CN110205528B

CN110205528B - Al-Mg alloy with high intergranular corrosion resistance and preparation method thereof

Info

Publication number: CN110205528B
Application number: CN201910462248.2A
Authority: CN
Inventors: 王斌; 马明阳; 易丹青
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2019-05-30
Filing date: 2019-05-30
Publication date: 2020-10-09
Anticipated expiration: 2039-05-30
Also published as: CN110205528A

Abstract

The invention discloses a high intergranular corrosion resistant Al-Mg alloy material, which consists of Ru, Mg, Mn, Zn, Ti and Al, wherein in a corrosive medium, Ru can improve the cathode reaction current density, so that the α (Al) surface can spontaneously generate Al with the thickness of 300nm₂O₃·3H₂O and has a dense, self-repairing and highly corrosion-resistant passive film, effectively blocks the β (Al) pair of corrosive media₃Mg₂) The corrosion of the phase greatly improves the intergranular corrosion resistance of the alloy. Tau (Mg) can be precipitated from the alloy by adjusting the proportion of M (Mg), M (Mn), M (Zn)₃₂(Al,Zn)₄₉) Phase, inhibition β (Al)₃Mg₂) The precipitation of the phase reduces the potential difference between the second phase and the aluminum matrix, and further improves the intergranular corrosion resistance of the alloy.

Description

Al-Mg alloy with high intergranular corrosion resistance and preparation method thereof

Technical Field

The invention relates to the field of materials, in particular to an Al-Mg alloy with high intergranular corrosion resistance and a preparation method thereof.

Background

The maximum solubility of Mg is reduced to about 1.7 wt% at room temperature when Al-Mg alloys containing more than 3.5 wt% Mg are used, the Mg atoms preferentially diffuse from supersaturated solid solution α (Al) to Grain Boundaries (GB), eventually forming β (Al) which is a lightweight alternative to steel₃Mg₂) Phase β (Al)₃Mg₂) The phase potential (-1.24V) is lower than α (Al) potential (-0.812V), and in a corrosive environment, preferentially corrodes the substrate, causing localized intergranular corrosion

Corrosion-resistant passive film (Al)₂O₃·3H₂O), β (Al) when the alloy is subject to corrosion₃Mg₂) The phase dissolution reaction and the passivation film formation reaction proceed simultaneously, but the dissolution rate of the β phase is much faster than the oxidation rate of the matrix, resulting in poor corrosion resistance of the alloy.

Intergranular corrosion is one of localized corrosion. Corrosion spreading inwardly along the interface between the metal grains. Mainly due to the difference in chemical composition between the surface and the interior of the grains and the presence of grain boundary impurities or internal stresses. Intergranular corrosion destroys intergranular bonds, and greatly reduces the mechanical strength of the metal. Moreover, after corrosion occurs, the surface of the metal and the alloy still keeps certain metal luster, and the damage is not seen, but the bonding force between crystal grains is obviously weakened, the mechanical property is deteriorated, and knocking cannot be withstood, so the corrosion is dangerous. Intergranular corrosion is an important factor affecting the performance of Al-Mg alloys.

The platinum group metals (Pt, Pd, Os, Ir, Ru, Rh) can on the one hand function as effective cathodes on the alloy surface, and on the other hand the exchange current density of the cathodic reaction on the platinum group metals is much greater. Meanwhile, the platinum group metal has the function of promoting the generation of an Al alloy passive film so as to improve the corrosion resistance of the alloy.

The selling price of Ru is the lowest among platinum group metals, and the addition of Ru into Al-Mg alloy has great practical production significance in consideration of practical production cost. However, the melting point of Ru is as high as 2334 ℃, while the boiling point of Al is 2327 ℃ which is lower than that of Ru, so that the Ru simple substance is difficult to be directly added into the aluminum alloy by the common smelting method. The main existing methods for adding Ru into aluminum alloy include eutectic metallurgy, powder metallurgy and mechanical alloying. However, these methods require expensive equipment support and are limited by the size of the equipment, and cannot prepare large-scale samples.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides an Al-Mg alloy with high intergranular corrosion resistance and a preparation method thereof.

The technical scheme adopted by the invention is as follows:

an intercrystalline corrosion resistant Al-Mg alloy, which comprises the following components by mass: 0.01-0.2% of Ru, 3.5-6.5% of Mg, 0.3-1.5% of Mn, 0.2-0.5% of Zn, 0.05-0.3% of Ti, inevitable impurities and the balance of Al.

