Aluminium alloy sheet for metallic bottle or aerosol container

Abstract

The invention relates to a process for the manufacture of an aluminum alloy sheet for metal bottles or aerosol cans. The invention also relates to a sheet manufactured by a process such as that described above, together with metal bottles or bottle-cans, together with aerosol cans or aerosol dispensers made from the said sheet.

Claims

1. Process for the manufacture of an aluminum alloy sheet for metal bottles or aerosol cans manufactured by drawing-ironing and necking comprising: casting a slab of aluminum alloy having a composition (% by weight): Si: 0.10-0.35, Fe: 0.30-0.55, Cu: 0.05-0.20, Mn: 0.70-1.0, Mg: 0.80-1.30, Zn: <0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum, scalping and homogenization of the slab at a temperature of 550 to 630 C. for at least one hour, hot rolling, first cold rolling stage with a reduction ratio of 35 to 80%, recrystallization annealing, repeated cold rolling with a reduction ratio of 10 to 35% to a thickness of 0.35 to 1.0 mm, wherein the recrystallization annealing is carried out at a temperature of 300 to 400 C. for a period of at least one hour, wherein the manufactured aluminum alloy sheet has a yield strength of 170 to 200 MPa and ultimate tensile strength of 200 to 230 MPa after a heat treatment at 205 C. for 10 minutes simulating a baking of varnishes.

2. Process according to claim 1 wherein the annealing crystallization is carried out at a temperature of 340 to 360 C. over a period of at least one hour.

3. A process according to claim 1, wherein the manufactured aluminum alloy sheet has a fall in the yield strength of 20 to 40 MPa before and after the heat treatment simulating baking of varnishes.

4. A process according to claim 1, wherein the manufactured aluminum alloy sheet has an anisotropy index of 1 to 4%, measured after cold rolling to a thickness of 0.35 to 1.0 mm by a cup method according to standard NF EN 1669.

5. A process according to claim 1, wherein on completion of a test according to a cup method according to standard NF EN 1669, said manufactured aluminum alloy sheet has ears at 45 on either side of a direction of rolling and substantially no ears at 0 and 180 to said direction.

6. A process according to claim 1, wherein the manufactured aluminum alloy sheet has a formability such that said sheet shows no cracks or folds when deep drawn in two passes, a former with a stamping ratio, the ratio between the diameter of a blank and the diameter of a punch, between 1.5 and 1.9, a latter with a stamping ratio of between 1.3 and 1.6.

7. A process according to claim 1, wherein the manufactured aluminum alloy sheet has an elongated grain microstructure with an aspect ratio from 2 and 10, wherein the aspect ratio is a ratio of a grain size in a direction of rolling in relation to the grain size in a direction of thickness, measured after cold rolling to a thickness of 0.35 to 1.0 mm and after anodic oxidation and using optical microscopy with polarized light.

8. A method according to claim 1, wherein the manufactured aluminum alloy sheet has an elongated grain microstructure with an aspect ratio from 3 and 5, wherein the aspect ratio is a ratio of a grain size in a direction of rolling in relation to the grain size in a direction of thickness, measured after cold rolling to a thickness of 0.35 to 1.0 mm and after anodic oxidation and using optical microscopy with polarized light.

9. The process of claim 1, wherein said aluminum sheet consists essentially of Si: 0.10-0.35, Fe: 0.30-0.55, Cu: 0.05-0.20, Mn: 0.70-1.0, Mg: 0.80-1.30, Zn: <0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum.

10. The process of claim 1, wherein said aluminum sheet consists of Si: 0.20-0.30, Fe: 0.35-0.50, Cu: 0.05-0.15, Mn: 0.80-0.90, Mg: 1.15-1.25, Zn: <0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum.

11. Process according to claim 1, wherein the aluminum alloy has the following composition (% by weight): Si: 0.20-0.30, Fe: 0.35-0.50, Cu: 0.05-0.15, Mn: 0.80-0.90, Mg: 1.15-1.25, Zn: <0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum.

12. Sheet manufactured by the process according to claim 11.

13. Sheet according to claim 12, wherein the aluminum alloy has the following composition (% by weight): Si: 0.25-0.27, Fe: 0.42-0.43, Cu: 0.11-0.12, Mn: 0.82-0.87, Mg: 1.19-1.22, Zn: <0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum.

