RU2253521C1 - Method for making sheets of magnesium-base alloy for electrochemical electric current sources - Google Patents

Abstract

FIELD: plastic working of special magnesium base alloys alloyed with elements capable to easy evaporation or to generation at deformation oxides hazard for environment, possibly manufacture of rolled sheets used for making anodes of electrochemical current sources.

SUBSTANCE: method comprises steps of preliminarily deforming heated blank of magnesium base alloy and warm rolling of preliminarily deformed blank for producing sheet; before preliminary deformation placing magnesium alloy blank into envelope of aluminum (Al-Mg-Si system) alloy without sealing. Length of envelope exceeds length of blank at least by 10%. Preliminary deformation is realized by hot rolling or upsetting in die set according to configuration of blank.

EFFECT: production of sheets with electrochemical properties uniform along the whole cross section and with enhanced surface quality, safety labor condition due to preventing evaporation of mercury, toxic oxides and other compounds containing mercury, thallium, gallium, cadmium.

12 cl, 4 tbl, 4 ex

Description

The invention relates to the field of pressure treatment of special magnesium alloys alloyed with volatile or forming oxides hazardous to the environment during deformation, and can be used in the rolling production of sheets for anodes of electrochemical current sources.

A known method of producing sheets of magnesium-based alloys, including the preparation of ingots, the preliminary deformation of a heated billet of magnesium alloy and its warm rolling to produce a sheet (see Magnesium alloys. Handbook edited by M.B. Altman, etc. t.2. The production technology and properties of castings and deformed semi-finished products. M: Metallurgy, 1978, p.150).

Sheets of magnesium alloys alloyed with, for example, mercury (an easily evaporated element) or gallium and a number of other elements, are used as an anode and provide a high potential difference with a cathode, for example, made of silver, nickel, copper and a number of oxides, serve as a powerful source current in aqueous electrolytes with low acidity.

Magnesium alloys in the cold state are slightly plastic, which is due to the hexagonal crystal lattice and only one slip plane in it.

Therefore, to ensure increased ductility, it is necessary to heat the workpiece to a temperature in the range of 360-420 ° C.

Rolling of magnesium alloys at lower temperatures at all degrees of deformation inevitably leads to the appearance of cracks not only along the edge, but also over the entire surface, and at some degrees of deformation, for example, more than 30%, already in the first passes leads to complete destruction.

In addition, it was experimentally established that during hot rolling of cast billets and during warm rolling of rolling it is necessary to heat the rolling rolls to temperatures in the range of 100-200 ° C, depending on the alloy.

These temperature parameters of rolling magnesium alloys in the case of alloying them with mercury, thallium, gallium and similar elements lead to unacceptable phenomena in terms of ecology and protection of human life and health.

When doping with mercury, intense evaporation of mercury from the surface of the sheet occurs both during heating and during rolling, and when doping with thallium, gallium, cadmium due to abrasion of the sheets during rolling, toxic thallium, gallium, cadmium oxides and naturally occurring mercury enter the atmosphere as aerosol mixture.

These mercury vapors and oxides of thallium, gallium, cadmium and their compounds accumulate rather quickly on equipment, walls and ceilings of premises and, most importantly, in the body, which for a person ends in either disability or death.

In addition, due to evaporation, for example mercury, the surface of the sheets is depleted in this element, and the electrochemical parameters are sharply worsened.

Upon receipt of the sheets of the described magnesium alloys in a known manner, all of the above disadvantages will be observed.

The objective of the invention is to obtain sheets with high, uniform over the entire cross section electrochemical properties, high quality rolling of rolling (no sunsets, captures on the surface, warping, and other defects) and providing safe working conditions and environmental standards with a complete solution to the problems of preventing evaporation of mercury and formation toxic oxides and other compounds containing mercury, thallium, gallium, cadmium and the like.

The problem is solved by a method of manufacturing magnesium alloy sheets, including pre-deformation of a heated magnesium alloy billet and warm rolling of a pre-deformed billet to produce a sheet, in which for the production of magnesium alloy sheets alloyed with easily evaporating elements or forming oxides of these oxides hazardous to the environment elements, for electrochemical current sources, before preliminary deformation of the workpiece from magnesium alloys is placed in an aluminum alloy shell of an Al-Mg-Si system.