In some examples of the intergranular corrosion resistant Al-Mg alloy, 0.05 to 0.1% of Ru, 3.5 to 4.5% of Mg, 0.3 to 0.85% of Mn0.2 to 0.35% of Zn, and 0.09 to 0.17% of Ti are added.

In some examples of the intergranular corrosion resistant Al-Mg alloy, M (Ti) and M (Ru) (65-99) are (1-35), and M (Ti) and M (Ru) (65-80) and M (20-35) are preferred.

In some examples of the intergranular corrosion resistant Al-Mg alloy, the mass ratio of the three elements Mg, Mn and Zn is: m (Mg), (M), (Zn), (13-35), (3), (1-2).

In some examples of intergranular corrosion resistant Al-Mg alloys, the content of unavoidable impurities does not exceed 0.1%.

A method for preparing an intercrystalline corrosion resistant Al-Mg alloy, the composition of which is as described above, comprising the operations of:

1) preparing materials: weighing raw materials according to the composition of the intergranular corrosion resistant Al-Mg alloy, wherein Ru is introduced in a Ru-Ti intermediate alloy form and is uniformly mixed;

2) smelting: putting the raw materials into a smelting furnace for smelting, wherein the smelting temperature is not more than 900 ℃, and after the smelting is finished, casting to obtain an ingot;

3) and carrying out homogenization heat treatment on the cast ingot, and quenching to obtain the intergranular corrosion resistant Al-Mg alloy.

In some examples of the preparation method, the temperature of the melting is 760 ℃ to 850 ℃.

In some examples of the preparation method, the temperature of the homogenization heat treatment is 550-580 ℃;

in some examples of the preparation method, the time for the homogenization heat treatment is 18 to 48 hours.

The invention has the beneficial effects that:

the Al-Mg alloy material can enhance the hydrogen evolution (H) of the alloy in a corrosive environment by adjusting the proportion of the Al-Mg alloy, adding Ru element into the traditional Al-Mg alloy and matching with other elements⁺+2e^-→H₂). The cathode reaction is higher than the critical anode current density, a critical anode loop is avoided, the corrosion potential and the corrosion current in the actual corrosion process are smaller, and the corrosion speed of the alloy is slowed down. Meanwhile, in a corrosive medium, Ru-2e occurs in preference to the matrix by Ru element^-→Ru²⁺In addition to the catalytic synergy of the cathodic reaction, the α (Al) surface spontaneously undergoes 2Al +3Ru²⁺+3H₂O→Al₂O₃+3Ru+6H⁺Reaction, after tomography by XPSAt present, α (Al) surface will form (Al) with a thickness of 300nm₂O₃·3H₂O) a passivation film. (Al)₂O₃·3H₂The O) passive film has the characteristics of compactness, self-repairing and high corrosion resistance, and effectively blocks β (Al) of corrosive medium pair₃Mg₂) The corrosion of the phase greatly improves the intergranular corrosion resistance of the alloy.

The Al-Mg alloy material of the present invention can precipitate β (Al) from α (Al) by controlling the content ratio of the element components M (Mg), M (Mn), M (Zn) (13-35), and (3) (1-2) based on the conventional Al-Mg alloy₃Mg₂) Phase sum tau (Mg)₃₂(Al,Zn)₄₉) Phase, at the same time τ (Mg)₃₂(Al,Zn)₄₉) Phase can also be suppressed β (Al)₃Mg₂) Precipitation of phases, partial replacement of β (Al)₃Mg₂) And (4) phase(s). Tau (Mg)₃₂(Al,Zn)₄₉) The corrosion potential (-0.813V) of the phase is substantially the same as that of α (Al), and the potential difference between the second phase and the aluminum matrix can be reduced to optimize the intergranular corrosion resistance of the alloy.

The tensile strength range of the Al-Mg alloy material is as follows: 310-340 MPa; the elongation is 18-25%, and according to GB/T7998-2005 'determination method for intergranular corrosion of aluminum alloy', after a sample is placed in 30g/L NaCl +10mL/L HCl corrosive solution at the temperature of 35 ℃ and soaked for 24 hours, intergranular corrosion does not occur.