14. The sheet of claim 12, wherein said aluminum sheet consists essentially of Si: 0.10-0.35, Fe: 0.30-0.55, Cu: 0.05-0.20, Mn: 0.70-1.0, Mg: 0.80-1.30, Zn: <0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum.

15. The sheet of claim 12, wherein said aluminum sheet consists of Si: 0.20-0.30, Fe: 0.35-0.50, Cu: 0.05-0.15, Mn: 0.80-0.90, Mg: 1.15-1.25, Zn: <0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum.

16. Metal bottle, wherein said metal bottle is manufactured by extrusion/drawing and necking the sheet manufactured according to the process of claim 1.

17. Shaped metal bottle, wherein said shaped metal bottle is manufactured by extrusion/drawing and necking the sheet manufactured according to the process of claim 1.

18. Aerosol container, wherein said aerosol container is manufactured by extrusion/drawing and necking the sheet manufactured according to the process of claim 1.

19. Shaped aerosol can, wherein said aerosol can is manufactured by extrusion/drawing and necking the sheet manufactured according to the process of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the earing, that is to say the shape of the perimeter developed at the top of the cups after the first stamping with the ratio of the height of the ear to the mean height of the cup as the ordinate and the angle in relation to the direction of rolling as the abscissa.

(2) The solid line section, with ears in particular at =0 and 180, corresponds to a cup according to the prior art of type 3104 alloy in the H19 state, and the dotted line profile a cup produced from sheet according to the invention using type 3104 alloy in the H14 state with intermediate annealing. The ears at =0 and 180 are absent.

(3) FIG. 2 shows the Vickers Hv microhardness of preforms prior to necking (having thus undergone baking of the varnishes) measured under a load of 100 g as a function of the R0.2 yield strength in MPa measured on the sheets before processing but after treatment simulating the baking of varnishes at 205 C. for 10 minutes.

(4) The black lozenges correspond to the material according to the invention, and the white squares to materials not according to the invention.

(5) This shows a linear correlation between these two values.

(6) FIG. 3 shows the rejection rate as a %, for three zones (A from 0 to 10%, B from 10 to 30% and C beyond that) during the necking operation as a function of the Vickers Hv microhardness above for materials according to the invention (black lozenges) and non-conforming materials (white squares).

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(7) The invention comprises a careful choice of the alloy and heat treatment, and the transformation range of the sheet or strip used to manufacture the metal bottles or bottle-cans or aerosol cans.

(8) The purpose of this optimization is to obtain a material capable of: undergoing extensive deep drawing to manufacture the cups with stamping ratios of up to 1.9 or even more, with high necking deformation, to obtain a large reduction in diameter in only two necking passes, limiting the risk of defects known to those skilled in the art as ears and folds, to prevent any breakage during drawing, allowing deformation without breakage when necking and during shaping the thread in the case of bottles and the curl in the case of bottles and aerosol cans, enabling the finished product to withstand a sufficient reversal and/or bursting pressure, typically varying from 6.2 (the standard minimum for bottle-cans) to 17 bars in the case of aerosol cans.

(9) For this purpose the chemical composition of the alloy expressed as percentages by weight (% by weight) is as follows:

(10) Si: 0.10-0.35, Fe: 0.30-0.55, Cu: 0.05-0.20, Mn: 0.70-1.0, Mg: 0.80-1.30, Zn: 0.25, Ti: <0.10, other elements <0.05 each, and <0.15 in all, the remainder aluminum.

(11) The concentration ranges imposed on the components of each alloy are explained by the following reasons: Si is essentially an impurity and as such its concentration must be limited to 0.35% and even better 0.30%.

(12) However a minimum of 0.10% and preferably 0.20% makes it possible to obtain a sufficient level of the Al(Fe, Mn).sub.12Si phase at the end of homogenization treatment after the strip has been cast. This type of abrasive phase has in effect the special feature of preventing fouling of the ironing dies by agglomerations of alloy and oxide particles and thus ensure a good surface quality for the blanks preventing what those skilled in the art know as jamming. Fe is also generally an impurity, and therefore its concentration increases during recycling. This must be less than 0.55% and preferably 0.50% to prevent the formation of coarse primary phases during casting, phases which have adverse effect on formability. However a Si content of at least 0.10% and better 0.20%, as well as a Fe concentration of 0.30% and better 0.35%, is necessary for good control of the anisotropy of the final product, that is to say the sheet or strip, and therefore subsequent shaping operations. The elements Cu, Mn and Mg are essentially hardening elements whose concentrations make it possible to control the mechanical properties of the sheet at various stages in manufacture, from the blank to the final product.

