermined friction and wear test, a fatigue strength of 100 MPa or more in a rotating bending fatigue test method, and a limit upsetting ratio of 30% or more in a cold upsetting property test method, and is excellent in wear resistance, fatigue strength, and caulking property.

[0011] By using the aluminum alloy billet for extrusion material according to the present invention, a wear-resistant aluminum alloy extrusion material excellent in caulking property and fatigue strength can be obtained even if 30% or more of scrap material generated in the production process or scrap material collected from the market is used.

[0012] The alloy composition used in the evaluation is shown. The billet casting conditions are shown. The extrusion conditions, fatigue strength, and mechanical properties are shown. The evaluation results are shown.

[0013] First, the reasons for selecting the alloy composition are as follows: <Si> The Si component is a mixture of the Mg component and Mg ２ By precipitating Si, strength is obtained through age hardening, and wear resistance is secured by Si particles. If there are too many Si particles, the Si particles become crack initiation points, and the caulking property decreases. Therefore, the range of Si: 3.0 to 6.0%, Mg: 0.2 to 0.5% is preferable. <Mg> Part of Si is converted into Mg. ２Since Si is reduced, the Si particles that contribute to wear resistance are significantly affected by the amount of Mg added. Wear resistance is stable at 3.5 to 5.0% Si particles. The presence of a large amount of hard, fine Si particles in the metal structure disperses chips starting from the Si particles. The fine dispersion of Si particles improves fatigue strength. A minimum of 0.2% Mg is required for strength, and 0.5% or less is preferred to ensure caulking properties. Fatigue strength is improved by improving tensile strength. <Cu> To improve strength while ensuring caulking properties, a Cu content of 0.01 to 0.5% is recommended. Since Cu dissolves to a certain extent, the solid solution effect improves strength and machinability. Since high Cu content increases the likelihood of potentiometric corrosion, it is preferably limited to 0.10 to 0.20%. <Fe> Fe particles disperse at grain boundaries, improving machinability starting from the Fe particles. Considering the use of scrap material, an Fe content of 0.01 to 0.5% is preferable. At 0.5% or more, caulking performance decreases. <Zr> Suppresses recrystallization, contributes to grain refinement and Si particle refinement, and inhibits fatigue propagation, improving fatigue strength and machinability. Zr: 0.5% or less is preferable. Suppresses recrystallization and refines grains, thereby inhibiting fatigue propagation and improving fatigue strength and machinability. Mn: 0.01 to 0.5% is preferable. Mn precipitates at grain boundaries, which may cause potential corrosion and reduce caulking performance. <Cr> Suppresses recrystallization and refines grains, which may increase fatigue propagation, improving fatigue strength and machinability. Cr: 0.01 to 0.5% is preferable. Cr may produce primary crystals, reducing caulking performance. <Ti> Has the effect of refining grains, and trace amounts also improve machinability. If it exceeds 0.1%, the life of the cutting tool will be shortened.Ti: The range of 0.01 to 0.1% is preferable.

[0014] The extruded material is manufactured using the following method. <Manufacturing Method> A 10-inch billet is cast and homogenized at 460-580°C for 2-12 hours or more. The billet is then preheated to 460-580°C to obtain a rectangular extruded material measuring approximately 40 mm x 100 mm. For the T6 heat treatment, the die edge is quenched immediately after extrusion, and artificial aging heat treatment is performed by heating at 160-200°C for 1-12 hours.

[0015] Next, the test items and test methods are as follows. <Fatigue properties> JIS-1 (1-8) rotating bending fatigue test pieces were prepared from the extruded material in accordance with JIS-Z2274, and fatigue tests were conducted using an Ono-type rotating bending fatigue tester in accordance with JIS standards. <Tensile properties> JIS-13 B tensile test pieces were taken from the extruded material, and tensile tests were conducted in accordance with JIS-Z2241. <HRB hardness> The surface hardness of the extruded material was measured in accordance with JIS-Z2245 using a Rockwell B-scale hardness tester. <Crackability> A cold upsetting test method was used. Test pieces measuring 14 mm in diameter and 21 mm in height were taken from the extruded material, and these were upset-pressed in the axial direction in the cold to determine the critical upsetting ratio at which microcracks began to appear on the side. The critical upsetting ratio was calculated using the following formula. εhc = h0 - hc / h0 x 100 εhc: Limiting upset ratio (%) h0: Original height of test piece hc: Height of test piece at crack initiation Test conditions were room temperature, compression speed 10 mm / sec, and a 25-ton autograph was used. <Wear Resistance> A friction and wear tester (Orientec EFM-3-F model) was used. The test method involved rotating two different cylindrical specimens (pin and test piece disc) aligned on their centerlines and applying a constant load to the pin to generate friction and wear. The pin was made of SCr20 (carburized and quenched) material, 5 mm in diameter and 8 mm in height. The test piece disc was cut from the extruded material and machined to a diameter of 60 mm, height 5 mm, surface roughness of 1.6Z or less, and flatness of 0.01 or less. Brake fluid was used as the lubricant, and the test was performed at a rotation speed of 160 rpm, for a test period of 50 hours, and a pressure load of 20 MPa. The test atmosphere temperature was 40°C or less. The wear amount was measured by measuring the worn area of ​​the test piece disk with a roughness measuring instrument. <Crystal grain size, Si grain size> A sample was cut out from the center of the extruded material, mirror polished, and then etched, and the metal structure was observed under a 400x brightness microscope. <Surface recrystallization depth> A sample was cut out from the surface of the extruded material, mirror polished, and then etched, and the metal structure was observed under a 50x brightness microscope. <Crystallized particle length, crystallized particle ratio> A sample was cut out from the center of the extruded material, mirror polished, and then etched, and the metal structure was observed under a 400x brightness microscope.<DAS> Samples were cut from the billet, and the billet surface was mirror-polished. Then, it was etched with Keller's reagent (0.5% HF) and measured under a microscope. <Corrosion Resistance> Test pieces measuring 35L x 35W x 35H were cut from the extruded material, and a Dacrobolt was attached to the central thread. <1 cycle> The test pieces were immersed in a 3.5% NaCl aqueous solution at 25°C for 10 minutes, then held in an atmosphere at 25°C and 40% humidity for 50 minutes, after which they were removed from the test furnace and allowed to air dry. 720 cycles were performed under these conditions, and evaluation was performed by measuring the corrosion depth at the contact surface of the Dacrobolt and its vicinity.

