SI24911A - High-strength aluminum alloy Al-Mg-Si and procedure for its manufacture - Google Patents

High-strength aluminum alloy Al-Mg-Si and procedure for its manufacture Download PDF

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Publication number
SI24911A
SI24911A SI201600063A SI201600063A SI24911A SI 24911 A SI24911 A SI 24911A SI 201600063 A SI201600063 A SI 201600063A SI 201600063 A SI201600063 A SI 201600063A SI 24911 A SI24911 A SI 24911A
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Slovenia
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wt
up
characterized
casting
temperature
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SI201600063A
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Slovenian (sl)
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Peter Cvahte
Marina Jelen
Vukašin Dragojevič
Matej Steinacher
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Impol 2000, d.d.
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Priority to SI201600063A priority Critical patent/SI24911A/en
Publication of SI24911A publication Critical patent/SI24911A/en

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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C21/00Alloys based on aluminium
    • C22C21/02Alloys based on aluminium with silicon as the next major constituent
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
    • C22F1/05Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys of the Al-Si-Mg type, i.e. containing silicon and magnesium in approximately equal proportions

Abstract

The object of the invention is a high-strength aluminum alloy Al-Mg-Si and its manufacturing process. The alloy contains 1.3-1.7 wt. % Si, 0.14-0.25 wt. % Fe, to 0.75 wt. % Cu, 0.7-0.8 wt. % Mn, 0.85-1.1 wt. % Mg, 0.15-0.25 wt. % Cr, up to 0.2 wt. % Zn, up to 0.1 wt. % Ti, 0.15-0.25 wt. % Zr, other elements up to 0.15 wt. % (individual element up to 0.05% by weight) and the remainder of Al. The manufacturing process is based on the preparation of a cartridge, melting, melt retention, casting of rods or rods, homogenization annealing, cutting of masts, extrusion, transformation and heat treatment. Alloy is characterized by high strength properties, good transformability, corrosion resistance, lower energy consumption and environmental protection in production and use.

Description

AL-Mg-Si HIGH-ALUMINUM ALLOY AND ITS MANUFACTURING PROCEDURE

The invention is in the field of metallurgy and materials and relates to the high-strength aluminum alloy Al-Mg-Si, useful in the automotive, aerospace, transportation and construction industries, and its manufacturing process.

Trends in the modern industry tend to produce i.e. green means of transport. This means that it is necessary to reduce CO2 emissions and, consequently, the weight of vehicles, without neglecting the safety of users. In practice, this means that the "heavier" steel parts need to be replaced with "lighter" equivalent materials, such as e.g. high-strength Al-Mg-Si aluminum alloys (6xxx series).

In Al-Mg-Si aluminum alloys, the major alloying elements are magnesium and silicon, forming the Mg2Si phase, which secretes the alloy during aging. In general, the 6xxx series aluminum alloys have good heat transferability, machinability, weldability, corrosion resistance and strength of between 230 and 450 MPa. In the patent EP 2548983 with the addition of 0.8-1.5 wt. % Cu and 0.05-0.3 wt. % Zr reached a strength above 450 MPa, but such an alloy has poor corrosion resistance due to its high copper content. On the other hand, Al-Zn aluminum alloys (7xxx series) achieve a strength greater than 500 MPa, but their use is limited due to poor deformability and corrosion resistance.

Al-Mg-Si aluminum alloys are basically manufactured in the following sequences: cartridge preparation and smelting, melt retention, semi-continuous pole casting, homogenizing annealing of poles, extrusion of rods or other end shapes, transformation (eg forging) and heat treatment. The latest continuous casting process, however, enables the direct conversion of • cast rods, i.e. in this case, homogenization annealing and extrusion are avoided.

Recently, zirconium has been added to Al-Mg-Si aluminum alloys, in addition to major alloy elements such as silicon, iron, copper, manganese, magnesium, chromium, zinc and titanium, which improves corrosion resistance, inhibits recrystallization, shrinks crystalline grains and consequently improves mechanical properties. The proportion of zirconium in Al-Mg-Si aluminum alloys is up to 0.3 wt. % [EP 1458898, EP 2554698, EP 2799564, EP 2644725, EP 2811042, EP 2003219, EP 0987344, EP 1737994, EP 0173632, EP 0787217, EP 1802782, JP 2004043907, JP 2001107168, JP 2003277868, US 2004062946, JP 2007177308, JP 2007177308 US 2010089503, US 5240519], The zirconium content of the alloy depends on the technological parameters of Al-Mg-Si aluminum alloy production.