(13) Hardening is mainly associated with the presence of these elements in solid solution within the primary aluminum matrix. Cu also makes hardening possible through precipitated fines. Cu has a concentration limited to 0.20% to encourage restoration during the varnish baking heat treatment and thus improve the formability required, particularly for necking and for threading and/or curling. Mn is limited to 1.0% and better 0.90% to prevent the formation of coarse primary phases during casting, which have an adverse effect on formability. Mg is limited to 1.3% and better 1.25% so as not to reduce formability too significantly, particularly for stamping operations. However, the minimum concentrations of Cu, Mn and Mg ensure the minimum mechanical properties required, in particular for withstanding the internal pressure at the bottom of the bottle or can. Zn is limited to 0.25% essentially because of legislation on products for food applications reflected in standard NF EN 602. Ti is an element which refines the structure of the cast material but also forms primary phases which are unfavorable for formability. For this latter reason its concentration is limited to less than 0.1%.

(14) The manufacture of strip according to the invention mainly comprises casting, typically continuous vertical casting (CVC) of slab and scalping it.

(15) Scalped slab then undergoes conventional homogenization and then hot rolling followed by first cold rolling with a reduction ratio of 35 to 80%. In fact the reduction ratio before intermediate annealing must be at least 35% to bring about recrystallization during the said intermediate annealing. It must not exceed 80% so that the reduction brought about after the said intermediate annealing is sufficient to provide mechanical properties within the ranges stated below after annealing at 205 C. for 10 minutes. After this first cold rolling the intermediate product undergoes recrystallization annealing at a temperature of between 300 and 400 C., better between 340 and 360 C., or at a target temperature of 350 C., for at least one hour.

(16) After this annealing, rolling is resumed with a cold reduction ratio of 10 to 35% to a final thickness of 0.35 to 1.0 mm.

(17) The sheets or strips so obtained have a yield strength Rp.sub.0.2 of between 170 and 210 MPa and an ultimate tensile strength of between 200 and 240 MPa after heat treatment at 205 C. for 10 minutes simulating the cumulative drying treatments after cleaning and baking of the varnishes and inner lining.

(18) These relatively low values in comparison with the prior art for an alloy of the 3104 type but in metallurgical state H19 obviously encourage shaping of the preform, that is to say of the blank after drawing, inner and outer linings and baking, and therefore most particularly for the necking stage.

(19) These are the result of softening during heat treatment at 205 C. for 10 minutes, i.e. a fall of between 20 and 40 MPa in the Rp.sub.0.2 yield strength in particular.

(20) Another advantage of the invention is an anisotropy index which reflects the ability of the metal to be shaped in a uniform way when manufacturing the cups and drawing them, measured by the cups method according to standard NF EN 1669, of between 0.5 and 4.0%.

(21) After stamping of the cups this is in particular reflected by the fact that the developed shape of the perimeter, known to those skilled in the art as earing has ears at 45 on either side of the rolling direction and substantially none at 0 and 180 to the said direction on completion of the test according to the cup method or after the cups had been stamped. Now it has been found that it is the ears at 0 and/or 180 C. which are responsible for the defects known to those skilled in the art as ears which can give rise to breakages or defects during subsequent drawing.

(22) Furthermore it is possible to stamp the material or strip according to the invention without breakages or folds with a stamping ratio of 1.5 to 1.9 in a first pass and with a stamping ratio of 1.3 to 1.6 in a second pass, which is equivalent to an overall stamping ratio of up to 2.8. This mode is not however exclusive, as stamping may be performed in more than two passes.

(23) Finally, the sheet according to the invention is also characterized in that after cold rolling to a thickness of 0.35 to 1.0 mm it has an elongated grain microstructure with an aspect ratio, the ratio between the grain size in the rolling direction in relation to the grain size in the direction of the thickness, of between 2 and 10 when measured by optical microscopy with polarized light after anodic oxidation.

(24) The details of the invention will be understood better with the help of the examples below, which are not however restrictive in their scope.

