CN1306052C - High corrosion resisting as cast magnalium and preparation method - Google Patents

Abstract

The invention relates to a high-corrosion-resistant cast magnesium-aluminum alloy and a preparation method thereof, belonging to the field of magnesium-aluminum alloys. The alloy composition (wt%) provided by the present invention is Al 7.5-10.5, Mn 0.2-1.0, La 0.1-0.8, Ce 0.1-0.8, Pr 0.05-0.3, Y 0.1-0.8, Zn 0.1-0.5, Sr 0.2-1.5 , and the balance is Mg element and impurity element. Its preparation method adopts CO ₂ +SF ₄ protective atmosphere melting, or solvent method melting, and the melting temperature is 710-750°C. The prepared alloy consists of α phase, Sr-containing Mg ₁₇ Al ₁₁ phase and MgAlLaPrCeYSr complex intermetallic compound phase. The high-aluminum-magnesium alloy provided by the present invention has a corrosion rate of only about 0.1 mg/ ^cm2 in the salt spray test, which is much better than the corrosion resistance of AZ91 (Mg-9Al) and Mg-9Al-1RE. The impedance value is obviously higher than the above comparative alloy.

Description

High-corrosion-resistant cast magnesium-aluminum alloy and preparation method thereof

technical field

The invention relates to a high-corrosion-resistant cast magnesium-aluminum alloy and a preparation method thereof, more precisely to a high-aluminum-content cast magnesium-aluminum alloy with an aluminum content of 7.5-10.5 mass percent and a preparation method thereof, belonging to the field of magnesium alloys.

Background technique

Magnesium alloy has low density, high specific strength, high specific stiffness, excellent electromagnetic shielding performance and shock absorption performance, good casting and processing performance, and is widely used in 3C products (computers, communication products and consumer electronics products) such as aerospace, automobile and electronic information. ) field has been more and more widely used, and its usage has grown at an annual rate of 20% in recent years.

However, the poor corrosion resistance of magnesium alloys is an important obstacle to its application. Due to its negative corrosion potential, magnesium alloys are prone to electrochemical corrosion in aqueous solutions or humid environments, especially in salty environments. The precipitated phase of magnesium alloys is often cathodic relative to the α phase of the magnesium alloy matrix, which is It will cause inevitable microgalvanic corrosion, and the natural oxide film of magnesium alloy is loose and porous, which cannot provide effective protection for the alloy matrix. Therefore, the further popularization and application of magnesium alloys is greatly restricted.

In the past ten years, the research on improving the corrosion resistance of magnesium alloys has been highly valued by the scientific and industrial circles in Europe, America, Japan and other countries, and has achieved remarkable results. Through proper alloying, reducing and controlling the content of heavy metal impurity elements and heat treatment can significantly improve and improve the corrosion resistance of magnesium alloys. However, the corrosion resistance of existing magnesium alloys is still insufficient, and it is difficult to adapt to the requirements of wide use in various natural environments. Therefore, it is more important to develop a high corrosion-resistant magnesium alloy that is more corrosion-resistant and does not require surface protection treatment.

In this regard, some patent applications for magnesium alloys with better corrosion resistance have been proposed in recent years. Such as CN1401805A (application number: 02130182.4) [JP252764/2001] patent application has proposed a kind of " magnesium alloy and magnesium alloy element with high corrosion resistance ", and the composition range of its corrosion-resistant magnesium alloy is: Al: 5～7mass% , Ca: 2-4mass%, Mn: 0.1-0.8mass%, Sr: 0.001-0.05mass%, 0.1-0.6mass% of rare earth elements, and the remainder is Mg and unavoidable impurities. The corrosion rate of the alloy is calculated based on the weight loss after the 100-hour salt spray test. Within the range of alloy composition, the corrosion rate is about 0.1 mg/ ^cm2.day .

Japanese patent JP2003166031 proposed "high corrosion-resistant magnesium alloy and its manufacturing method". 0.9mass%, the balance is Mg and unavoidable impurities. Its corrosion resistance is measured by the weight loss of the alloy sample after soaking in 5mass% Nacl solution. The corrosion rate of the alloy is less than 0.1 mg/cm ² .day.

