KR20240101383A - Cast, hot-worked product of al-mg-si aluminum alloy and production method therefor - Google Patents

Abstract

The present invention provides a cast hot-worked product of Al-Mg-Si-based aluminum alloy that can suppress crack growth when a tensile load is applied at a constant load in high humidity, and a method for manufacturing the same.
A cast hot worked product of an Al-Mg-Si aluminum alloy, wherein the aluminum alloy contains Si and Cu, and the Si/Cu ratio, which is the ratio of the mass % of the Si to the mass % of the Cu, is less than 3.3. Hot processed products.

Description

Casting hot worked products of Al-Mg-Si aluminum alloy and manufacturing method thereof {CAST, HOT-WORKED PRODUCT OF AL-MG-SI ALUMINUM ALLOY AND PRODUCTION METHOD THEREFOR}

The present disclosure relates to a cast hot-worked product of an Al-Mg-Si-based aluminum alloy and a method for manufacturing the same.

Patent Document 1 discloses a method for manufacturing an Al-Zn-Mg (7000 series) cast material that is resistant to stress corrosion cracking (SCC).

Japanese Patent Publication No. 2002-348631

In conventional aluminum alloys, crack propagation may not be suppressed when a tensile load is applied at a constant load in high humidity. In the prior art, the SCC test has been examined for aluminum alloys, but the HG-SCC (Humid Gas Stress Corrosion Cracking) test has not been examined for aluminum alloys.

The present disclosure has been made in consideration of the above circumstances, and provides a cast hot-worked product of an Al-Mg-Si-based aluminum alloy that can suppress crack growth when a tensile load is applied at a constant load in high humidity and a method for manufacturing the same. The main purpose is to

The cast hot-worked product of the present disclosure is a cast hot-worked product of an Al-Mg-Si-based aluminum alloy, wherein the aluminum alloy includes Si and Cu, and Si is the ratio of the mass% of the Si to the mass% of the Cu. The /Cu ratio is less than 3.3.

In the present disclosure, there is a method for manufacturing a cast hot worked product of an Al-Mg-Si-based aluminum alloy, which includes casting the Al-Mg-Si-based aluminum alloy to obtain an ingot, hot working the ingot, and In order to obtain a cast hot-worked product, the reduction ratio of the cast hot-worked product during the hot working may be 10% or more.

In the present disclosure, the hot working may be hot forging.

The present disclosure can provide a cast hot-worked product of an Al-Mg-Si-based aluminum alloy that can suppress crack growth when a tensile load is applied at a constant load in high humidity, and a method for manufacturing the same.

1 is a graph showing the relationship between the Si/Cu ratio and the initial crack length.
Figure 2 is a graph showing the relationship between reduction rate and initial crack length.

1. Casting hot work products

The cast hot-worked product of the present disclosure is a cast hot-worked product of an Al-Mg-Si-based aluminum alloy, wherein the aluminum alloy includes Si and Cu, and Si/, which is the ratio of the mass% of the Si to the mass% of the Cu. Cu ratio is less than 3.3.

High-strength aluminum alloys have been developed to miniaturize molds and valve parts for high-pressure hydrogen tanks for next-generation fuel cell vehicles (FCEVs). In recent years, in the international regulations scheduled to be enacted regarding materials that can be used in a high-pressure hydrogen environment, when using aluminum alloys other than A6061 material, it is necessary to pass the four hydrogen embrittlement investigation tests specified. For aluminum alloys, passing has already been confirmed in three tests: the tensile test in air, the slow strain rate tensile rupture test (SSRT: Slow Strain Rate Technique), which is a tensile test in hydrogen, and the fatigue test in hydrogen, but the remaining HG -It was not possible to confirm passing the SCC exam. In existing research, it has been reported that even aluminum alloys outside the range of 6061 components meet the test passing conditions if the Si and Cu components are adjusted within the predetermined range. However, aluminum alloys produced within the predetermined range also fail. I found out that this can happen.

