AU655433B2 - Mechanically and thermally treated AL Base-ZN-MG-SI-CU alloy for deepdrawn liquid containers - Google Patents

Description

OPI DATE 17/03/92 AOJP DATE 30/04/92 APPLN- ID 84075 91 PCT NUMBER PCT/AU91/00376 TREATY (PCT) (51) International Patent Classification 5 (11) International Publication Number: WO 92/03586 C22F 1/053, 1/047, C22C 21/10 C22C 21/08 B65D 1/12 Al (43) International Publication Date: 5 March 1992 (05.03.92) (21) International Application Number: (22) International Filing Date: Priority data: PK 1894 22 Augus PCT/AU91/00376 21 August 1991 (21.08.91) st 1990 (22.08.90) AU (71) Applicant (for all designated States except US): COMALCO ALUMINIUM LIMITED [AU/AU]; Research Technology, 31st Floor 55 Collins Street, Melbourne, VIC 3000 (AU).

(72) Inventor; and Inventor/Applicant (for US only) MOHR, James, Christopher [US/US]; 106 Lindsay Lane, Russelville, KT 42276

(US).

(74) Agent: CARTER SMITH BEADLE; Qantas Building, 2 Railway Parade, Camberwell, VIC 3124 (AU).

(81) Designated States: AT, AT(European patent), AU, BB, BE (European patent), BF (OAPI patent), BG, BJ (OAPI patent), BR, CA, CF (OAPI patent), CG (OAPI patent), CH, CH (European patent), CI (OAPI patent), CM (OAPI patent), CS, DE, DE (European patent), DK, DK (European patent), ES, ES (European patent), FI, FR (European patent), GA (OAPI patent), GB, GB (European patent), GN (OAPI patent), GR (European patent), HU, IT (European patent), JP, KP, KR, LK, LU, LU (European patent), MC, MG, ML (OAPI patent), MR (OAPI patent), MW, NL, NL (European patent), NO, PL, RO, SD, SE, SE (European patent), SN (OAP' patent), SU+,TD (OAPI patent), TG (OAPI patent), US.

Published With international search report.

655433 (54)Title: ALUMINIUM ALLOY SUITABLE FOR CAN MAKING (57) Abstract Temperatures Process Sizes Aluminium can stock which has strength, ductility and anisotropic properties in excess of conventional all.- -ium can stocks, The aluminium can stock is produced from an ali.. vith 3.0-8.0 wt% zinc, 0.5-3.0 wt% magnesium, less than 0.7 wt% iron, 0.01-2.0 wt% silicon, 0.05-0.9 wt% copper, 0.1-1.1 wt% manganese, less than 0.3 wt% chromium and incidental impurities less than 0.15 wt%. While zirconia is not generally an impurity in these aluminium alloys it is preferable that the amount present is less than 0.01 wt%. The aluminium can stock is produced by a process comprising the steps of forming melt of the alloy metal suitable for casting, casting the melt into a form suitable for rolling, performing an intermediate rolling to an intermediate thickness, treating the alloy material with heat, performing finish rolling by a cold rolling reduction within the range of 2 to 85 and temper heat treating the material to the desired ductility and strength properties.

500%C (930'F) S00*C 300C (950F -570*F 500 C/lhr (930' F) 100,300' 2000 (1 12'' 8' 6 passes 35--.5mm 1.,35'-0.10" 2 passes 2.5 -Imm 2 passes imm-0.32 (0.25' 0.015') R.T. 24-48 hrs 121C/3 hrs 155'C/3 hrs (2SO'F) (315'F) See back of page WO 92/03586 PCT/AU91/00376 I TITLE: ALUKMIUM M ALLOY SUITABLE FOR CAN MKING This invention relates to the use of aluminium based alloys for the manufacture of liquid containers and in particular to a high zinc content aluminium base alloy suitable for liquid container construction.

Conventional two-piece aluminium beverage containers are generally fabricated from two distinct alloys such as the Aluminium Association Specification 3004 and 5182 (See Table 3004 alloy is generally used for body stock by deep drawing and wall ironing forming methods but lacks the necessary rigidity and strength properties to be a useful lid stock whereas 5182 alloy which is unsuitable for body stock has the properties desirable for can lid fabrication. Increased demand for this type of container and the need for stronger cans of thinner gauge material has spurred development of new alloys and in particular alloys which can be used for both body and lid stock.