However, since magnesium alloys are usually processed by die-casting or semi-solid forming, the alloys are required to have high fluidity and casting performance. Considering casting performance and mechanical properties, the most commonly used cast magnesium alloy is AZ91 type magnesium containing 9mass% Al. Alloy (the main component range is: Al: 8.5-9.5mass%, Mn: 0.17-0.4mass%, Zn: 0.45-0.9mass%, Si: <0.05mass%, impurities: <0.01mass%). Considering the high fluidity and casting performance of the alloy required by the high yield of die-casting, the Al content of the alloy should be increased as much as possible, so the Al content of the die-casting magnesium alloy is generally required to be ≥ 9mass%.

The Al content of the above two patented alloys is ≤8mass%. Considering the casting performance and comprehensive performance, these two alloys cannot completely replace the AZ91 alloy, but if the Al content is increased to >8mass% in order to improve the casting performance, the two This proprietary alloy cannot maintain high corrosion resistance.

For high Al magnesium alloys with Al content > 8mass%, their corrosion resistance is generally poor. Our test shows that: AZ91D alloy, its 100-hour salt spray test corrosion rate usually exceeds 10 mg/cm ² .day.

The test results of the alloys involved in the above two patent applications also show that when the Al content of the alloy reaches above 8mass%, the corrosion rate of the alloy is relatively large.

Comparative document 1 shows that when the Al content of the alloy reaches 8mass%, its corrosion rate is as high as 4-6 mg/cm ² .day.

Comparative document 2 (JP2003166031) shows that when the Al content of the alloy is close to 9mass%, its corrosion rate is also greater than 0.3 mg/cm ² .day.

Therefore, the poor corrosion resistance of magnesium alloys is an unresolved problem when the Al content of the alloy reaches the 8-9 mass% required to maintain good castability and mechanical properties.

Contents of the invention

The purpose of the present invention is to provide corrosion-resistant magnesium-aluminum alloys and alloying approaches thereof with an Al content in the high Al content range of 7.5-10.5 mass%, aiming at the needs of the industry.

The present invention transforms the precipitated phase of the Mg-Al alloy from a strongly cathodic Mg ₁₇ Al ₁₂ phase into a diffusely distributed multi-element rare earth containing a small amount of rare earth elements and alkaline earth metal Sr. Sr, Mg, the composite intermetallic compound phase of Al, thereby significantly reducing the microgalvanic corrosion of the Mg-Al alloy, and promoting the formation of a passive and protective composite oxide film at the same time, so that the alloy of the present invention has excellent corrosion resistance sex.

Therefore, the present invention provides a cast magnesium-aluminum alloy with extremely high corrosion resistance, which is composed of the following elements in mass percentage: Al: 7.5-10.5, Mn: 0.2-1.0, La: 0.1-0.8, Ce: 0.1-0.8 , Pr: 0.05 to 0.3, Y: 0.1 to 0.8, Zn: 0.1 to 0.5, Sr: 0.2 to 1.5, and the rest of the magnesium alloy is composed of Mg and unavoidable impurities.

The inevitable impurity elements in the magnesium alloy are mainly: Si, Cu, Fe, Ni. Its content is: Si≤0.05mass%, Cu≤0.004mass%, Ni≤0.002mass%, Fe≤0.004mass%.

The alloy can be smelted by protective atmosphere (CO ₂ +SF ₆ ) or by solvent method. The raw materials used are: Mg, Al, Zn use industrial pure metals, Mn can use Al-Mn master alloy or electrolytic manganese, La, Pr, Ce, Y use Mg-rich La with rare earth content of 15-25%, Mg- Pr-rich, Mg-Ce-rich, Mg-Y-rich or Mg-LaPrCe-rich master alloys, Sr adopts industrial pure Sr or AlSr10 master alloys, and is melted into alloys with the above raw materials. And La:Ce:Pr=6:3:1 in the Mg-rich LaPrCe master alloy. The specific preparation is to melt Mg and Al in a solvent furnace first, and then add Mg-rich La, Mg-rich Pr, Mg-rich Ce, Mg-rich Y or Mg-rich LaPrCe and Al-Mn intermediate metal or electrolytic manganese and metal Zn, finally add industrial pure metal Sr or AlSr10 master alloy.

