PRODUCTION METHOD OF AN ALUMINUM ALLOY MATERIAL SUITABLE FOR USE IN THE FOOD INDUSTRY

Abstract

Disclosed is a method for producing aluminum alloy materials suitable for use in the food industry including processing of a liquid metal mixture having strontium in addition to aluminum by the twin roll continuous casting technique.

Claims

1. A method for the production of aluminum alloy materials suitable to be used in the food industry, characterized by comprising: processing of a liquid metal mixture comprising strontium in addition to aluminum by a twin roll continuous casting technique.

2. The method according to claim 1, wherein said liquid metal mixture comprises also at least one more component selected from the group consisting of silicon, iron, copper, manganese, magnesium and zinc.

3. The method according to claim 1, comprising the process steps of: i. Casting of liquid metal mixture as a coil in the twin roll continuous casting system, ii. Annealing of the coil, iii. Thinning the annealed coil by cold rolling, iv. Thinning the thinned material until it reaches the thickness of the final product by rolling again, v. Annealing of the aluminum alloy material which has been brought to the thickness of the final product.

4. The method according to claim 3, wherein the liquid metal mixture mentioned in process step number (i) comprises aluminum in the ratio of at least 95% by weight, as well as strontium in the ratio of 0.001-0.50% by weight and also at least one more component selected from the group comprising silicon, iron, copper, manganese, magnesium and zinc.

5. The method according to claim 3, wherein the casting process mentioned in process step number (i) is performed at the rate of 50-150 mm/minute.

6. The method according to claim 3, wherein the casting process mentioned in process step number (i) is performed at the thickness of 3-10 mm.

7. The method according to claim 3, wherein the casting process mentioned in process step number (i) is performed at the temperature range from 660 to 710 C.

8. The method according to claim 3, wherein the annealing process mentioned in process step number (ii) is performed at a temperature of 500-600 C. for 4-10 hours.

9. The method according to claim 3, wherein the rolling process mentioned in process step number (iii) is continued until the foil thickness becomes 0.20-0.40 mm.

10. The method according to claim 3, wherein the rolling process mentioned in process step number (iv) is continued until the final thickness becomes 0.030-0.20 mm.

11. The method according to claim 3, wherein the annealing process mentioned in process step number (v) is performed at a temperature of 300-450 C. for 2-6 hours.

12. (canceled)

13. (canceled)

14. (canceled)

Description

DESCRIPTION OF DRAWINGS

[0018] FIG. 1. open circuit potential measurement graphs that provide information about the corrosion resistance of materials.

[0019] a: Corrosion potential of the material produced from strontium-free aluminum alloy by continuous casting method [0020] b: Corrosion potential of the material produced from strontium-free aluminum alloy by direct chill casting method [0021] c: Corrosion potential of the material produced from strontium-containing aluminum alloy by continuous casting method

DETAILED DESCRIPTION OF THE INVENTION

[0022] In this detailed description, an aluminum alloy material of the invention suitable for use in food industry and production method thereof are described aimed at only better understanding of the subject and without forming any limiting effects.

[0023] The invention is a method for the production of aluminum alloy materials suitable for use in food industry, and it comprises processing of a liquid metal mixture comprising strontium in addition to aluminum by twin roll continuous casting technique.

[0024] In the preferred embodiment of the invention, said liquid metal mixture comprises also at least one more component selected from the group comprising silicon, iron, copper, manganese, magnesium and zinc.

[0025] In the preferred embodiment, the method of production of the invention comprises the processing steps of; [0026] I. Casting liquid metal mixture as a coil in the twin roller continuous casting system, [0027] II. Annealing of the coil, [0028] Ill. Thinning the annealed coil by cold rolling, [0029] IV. Thinning the thinned material until it reaches the thickness of the final product by rolling again, [0030] V. Annealing of the aluminum alloy material which has been brought to the thickness of the final product.

[0031] According to a preferred embodiment of the invention, the liquid metal mixture mentioned in process step number (i) comprises at least one more component selected from the group comprising aluminum in the ratio of at least 95% by weight, as well as strontium in the ratio of 0.001-0.50% by weight and also silicon, iron, copper, manganese, magnesium and zinc. Said casting process mentioned again in the same process step is being performed at the rate of 50-150 mm/minute, preferably at 63-90 mm/minute. Thickness of the casting is in the range from 3 to 10 mm, more preferably in the range from 7 to 10 mm. The temperature at which casting is performed is selected in the range from 660 to 710 C.