To be suitable for can body stock an alloy must possess the required combination of good formability and strength properties whilst also being economical to manufacture.

The AA3004 type alloy composition alloys are traditionally produced by casting the alloy using the direct chill casting method (DC-cast) into an ingot block of cross-section around 500 mm thick x 700 mm I SUBSTITUTE SHEET I i PCT/AU91/00376 WO 92/03586 2 wide. The ingots are then homogenised at temperatures between 500 and 620°C for 4-24 hours and hot rolled.

The hot rolling procedure reduces the ingot thickness to a gauge of about 2-3 mm by a series of breakdown passes.

The material is then usually annealed at temperatures of 300 400*C for periods between 0.5 and 4 hrs to allow the metal to recrystallise. The annealed metal is then subjected to a cold rolling schedule to develop strength and other properties. This normally consists of 2 5 passes using 20 50% reductions to achieve a final gauge of about 0.3 0.33 mm.

The final gauge sheet is then fabricated into aluminium cans by use of a cupping machine and can body maker. Circular discs approximately 135 mm diameter are cut or punched from the cold worked sheet on the cupping machine and drawn into shallow cups. The cup then enters the bodymaker and is first redrawn into a cup close to that of its final diameter. The sidewalls are then reduced in thickness in one or more wall ironing operations to produce a can body around 65 mm diameter and 140 mm high with a wall thickness of between 0.10 0.18 mm.

The material from which the body is drawn has anisotropic properties the properties differ with direction) and so the top of the drawn body has a scalloped top, with approximately 4 peaks oriented apart the peaks of which are called ears. The degree of SUBSTITUTE SHEET WO 92/03586 PC/AU91/00376 3 "earing" is determined simplistically by the following equation: 2x e x 100 Earing (b.+he) where h. is the distance between the bottom of the cup and peak of the ears and h, is the distance between the bottom of the cup and valley of the ear.

For the body to be acceptable for further fabrication into a beverage container the formed body must have earing levels of no more than 3-5% and preferably less than The tops of the can bodies are trimmed off (fixed for a given process), during a slitting operation and the "eared" area is scrapped.

Another major consideration of the quality of the finished body is its ability to form in the body maker without tearing and to have a smooth surface finish, free of drawing streaks and lines. Deep grooves caused by "galling" may appear on the finished can walls if the material is not of the correct microstructure.

Downgauging of conventional strain-hardened alloys to reduce the cost of body manufacture requires the use of increased alloying element concentrations (e.g.

copper, manganese and magnesium) to increase strength.

However, as these concentrations are increased, the formability of the resultant alloy decreases; in fact, SUBSTITUTE SHEET WO 92/03586 PCT/AU9 /00376 PCT/AU91/00376 4 the potential strength of the 3xxx series based alloys is ultimately limited by the amount of rolling strain which can be sustained during processing before surface finish and material properties deteriorate. Other aluminium alloy systems currently used for other applications are potentially capable of achieving much higher strength levels than 3xxx series alloy.

Although, ultimately, a container can be formed from a fabricated downgauged high strength 3004 type alloy of non-galling, low earing characteristics, unless the strength is great enough to offset the strength lost from reduced wall thickness the buckle resistance of the can will be reduced.

Buckle strength of resistance is determined by applying pressure within a drawn and wall ironed can and then gradually increasing the pressure until the bottom end of the can deforms and bulges out, i.e. it buckles or the inverted dome reverses. The pressure at which the bottom buckles is then designated as the buckle strength or dome reversal pressure. To be acceptable as a can body a can formed from the alloy sheet must exhibit a buckle strength of at least 85 p.s.i. Cans drawn from high strength 3004 alloy produced using conventional direct chill cast methods exhibit a buckle strength of about 90 p.s.i.