The refining solvent used in the solvent method has a composition (wt%) of: KCl25-30, NaCl5-10, _CaCl25-10 , _CaF225-30 , MgO2-3, and the balance is _MgCl2 .

The protective atmosphere is Co ₂ :SF ₆ =100-200:1.

The melting temperature of the alloy is 710-750°C, and the pouring temperature of the alloy is 680-720°C. The alloy can be poured into an alloy ingot at the casting temperature, or the temperature of the alloy liquid can be controlled at 680-720°C for high-pressure casting to form a magnesium alloy product. Or heat the ingot to (560~590)±2°C, semi-solid casting when the alloy is at a solid phase rate of 50% or below, or process the alloy into chips and heat it to (560~590)±2°C Afterwards, the alloy is in a semi-solid state with a solid phase ratio of 50% or less for injection molding to make a magnesium alloy product.

The prepared alloy is composed of α phase, Mg ₁₇ Al ₁₁ phase containing Sr and complex intermetallic compound phase containing Sr and La, Pr, Ce, Y, Al, Mg - MgAlLaPrCeYSr.

The alloy provided by the invention has excellent corrosion resistance, and its corrosion rate in a salt spray test is about 0.1 mg/cm ² .day. (See Figure 2 and Table 1)

a) Corrosion rate of salt spray test

The corrosion resistance of the alloy was determined by the corrosion rate of the general salt spray test. After the alloy was corroded in 5mass% NaCl salt spray at 35°C for 100 hours, the weight loss before and after corrosion was measured to calculate the corrosion rate. The corrosion rates of the alloy provided by the present invention and the comparison alloy AZ91 (Mg-9Al) and Mg-9Al-1RE alloy are shown in Figure 2 and Table 1.

b) Electrochemical AC impedance measurement

The polarization resistance Rp value measured by electrochemical AC impedance represents the corrosion resistance (its reciprocal is the corrosion rate), and the larger the Rp value, the more corrosion-resistant the alloy is. Electrochemical AC Impedance Measurement In pH10.5, 25°C, 3.5% NaCl solution, after soaking for 35 minutes, it was measured with SolartronSI1287 electrochemical interface and 1255B frequency response instrument. The complex plan views and Rp values of the four examples and comparative alloys of the present invention are shown in Figure 3 and Table 2.

Table 1. The corrosion rate of the alloy provided by the embodiment of the present invention and the comparison alloy Mg-9Al and Mg-9Al-1RE (RE is a mixed rare earth with a Ce content of about 50%) at 5mass%NaCl35°C salt spray test alloy Corrosion rate (mg/ ^cm2.day ) Comparative alloy AZ91 (Mg-9Al) >10 Comparative alloy Mg-9Al-1RE (RE: Ce-based mixed rare earth) 0.232 Example 1 0.057 Example 2 0.115 Example 3 0.068 Example 4 0.096

Table 2. The Rp value of the magnesium-aluminum alloy provided by the present invention and the comparison alloy electrochemical impedance measurement alloy AC impedance (Rp) value (Ω·cm ² ) Comparative alloy Mg-9Al alloy 263 Comparative alloy Mg-9Al-1RE (RE: Ce-based mixed rare earth) 986 this invention 1250

It can be seen from Figure 3 and Table 2 that the Rp value of the alloy provided by the present invention is significantly higher than that of the comparative AZ91 alloy (Mg-9Al) and Mg-9Al-1RE (RE: mixed rare earth with Ce accounting for more than 50%). Therefore, the alloy provided by the present invention has stronger corrosion resistance.

Therefore, the corrosion resistance of the alloy provided by the present invention significantly exceeds the general-purpose AZ91 alloy, and is also much better than the corrosion resistance of the Mg-9Al-1RE alloy that adds Ce-based mixed rare earths, and it has excellent corrosion resistance Mg-Al alloy.

In addition, the mechanical properties of the patented alloy provided by the present invention and the comparative alloy (AZ91) are shown in Table 3.

Table 3. The mechanical properties of alloys provided by the invention and comparative alloy (AZ91) alloy Room temperature tensile strength σ _b (Mpa) Elongation (δ%) Impact toughness Ak (J Joule) this invention >170 >6 >4 Comparative Alloy AZ91 >160 >3 >4

Therefore, the mechanical properties of the alloys provided by the present invention are equal to or better than those of the AZ91 control alloy.