According to the preparation method, the Ru element is introduced into the Al alloy by the traditional smelting method for the first time, the solid solubility of Ru in Al is combined, the addition amount of Ru is controlled to be 0.05-0.2 wt%, the smelting temperature is controlled to be 760-850 ℃, and Ru can be fully dissolved in Al and dispersed. Realizes the low-cost large-scale production of the RuAl-Mg-doped alloy.

Drawings

FIG. 1 is a structural diagram of an Al-Mg alloy produced in example 5;

FIG. 2 is a graph of intercrystalline corrosion of the Al-Mg alloy prepared in example 5 after soaking in 30g/L NaCl +10ml/L HCl etchant solution at 35 ℃ for 24 h;

FIG. 3 is a graph showing the measurement of the composition and thickness of a passivation film of the Al-Mg alloy prepared in example 5 after intergranular corrosion measurement.

Detailed Description

The present invention will be described in detail below with reference to examples, comparative examples and experimental data.

The weight percentage of the alloy chemical components in each embodiment is 3.5-6.5 wt% of Mg; 0.3 to 1.5 weight percent of Mn; 0.2 wt% -0.5 wt% of Zn; 0.05 wt% -0.3 wt% of Ti; 0.05 wt% -0.2 wt% of Ru; the balance being Al.

For convenience of comparison, Ru in the Al-Mg alloys in the following examples and comparative examples was introduced in the form of Ru-Ti master alloys. The preparation method of the Ru-Ti intermediate alloy comprises the following steps: pure Ti powder and pure Ru powder are used as raw materials, and the raw materials are mixed according to the weight percentage of M (Ti) to M (Ru) 65-99 to 1-35. Pressing the materials into a consumable electrode, and smelting for 2 times in a vacuum consumable smelting furnace to obtain the Ti-Ru intermediate alloy.

The multi-element refining agent and the degasifier are common in the field. For convenience of comparison, in the following examples and comparative examples, the composition of the multi-component refining agent includes: 20 wt% NaCl, 20 wt% KCl, 35 wt% NaF, 25 wt% LiF; the mass ratio of the refining agent to the smelting ingredients is (1-3): 100. the degasifier is hexachloroethane, and the mass ratio of the degasifier to the smelting ingredients is 1: 100. when the purity of the raw material is high, the multicomponent refining agent and the degasifier are not required to be added. The multi-element refining agent and the degasifier have no influence on the performance of the alloy.

In order to make the alloy more uniform during the casting process, low frequency electromagnetic stirring can be performed. Of course, other methods commonly used in the art may be used for the purpose of achieving uniform mixing.

Example 1

1) According to the weight percentage of the components, 3.5 wt% of Mg, 0.3 wt% of Mn, 0.2 wt% of Zn, 0.09 wt% of Ti, 0.05 wt% of Ru and the balance of Al are taken. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

2) adding a multi-element refining agent and a degassing agent into the alloy melt, refining, degassing and deslagging, and standing for 8 min;

3) pouring the alloy melt into a cylindrical mold in an electromagnetic stirring device, carrying out low-frequency electromagnetic stirring for 15Hz for 30s, and then carrying out water cooling to obtain an ingot;

4) homogenizing the cast ingot at 560 deg.C for 48h, and water quenching at room temperature.

Example 2

1) Taking the weight percentages of the components as Mg 4.2 wt%, Mn 0.6 wt%, Zn 0.25 wt%, Ti 0.09 wt%, Ru 0.05 wt% and the balance Al. Smelting the materials in a smelting furnace at 760 ℃ until the materials are molten;

4) homogenizing the cast ingot at 570 deg.C for 18h, and water quenching at room temperature.

Example 3

1) Taking the weight percentages of Mg of 4.2 wt%, Mn of 0.6 wt%, Zn of 0.3 wt%, Ti of 0.15 wt%, Ru of 0.08 wt% and the balance Al. Smelting the materials in a smelting furnace at 800 ℃ until the materials are molten;

4) homogenizing the cast ingot at 550 deg.C for 48h, and water quenching at room temperature.

Example 4

1) Taking the weight percentages of the components as Mg 4.3 wt%, Mn 0.44 wt%, Zn 0.35 wt%, Ti 0.15 wt%, Ru 0.08 wt% and the balance Al. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

4) homogenizing the cast ingot at 580 deg.C for 18h, and water quenching at room temperature.

