RU2492274C1 - Method of extruding semis of high-strength aluminium alloy and parts thus made - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: proposed method comprises casting the ingots of alloy containing the following components in wt %: zinc - 6.-4.1, magnesium - 0.6-1.1, manganese - 0.2-0.5, zirconium - 0.05-0.12, chromium - 0.05-0.15, copper - 0.1 -0.2, titanium - 0.01 -0.06, molybdenum - 0.01 -0.06, aluminium making the rest, at the temperature of 690-710°C and casting rate of 25-50 mm/min. Ingots are homogenised at 450-470°C for 8-12 hours and subjected to hot forming at 10-530°C and outflow rate of 0.1-4.0 m/min. Besides it includes air or air-water mix quenching and two-step ageing: at 90-110°C for 6-12 hours and at 160-190°C for 4-10 hours.

EFFECT: production of log parts with high operating properties.

4 cl, 1 ex, 6 tbl, 4 dwg

Description

The present invention relates to a method for the production of long, thin-walled panels and profiles intended for use in railway transport, but is not limited to this area, from high-strength aluminum alloy having the following ratio of components, wt.%:

Zinc 3.6-4.1

Magnesium 0.6-1.1

Manganese 0.2-0.5

Zirconium 0.05-0.12

Chrome 0.05-0.15

Copper 0.1-0.2

Titanium 0.01-0.06

Molybdenum 0.01-0.06

Aluminum rest

Over the nearly 200-year history of railway transport, carriage building has gone from wooden body structures to integrated aluminum and hybrid structures.

The transition to new structural materials has always been accompanied by an improvement in the technical characteristics of the rolling stock, changes in the design and technology of its manufacture, a reduction in the unit costs of material, financial and energy resources per unit of useful work, for example, per passenger-kilometer.

The use of large extruded panels allows reducing the laboriousness of bodywork production by 40% and reducing its weight to 7.5 tons for cars with a length of 26 m compared to 11 tons for the same body made of steel.

Innovations in this technology have led to even more, up to two times compared with steel, reducing the time spent on the manufacture of aluminum bodies. The total cost of a typical aluminum body is less than 85% of the cost of a conventional steel body.

The technology for the production of cars from large aluminum profiles and panels is a cost-effective solution. Oversized profiles can replace many complex classic parts. Pressed profiles can be supplied as integral parts ready for installation. Such technologies can be used in many fields of technology. The existing advantages and applications of aluminum alloy products allow them to compete successfully with steel structures

The aluminum alloys from which the panels are made, intended for use in car building, must meet the following requirements:

1. To possess the necessary strength, high energy intensity of destruction, high resistance to cyclic loads that act on cars during their movement, high corrosion resistance. [1, 6, 8].

2. Possess good manufacturability in mechanical engineering, (it is good to be welded by argon-arc welding, have a low tendency to crack formation during welding, the softening of the metal in the welded joint should not exceed 0.85 of the base metal, and have a certain plasticity margin for performing small edits and moldings )

3. Since the output of semi-finished products for car building is large, then the alloys must have high manufacturability in the press industry, namely a high flow rate; low specific pressing pressure; the possibility of pressing complex thin-walled products, including hollow ones, as well as having a wide temperature range of existence and high stability of the solid solution of the main alloying components in aluminum, which provide the possibility of hardening on the press.

Known aluminum alloy (RF Patent No. 2288293, publ. 11/27/2006) corresponding to the above requirements and having the following chemical composition wt.%:

Zinc 3.6-4.1

Magnesium 0.6-1.1

Manganese 0.2-0.5

Zirconium 0.05-0.12

Chrome 0.05-0.15

Copper 0.1-0.2

Titanium 0.01-0.06

Molybdenum 0.01-0.06

The rest is aluminum.

A known method of manufacturing products from wrought aluminum alloys containing at least one transition metal, comprising the following operations: heating the ingot to a temperature of preliminary plastic deformation of 262-398 ° C with a delay of 0.5-7 hours, preliminary plastic deformation at this temperature, heating before the final plastic deformation to a temperature of 405-445 ° C, holding at this temperature for 0.5-7 hours and subsequent final plastic deformation, heat treatment (RF Patent No. 2152451).

A known method of producing semi-finished products from alloys of the Al-Zn-Mg-Cu system with increased static mechanical characteristics, consisting of the following operations: two-stage homogenization - temperature 460 ° C, holding 7 hours + temperature 466 ° C, holding 23 hours, forging at a temperature of 400 ° C, quenching from a temperature of 475 ° C and two-stage aging according to the regime: temperature 120 ° C, holding 6 hours + temperature 135 ° C, holding 7 hours (US Application No. 2003/219353).

The disadvantages of these methods are the heterogeneity of the structure of the semi-finished products, low fracture toughness indices K1C, significant anisotropy of the mechanical properties and reduced corrosion properties, which leads to a decrease in the resource and reliability in the operation of the products.