The known chemical compositions of Al-Mg-Si aluminum alloys do not contain 1.3-1.7 wt. % Si, 0.14-0.25 wt. % Fe, up to 0.75 wt. % Cu, 0.7-0.8 wt. % Mn, 0.85-1.1 wt. % Mg, 0.15-0.25 wt. % Cr, up to 0.2 wt. % Zn, up to 0.1 wt. % Ti, 0.15-0.25 wt. % Zr, other elements up to 0.15 wt. % (single element up to 0.05 wt.%) and the rest of Al.

The impact of each alloy element in the Al-Mg-Si aluminum alloy is as follows:

• In addition to magnesium and copper, silicon (1.3-1.7% by weight) is a major alloy that improves strength. This contribution can be attributed to MgSSi secretions that strengthen the basis of α-AI during aging. The contribution of elimination hardening is increased in the silicon content above 1.7 wt. %, but the resistance to stress corrosion cracks, and generally to corrosion, is significantly impaired. Coarse primary β-Si crystals are also beginning to be secreted, which also impair corrosion resistance and toughness. Under 1.3 wt. % Si, however, the contribution of elimination hardening is significantly lower.

• Iron (0.14-0.25% by weight) forms the phases of AI-Fe-Si- (Mn, Cr) and secretions such as Al7Cu2Fe, Ah2 (Fe, Mn) 3Cu2, (Fe, Mn) Afe and the like. When the iron content exceeds 0.25 wt. %, the proportion of phases and secretions is increased to such an extent that they impair mechanical and corrosion properties and workability.

• In addition to silicon and magnesium, copper (up to 0.75% by weight) is an element that improves strength by separating hardening a-AI solid solution as it ages. The effect of elimination hardening is proportionally increased by the proportion of copper in the alloy. Above 0.75 wt. % Cu greatly increases the sensitivity to intercrystalline and stress corrosion (cracks), i.e. the durability of the aluminum alloy is greatly impaired.

• Manganese (0.7-0.8 wt.%) Is excreted in the form of phase AI-Fe-Si- (Mn, Cr) and dispersed ΑΙβΜη secretions. These secretions occur during homogenization annealing and solute annealing and inhibit the growth of crystalline grains. Fine-grained crystalline grains and sub-grains improve mechanical properties, fracture toughness and fatigue. With a manganese content below 0.7 wt. % is an aluminum alloy subjected to recrystallization. On the other hand, the manganese content exceeds 0.8% by weight. % in the microstructure coarse ΑΙεΜη secretions occur, which adversely affect the mechanical properties and transformability.

• Magnesium (0.85-1.1% by weight) is secreted during the solidification process with silicon in the form of Mg2Si phase at the boundaries of crystalline grains. During homogenization annealing, part of the Mg2Si phases is dissolved in a-AI solid solution and part of them remains undissolved at the crystal grain boundaries. These undissolved particles inhibit the growth of crystalline grains upon further • ·

processes. During aging, however, dissolved magnesium and silicon are released in the form of MgSiS secretions, which strengthen the α-AI base and, consequently, improve the mechanical properties of the aluminum alloy. With a magnesium content below 0.85 wt. % the effect of curing is not so pronounced, with a content above 1.1 wt. % increases, however, coarse MgzSi secretions decrease elongation, poorer wear, and material is more susceptible to intercrystalline corrosion.

• Chromium (0.15-0.25% by weight) is excreted in the form of AI-Fe-Si- (Mn, Cr) phases during solidification and dispersed secretionsSii2Mg2Cr and AbMg2Cr during homogenization annealing. These secretions inhibit the growth of crystalline grains. Above 0.25 wt. % Cr is separated by coarse phases of AI-Fe-Si- (Mn, Cr), which represent the initial sites of crack formation.

• Zinc (up to 0.2% by weight) can, together with magnesium, form MgZn2 secretions during curing, which contributes to the strength of the aluminum alloy. On the other hand, MgZn2 secretion consumes magnesium, which is involved in the secretion of Mg2Si secretions, whose contribution to strength is significantly greater. Zinc also degrades the corrosion resistance of aluminum alloy.