To sum up, the magnesium-aluminum alloy with high aluminum content provided by the present invention has good corrosion resistance compared with magnesium alloys such as AZ-91, and the preparation process is similar to that of general magnesium alloys.

Description of drawings

Fig. 1 The metallographic microstructure (X500) of the high-aluminum magnesium-aluminum alloy provided by the present invention

Fig. 2 Corrosion resistance comparison of embodiment 1-4 of the present invention and two kinds of comparison alloys

Fig. 3 Comparison of the electrochemical impedance complex plane diagrams of the magnesium-aluminum alloy provided by the present invention and the comparison alloy

Detailed ways

Below through specific embodiment, further clarifies the substantive characteristic and remarkable progress of the present invention, but the present invention is by no means limited to embodiment.

Example 1

The composition (mass percentage) of the alloy is: Al: 9.0%, La: 0.6%, Ce: 0.3%, Pr: 0.1%, Y: 0.33%, Mn: 0.3%, Zn: 0.4%, Sr: 1.0%. Unavoidable magazine elements are limited to: Si≤0.05%, Cu≤0.004%, Ni≤0.002%, Fe≤0.004%, and the rest is Mg.

Industrial pure magnesium, industrial pure aluminum, Mg-LaPrCe master alloy (the total amount of La, Pr, Ce accounts for about 20%, of which La: Ce: Pr≈6:3:1), Mg-Y master alloy (Y: 21%), Al-Mn master alloy, industrial pure Zn, metal Sr, the alloy is formulated according to the above-mentioned composition. In a protective atmosphere (CO2:SF6≈200:1 mixed atmosphere) magnesium alloy melting furnace, first melt Mg and Al, and then add Mg-LaPrCe, Mg-Y, Al-Mn master alloy and Zn after the magnesium alloy is melted. , finally add metal Sr, after all the alloying elements are melted (about 710°C), raise the temperature to 730°C, let it stand for 30 minutes, control the temperature not to exceed 750°C, then lower the temperature of the alloy liquid to about 710°C, Slag, ingot. During die casting, the alloy liquid temperature is controlled at 700°C for high pressure casting to form magnesium alloy products. Either heat the ingot to 580°C, and perform semi-solid casting when the alloy is at a solid phase ratio of 50% or below, or process the alloy into chips, and heat the alloy to 580°C, so that the alloy is at a solid phase ratio of 50% Or the following semi-solid state for injection molding, made of magnesium alloy products. The corrosion rate of the alloy of this embodiment in the 5% NaCl salt spray test is 0.052 mg/cm ² .day, its tensile strength at room temperature is 175 MPa, elongation is 6.3%, and impact toughness is 5 J (Joules).

Example 2

The composition (mass percentage) of the alloy is: Al: 10%, La: 0.3%, Ce: 0.15%, Pr: 0.05%, Y: 0.26%, Mn: 0.6%, Zn: 0.4%, Sr: 0.5%, Unavoidable impurity elements are limited to: Si≤0.05%, Cu≤0.004%, Ni≤0.002%, Fe≤0.004%, and the rest is Mg. Using industrial pure magnesium, industrial pure aluminum, Mg-LaPrCe master alloy (the total amount of LaPrCe accounts for about 20%, wherein La: Ce: Pr≈6:3:1), Mg-Y master alloy (Y: 21%), Al-Mn master alloy, industrial pure zinc, metal Sr, the alloy is formulated according to the above ingredients. In a protective atmosphere (CO2:SF6≈200:1 mixed atmosphere) magnesium alloy melting furnace, first melt Mg and Al, and then add Mg-LaPrCe, Mg-Y, Al-Mn master alloy and Zn after the magnesium alloy is melted. , finally add metal Sr, after all the alloying elements are melted (about 710°C), raise the temperature to 730°C, let it stand for 30 minutes, control the temperature not to exceed 750°C, then lower the temperature of the alloy liquid to about 710°C, Slag, ingot. During die-casting, the temperature of the alloy liquid is controlled at 680-720°C for high-pressure casting to form magnesium alloy products. Or heat the ingot to 560±2°C, and perform semi-solid casting when the alloy is in a solid phase rate of 50% or less, or process the alloy into chips, and heat the alloy to 560±2°C to make the alloy in a solid phase The semi-solid form with a ratio of 50% or less is injection-molded to make magnesium alloy products. The corrosion rate of the alloy of this embodiment in the 5% NaCl salt spray test is 0.132 mg/cm ² .day, its tensile strength at room temperature is 180 MPa, elongation is 6%, and impact toughness is 4J (Joule).