Closest to the proposed method, adopted as a prototype, is a method of manufacturing pressed semi-finished products from aluminum alloy and a product obtained from them including casting ingots, annealing them at a temperature of 320-395 ° C, hot pressing, heat treatment for solid solution at a temperature of 430-565C hardening and aging.

The disadvantage of this method is that the method is specialized for the manufacture of power parts for an airframe and does not satisfy the technological requirements for the mass production of thin-walled, long-length, hollow panels and profiles used in the construction of railway cars, and does not guarantee their stability properties, and is also not economically competitive.

The objective of the present invention is to develop an economical method of manufacturing extruded, long, thin-walled, hollow panels with a width of up to 790 mm and profiles designed for railway transport with a set of strength, technological and operational properties that meet promising requirements in this technical field.

The technical result achieved by the application of the proposed method is the creation of a competitive technology for the production of semi-finished Al-Zn-Mg-Cu-Zr semi-finished products from a highly alloyed aluminum alloy, in which good mechanical, technological and corrosion properties of the products are ensured by optimal thermomechanical processing conditions.

The specified technical result is achieved in that in the method of pressed semi-finished products from high-strength aluminum alloy, including ingot casting, hot pressing, heat treatment for solid solution, quenching and aging, characterized in that the ingots are cast from an alloy having the following ratio of components, wt.% :

Zinc 3.6-4.1

Magnesium 0.6-1.1

Manganese 0.2-0.5

Zirconium 0.05-0.12

Chrome 0.05-0.15

Copper 0.1-0.2

Titanium 0.01-0.06

Molybdenum 0.01-0.06

The rest is aluminum

at a casting temperature of 690-710 ° C at a speed of 25-50 mm / min, homogenize at a temperature of 450-470 ° C for 8-12 hours, hot pressing is carried out at a temperature of 410-530 ° C at a flow rate of 0.1-4 , 0 m / min, hardening is carried out from the deformation temperature immediately after pressing on a press, in air or with an air-water mixture and two-stage aging according to the regime: temperature 90-110 ° С, holding time 6-12 h + temperature 160-190 ° С, 4-10 hours exposure

With a significant thickness in the cross section of the profile elements, the product is quenched with water after heating in a furnace from a temperature of 450 ° C.

It is also possible to perform natural aging for at least 7 days.

Of the semi-finished products obtained in this way, long, thin-walled panels and profiles are made for use in railway transport.

The choice of an aluminum alloy of this chemical composition is due to the fact that during the smelting of large ingots from this alloy, Al ₃ Zr intermetallic compounds of crystallization origin are not formed, and the presence of transition metals Cr, Mo, Ti in the composition of copper and microadditives, as well as the correction of the two-stage aging mode, allowed get high resistance to delaminating corrosion (3 points) and stress corrosion at a high level of mechanical properties.

The mechanical properties of the alloy significantly exceed the mechanical properties of alloys of the type AD31 used for the manufacture of cars abroad, and are very close to the properties of the alloy 1915, passenger cars of which have been operated in Russia for more than thirty years.

Casting modes at a temperature of 690-710 ° C and a casting speed of 25-50 mm / min are selected empirically and provide a uniform alloy structure throughout the entire volume of the ingot.

The preparation of the alloy structure for quenching on the press begins during the homogenization annealing of cast ingots. During aging at the homogenization temperature, the coarse particles of the excess Mg2Si phase are dissolved, which formed during crystallization of the melt by the eutectic reaction and precipitated along the boundaries of grains and dendritic branches. By the end of the exposure, Mg2Si particles are practically absent in the structure of the ingot, and magnesium and silicon are in solid aluminum solution. Homogenization of ingots is carried out at a temperature of 450-470 ° C for 8-12 hours, exceeding these boundaries leads to the release of fusible elements along the grain boundaries, homogenization at lower parameters does not guarantee acceptable alignment of the chemical microinhomogeneity of the grains.

The formation of a solid solution of the main alloying components in aluminum in this alloy occurs with increasing temperature much easier and faster than, for example, in the AD31 alloy, which is doped with silicon, due to the easier and faster dissolution of η (MgZns) particles relative to Mg ₂ Si particles ( the Mg ₂ Si phase is one of the most thermally stable phases that form the main alloying components in industrial aluminum alloys (Cu, Mg, Zn, Si) between themselves and aluminum).

Thus, this alloy has high stability of a supersaturated solid solution of the main alloying components (zinc and magnesium) in aluminum, the temperature range of the reduced stability of the solid solution is shifted to lower temperatures, and the pressing temperature coincides with the temperature range of the existence of a solid solution of zinc and magnesium in aluminum, which is very wide (340-615 ° C). These features provide a good opportunity for press hardening of pressed semi-finished products.