Whilst the production of 3004 body stock by the ingot casting method is widely used, economic and energy SUBSTITUTE

SHEET

WO 92/03586 PCT~/AU91/00376 5 considerations would favour the manufacture of aluminium sheet by a continuous cast route. The prior art has addressed the continuous strip cast method where aluminium is cast into a thin alloy web about one inch thick. The homogenisation process may be eliminated and the hot rolling reductions to intermediate gauge are minimised using this technique and the process of hot rolling can be eliminated entirely if the desired microstructure is achieved during continuous casting of very thin strip. The material is then annealed and processed in a manner similar to ingot cast materials. At this stage, can stock produced by this method has proven unsatisfactory for further processing and can body manufacture.

Thus, it is an object of the present invention to provide an aluminium alloy suitable for can stock which has non-galling, low earing and high strength characteristics with good formability at least comparable with existing AA3004 type alloys which will allow can bodies to be made from thinner sheet feed stock. It is also an object of the present invention to provide can stock which is also suitable for the manufacture of can lids thus, allowing manufacturing of a complete two-piece bevrage can from one alloy composition. The alloy will be amenable to fabrication into can stock via both the direct chill cast and the continuous strip cast methods. Accordingly, the invention relates to a c-- an-a k -and process for SUBSTITUTE SHEET 6 producing a can stock from an aluminium alloy including 3.0 to wt% zinc, 0.5 3.0 wt% magnesium, less than 0.7 wt% iron, 0.01 2.0 wt% silicon, 0.05 0.9 wt% copper, 0.1 1.1 wt% manganese, less than 0.3 wt% chromium and incidental impurities less than a total of 0.15 wt%, and the balance aluminium, said process comprising the steps of forming melt of the alloy metal suitable for casting, casting the melt into a form suitable for rolling homogenizing the alloy material to produce a homogenized material, hot rolling the homogenized material to an intermediate thickness, to produce a strip or sheet and cold rolling the strip or sheet, solution heat treating and quenching the strip or sheet, allowing the strip or sheet to stand at room temperature performing finish rolling by a cold rolling reduction within the range of 2 to 85% and artificially ageing the cold rolled strip or sheet material to the desired ductility and strength properties.

In accordance with another aspect of the invention, there is provided aluminium can stock produced by the above process.

The alloy preferably comprises constituents in following weight percent ranges, zinc 4.0 6.5, magnesium 1.0 manganese 0.3 0.8, silicon 0.15 0.3, iron up to 0.45, copper 0.10 0.50, chromium up to 0.20 total incidental impurities less than 0.1.

.o *o o* e* BC:JH:#8a76 11 August 1994 WO 92/03586 PCT/AU91/00376 7 While an alloy containing zirconium up to a maximum level of 0.25 wt% may be suitable for can stock, to produce a can body with low earing, it is preferable that the zirconium level is less than 0.08 wt% and most preferable that it is not added to the melt and its level is below tbh standard level of impurity for that element of 0.01 wt%.

It has been found that an alloy which falls within the above composition range achieves high tensile and yield strength properties as well as good formability and "non-galling" wall ironing quality. Thus the alloy is preferably used to produce both the body and the lid of the beverage container.

The alloy is capable of producing a can body which has a dome reversal strength in excess of 90 p.s.i. and a wall ironed thickness of less than 0.16 mm. A 3004 alloy is generally only capable of achieving such a dome reversal strength with a wall thickness equal to or greater than 0.16 mm.

The above alloy may suitably be cast by the direct chill casting method, continuous roll casting or continuous strip casting. However, if the alloy is to be produced using roll or strip casting the compositional range of the alloy can be broadened.

The amount of Zn, Mg, Mn, Fe and Si may be increased which results in higher volume fraction of SUBSTITUTE SHEET WVO 92/03586 PCr/AU91/00376 8 alpha phase particles after casting and a greater amount of precipitation during final processing.

The alloy sheet may be produced by a combination of rolling reduction and heat treatmant in the final stages of manufacture. Consequently, fabrication steps vary with end use requirements. However, during the performance of the heat treatment processes, it has been found that the al.oy thus formed was especially adaptable to solution heat treatment of very short duration, while more lengthy heat treatments can be used to simultaneously anneal the sheet using recrystallisation anneal or recovery anneal techniques.