Example 3

The composition (mass percentage) of the alloy is: Al: 9.2%, La: 0.8%, Ce: 0.6%, Pr: 0.2%, Y: 0.53%, Zn: 0.2%, Mn: 0.4%, Sr: 0.6%, Unavoidable impurity elements are limited to: Si≤0.05%, Cu≤0.004%, Ni≤0.002%, Fe≤0.004%, and the rest is Mg. Using industrial pure magnesium, industrial pure aluminum, Mg-LaPrCe master alloy (the total amount of LaPrCe accounts for about 20%, wherein La: Ce: Pr≈6:3:1), Mg-Ce master alloy (Ce: 20%), Mg-Y master alloy (Y: 21%), Mg-Pr master alloy (Pr: 10%), Al-Mn master alloy, industrial pure zinc, metal Sr, and formulate the alloy according to the above ingredients. In a protective atmosphere (CO ₂ : SF ₆ ≈200:1 mixed atmosphere) magnesium alloy melting furnace, first melt Mg and Al, and then add Mg-LaPrCe, Mg-Ce, Mg-Pr, Mg after the magnesium alloy is melted -Y, Al-Mn intermediate alloy and Zn, finally add metal Sr, after all the alloy elements are melted (about 710°C), raise the temperature to 740°C, let stand for 30 minutes, control the temperature not to exceed 750°C, and then make The temperature of the alloy liquid drops to about 710°C, the slag is removed, and the ingot is cast. During die-casting, the temperature of the alloy liquid is controlled at 680-720°C for high-pressure casting to form magnesium alloy products. Either heat the ingot to 590°C, and perform semi-solid casting when the alloy is at a solid phase ratio of 50% or less, or process the alloy into chips, and heat it to 570±2°C to make the alloy at a solid phase ratio 50% or less of the semi-solid form is injection molded to make magnesium alloy products. The corrosion rate of the alloy of this embodiment in the 5% NaCl salt spray test is 0.073 mg/cm ² .day, its tensile strength at room temperature is 180 MPa, elongation is 6.5%, and impact toughness is 5.3 J (Joule).

Example 4

The composition (mass percentage) of the alloy is: Al: 8.5%, La: 0.8%, Ce: 0.8%, Pr: 0.30%, Y: 0.60%, Mn: 0.3%, Zn: 0.4%, Sr: 1.5%, Unavoidable impurity elements are limited to: Si≤0.05%, Cu≤0.004%, Ni≤0.002%, Fe≤0.004%, and the rest is Mg. Using industrial pure magnesium, industrial pure aluminum, Mg-LaPrCe master alloy (the total amount of LaPrCe accounts for about 20%, wherein La: Ce: Pr≈6:3:1), Mg-Ce master alloy (Ce: 20%), Mg-Pr master alloy (Pr: 10%), Mg-Y master alloy (Y: 21%), Al-Mn master alloy, industrial pure zinc, metal Sr, and formulate the alloy according to the above-mentioned composition. Melting by solvent method, using a special refining solvent, its composition (wt%): MgCl ₂ 25, KCl 25, NaCl 10, CaCl ₂ 8, CaF ₂ 30, MgO 3. In the magnesium alloy melting furnace, Mg and Al are melted first, and after the magnesium alloy is melted, Mg-LaPrCe, Mg-Ce, Mg-Pr, Mg-Y, Al-Mn intermediate alloy and Zn are added, and finally metal Sr is added, After all the alloying elements are melted (about 710°C), raise the temperature to 730°C, let stand for 30 minutes, control the temperature not to exceed 750°C, then lower the temperature of the alloy liquid to about 710°C, remove slag, and cast ingots. During die-casting, the temperature of the alloy liquid is controlled at 680-720°C for high-pressure casting to form magnesium alloy products. Or heat the ingot to (560~590)±2°C, and perform semi-solid casting when the alloy is at a solid phase rate of 50% or less, or process the alloy into chips and heat it to (560~590)±2 After ℃, the alloy is in a semi-solid state with a solid phase rate of 50% or less for injection molding to make magnesium alloy products. The corrosion rate of the alloy of this example in the 5% NaCl salt spray test is 1.02 mg/cm ² .day, its room temperature tensile strength is 173 MPa, elongation is 6%, and impact toughness is 5J.