EXAMPLES

Example 1

(25) Two type 3104 alloy slabs were cast by continuous vertical casting and their compositions are summarized in Table 1 below as percentages by weight (% w/w):

(26) TABLE-US-00001 TABLE 1 Si Fe Cu Mn Mg Reference 0.13 0.45 0.17 0.86 1.2 Invention 0.27 0.42 0.11 0.86 1.19

(27) Both were scalped and then homogenized at a temperature of approximately 580 C. for around 3 hours before being hot rolled to a thickness of 2.8 mm.

(28) One of these (Reference) was then directly cold rolled to a final thickness of 0.505 mm, that is in metallurgical state H19.

(29) The other (Invention) was cold rolled to a thickness of 0.65 mm and then received recrystallization annealing at 350 C. for one hour followed by final cold rolling to a thickness of 0.505 mm. Metallurgical state H14 was thus achieved. Cups were made from the two types of sheet reference 3104 H14 and 3104 H19 with the following parameters:

(30) Diameter of the circular blank: 140 mm

(31) Punch diameter: 88.9 mm

(32) Stamping clearance ((diameter of the stamping diediameter of the punch2thickness of the sheet)/2thickness of the sheet): 30%

(33) Prelubrication of the tool with Quakerol 30 LVE with a target quantity of 20 mg/cup. Stamping rate: 60 strokes/min.

(34) The ear profiles are summarized in FIG. 1 corresponding on average to 10 cups of each type (3104 H14 according to the invention and 3104 H19 according to the prior art).

(35) It was noted that the cups according to the invention were of better quality than those in the prior art, i.e. they had fewer folds and above all, as FIG. 1 shows, there were no ears at 0 and 180 C. to the rolling direction, thus no earing, which is not the case with cups according to the prior art.

(36) The profile according to the invention has ears at 45 on either side of the rolling direction, that is 45, 135, 225 and 315, which do not give rise to the risk of earing, unlike the ears at 0 and 180 in the cups according to the prior art.

Example 2

(37) Nine alloy slabs of the 3104 type were cast by continuous vertical castings and their compositions are summarized in Table 2 below as percentages by weight (% w/w):

(38) TABLE-US-00002 TABLE 2 Si Fe Cu Mn Mg Reference 1 0.13 0.45 0.17 0.86 1.20 Reference 2 0.26 0.42 0.15 0.95 1.20 Invention 3 0.27 0.42 0.11 0.86 1.19 Invention 4 0.26 0.42 0.12 0.85 1.20 Invention 5 0.25 0.42 0.11 0.85 1.22 Invention 6 0.26 0.43 0.12 0.84 1.21 Invention 7 0.26 0.42 0.11 0.87 1.20 Invention 8 0.27 0.43 0.11 0.82 1.21 Invention 9 0.27 0.43 0.11 0.82 1.21

(39) Slab 1 underwent the same range of transformation as the reference slab in example 1, that is without recrystallization annealing, and the other strips 2 to 9 underwent the same range of transformation as the previous one as far as cold rolling, namely:

(40) They were all scalped and then homogenized at a temperature of around 580 C. for approximately 3 hours before being hot rolled to a thickness of 2.8 mm.

(41) They were then cold rolled with difference reduction ratios in accordance with Table 3 below:

(42) TABLE-US-00003 TABLE 3 Thickness Ratio Rp.sub.0.2 Rm Rp.sub.0.2 before reduction after after before - Hv Rejection annealing further 10 min. - 10 min. - after of the during mm % 205 C. 205 C. 205 C. preforms necking Reference 1 233 257 15.0 86 C Reference 2 0.80 37 214 247 30.0 90 C Invention 3 0.77 34 204 231 31.0 84 B Invention 4 0.77 34 204 229 30.0 84 B Invention 5 0.77 34 206 234 34.0 87 B Invention 6 0.72 30 200 225 32.0 85 B Invention 7 0.72 30 202 229 35.0 84 B Invention 8 0.65 22 199 221 26.0 83 A Invention 9 0.58 13 193 204 20.0 79 A

(43) Materials 1 and 2 are not conforming to the invention because there was no intermediate annealing and the reduction ratio and cold rolling after annealing was 37% against a maximum of 35% according to the invention. The Rp.sub.0.2 yield strength in MPa and the ultimate tensile strength Rm in MPa after the said treatment were then measured on sheets after cold rolling before and after treatment simulating baking of the varnishes.