The HG-SCC test is a test to determine whether stress corrosion cracking (SCC), which is characteristic of aluminum alloys and occurs when a certain load is applied at high humidity, occurs. On the other hand, a crescent-shaped fracture surface was confirmed in the rejected aluminum alloy. A crescent-shaped fracture is a fracture shape that is easily formed in materials with low toughness. Additionally, if the material has high toughness, the fracture surface extends in parallel. Therefore, in the HG-SCC test, it is expected that not only the stress corrosion cracking phenomenon but also the toughness of the aluminum alloy will be greatly affected. In addition, in existing research, there are reports that even if a large amount of Si is added to the aluminum alloy, the test passing conditions are met if Cu is added at 0.3% or more, but there is no knowledge that has investigated the actual range of Si/Cu ratio that would fail. , it is unclear whether all the identified cracks are due to the lack of toughness of the aluminum alloy, and it is possible that the cracks are caused by stress corrosion cracking phenomenon.

In this disclosure, it is expected that the results of the HG-SCC test are greatly influenced by the toughness of the aluminum alloy, and a standard product is manufactured in which the reduction ratio of hot working and the components of Si and Cu, which affect the toughness of the aluminum alloy, are changed. and discovered conditions that can suppress crack growth when a tensile load is applied at a constant load in high humidity.

In the present disclosure, a method for producing an aluminum alloy was discovered in which a constant tensile load is applied to a test piece (TP) in high humidity for 90 days, and the crack length that develops is equal to or less than a predetermined length.

In order to improve the toughness of an aluminum alloy, it is effective to perform hot working during the manufacturing process, and in this disclosure, an attempt was made to improve the toughness of an aluminum alloy by hot working.

The cast hot-worked product of the present disclosure is a cast hot-worked product of an Al-Mg-Si-based aluminum alloy.

The Al-Mg-Si-based aluminum alloy contains Si and Cu, and the Si/Cu ratio, which is the ratio of the mass % of Si to the mass % of Cu, is less than 3.3. The Si/Cu ratio may be 1.6 or more.

The Al-Mg-Si series aluminum alloy used in this disclosure is a 6000 series aluminum alloy.

The chemical composition (mass %) of the Al-Mg-Si-based aluminum alloy used in the present disclosure is 0.80 to 3.00 mass % of Mg, 0.40 to 1.26 mass % of Si, 0.15 to 0.52 mass % of Cu, and 0.70 mass % of Fe. % or less, Cr may be 0.04 to 0.35 mass%, Mn may be 0.15 mass% or less, Zn may be 0.25 mass% or less, and Ti may be 0.15 mass% or less, with the balance consisting of aluminum and inevitable impurities.

Mg: 0.80 to 3.00 mass%

Mg is effective in improving mechanical properties. In case of Mg deficiency, mechanical properties are insufficient. If Mg is excessive, castability, forgeability, stress corrosion cracking resistance, and elongation deteriorate. Mg may be 1.20 mass% or less.

Si: 0.40 to 1.26 mass%

Si may be 0.79 mass% or more. If the Si content increases too much, the mechanical properties deteriorate.

Cu: 0.15 to 0.52 mass%

Cu is effective in improving mechanical properties and stress corrosion cracking resistance. When Cu is insufficient, mechanical properties are insufficient and improvement in stress corrosion cracking resistance is insufficient. If Cu is excessive, corrosion resistance and elongation decrease. Cu may be 0.30 mass% or more.

Fe: 0.70% by mass or less

Fe is an impurity that is easily incorporated during the refining and casting process of aluminum, and as the content increases, the mechanical properties deteriorate. Fe may be 0.35 mass% or less, and may be 0.25 mass% or less.

Cr: 0.04 to 0.35 mass%, Mn: 0.15 mass% or less, Zn: 0.25 mass% or less, Ti: 0.15 mass% or less

Cr, Mn, Zn, and Ti are optional components in the aluminum alloy of the present disclosure.

Cr and Mn are effective in preventing recrystallization during heating such as heat treatment, and are also effective in improving stress corrosion cracking resistance and mechanical properties. If Cr and Mn are excessive, the effect becomes a limitation, and insoluble compounds may increase and mechanical properties may deteriorate.

Zn is effective in improving mechanical properties. If Zn is lacking, mechanical properties are lacking. If Zn is excessive, casting cracks, etc. are likely to occur, and castability, forgeability, stress corrosion cracking resistance, and elongation are reduced.

Ti is effective in refining the grains of the solidified structure. If Ti is insufficient, the crystal grains become coarse, causing cracks during casting and surface roughness during forging. If Ti is excessive, the effect becomes limiting, and insoluble compounds increase and mechanical properties deteriorate.