The comparison of the corrosion resistance of the above four examples provided by the present invention and the comparative alloys is summarized in Table 1 and FIG. 2 .

Claims (7)

1. high corrosion resistant casting magnesium aluminium alloy, it is characterized in that consisting of of alloy contain the element of following mass percent: Al 7.5-10.5, Mn 0.2-1.0, La 0.1-0.8, Ce 0.1-0.8, Pr 0.05-0.3, Y 0.1-0.8, Zn 0.1-0.5, Sr 0.2-1.5, surplus is Mg element and impurity element.

2. by the described high corrosion resistant casting magnesium aluminium alloy of claim 1, it is characterized in that the mass percent of described impurity element is respectively: Si≤0.05, Cu≤0.004, Ni≤0.002 and Fe≤0.004.

3. by the described high corrosion resistant casting magnesium aluminium alloy of claim 1, it is characterized in that alloy is by the α phase, contains the Mg of Sr ₁₇Al ₁₁Phase and MgAlLaPrCeYSr are complicated, and intermetallic compound constitutes mutually.

4. the method for preparing the described high corrosion resistant casting magnesium aluminium alloy of claim 1 is characterized in that concrete processing step is:

(a) mass percent of pressing alloy is formed: Al 7.5-10.5, Mn 0.2-1.0, La 0.1-0.8, Ce 0.1-0.8, Pr 0.05-0.3, Y 0.1-0.8, and Zn 0.1-0.5, Sr 0.2-1.5, surplus is the Mg batching, is smelted into alloy;

(b) adopt CO ₂+ SF ₆Protective atmosphere melting or solvent method melting; the smelting temperature of alloy is 710～750 ℃; teeming temperature is 680～720 ℃; alloy or under casting temp, pour into alloy pig; or the alloy liquid temp is controlled at 680～720 ℃ carries out high-pressure casting and become magnesium alloy product or ingot casting is heated to 560-590 ℃; alloy is in solid rate to be 50% or to carry out semi-solid casting when following; or after alloy is processed into bits sheet bits piece and is heated to 560-590 ℃; make alloy be in solid rate be 50% or following semi-solid state form carry out injection forming, make magnesium alloy product.

5. press the preparation method of the described high corrosion resistant casting magnesium aluminium alloy of claim 4, it is characterized in that molten alloy is earlier in smelting furnace, melt Mg and Al earlier, add the rich Y of rich Ce, Mg-of rich Pr, Mg-of Mg-rich La, Mg-or the rich LaPrCe of Mg-and Al-Mn intermediate metal or electrolytic manganese and Metal Zn again, add technical pure metal Sr or AlSr10 master alloy at last.

6. by the preparation method of claim 4 or 5 described high corrosion resistant casting magnesium aluminium alloys, it is characterized in that the protective atmosphere molten alloy is at CO ₂: SF ₆=100-200: 1 mixed atmosphere protection is carried out down; The solvent that the solvent method melting is used, its quality percentage composition is: KCl 25-30, NaCl 5-10, CaCl ₂5-10, CaF ₂25-30, MgO 2-3, surplus is MgCl ₂

7. press the preparation method of the described high corrosion resistant casting magnesium aluminium alloy of claim 5, it is characterized in that the LaPrCe total amount is about 15-25% in the rich LaPrCe master alloy of Mg-, and La: Ce: Pr=6: 3: 1, the rich La of Mg-, the rich Ce of Mg-, the rich Pr of Mg-, contain La respectively in the rich Y master alloy of Mg-, Ce, Pr, Y are 15-25%.

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