Example 5

1) Taking the weight percentages of Mg of 4.3 wt%, Mn of 0.64 wt%, Zn of 0.28 wt%, Ti of 0.17 wt%, Ru of 0.1 wt% and the balance Al. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

4) homogenizing the cast ingot at 580 deg.C for 24 hr, and water quenching at room temperature.

Example 6

1) Taking the weight percentages of Mg of 4.3 wt%, Mn of 0.64 wt%, Zn of 0.32 wt%, Ti of 0.17 wt%, Ru of 0.1 wt% and the balance Al. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

Example 7

1) Taking Mg 4.5 wt%, Mn 0.65 wt%, Zn 0.2 wt%, Ti 0.17 wt%, Ru 0.1 wt% and Al in balance according to the weight percentage of the components. Smelting the materials in a smelting furnace at 820 ℃ until the materials are molten;

Example 8

1) Taking the weight percentages of Mg of 4.0 wt%, Mn of 0.5 wt%, Zn of 0.33 wt%, Ti of 0.17 wt%, Ru of 0.1 wt% and the balance Al. Smelting the materials in a smelting furnace at 850 ℃ until the materials are molten;

4) homogenizing the cast ingot at 560 deg.C for 36h, and water quenching at room temperature.

Example 9

1) Taking the weight percentages of Mg of 4.0 wt%, Mn of 0.85 wt%, Zn of 0.28 wt%, Ti of 0.17 wt%, Ru of 0.1 wt% and the balance Al. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

4) homogenizing the cast ingot at 575 deg.c for 24 hr, and water quenching at room temperature. Comparative example 1:

1) taking the weight percentages of Mg of 4.3 wt%, Mn of 0.64 wt%, Zn of 0.28 wt%, Ti of 0.17 wt% and the balance Al. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

4) homogenizing the cast ingot at 580 deg.C for 24 hr, and water quenching at room temperature. Comparative example 2:

1) taking the weight percentages of Mg of 4.3 wt%, Mn of 0.64 wt%, Ti of 0.17 wt%, Ru of 0.1 wt% and the balance Al. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

Comparative example 3:

1) taking Mg 4.3 wt%, Mn 0.64 wt% and Al in balance according to the weight percentage of the components. Smelting the materials in a smelting furnace at 780 ℃ until the materials are molten;

The experimental results are as follows:

FIG. 1 is a structural diagram of Al-Mg alloy prepared in example 5, and it can be seen that the Al-Mg alloy with high intergranular corrosion resistance prepared by the present invention has fine and uniform grain size, no overburning phenomenon, no obvious coarse and reticular primary phase at grain boundary, β (Al) appears in the crystal₃Mg₂) Phase sum tau (Mg)₃₂(Al,Zn)₄₉) Phase, and τ (Mg)₃₂(Al,Zn)₄₉) The number of phases is significantly greater than that of conventional β (Al)₃Mg₂) The number of the phases is beneficial to reducing the potential difference between the second phase and the aluminum matrix, optimizing the intergranular corrosion resistance of the alloy and improving the intergranular corrosion resistance of the alloy.

FIG. 2 is a graph showing intercrystalline corrosion of Al-Mg alloy prepared in example 5 after soaking in 30g/L NaCl +10ml/L HCl etchant solution at 35 ℃ for 24 hours,

FIG. 3 is a graph showing the measurement of the composition and thickness of the passivation film of the Al-Mg alloy prepared in example 5 after intergranular corrosion measurement, and it can be seen that the Ru element is present in the form of a simple substance (valence 0) in the matrix from the surface of the sample to a depth of 450nm from the surface. The simple substance Ru effectively ensures Ru-2e^-→Ru²⁺And (3) carrying out the reaction. Meanwhile, stronger Al is always in the passivation film from the surface of the sample to the position 300nm away from the surface of the sample₂O₃To a distance of 450nm from the surface, Al₂O₃The peak of (a) is not seen, while the peak of the matrix aluminum is stronger. This demonstrates that a highly intergranular corrosion resistant Al-Mg alloy prepared by the present invention has a passive film on the surface of at least 300nm in thickness.

As can be seen from FIGS. 1 to 3, the Al-Mg alloy with high intergranular corrosion resistance prepared by the method has no intergranular corrosion phenomenon after being measured by the intergranular corrosion performance, and the comparative groups have intergranular corrosion phenomena of different grades. The scientific component proportion and the reasonable heat treatment system are fully shown. Greatly improves the defect of insufficient intergranular corrosion resistance of the traditional Al-Mg alloy.