(44) These values are shown in Table 3 together with the difference in Rp.sub.0.2 before and after the said treatment.

(45) It will be noted that the yield strength measured in this way varies from 193 to 204 MPa, whereas it is higher (214 MPa) for reference 2 and even more so in the case of reference 1 (233 MPa), which is encouraging for the formability of the sheets according to the invention.

(46) It will also be noted that the difference in yield strengths before and after the said treatment vary from 20 to 35 MPa for sheets according to the invention, whereas it is only 15 MPa for reference 1 in the prior art, with the same conclusion as before. The anisotropy index S45 for all the sheets and S0 for the sheet according to the prior art in metallurgical state H19 (reference 1) was also measured by the cup method according to standard NF EN 1669 after cold rolling to a thickness of 0.505 mm.

(47) The values obtained are shown in Table 4 below.

(48) It will be noted that in the case of sheets according to the invention they all lie between 0.5 and 4.0%, which is not the case for the reference sheets not according to the invention. Finally the grain structure was identified for these sheets using optical microscopy in polarized light after anodic oxidation with a magnification of 50. The ratio of the grain size in the rolling direction L to that of the grain size in the direction of the thickness or short cross-section Tc, or in a plane (L, Tc) substantially half way across the width of the initial sheet was measured for this purpose.

(49) The values shown in Table 4 below correspond to an average of approximately 50 measurements for each case.

(50) It will be noted that the sheets according to the invention all have a slenderness ratio of between 1 and 10, and in the case in point between 3 and 5, whereas this reaches a value of 30 in the case of the sheet according to the prior art in metallurgical state H19 (reference 1).

(51) TABLE-US-00004 TABLE 4 Anisotropy Anisotropy Grain index index aspect S 45 (%) S 0 (%) ratio Reference 1 4.5 1.7 30 Reference 2 4.1 5 Invention 3 3.4 5 Invention 4 3.5 5 Invention 5 3.8 5 Invention 6 2.0 5 Invention 7 3.2 5 Invention 8 3.0 4 Invention 9 2.9 3

(52) A series of manufacturing tests for metal bottles of the bottle-can type having a capacity of 33 cl was then performed using blanks and cups identical to those in Example 1 made from sheet of types 1 to 9 in accordance with Table 3 in a wholly conventional range.

(53) Necking or tapering consisted of reducing the diameter of the preform from 57 mm to 28 mm over a neck height of 70 mm.

(54) After tapering the neck was threaded and then curled.

(55) These tests were carried out on 3000 to 5000 bottles for each material 1 to 9.

(56) In the course of the tests, samples were obtained at the stage of the varnished preform after baking, that is precisely before the necking operation, to measure the Vickers microhardness of the preforms under a load of 100 grams, after cutting, coating and polishing.

(57) The results are shown in Table 3 and FIG. 2 shows the values for this hardness of the preforms as a function of the yield strength of the sheets after heat treatment simulating baking of the varnishes.

(58) The black lozenges correspond to the metal according to the invention, and the white squares to materials 1 and 2 not conforming to the invention.

(59) This figure shows a linear correlation between these two values for materials prepared with intermediate recrystallization annealing (black lozenges and white squares) having the coordinates: 90 Hv and 214 (MPa)

(60) After the necking operation visual checks were made to eliminate any items showing defects such as folds in the neck of the bottle, folds on the screw, the curl of the bottle showing cracks which were open to a greater or lesser extent, known as split curl, absence of varnish, incrustations, crushed thread, scratches, etc.

(61) A classification from A to C was made on the basis of the number of items eliminated as a %, i.e. the rejection rate. This classification was established as follows:

(62) A for a rejection rate of 0 to 10%, B for 10 to 30% and C above that.

(63) The results are shown in Table 3 and FIG. 3 shows the rejection rate as a % according to the three predetermined zones from A to C during the necking operation as a function of the Vickers Hv microhardness above, for materials according to the invention (black lozenges) and non-conforming materials (white squares).

(64) The better performance of the materials according to the invention in relation to the materials not conforming to the invention can be seen unambiguously and in particular the material according to the prior art yielded the worst result (highest rejection).