• Titanium (up to 0.1% by weight) is added to aluminum alloys in the form of Al-Ti-B alloys, in which it is eliminated in the form of the AbTi and T1B2 phases. The AbTi particles dissolve relatively quickly in the melt, while the T1B2 particles with the thin AbTi layer act as germs, i.e. crushing crystalline grains aAl. Likewise, dissolved titanium in the melt inhibits the growth of α-AI crystalline grains. The fine-grained microstructure enhances the transformability and mechanical properties.

• Zirconium (0.15-0.25% by weight) is excreted in the form of fine AbZr and Si2Zr secretions at the boundaries of crystalline grains and subgranules during homogenization mourning. These excretions improve corrosion resistance, inhibit recrystallization, fragment crystalline grains, and consequently improve mechanical properties.

• Other elements (up to 0.15% by weight, individual elements up to 0.05% by weight) are most often present in the traces that enter the melt together with the secondary insert. These elements do not affect the properties of aluminum alloys.

The production of high-strength Al-Mg-Si aluminum alloy, as shown in Figure 1, begins with the preparation of a cartridge consisting of primary aluminum (technically pure aluminum, 99.7 wt% Al), reclaimed aluminum, secondary aluminum and alloy elements . The alloy elements are added in pure or pre-alloy form. The cartridge thus prepared is deposited in the melt furnace (induction or gas) where melting begins. After melting, the chemical composition of the aluminum alloy is monitored so that if the required chemical composition deviates, it can be adjusted accordingly. The melt temperature in the melting furnace depends on the content of zirconium in the melt and ranges from 700 to 780 ° C. The melting takes up to 5 hours, with the zirconium dissolving being advantageous for mixing the melt, which takes place naturally in induction furnaces and mechanically in the gas furnaces. The melting time is shortened by the use of the Al-Zr pre-alloy, in which zirconium is eliminated in the form of the finest AbZr phases. When the required chemical composition is achieved, the melt is poured into a holding furnace, where the melt is purified by blowing hydrogen or nitrogen and kept above the liquidus temperature for up to 4 hours. It depends on the zirconium content and ranges from 700 to 750 ° C. If the holding temperature falls below the liquidus temperature, the zirconium begins to be eliminated in the form of the AbZr phase, which settles to the bottom of the holding furnace due to a density of 4.1 g / cm 3 . These secreted AbZr phases (sizes up to a few 100 μιη) represent defects in the final product (maximum inclusions size should not exceed 40 μίτι) and the effect of zirconium is also reduced. In the first case, the alloy can be semi-continuous • cast with different casting systems (floats, hotheads, or in low-frequency electromagnetic fields) into poles 218 to 450 mm in diameter and up to 8 m in length. The casting temperature ranges from 680 to 730 ° C and the casting speed from 50 to 85 mm / min. In the second case, the alloy may be continuously poured into rods of 30 to 150 mm in diameter, with a casting temperature of 680 to 730 ° C and a casting speed of 100 to 1000 mm / min. Horizontally cast bars are further cold or hot transformed and heat treated or heat treated only. The melt temperature in the holding furnace between semi-continuous and continuous casting should not fall below the liquidus temperature. After casting, the rods are homogenized at 400 to 550 ° C for up to 24 hours and cooled in air, with fans, with water mist or water spray and examined by ultrasound. In homogenization annealing, it is important that it takes place below the solidus temperature, since at higher temperatures the Mg2Si phase precipitates and creates pores in the microstructure. The poles are then cut into extrusion rings 600 to 1600 mm in length and scraped if necessary. The pellets are further preheated to a homogeneous temperature or temperature profile (wedge). The bead temperature ranges from 470 to 550 ° C. The extrusion is carried out on a direct or indirect extruder into bars with a diameter of 20 to 180 mm or other shapes up to a cut circle of 270 mm at a speed of 0.1 to 25 mm / s. The temperature of the recipient on the direct and indirect extruder and the temperature of the tool or of the matrix ranges from 360 to 520 ° C. As soon as the stick or other shape comes out of the die, it is cooled rapidly in a water wave or water shower. The extruded bars (thermal state T1) are then cold or hot milled and heat treated or heat treated only according to the desired thermal state. For the thermal state of T6, rods, other shapes or forgings are solubilized in the temperature range from 450 to 550 ° C and from 1 to 3 h, germinated in water and artificially aged in the temperature range from 120 to 210 ° C and up to 15 h . For the T5 thermal state, they are artificially aged after tempering on the extruder in the temperature range from 120 to 210 ° C and times up to 15 h, and for the T4 thermal state after dissolving

annealing in the temperature range from 450 to 550 ° C and from 1 to 3 hours is still naturally aging.