Comparison of Properties of different Al-Mg alloys

Respectively taking the Al-Mg alloys prepared in the examples and the comparative examples to perform performance tests, wherein the intercrystalline corrosion judgment standard is judged according to GBT7998-2005 'determination method for intercrystalline corrosion of aluminum alloy'; the test methods of strength and elongation are according to GB/T228.1-2010 part 1 of the tensile test of metallic materials: determination was performed by Room temperature test method.

Numbering	Grade of intergranular corrosion	strength/Mpa	Elongation/percent
				Example 1	Without intergranular corrosion	320	19.6
Example 2	Without intergranular corrosion	328	25.0
				Example 3	Without intergranular corrosion	342	24.4
Example 4	Without intergranular corrosion	333	19.2
				Example 5	Without intergranular corrosion	350	21.8
Example 6	Without intergranular corrosion	345	24.2
				Example 7	Without intergranular corrosion	325	22.2
Example 8	Without intergranular corrosion	337	20.9
				Example 9	Without intergranular corrosion	328	23.1
Comparative example 1	2	324	18.2
				Comparative example 2	2	311	21.0
Comparative example 3	3	311	21.0

By comparing various performances of the implementation group and the comparison group, the Al-Mg alloy with high intergranular corrosion resistance prepared by the method is free from intergranular corrosion after being soaked in 30g/L NaCl +10ml/L HCl corrosive solution at 35 ℃ for 24 hours. Meanwhile, the strength and the elongation of the alloy are improved. The control group 1 has no Ru element, the control group 2 has no Zn element, and the control group 3 has no Ru and Zn elements. The three control groups all exhibited different degrees of intergranular corrosion and were not as strong as the example group. This shows that the intergranular corrosion resistance of the alloy can be improved only by the combined action of the Ru and Zn elements. In one aspect, tau (Mg) is formed by adding Zn element₃₂(Al,Zn)₄₉) Phase, partial substitution β (Al)₃Mg₂) On the other hand, by adding Ru element, the evolution of hydrogen evolution of the alloy in a corrosive environment can be enhanced, so that the corrosion potential and the corrosion current in the actual corrosion process are smaller, and the corrosion speed of the alloy is slowed down₂O₃·3H₂O) a passivation film. One of them is not enough. Therefore, the alloy of the invention has scientific component proportion and excellent performance.

Claims

1. An intercrystalline corrosion resistant Al-Mg alloy comprises, by mass, 0.01-0.2% of Ru, 3.5-6.5% of Mg, 0.3-1.5% of Mn, 0.2-0.5% of Zn, 0.05-0.3% of Ti, inevitable impurities and the balance Al, wherein the mass percentages of M (Ti) and M (Ru) = (65-80) and (20-35) are M (Mg), M (Mn) and M (Zn) = (30-35) and the mass ratios of M (Mg), M (Mn) and M (Zn) = (30-35) are (1-2) and can be αβ (Al) precipitated in (Al)₃Mg₂) Phase sum tau (Mg)₃₂(Al,Zn)₄₉) Phase, at the same time τ (Mg)₃₂(Al,Zn)₄₉) Phase can also be suppressed β (Al)₃Mg₂) Precipitation of phases, partial replacement of β (Al)₃Mg₂) And (4) phase(s).

2. An intergranular corrosion resistant Al-Mg alloy according to claim 1, wherein: wherein, Ru is 0.05-0.1%, Mg is 3.5-4.5%, Mn is 0.3-0.85%, Zn is 0.2-0.35%, Ti is 0.09-0.17%.

3. An intergranular corrosion resistant Al-Mg alloy according to claim 1, wherein: the mass ratio of the three elements of Mg, Mn and Zn is as follows: m (Mg), M (Zn) (30-35) and (3: 2).

4. An intergranular corrosion resistant Al-Mg alloy according to claim 1, wherein: the content of the inevitable impurities does not exceed 0.1%.

5. A method for preparing an intergranular corrosion resistant Al-Mg alloy, the composition of which is as defined in any one of claims 1 to 4, comprising the operations of:

6. The method of claim 5, wherein: the smelting temperature is 760 ℃ to 850 ℃.

7. The production method according to claim 5 or 6, characterized in that: the temperature of the homogenization heat treatment is 550-580 ℃; the time of the homogenization heat treatment is 18 to 48 hours.