For container construction or for other requirements where strength and formability are important the ingot or strip cast material may be heat treated to homogenise the cast material and preferably hot rolled and then cold rolled. The material is then solution heat treated and given a cold rolling reduction. Lastly to improve strength and ductility, the alloy is aged to a temper dependent on the end use requirements.

Preferably the cast material, if ingot cast, is subjected to an additional heat treatment step to homogenise the alloy and preferably followed by a hot rolling step.

The intermediate rolling preferably is a cold SUBSTITUTE SHEET WO 92/03586 PCT/IAU91/00376 9 rolling stage and may employ a full anneal or recovery intermediate anneal during the cold rolling practice.

The step of treating the alloy with heat is preferably a solution heat treatment which may be followed by a natural ageing stage.

The finish rolling step is essential to the invention to provide the necessary strength properties to the final product but still must maintain sufficient ductility and formability properties to be a suitable can stock. The finish rolling is thus a cold rolling reduction in the range 2-85% and preferably within the range of 10-80% and most preferably within the range of 30-80%. The final temper heat treatment is preferably artificial ageing.

In accordance with a further aspect of the invention there is provided a can line feed produced from the alloy of the invention which preferably has yield and tensile strength of in excess of 400 MPa and a total elongation of 4% or more.

The alloy of the invention may also be used to produce can endstock which in a tempered state must have a miniumum yield stress of 310 MPa, a minimum ultimate tensile stress of 355 MPa and MIN 6% elongation.

The strengths and elongations specified above for can end stock relate to the post bake strength of the material.

SUBSTITUTE SHEET WO 92/03586 PPG/A U91 /00376 10 Generally endstock is manufactured in coil form and is sent to the end makers who then coat the material and bake the coated sheet at modest temperatures of between 155 0 C and 210°C for 10 30 minutes. Usually a specified test for the metal is 205°C bake for 20 minutes. The can end maker then produces the can ends by conventional metal farming processes which are well known to those skilled in the art.

As can endstock made in accordance with the invention has strength and ductility properties in the "post baked" state in excess of the above miniumum values, suitable can ends can be produced from the alloy in accordance with the invention.

A further aspect of the invention is a two piece beverage container produced from the alloy of the invention. The container preferably has a wall thickness of less than 0.12 mm and a dome reverasal strength of greater than 90 p.s.i.

The foregoing and other features objects 2aid advantages of the present invention will become more apparent from the following description of the preferred embodiments and accompanying drawings.

Table 1 contains details of the invention alloy range and preferred range.

Figure 1 is a flow diagram shouing the overall processing details for the alloys; SUBSTITUTE SHEET WO 92/03586 PCT/AU91/00376 11 Figure 2 is a Differential Scanning Calorimetry Thermal Analysis curve for the invention alloy; Figure Figure 3(a) is a flow diagra4 representing the final stage fabrication of the alloy; Figure 3(b) illustrates the effect of the final cold rolling reduction, and Figure 3(c) represents the effects of cold working and artificial ageing on the alloy of Example 1; Figure 4 shows micrographs of alloy 2 of Example 2 at various stages of processing in which 4,a) is the microstructure after the material is hot rolled, 4(b) is the microstructure after the material has been annealed 4(c) is the microstructure after the final cold rolling reduction Figure 5 shows the effect of natural ageing on Alloys 1, 2 and 3 (Example 2).

Figures 6 8 are graphs representing the response of the alloys of Example 2 to time at a given temperature in the final ageing treatment.

Figure 9 represents the effects of natural ageing and coldwork on the alloy; SUBSTITUTE SHEET WO 92/03586 PC/AU91/00376 12 Figure 10 represents the effect of using a double heat treatment in the artificial ageing step and the effect of coldwork; Figure 11 represents tensile results for the alloys of the invention; Figure 12 represents strength and ductility characteristics for the alloys of the invention compared to those of conventional 3004 body stock; and Figure 13 represents an overview of the benefits of the alloys of the invention.

An alloy in accordance with the invention comprises the following basic alloying elements copper (0.05 manganese (0.1 magnesium (0.5 and a relatively high concentration of zinc (3.0 Furthermore, the following additives are included in the melt: chromium (0.0 silicon (0.1 2.0) and iron (0.0 It has been found that, after solution heat treatment the majority of the magnesium and zinc are suspended in solid solution and precipitate during the tempering heat treatment adding the required strength to the alloy.