The attractiveness of low pressing temperatures lies in the fact that this achieves a high surface quality of the pressed semi-finished product and reduces the likelihood of internal delamination.

Pressing at a pressing temperature below 410 ° C is not rational, because pressing forces increase, pressing at temperatures above 530 ° C leads to a decrease in product quality.

The flow rate varies from 0.1-4.0 m / min and depends on the area and configuration of the product cross sections, in particular when pressing complex thin-walled hollow panels or profiles to reduce the pressing force, the heating temperature can be increased to 500-530 ° C. The pressing of such complex semi-finished products is carried out with reduced flow rates, and the generated deformation heat manages to go into the tool. In this case, the temperature increase is small.

Due to the fact that the temperature range for the existence of a solid solution in the alloy has a very wide range (340-615 ° C), cooling the air or water-air mixture is sufficient for fixing the solid solution when pressing thin-walled panels and profiles, which allows this operation to be performed immediately after pressing on the table press.

In the manufacture of monolithic profiles having a significant cross-sectional area, water is quenched from a temperature of 450 ° C after heating in a furnace, which guarantees uniformity of properties throughout the entire volume of the product.

Semi-finished products from this alloy can be used both in a naturally aged state and after artificial aging. Strength properties in a naturally aged state after long months of aging are even slightly higher than after artificial aging, however, pressed semi-finished products in a naturally aged state are more sensitive to delaminating corrosion. Therefore, when choosing the state of the semi-finished product for specific operating conditions, one should be guided by the choice of the optimal combination of strength and corrosion resistance.

Artificial two-stage aging according to the regime: temperature 90-110 ° C, holding 6-12 h + temperature 160-190 ° C, holding 4-10 h. At the first stage there is an intensive formation of Guinier-Preston zones, which at the second stage serve as nuclei of formation hardening particles of the η (MgZn2) phase. As a result, particles are released with a high density per unit volume of the matrix and maximally strengthen the alloy. In this case, when overcooking, a minimal loss of strength properties occurs.

The temperature of the second stage of aging for the alloy was chosen 160-190 ° C. The reason for this choice was the fact that at a lower temperature with increasing exposure time, as shown by preliminary experiments, there is no noticeable increase in the resistance to delamination corrosion. A slight increase in the temperature of the second stage to 200 ° C leads to a strong decrease in strength characteristics. The optimal drawing times in the first and second stages, at which, with a minimum decrease in properties, a maximum increase in the resistance to delaminating corrosion would be achieved, were experimentally selected.

The invention is illustrated by photographs showing cross sections:

Figure 1 - profile (dimensions 350 × 110 mm);

Figure 2 - panel (dimensions 790 × 52 mm);

Figure 3 - cipher panels (dimensions 790 × 50 mm).

In Fig. 4 (a-d is a bright-field image, e is a dark-field image in the Al ₃ Zr phase reflection, a - × 500 × 2; 6 - × 5800 × 2; g - × 48000 × 2; e, e - 36000 × 2)

An example of a specific implementation.

In an electric melting furnace of resistance type SAN with a capacity of 10 tons, 2 melts of the following chemical composition were performed, table 1:

Table 1 Swimming trunks number Mass fraction of elements in% Cu Mg Mn Fe Si Cr Zn Ti Mo Zr one 0.117 0.831 0.296 0.190 0,0672 0,081 3.80 0.0275 0.0108 0,088 2 0.127 0.871 0,309 0.165 0,0514 0,0643 4.07 0.0265 0,0202 0.103

Then flat and round ingots were cast. Ingot casting was carried out according to the following modes, table 2:

Table 2 Swimming trunks number Ingot size, mm Casting options temperature, ° С speed mm / min Water pressure, Pa one 310 × 1110 705 46.6 1.4 × 10 ⁵ 2 0510 700 26.7 4,558 × 10 ⁴

Modes of homogenization of cast ingots are shown in table 3.

Table 3 Ingot size, mm Homogenization temperature, ° С Duration of exposure, hour 310 × 1110 455-460 12 0510 460-463 12

Of the cast ingots were made experimental batch of 2 types of panels (Fig.2 and 3) and 1 type of profiles (Fig.1). Hardening of the profiles was carried out in water after holding in a vertical quenching furnace from a temperature of 450 ° C. The hardening of the panels was carried out on the press table from the temperature of deformation by forced air supply. Press modes are shown in table 4.

Table 4 Workpiece temperature, ° С Matrix temperature, ° С Container temperature, ° С Expiration rate, m / min The value of residual deformation during dressing,% Artificial aging I stage II stage 410-530 360-460 410-450 0.1-4.0-0.1 1.0-3.5 100 ° C 6-12 h 170-180 ° C 4-10 h

The mechanical properties of pressed semi-finished products in a naturally aged and artificially aged state according to the selected mode (100 ° C, 10 hours + 175 ° C, 6 hours) are given in Tables 5 and 6.