[0016] Molten aluminum alloys having the compositions shown in the table of Fig. 1 were used to cast billets as shown in Fig. 2, and then extrusion and artificial aging treatment were carried out under the conditions shown in Fig. 3. The evaluation results are shown in the tables of Fig. 3 and Fig. 4. Note that Figs. 2 to 4 show the target values ​​that the present invention aims for, and results that were within the target values ​​were judged as "Good."

[0017] In Examples 1 to 12, billets were cast under the conditions shown in Figure 2 and extruded and heat treated under the conditions shown in Figure 3, achieving all targets. In contrast, Comparative Example 13 had a low Cu content, and the fatigue strength, yield strength, and hardness targets were not achieved. Comparative Example 14 did not contain any of Mn, Cr, or Zr, and the solidification rate was slow, so the fatigue strength and caulking properties were not achieved. Comparative Example 15 had excessive Cu, and the caulking properties were not achieved. Comparative Example 16 had low Si content and therefore contained a large amount of Mg, which provided strength but poor wear resistance. Comparative Examples 17 to 19 had a small extrusion ratio of less than 8, resulting in poor caulking properties.

[0018] The table in Figure 1 shows the percentage of scrap material added when preparing the aluminum alloy. The percentage of scrap material added is shown. In the table, "total (%)" refers to the percentage of the total amount of scrap material contained in the aluminum alloy, and "in-process scrap (%)" refers to the percentage of scrap material, such as scrap scrap generated during the manufacturing process of the extrusion material. "Commercial scrap (%)" refers to scrap material collected from the market, "sash scrap" refers to aluminum extrusion profiles, "chips and scrap" refers to chips and scraps collected from the market, and "wheel scrap" refers to vehicle wheels made of aluminum alloy. In the present invention, as shown in the examples, the target material properties were obtained even when using an aluminum alloy containing 30% or more recycled material.

[0019] The aluminum alloy billet for extrusion material according to the present invention can be used in a wide range of applications because it can provide extrusion materials that are excellent in wear resistance, fatigue strength and caulking properties even when the proportion of recycled material used is high.

Claims

1. An aluminum alloy billet for extrusion material, which is cast using an aluminum alloy containing, by mass%, Si: 3.0-6.0%, Mg: 0.2-0.5%, Cu: 0.1-0.5%, Fe: 0.01-0.5%, Ti: 0.01-0.1%, and one or more of Mn, Cr, and Zr, with a total of 0.01-0.6%, and the balance being Al and unavoidable impurities, and which is characterized in that the average length of crystallized particles in the metal structure is 100 μm or less and the area ratio of the crystallized particles is 6% or less.

2. An aluminum alloy extrusion material made using the aluminum alloy billet for extrusion material according to claim 1, characterized in that the average length of the crystallized particles in the metal structure of the extrusion material is 20 μm or less and the area ratio of the crystallized particles is 6% or less.

3. A method for producing an aluminum alloy extrusion material, comprising extruding the aluminum alloy billet for extrusion material described in claim 1 at an extrusion ratio of 8 or more, cooling the extruded material from a temperature of 400 to 550°C at a rate of 50 to 750°C / min, and then artificially aging the extruded material.

4. A method for manufacturing an aluminum alloy extrusion material according to claim 3, characterized in that it has a tensile strength of 250 MPa or more, a 0.2% yield strength of 200 MPa or more, a wear amount of 10 μm or less in a specified friction and wear test, a fatigue strength of 100 MPa or more in a rotating bending fatigue test method, and a limit upsetting rate of 30% or more in a cold upsetting property test method, and is excellent in wear resistance, fatigue strength and caulking properties.

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