It is essential to the invention that the silicon, manganese and iron additives be within the ranges specified above as these elements are required to form SUBSTITUTE SHEET WO 92/03586 PCT/AU91/00376 13 the desired dispersed second phase distribution (alpha phase) in the alloy which is critical for the production of a non-galling wall ironed can.

Zirconium and chromium are typically found in the melt at impurity levels of less than 0.01 wt%, but if already present or added to the melt for additional strength properties, it is preferable that they are present at levels less than 0.08 wt% and less than 0.05 wt% respectively.

The effect of the very low levels of grain refining elements chromium and preferably zirconium, is that full recrystallisation of the product after, for example, hot rolling or low temperature annealing (345 0 C for 0.5 2 hours) can take place.

If the zirconium and chromium levels in the alloy exceed the specified levels in the present invention, then the wrought structure created by hot and cold rolling will be retained during solution heat treatment or anneal and the properties of the final gauge sheet will be more anisotropic. This is particularly disadvantageous if the sheet material is to go through deep drawing operations as the anisotropic properties result in material of high earing which is undesirable for the can body making process. High strengths can be obtained by increasing the concentration of these elements but formability and earing suffer as a result.

SUBSTITUTE SHEET WO 92/03586 PCU91/00376 14 The yield strength and tensile strength of the alloy in accordance with the invention is far greater than that of a 3xxx series can body material. The 3004 alloy has yield and tensile strengths of around 285 and 330 MPa respectively with 4% elongation whereas the alloy of the invention exhibits yield and tensile strengths around 420 and 480 MPa respectively with a total elongation measured on a 50 mm gauge length of 4% or more. When such a sheet is drawn and wall ironed into a body for a two-piece beverage container it possesses can buckle strengths in excess of 100 p.s.i.

with a wall thickness of 0.12mm. The very high strength and improved ductility of this alloy over any type of 3004 or modified 3xxx series alloy allows the gauge of sheet used for the initial forming operation (can line feed) to be reduced by at least 10% while still retaining buckle strength and formability in the finished body.

The high strength of this alloy also allows it to be made into lid stock for cans. Alloy AA5182 which is currently used for beverage can lids has a tensile strength of 395 MPa and an elongation of The 3004 alloy is generally not used to produce lid stock as it does not have sufficient strength for the desired lid thickness. The invention alloy can match the properties of AA5182, and thus a two-piece can may be made from one alloy composition instead of the conventional two.

SUBSTITUTE SHEET WO 92/03586 PCT/AU91/00376 15 When the alloy is cast by the DC-casting method to produce can bodies it is first homogenised. The cast is preferably homogenised as a block between 480° and 5000o for a period of 5 to 10 hours. The material is then hot rolled preferably from a temperature of up to 500°C down to a thickness suitable for coiling (preferably less than 5 mm). It is preferable that the hot rolling coil finishing temperature is above -abe-- 300°C as the alloy will automatically anneal during the coiling operation.

The material is then cold rolled and preferably employs a full anneal or recovery intermediate anneal during the cold rolling practice. After this rolling stage the strip preferably has a thickness of between 0.8 and 0.4 mm. These thicknesses are required as a rolling reduction must be effected during the final processing to can sheet gauge to provide the necessary sheet flatness and final gauge strength. Next a solution heat treatment at temperatures preferably between 480 C and 595 0 C for duration times between seconds and 1 hr is followed by a water quench to ambient temperature.

A solution heat treatment for duration times toward the upper end of the range will also anneal the material if it has been cold rolled prior to the solution heat treatment. Nevertheless, the composition of the alloy allows the material to be heat treated for much shorter times than would normally be performed in processing SUBSTITUTE SHEET WO 92/03586 PCT/A U91 /00376 16 3004 alloys.

The alloy strip may then be allowed to naturally age at room temperature preferably for a period of zero to 48 hours prior to cold rolling of the strip.