Table 5 Profile Properties condition Direction σ _in MPa σ ₀₂ MPa δ,% ψ,% Naturally aged Longitudinal 347 236 14.3 21.8 Transverse 369 264 13,2 33.5 Artificially aged 100 ° С, 10 h + 175 ° С, 6 h Longitudinal 309 243 15.9 38.9 Transverse 333 275 15,2 54.3

Table 6 Panel properties (longitudinal samples) Sample Cutting Location condition σ _in MPa σ ₀₂ MPa δ,% RSK, Score Canvas panels Naturally aged 353 219 20,0 8.5 Artificially aged 100 ° C, 104 + 175 ° C, 64 322 252 18.9 3 Partition Naturally aged 350 217 19.0 - Artificially aged 100 ° C, 104 + 175 ° C, 64 332 253 18.3 -

The properties of samples cut from the panel walls (Table 6) are not inferior to the properties of samples cut from the panel canvas and are characterized by rather high values. This once again confirms that the alloy subjected to processing by this method has a very high stability of the solid solution, allowing its fixation at low cooling rates from high temperatures.

As in the case of a profile, the properties of a panel in a naturally aged state are slightly higher than those in an artificially aged state. However, the resistance to delaminating corrosion, as the panel tests showed, is much better in artificially aged condition. After natural aging, the tendency of panels to stratify corrosion is estimated at 7-8 points, and after artificial aging - 3 points.

Figure 4 presents the results of electron microscopy studies of the structure of the profile in the delivery state. At low magnifications in an electron microscope, a subgrain structure is clearly visible (Fig. 4a, b), and at higher magnifications, the particles of the intermetallic transition metals of manganese, chromium (Fig. 4c), zirconium (Fig. 4d, e) are clearly distinguished. Figure 4g shows the boundary of the subgrain restrained by intermetallic manganese (type Al6Mn) and zirconium (Al3Zr).

After hardening, the pressed semi-finished products are guaranteed to retain a completely non-crystallized structure.

The non-crystallized (polygonized) structure in pressed semi-finished products provides an increased range of service characteristics. First of all, these are increased strength properties with good ductility, high impact toughness and higher stress corrosion resistance.

High structural and technological properties of products manufactured by this method were also confirmed by testing welded joints. After 60 days of natural aging after welding, the welded joint of SP50 profiles has σ _in ^sv = 255 MPa, bending angle = 77 degrees, KSU of the _weld = 28 J / cm ² , KSV of the _weld = 21 J / cm ² , KCV of the fusion zone = 38 J / cm ² . A study of the weldability of extruded profiles from 1935 B alloy showed that the alloy has a low tendency to crack formation during welding, and the coefficient of weakening of the welded joint is 0.80-0.95; welded joints and actually seams are plastic and viscous. Welded joints have high resistance to stress corrosion in naturally and artificially aged conditions. The tendency to delaminating corrosion of welded joints is estimated at 7-8 points in a naturally aged state and 2-3 points after artificial aging.

The proposed method of pressing semi-finished products from high-strength aluminum alloy allows to obtain unique, long-length, thin-walled profiles and panels up to 790 mm wide, designed for use in railway transport, which have a set of strength, technological and operational properties that meet promising requirements in this technical field.

Claims (4)

1. A method of manufacturing pressed semi-finished products from high-strength aluminum alloy, including casting ingots, hot pressing, heat treatment for solid solution, quenching and aging, characterized in that the ingots are cast from an alloy having the following ratio of components, wt.%:
Zinc 3.6-4.1 Magnesium 0.6-1.1 Manganese 0.2-0.5 Zirconium 0.05-0.12 Chromium 0.05-0.15 Copper 0.1-0.2 Titanium 0.01-0.06 Molybdenum 0.01-0.06 Aluminum Rest,
at a casting temperature of 690-710 ° C, at a speed of 25-50 mm / min, the ingots are homogenized at a temperature of 450-470 ° C for 8-12 hours, hot pressing is carried out at a temperature of 410-530 ° C at a flow rate of 0, 1-4.0 m / min, hardening is carried out from the deformation temperature immediately after pressing on a press in air, in water or in an air-water mixture and natural aging or artificial aging is carried out according to a two-stage mode: temperature 90-110 ° С exposure 6- 12 hours, temperature 160-190 ° С, holding time 4-10 hours. 2. The method according to claim 1, characterized in that the hardening is carried out with water from a temperature of 450 ° C. 3. The method according to claim 1, characterized in that they produce natural aging for at least 7 days. 4. The product obtained from semi-finished products from high-strength aluminum alloy, characterized in that it is obtained from semi-finished products made by the method according to any one of claims 1 to 3.

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