A new high-strength Al-Mg-Si aluminum alloy, in the shape of a rod, in the second form or forged, manufactured according to the procedure described and with the said chemical composition achieves a tensile strength of 452 MPa to 495 MPa in thermal state T6, a tensile strength of 418 MPa to 465 MPa , elongation from 9 to 12.5% and hardness from 141 HB to 145 HB. In addition to its high mechanical properties, the alloy has good corrosion properties that meet automotive standards. The intercrystalline corrosion test was carried out in accordance with VW PV 1113, where the depth of intercrystalline corrosion of the bar in thermal state T6 is below 200 μηη.

Claims (12)

  1. PATENT APPLICATIONS
    1. The chemical composition of the high-strength Al-Mg-Si aluminum alloy is characterized in that it contains 1.3-1.7 wt. % Si, 0.14-0.25 wt. % Fe, up to 0.75 wt. % Cu, 0.7-0.8 wt. % Mn, 0.85-1.1 wt. % Mg, 0.15-0.25 wt. % Cr, up to 0.2 wt. % Zn, up to 0.1 wt. % Ti, 0.15-0.25 wt. % Zr, other elements up to 0.15 wt. %, up to 0.05 wt. %, and the remainder of Al.
  2. 2. The process of manufacturing a high-strength Al-Mg-Si aluminum alloy is characterized by the preparation of a cartridge, melting, holding, casting of poles or rods, homogenizing annealing, cutting of poles, extrusion, transformation and heat treatment.
  3. Process according to claim 2, characterized in that the melt temperature in the melting furnace is from 700 to 780 ° C and the melting time is up to 5 hours.
  4. Process according to claim 2, characterized in that the melt temperature in the holding furnace is from 700 to 750 ° C and the dwell time before casting is up to 4 hours, nor does the melt temperature in the holding furnace during casting fall below the liquidus temperature.
  5. 5. The method according to claim 2, characterized in that the casting is performed with a semi-continuous floating casting system, with a hot head or in an electromagnetic field at low frequencies into poles from 218 to 450 mm in diameter, up to 8 m in length, at a casting temperature of 680 to 730 ° C and a casting speed of 50 to 85 mm / min, or for casting to be carried out with a continuous casting system of rods of 30 to 150 mm in diameter, at »·· a casting temperature of 680 to 730 ° C and a casting speed of 100 to 1000 mm / min.
  6. Method according to claim 2, characterized in that the poles are annealed homogenized at a temperature of from 400 to 550 ° C for up to 24 hours and cooled in air, by fans, by water mist or water spray.
  7. Method according to claim 2, characterized in that the beads are heated to a temperature of from 470 to 550 ° C before extrusion.
  8. The method according to claim 2, characterized in that the temperature of the recipient is on the direct and indirect extruder and the temperature of the tool or. dies from 360 to 520 ° C.
  9. The method according to claim 2, characterized in that the beads on the direct and indirect extruders are extruded into rods with a diameter of 20 to 180 mm or other shapes to an outlined circle of 270 mm at a speed of 0.1 to 25 mm / s.
  10. The method of claim 2, characterized in that the bars, other shapes and forgings for the thermal state T6 are solubilized in the temperature range from 450 to 550 ° C and from 1 to 3 hours, germinate in water and age artificially in temperature range from 120 to 210 ° C and up to 15 h.
  11. 11. The method according to claim 2, characterized in that the bars, other shapes and forgings for the thermal state of T5 are artificially aged after tempering on the extruder in the temperature range from 120 to 210 ° C and from time to 15 hours.
  12. 12. The method according to claim 2, characterized in that the bars, other shapes and forgings for the T4 thermal state are solubilized in the temperature range from 450 to 550 ° C and from 1 to 3 hours and naturally age.
SI201600063A 2016-03-04 2016-03-04 High-strength aluminum alloy Al-Mg-Si and procedure for its manufacture SI24911A (en)

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EP17468001.7A EP3214191A1 (en) 2016-03-04 2017-03-02 A high-strength al-mg-si aluminium alloy and its manufacturing process

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