To provide the necessary strength properties in the metal, it is necessary that the finish rolling step, has a cold rolling reduction within the range 2 to percent, the reduction preferably being 10 and 80% and most preferably 30 and 70%. It has been found that even with a cold rolling reduction towards the upper limits of this range, the necessary ductility and formability properties for a viable can stock are present.

Finally the sheet material is aged to a temper between the underaged and over-aged states. The ageing will depend on the equipment used and the can manufacturer's strength and ductility specifications and is preferably within the range 120 tow-&sL for a time of between 1 minute and 4 hours.

Solution heat treatment of the material prior to the final processing recrystallises the material and reduces the anisotropic properties created by the cold rolling schedule. This means that when given a final rolling reduction and fully aged to the desired temper, a deep drawing material is created which has very low anisotropic properties and very low earing levels. A cup formed from final gauge 3004 or modified alloy SUBSTITUTE SHEET WO 92/03586 PC/AU91/00376 17 typically has an earing level of whereas a cup formed from an alloy of the present invention has earing levels of less than 2%.

An alternative to the direct chill cast method is that the alloy can be strip cast in a conventional strip caster and solidified into a web approximately an inch or less in thickness. The molten alloy feedstock for this, may be richer in composition than that used in the DC cast alloy but would be of the preferred invention alloy range (see Table It is then preferred that the strip is given a hot or cold rolling reduction in sheet thickness of at least 25% and more preferable to The alloy composition of the present invention and processing technique allows liquid container bodies to be made from thinner gauge sheet stock and achieve cost reductions. Furthermore, one alloy can be used for body end stock and easy-open tab stock by varying the processing steps of the alloy. The use of a single alloy type for all of the component parts of liquid container results in production costs benefits and improvements in scrap recycling efficiency.

The alloy of the invention is now demonstrated in the following Examples.

An alloy with the following composition was direct chill cast to an ingot size of 50 cm x 120 cm SUBSTITUTE SHEET 18 Zn Mg Fe Si Cu Mn Cr Al 4.83 1.53 0.35 0.16 0.019 0.47 0.01 balance The ingot was subjected to the following schedule to produce a coil of the sheet.

homogenise 5 hours 480" 595°C hot roll to 3.175 mm coil exit gauge temperature 295 315°C standard edge trim applied anneal 370°C 373°C for 3 hours cold roll 60% reduction to 1.22 mm solution heat treatment at 1.22 mm flash solutionise at 585 0 C for 10 seconds cold rolling reductions 40% to 0.73 mm 37% to 0.454 35% to 0.303 mm level and solvent wash artificial ageing to T87 temper age at 150°C for 1 hour In the schedule, the coil, once heat treated, was rolled in back-to-back passes to final gauge with a 99 6* 9 9 99 9 9 9 9** AM:04:B376:RES 10 May 1994 WO 92/03586 PCT/AU91/00376 19 maximum delay of 48 hours before commencing to roll.

Levelling was performed within 5 days of cold rolling to avoid eccessive natural ageing as the material age hardens after cold rolling.

An average of 50 samples tested gave yield strength 393 MPa ultimate tensile strength 406 MPa elongation 4% ductility 4.34 mm Can bodies produced from the samples showed a dome reversal of 105 p.s.i. from 0.30 mm dome wall thickness.

Figure 3(b) illustrates the effect of the final cold rolling reduction on the strength and ductility of the alloy and Figure 3(c) demonstrates the effect of artificial ageing time on strength and ductility of the above alloy after solution heat treatment and cold rolling reduction. The ageing temperature is 250°F (121 0

C).

EXAMPLE 2 Three alloys in accordance with the invention of compositions shown in Table 1 were direct chill cast into ingots 100 x 300 mm in cross-section of 1.2 m length. The ingots were then scalped into blocks 190 mm wide and 100 mm thick and lengths of 200 mm. Each of hoMoenise4 the ingots were then lsoeoganiaod at temperature between 500*C and 5850C. A higher homogenisation temperature was SUBSTITUTE SHEET PCT/AU91/00376 WO 92/03586 20 used for the alloys of highest solute content to allow for more complete homogenisation. The thermal analysis curve of the precipitation reaction in the alloy during Heomogenisation is shown in Figure 2. The following letters represent the positions in Figure 2, where changes in the various phases occur. As is the dissolution of GP zones; B is the precipitation of rT if (MgZn 2 phase, C, the dissolution of rf i phase; D, the precipitation of T phase; E, the dissolution of T phase; and F the localized GB liquidation.