[0032] Parameters given here directly affect both the capability of the casted material to take shape and also the microstructure formed in the final material. With these specifically determined parameters, casting material taking shape by being casted in a uniform manner and the final material that is formed in this manner having a uniform microstructure are being ensured.

[0033] Annealing process of the liquid metal mixture taken to the twin roll continuous casting system in process step number (ii) is being performed preferably at a temperature of 500-600 C. Annealing process is being continued between 4-10 hours, preferably for 8 hours. The high temperature applied here is the temperature required for realizing a uniform variation in the microstructure of the casting material. Said temperature value is essential for the invention of the patent to carry out its function. The cast material annealed in process step number (ii) gets uniform gradually and elimination of the segregations in the structure is being provided. This process also provides the deformation realized in process step number (iii) which follows this step to be applied more easily.

[0034] According to the preferred embodiment of the invention, cold rolling mentioned in the scope of process step number (iii) is being performed by deforming the annealed metal mixture in the ratio of at least 90%, that is to say by thinning it. This deformation ratio is preferably 96%, and the foil thickness of the material at the end of this process is in the range from 0.20 to 0.40 mm. That is to say, the material is being thinned by the rollers until it reaches this thickness.

[0035] The purpose of the cold rolling process repeated in process step number (iv) following this is to bring the material to the thickness of the final product. The final thickness mentioned here is preferably in the range from 0.030 to 0.20 mm, and deformation in the ratio of at least 70% is being realized on the material for this.

[0036] Rolling processes applied in steps number (iii) and (iv) provide the material to reach to the desired thickness on one hand and increase its strength on the other hand.

[0037] Aluminum alloy whose strength is finally increased by rolling and brought to the final thickness is being subjected to annealing process at a temperature of preferably 300-450 C. for a range from 2 to 6 hours. This process provides the entire structure to be uniformly re-crystallized; having uniformity in the mechanical and electrochemical sense, and similar properties in each direction in the deep drawing process of the material.

[0038] The invention is also an aluminum alloy material produced with a method such as the one in any of the above applications, and being suitable for use in the food industry.

[0039] According to the preferred embodiment of the invention, said aluminum alloy material is in the form of foil or sheet.

[0040] In the preferred embodiment of the invention, said aluminum alloy material comprises; [0041] 95.85-98.35% aluminum, [0042] 0.05-0.25% strontium, [0043] 0.10-0.40% silicon, [0044] 1.20-2.00% iron, [0045] 0-0.30% copper, [0046] 0.30-1.00% manganese, [0047] 0-0.10% magnesium, [0048] 0-0.10% zinc by weight.

[0049] It has been seen that mechanical and electrochemical properties of the final product has been improved by using strontium in the aluminum alloy produced with the twin roll continuous casting method. In relation therewith, FIG. 1 (a, b, c) shows the effect of addition of strontium in the twin roller continuous casting method over the corrosion resistance of the aluminum alloy. Accordingly, as the amount of strontium in the alloy increases, the open circuit potential graph of the final material moves towards a more positive value and it is seen that the corrosion resistance increases accordingly.

[0050] Iron which is one of the other components likely to be present within the aluminum alloy material of the invention is a compulsory impurity coming from the raw material. It increases the strength by forming the AlFe intermetallic. However, since higher iron ratios lower the ductility, the iron ratio within the material is being kept in the ratio of at most 2% in the scope of the invention.

[0051] While copper increases the tensile and fatigue strength of the alloy together with strength, high copper ratios cause decrease in the ductility and corrosion resistance of the alloy material. Therefore, the copper ratio in the final material is at most 0.30% in the scope of the invention.

[0052] Manganese provides increase in the fatigue strength and corrosion resistance alloy material of the invention. Furthermore, it has positive effect for ductility in alloys comprising FeSi.

[0053] Magnesium provides increase in mechanical strength without creating decrease in ductility.

[0054] Since zinc increases the corrosion tendency of the alloys although playing a role in increasing strength in magnesium alloys, its use or preference within the material of the invention has been kept very low.

[0055] Aluminum alloy materials developed with the method of the invention are suitable for use to be in direct contact with all kinds of food during processing, heating, cooling and preserving of food. Since the aluminum alloy material produced with the method of the invention lowers the amount of the aluminum released to the food, it is much more reliable compared to aluminum foil and similar products in the prior art. Also, by means of the process (annealing and rolling) steps applied in the method of the invention and the synergy arising from the composition of the processed liquid metal mixture, not only providing an aluminum alloy material having improved mechanical and electrochemical properties is possible but at the same time production cost is being decreased by saving energy and time.