In the present disclosure, the crack length (HG-SCC crack length) of the cast hot worked product measured by the wet gas stress corrosion cracking (HG-SCC) test may be less than 1.57 mm, may be less than 1.27 mm, and may be less than 0.92 mm. , may be 0.50 mm or less, and may be 0.16 mm or less.

2. Manufacturing method of casting hot worked products

In the present disclosure, there is a method for manufacturing a cast hot worked product of an Al-Mg-Si-based aluminum alloy, which includes casting the Al-Mg-Si-based aluminum alloy to obtain an ingot, hot working the ingot, and In order to obtain a cast hot-worked product, the reduction ratio of the cast hot-worked product during the hot working may be 10% or more.

The manufacturing method of the present disclosure is performed in the following order: a casting process and a hot working process.

The manufacturing method of the present disclosure may be performed in the following order: a casting process, a homogenization treatment process, a hot working process, and a T6 heat treatment process.

The casting process is a process of casting an Al-Mg-Si aluminum alloy and obtaining an ingot.

The Al-Mg-Si-based aluminum alloy contains Si and Cu, and the Si/Cu ratio, which is the ratio of the mass % of Si to the mass % of Cu, may be less than 3.3, and the Si/Cu ratio may be 1.6 or more. .

The ingot may be a continuously cast bar (rolling bar).

In casting, an aluminum alloy may be melted at a melting temperature of 750°C, the molten metal may be cast in a mold with a casting temperature of 150°C, and solidified to obtain a cast material.

The melting temperature of the aluminum alloy is not particularly limited as long as it is a temperature at which the aluminum alloy melts.

The homogenization treatment process is a process of homogenizing the ingot.

The homogenization treatment may be performed by heating the ingot in a hot state at 430 to 470°C for 5 to 10 hours, for example.

The hot working process is a process of hot working the ingot and obtaining the cast hot worked product.

Hot working may be hot extrusion or rolling of the ingot, hot forging, or both. In the case of hot forging, since the obtained cast material is tempered at a predetermined reduction ratio, a test piece of a predetermined length may be obtained by cutting a test piece with a rectangular cross section of a predetermined width and a predetermined thickness and a predetermined length. The extruded material may be pressed into a forging mold of a predetermined shape and hot forged to obtain a cast hot forged product. The forging temperature of the extruded material may be, for example, 300 to 470°C, and the mold temperature of the forging die may be, for example, 200°C. The hot forging temperature in the case of hot forging may be higher than the recrystallization temperature or may be 300 to 480°C.

In hot working, the reduction ratio (also referred to as rolling ratio) of the cast hot-worked product may be 10% or more, 35% or more, and may be 60% or less.

The reduction ratio (%) means the ratio of the amount of reduction in the thickness of the metal material when plastic working the metal material and the thickness of the original metal material.

Specifically, when hot working is performed on an ingot of thickness A and the thickness of the cast hot worked product after hot working is set to B, the reduction ratio is calculated as follows.

Reduction rate (%)={(A-B)/A}*100

The T6 heat treatment process is a process of performing T6 heat treatment on the cast hot-worked product.

T6 heat treatment is performed on cast hot-worked products in the order of solution heat treatment, quenching, and artificial aging treatment. The strength of cast and hot-worked products can be increased by T6 heat treatment.

Solution treatment is a treatment that uniformly infiltrates added elements in a cast hot-worked product. In the solution treatment, the cast hot-worked product may be heated and held in an air atmosphere at a temperature of 440°C or higher and at a temperature that does not partially melt for about 3 to 6 hours. In solution treatment, if the temperature is too low, a solid solution is not created, and if the temperature is too high, it partially melts.

In quenching, after solution treatment, the cast hot worked product may be rapidly cooled with water at 25 to 80°C.

Artificial aging treatment refers to a treatment that precipitates a secondary phase by heating a cast hot-worked product to a predetermined temperature. In artificial aging treatment, after quenching, the cast hot-worked product may be heated and held at 140 to 240°C for 0.3 to 48 hours.

[Example]

(Example 1)

[Evaluation of initial crack length]

The composition range of the aluminum alloy was conducted in a composition range different from that of the A6061 alloy.