Advantageously, an aluminum alloy shell of the AD31, 6063 or ABB grade is used.

In private embodiments of the invention, the problem is solved in that the preform is placed in a shell of aluminum alloy, the length of which exceeds the length of the preform by at least 10%.

In the most attractive embodiments, the preform is placed in a shell whose length exceeds the length of the preform by 20-40%.

In addition, the preform is placed in a shell with a gap of 0.5 to 2 mm.

If the preform in the cross section is round, then such a preform is placed in an aluminum alloy shell made in the form of a pressed pipe, the length of which exceeds the length of the preform by 10-30%, embossed on both sides, and preliminary hot deformation is carried out by heating the preform to 380 -420 ° C by rolling at a heating temperature of the rolls of 140-160 ° C for several passes to a thickness allowing further warm rolling. The length of the pressed pipe exceeds the length of the workpiece by 10-30% on each side.

If the workpiece has a flat shape, then the preliminary deformation of the workpiece in the shell is carried out in dies.

In this case, the blank in the shell is placed in the lower die, made in the form of a trough, the size of which is calculated on the basis of ensuring the free flow of the magnesium alloy and the specified thickness of the final blank, while the stamps are heated to 120-150 ° C, and the blank is heated to 380 ± 25 ° FROM.

It is also possible to preliminarily deform a flat billet by settling in flat dies with heating the billet to 420 ± 25 ° C, and a die not less than 150 ° C.

Heating the preform before warm rolling is carried out to 360-390 ° C with holding in the oven for 30 to 60 minutes, and warm rolling of the preform in the shell is carried out in rolls heated to 120-140 ° C with a deformation of 10-30% per pass.

After preliminary deformation, the workpiece is cooled in air, while its cooling during warm rolling provides at least 320 ° C.

In the process of warm rolling carry out intermediate heating of the workpiece.

The essence of the proposed method is as follows.

The blank is enclosed in a specially selected aluminum alloy shell. Subsequently, a round billet or a flat billet placed in an aluminum shell can be subjected to two operations:

- heating and sediment in a special heated stamp to obtain a flat workpiece with a thickness of about 10-40 mm for the purpose of further warm rolling on a sheet;

- heating in an aluminum alloy shell and hot rolling on a rolling mill with rolls heated to 160 ± 10 ° C, regardless of the shape of the workpiece — flat or round, then, as in the first case, warm rolling of the workpiece onto a sheet.

Usually rolling on sheets to various thicknesses is carried out with several heatings.

Most often, rolling is carried out to a thickness of 0.3-0.6 mm for the main magnesium alloy.

Example 1

Table 1 shows the main modes of production of the workpiece by precipitation.

Table 1 the name of the operation Temperature ° C Min time Sheathing the workpiece twenty 1 Sheath blank heating 420-10 90 Flat die heating for precipitation 150 + 10 thirty Stamp heating with a recess (“trough”) 150 twenty

When hot draft on flat or special dies, the lower of which has a trough-like recess, equal in length to the length of the workpiece in the shell, and a width that provides free flow of metal and the design of a flat rectangular workpiece.

Sediment is carried out on a heated billet (see Table 1) in dies heated to 150 ° C. The workpiece is cooled in air.

Example 2

Heating and hot rolling of blanks in a shell.

table 2 the name of the operation Temperature ° C Min time Sheath blank heating 380-400 120 Rolling Start 400 ± 15 3 end 360 - Roll heating 160 ± 5 During rolling

Example 3. Warm rolling of workpieces.

Table 3 the name of the operation Temperature ° C Min time Number of passes 1st heating before warm rolling 360-420 40-60 10-12 Intermediate heating 360 15-20 18-22 Rolls 100-120 During rolling -

As already indicated, a special aluminum alloy of the Al-Mg-Si system is selected for the shell. The choice of aluminum alloy is due to the need to select parameters for deformation resistance equal to or close to the deformation resistance of the main magnesium alloy.

The alloys closest in properties to magnesium alloys at hot and warm rolling temperatures are suitable

- alloy AD31 GOST 4784-97, analogue 6063 according to ASTM ANSI H35.1,

- Alloy ABB GOST 4784-97.

