EP1330556B1 - Method for producing a magnesium hot strip - Google Patents

Abstract

The invention relates to a method for producing a magnesium hot strip, in which a melt from a magnesium alloy is continuously cast to form a roughed strip with a thickness of maximum 50 mm, and in which the cast roughed strip is hot-rolled directly from the cast heat at a hot-rolling initial temperature of at least 250° C. and maximum 500° C. to form a hot strip with a final thickness of maximum 4 mm, whereby in the first hot-rolling pass a reduction in the thickness of at least 15% is achieved. With the method according to the invention, magnesium sheets with improved deformability can be produced with reduced manufacturing effort and expenditure.

Description

The invention relates to a method for generating Hot strip made from wrought magnesium alloys. Magnesium is that Metal with the lowest density Strength properties similar to aluminum and could substitute this as a lightweight material. A essential prerequisite for the advance of Magnesium, however, is the lightweight material Availability of inexpensive sheet materials. Magnesium sheets are currently only in small quantities and too high Prices in the market. This can be explained from the big one Effort that comes from hot rolling sheet or strip Wrought magnesium alloys according to the current state of the Technology has to be applied. This is detailed in Magnesium paperback (Aluminum-Verlag Düsseldorf, 2000, 1st ed., Pp. 425 to 429). described. A basic problem hot rolling of wrought magnesium alloy sheets consists in that the common starting material Block or continuous casting solidified coarse-grained and porous, also strong segregations and coarse excretions contains. The cast blocks often become one Subjected to homogenization annealing and then at Temperatures between approx. Hot rolled at 200 and 450 ° C. These requirements usually require a number of repetitions Intermediate heating of the rolling stock, otherwise failures as a result Cracks develop.

It has been tried the deformability and the Properties of a hot-rolled magnesium sheet To improve the production of suitable materials which the hot strip is then rolled. Such one The method is for example from US 5,316,598 known. According to the known method, one lets Temperatures of 150 - 275 ° C pressed magnesium powder freeze quickly. By extrusion or forging from this block a primary material is generated, which then to a sheet with a thickness of rolled at least 0.5 mm. The rolling temperatures are between 200 ° C and 300 ° C. The so obtained Magnesium hot strip has superplastic properties and has high strength at room temperature and good toughness in the rolling direction.

A disadvantage of the known method, however, is that for the production of the primary material Magnesium powder creates this powder that compresses and that then accelerated cooling must be carried out. The associated apparatus and personnel expenditure leads to high manufacturing costs. It also shows that the forming of the primary material in In the course of hot rolling despite the complex production of Is difficult to master.

In addition to the prior art explained above from JP 06293944 A a method for producing a Magnesium sheet known, in which initially from a 0.5 -1.5% SEM, 0.1 - 0.6% zircon, 2.0 - 4.0% zinc and as Remaining magnesium-containing melt poured a slab becomes. This slab is then made in two stages hot rolled, being in the second stage of hot rolling the rolling temperatures between 180 - 230 ° C, preferably 180 - 200 ° C and a total deformation of 40-70%, preferably 40-60% is reached. That so tape obtained should have good ductility. The two-stage hot rolling does however also the rolling process and the one to be observed Temperature control is complex and difficult to control.

Based on the status of the Technology, the invention was based on the object Specify the procedure with which reduced Manufacturing cost magnesium sheets with improved Let formability be created.

According to the invention, this object is achieved by a method solved to create a magnesium hot strip, in which a melt from a magnesium alloy continuously to a supporting strip with a thickness of is cast at most 50 mm and in which the cast Supporting tape directly from the pouring heat at one Hot rolling start temperature of at least 250 ° C and at most 500 ° C to a hot strip with a final thickness of is hot rolled at most 4 mm, whereby in the first Rolling of hot rolling a reduction in thickness of at least 15% is achieved.

According to the invention, a supporting strip with a thickness of cast up to 50 mm, which due to its low Thickness cools down quickly and as a result an improved, has fine-grained and low-pore structure. Micro and Macro segregations are to a minimum in this state reduced. There are also any existing ones Primary excretions in fine, evenly distributed Form before, which causes the formation of a fine rolling structure is further supported. The so achieved particularly fine-grained structure favors formability during the subsequent hot rolling by the softening that is favorable for further forming facilitated. The training of one is also supported fine structure through the first hot rolling pass achieved thickness reduction of at least 15%. By the existing in the as-cast state and further in the rolling process The result is a refined structure that becomes a magnesium sheet received, its performance characteristics compared conventionally produced sheet is significantly improved.