An Al-Mg-Si aluminum alloy having the Si/Cu ratio shown in Table 1 was prepared. Aluminum alloy is cast under conditions where casting cracks do not occur, homogenized at 470°C for 7 hours, hot forged at 300 to 470°C, and as T6 heat treatment, solution treated at 555°C for 3 hours, dissolved in water. Quenching and artificial aging treatment at 180°C for 6 hours were performed to obtain T6 material as a cast hot worked product. The reduction ratio during hot forging is shown in Table 1.

The cast hot-worked product was cut to a predetermined size to produce a test piece. As a simple HG-SCC test on the produced test piece, it was conducted for one day in an atmospheric environment without humidity control. After the test, the test piece was taken out, the crack fracture surface was observed, and the initial crack length (crack length that grows in 1 day) was evaluated. The evaluation results are shown in Table 2.

[HG-SCC test]

The HG-SCC test was performed on the produced test piece, and the crack length was evaluated. The evaluation results are shown in Table 2 as HG-SCC crack length.

The standard for the HG-SCC (wet gas stress corrosion cracking) test method is HPIS E 103:2018, which is a standard produced by the Japan High Pressure Technology Association, a general association, “Wet gas stress corrosion cracking of aluminum alloys for compressed hydrogen containers.” It is a “standard test method.”

[Other tests]

In addition, the tensile strength, proof strength, load stress, and fracture toughness values of the produced test specimens in an atmospheric environment were measured. These results are shown in Table 2.

(Examples 2 to 6, Comparative Examples 2 to 4)

Conditions were the same as in Example 1 except that an Al-Mg-Si aluminum alloy having the Si/Cu ratio shown in Table 1 was prepared, and hot forging was performed so that the reduction ratio of the cast hot worked product was the value shown in Table 1. A casting hot worked product was obtained. For the obtained cast hot-worked product, a test piece was produced in the same manner as in Example 1, and the initial crack length, HG-SCC crack length, tensile strength, proof stress, load stress, and fracture toughness values were measured. These results are shown in Table 2.

(Comparative Example 1)

An Al-Mg-Si aluminum alloy having the Si/Cu ratio shown in Table 1 was prepared, and a cast product was obtained under the same conditions as in Example 1 except that hot forging was not performed. For the obtained cast product, a test piece was produced in the same manner as in Example 1, and the initial crack length, HG-SCC crack length, tensile strength, proof strength, load stress, and fracture toughness values were measured. These results are shown in Table 2.

[Evaluation results]

1 is a graph showing the relationship between the Si/Cu ratio and the initial crack length.

Figure 2 is a graph showing the relationship between reduction rate and initial crack length.

As shown in Figures 1 and 2 and Tables 1 and 2, in Comparative Example 1 with a reduction ratio of 0%, the initial crack length was large without being affected by the Si/Cu ratio, and the HG-SCC crack length also exceeded 0.16 mm. You can see that In Comparative Example 2, where the reduction ratio is 10%, the Si/Cu ratio is high at 4.0, so it can be seen that the initial crack length is large. In Comparative Example 3, where the reduction ratio is 60%, the Si/Cu ratio is high at 4.0, so it can be seen that the initial crack length is large.

Additionally, in Examples 2, 3, and 5, it can be seen that the initial crack length and the HG-SCC crack length are 0 mm, satisfying the acceptance criteria for the HG-SCC test.

Therefore, in order to suppress crack growth in aluminum alloys when a tensile load is applied at a constant load in high humidity, a cast hot worked product must be formed under the conditions that the Si/Cu ratio is at least less than 3.3 and the reduction ratio of hot working is 10% or more. You can see what is needed.

Claims (3)

A cast hot-worked product of an Al-Mg-Si-based aluminum alloy, wherein the aluminum alloy contains Si and Cu, and the Si/Cu ratio, which is the ratio of the mass % of the Si to the mass % of the Cu, is less than 3.3. Hot processed products. A method for producing a cast hot worked product of the Al-Mg-Si aluminum alloy according to claim 1, comprising casting the Al-Mg-Si aluminum alloy to obtain an ingot, hot working the ingot, and A method for producing a cast hot-worked product, comprising obtaining a cast hot-worked product, wherein the reduction ratio of the cast hot-worked product in the hot working is 10% or more. According to paragraph 2,
A method of manufacturing a cast hot-worked product, wherein the hot working is hot forging.