Aluminum cast alloys according to GOST 1583-93 are unsuitable, since they form open porosity: 12 pores ⌀ 0.3 mm per 1 cm ^{2 of the} surface, and do not prevent the evaporation of alloying elements.

Alloys of the Al-Mg-Si system are chosen because they are uniformly deformed together with the magnesium alloy, not sliding off the surface, such as pure aluminum, and not cracking.

In addition, during heating and hot deformation, an interaction occurs between the magnesium alloy and the aluminum shell with the formation of an intermetallic layer. The formation of this layer very significantly affects the results of warm rolling (by changing the number of passes and affecting crack formation).

The thickness of the shell (cladding) is calculated based on the scheme and the degree of deformation. For a workpiece diameter of 100 mm, the shell thickness should be 5 mm. The workpiece fits freely into the shell. The clearance is 1 mm. The length of the shell is 30% greater than the length of the workpiece (15% from each end) and is choked without complete sealing, which ensures free exit of gases during hot deformation after upsetting and hot rolling. If the preform is sealed, then during deformation there will be a rupture of the shell from the end and an emission of gases, including mercury vapor, with a strong “pop”. For example, table 4 shows the results of measurements on the mercury content in the environment during the hot deformation of blanks and sheets without protective cladding.

Example 4

Heating and rolling of non-sheathed blanks of alloy alloyed with mercury, thallium and other elements.

The data in this table clearly show that it is impossible to perform normal rolling without a casing. In addition, in the case of an alloy with mercury, the depletion of the surface layer of the sheets, starting with hot rolling, is up to 40% to a depth of 0.1 mm.

Claims (12)

1. A method of manufacturing sheets of magnesium alloys, comprising pre-deformation of a heated billet of magnesium alloy and warm rolling of a pre-deformed billet to produce a sheet, characterized in that for the production of sheets of magnesium alloys doped with easily evaporating elements or forming oxides hazardous to the environment of these elements, for electrochemical current sources, before preliminary deformation, the billets of magnesium alloys are placed in an aluminum shell and Magnesium alloy of Al-Mg-Si without sealing. 2. The method according to claim 1, characterized in that they use a shell made of aluminum alloy brand AD31, 6063 or ABB. 3. The method according to claim 1, characterized in that the preform is placed in a shell of aluminum alloy, the length of which exceeds the length of the preform by at least 10%. 4. The method according to claim 1, characterized in that the preform is placed in a shell with a gap of 0.5 to 2 mm. 5. The method according to claim 1, characterized in that the magnesium billet having a circular cross-section is placed in an aluminum alloy shell made in the form of a pressed pipe hammered on both sides, and preliminary deformation is carried out by rolling a magnesium alloy billet in an aluminum shell alloy, heated to a temperature of 380-420 ° C, and when heated to 140-160 ° C rolls for several passes to a thickness that allows warm rolling. 6. The method according to claim 5, characterized in that the preform is placed in a pressed tube of aluminum alloy, the length of which exceeds the length of the preform by 10-30% on each side. 7. The method according to claim 1, characterized in that the preliminary deformation of the flat billet of magnesium alloy in a shell of aluminum alloy is carried out in dies. 8. The method according to claim 7, characterized in that the billet in the shell is placed in the lower die, made in the form of a trough, the size of which is calculated based on the free flow of the magnesium alloy and the specified thickness of the final billet, while the dies are heated to 120-150 ° C, and the workpiece is up to (380 ± 25) ° C. 9. The method according to claim 7, characterized in that the preliminary deformation is carried out by upsetting in flat dies with heating the workpiece to (420 ± 25) ° C, and the stamp not less than 150 ° C. 10. The method according to claim 1, characterized in that before warm rolling preheated workpiece is heated to 360-390 ° C with holding in the oven for 30 to 60 minutes, and warm rolling is carried out in rolls heated to 120-140 ° C deformation of 10-30% per pass. 11. The method according to claim 10, characterized in that after pre-deformation, the pre-deformed billet is cooled in air, while its cooling during warm rolling is ensured at least 320 ° C. 12. The method according to claim 10, characterized in that in the process of warm rolling carry out intermediate heating of the workpiece.