Another advantage of the applied according to the invention continuous casting from pre-strips Magnesium material with subsequent, from the casting heat Rolling takes place is that the previously at Manufacture of magnesium sheets to be accepted Proportion of scrap is significantly reduced. By using a suitable remelting and casting technique results in addition, extensive procurement independence of the starting material. In addition, the Energy requirement in the applied according to the invention Casting rolling technology minimized and great flexibility with regard to the spectrum of the products produced guaranteed.

The invention can be particularly economical Carry out the process by directly opening the supporting strip the casting heat is hot rolled out. Depending on the Properties of the processed alloy and the equipment conditions, it can also be favorable Rolling temperature of the preliminary strip in the course of a before Hot rolling performed temperature compensation adjust. Through this temperature compensation a uniform temperature distribution in the opening and a additional structural homogenization achieved.

Oxidation of the belt surface and the formation of unwanted oxides in the structure can surely be avoided that the casting of the melt in one suitably trained solidification device under Shielding gas is carried out.

The microstructure can be further favored if the reduction in thickness in the first pass of hot rolling is at least 20%.

The deformability of the strip during hot rolling ensure the hot rolling start temperature be at least 250 ° C.

Those already produced in the opening act according to the invention existing good ductility makes it possible Hot strip continuously in several after the first stitch Finish rolling the stitches to their final thickness. A warming between the individual rolling passes is due to the forming heat is not required.

There is a rolling mill for finishing the hot strip not available, so hot magnesium band can be in produce the inventive method even if hot rolling is reversed in several passes.

If there is a need for hot rolling, Bridge downtime during which one continuous continuation of the rolling process is not is possible, it is favorable if the hot strip at least after the first stitch on a warm reel coiled and at the respective forming temperature is held. In the case of the returning Hot rolling it is advantageous to use the hot rolled hot strip between each roll pass on a warm reel reel and at the respective forming temperature hold. The forming temperature at which the hot strip is on the reel is preferably included at least 300 ° C.

With regard to the deformation properties and the desired thickness of the finished rolled strip should be the total degree of forming achieved during hot rolling at least 60% be.

The process according to the invention can preferably be carried out under Use a wrought magnesium alloy that up to 10% aluminum, up to 10% lithium, up to 2% Contains zinc and up to 2% manganese. For fine grain formation in the solidification structure an addition of zirconium or Contribute cerium in contents of up to 1% each.

The invention is described below with reference to Embodiments explained in more detail. The only figure shows the schematic structure of a casting and rolling system 1 for Pre-slab thicknesses down to 25 mm in one view from above.

The casting and rolling system 1 comprises in the conveying direction F arranged one behind the other a melting furnace 2 Solidification device 3, a first driver device 4, scissors 5, a second driver device 6, one Homogenization furnace 7, a first coiler 8, a third driver 9, a reversing roll stand 10, a fourth driver 11, a fourth reel device 12 and a roller table 13.

The reel device 12 and the roller table 13 are on a platform 14 set up transversely to Conveying direction F can be moved in such a way that in a first operating position the reel device 12 and in a second operating position of the roller table 13 at the end of the conveyor path 15 one generated in the casting and rolling mill 1 Magnesium tape is arranged. Are in the same way the homogenization furnace 7 and the coiler 8 arranged on a platform 16, so that one of these facilities in a first operating position next to conveyor 15 and in a second Operating position in the conveyor path of the to be generated Magnesium tape is arranged. At the start of production of a magnesium hot strip are Homogenization furnace 7 and reel 12 in conveyor path 15, while the reel 8 and the roller table 13 next to the Conveyor path 15 are arranged.

The reel devices 8 and 12 are not with here heaters shown equipped via the each on the reels, also not shown wound strip at the respective forming temperature can be held until the next rolling pass is carried out.

Within the solidification device 3, a melt is continuously cast under a protective gas atmosphere with the exclusion of oxygen to form a preliminary strip. Typical alloys of this melt are given in Table 1 below:

The use of HP has proven to be particularly advantageous (high purity) - Magnesium alloys proven. Such For example, alloys contain less than 10 ppm Ni, less than 40 ppm Fe and less than 150 ppm Cu.

The emerging from the solidification device 3, solidified supporting tape is scooped using scissors 5 and by the drivers 4 and 6 on the conveyor path 15 through the Homogenization furnace 7 promoted. There takes one Temperature compensation instead, in the course of which one evenly distributed over the cross-section of the supporting strip Rolling temperature is set, which is in the range from 250 - 500 ° C.

The supporting strip tempered in this way then reaches the Driver 9 promoted in the reversing stand 10 and undergoes a first hot rolling pass there. The the thickness reduction achieved is at least 15%. The hot strip leaving the rolling stand is removed from the Coiler device 12 coiled and in the for next forming stitch optimal forming temperature.

After the first rolling pass has been completed, the platform 16 brought into the operating position in which the Reel device 8 is in the conveyor path 15. Subsequently the hot strip is cut to its final thickness in several passes rolled of less than 4 mm, being each alternately through the reel devices 8 and 12 wound up and at the respective forming temperature is held. The latter is above 250 ° C.

Before the last rolling pass, the platform 14 in moves the operating position in which the Roller table 13 is arranged at the end of the conveyor path 15. The reversing roll stand 10 after the last stitch leaving, completely rolled magnesium hot strip is over the roller table 13 fed to further processing.

Typical properties of the magnesium hot strips produced in the manner described in the casting and rolling mill 1 from the alloys listed in Table 1 at room temperature are given in Table 2. The sheet thickness was between 1.2 and 1.5 mm.

It can be seen that the tapes produced according to the invention a fine structure and, due to this, a have excellent ductility. So is found that the properties Sheets produced according to the invention by at least 20% are better than the respective properties conventionally produced sheets.

REFERENCE NUMBERS

F

conveying direction

1

continuous casting and rolling

2

furnace

3

solidification facility

4

driving means

5

scissors

6

driving means

7

homogenizing

8th

coiler

9

driver

10

reversing

11

driver

12

coiler

13

roller table

14

platform

15

conveying

16

platform

Claims (11)

1. A method for producing a magnesium hot strip

   in which a melt from a magnesium alloy is continuously cast to form a roughed strip with a maximum thickness of 50 mm, and

   in which the cast roughed strip is hot-rolled directly from the casting heat at a hot-rolling initial temperature of at least 250 °C and maximum of 500 °C to form a hot strip with a final thickness of maximum 4 mm, whereby in the first hot-rolling pass a reduction in thickness of at least 15 % is achieved.
2. The method according to Claim 1, characterised in that the casting of the melt takes place under a protective or inert gas.
3. The method according to one of Claims 1 or 2, characterised in that the roughed strip is brought to the hot-rolling initial temperature before the hot-rolling in the course of a temperature equalization.
4. The method according to one of the foregoing claims, characterised in that the reduction in thickness in the first hot-rolling pass amounts to at least 20 %.
5. The method according to one of the foregoing claims, characterised in that the hot strip is continuously finish-rolled after the first pass to final thickness in several passes.
6. The method according to one of Claims 1 to 4, characterised in that the hot-rolling takes place in several passes in reversing fashion.
7. The method according to one of Claims 5 or 6, characterised in that the hot strip is coiled on a hot coiler at least after the first pass, and is maintained at deformation temperature.
8. The method according to Claims 6 and 7, characterised in that the reversing hot-rolled hot strip is coiled between each rolling pass on a hot coiler.
9. The method according to one of Claims 7 or 8, characterised in that the deformation temperature at which the hot strip is maintained on the coil amounts to more than 300 °C.
10. The method according to one of the foregoing claims, characterised in that the overall degree of deformation achieved during hot-rolling amounts to at least 60 %.
11. The method according to one of the foregoing claims, characterised in that the magnesium alloy is a wrought alloy with up to 10 % aluminium, up to 10 % lithium, up to 2 % zinc, up to 2 % manganese, up to 1 % zirconium, and up to 1 % cerium.

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