Homogenisation and hot rolling schedules for each of the sample alloys are shown in Table 2.

To hot roll the alloys the scalped blocks were cooled to a rolling temperature of between 500 and 485°C in the furnace. The blocks were then removed from the furnace and individually rolled from a gauge of 100 mm to a finished gauge of approximately 2 3 mm. The microstructure of the hot rolled material is shown in Figure 4a.

The finishing temperature of hot rolling was often above 200°C which was sufficient to allow some recovery of the rolled structure prior to cold rolling to the solution heat treatment gauge. However, in the case of some of the alloy 3 samples, the material was given a recrystallisation anneal at a temperature of 345°C for 3 hours. This allowed the material to fully recover and recrystallise. The fully recrystallised grain size of SUBSTITUTE SHEET WO 92/03586 PCT/AU91/00376 21 the alloy had an average diameter of 19m (ASTM (Figure 4b).

In this softened condition the alloys were cold rolled to a number of different gauges as shown in Table 4. This was to allow for a number of different final cold rolling reductions to be made to the given final gauge material for body stock forming. A schematic of the final material processing is included in Figure 3a.

Figure 4(c) shows the microstructure of alloy 2 in Example 2 after the final cold rolling reduction and as can be seen from the micrograph the material has an alpha phase (a Al(Fe,Mn)Si) totally dispersed within the matrix. This microstructure results in a wall ironed can body with excellent non-galling properties.

Solution heat treatment of the plate was conducted at a temperature of 500 0 C to put elements into solution in preparation for the final ageing procedures. A study of the natural ageing behaviour of the three alloys after solution heat treatment of 2 hours at 5000C is shown in Figure 5. The material was cold water quenched and then given a number of heat treatments. Ageing studies and hardness measurements were used to charactise the response of the alloys to various treatments. Tensie studies were then made of sheet in certain conditions to establish the yield strengths and elongations of the specific alloy treatments.

SUBSTITUTE SHEET WO 92/03586 PCT/AU91/00376 22 Final ageing treatment studies are show in Figures 6 8.

Figures 6(b) and 6(c) show the response of the alloys to ageing at 155°C after a first ageing stage at 1210C for 1, 2 and 3 hours respectively.

Figures 7(b) and 7(c) represents the ageing response of the alloys at 111°C with a preceding natural ageing stage of 0, 24 and 48 hours respectively.

Figures 8(b) and 8(c) represent the ageing response of the alloys at 131oC with a preceding natural ageing stage of 0, 24 and 48 hours respectively.

SUBSTITUTE SHEET TABLE 1 COMPOSITION 3004 Range Typically 5182 Range Invention Alloy Range (ingot) Preferred Mg 0.8 1.3 1.25 4.0 5.0 0.5 3.0 1.0 Mn 1.0 1.5 1.0 0.2 0.5 0.1 1.1 0.3 0.8 Cu 0.25 max 0.22 0.15 max 0.05 0.9 0.10 0.50 Si 0.30 max 0.23 0.20 max 0.01 2.0 0.15 0.3 Fe 0.70 max 0.37 0.35 max 0.7 max 0.45 max Zn 0.25 max 0.013 0.25 max 3.0 8.0 4.0 Cr 0.014 0.10 max 0.3 max 0.05 max Ti 0.05 Others 0.05 max (total) 0.15 max 0.15 max 0.10 max Ni Zr 0.01 max Sr WO 92/03586 WO 9203586PCf/A U9 1/00376 24 TABLE 2 HIGH STRENGTH CAN STOCK ALLOY COMPOSITION CHEMICAL COMPOSITION (wt%) Zn Mg Mn Si Fe cu Cr Alloy 1 Sal 3.8 1.1 0.46 0.2 0.3 0.12 <.007 Aloy 2 Bal 4.6 1.3 0.42 0.2 0.4 0.10 <.008 Alloy 3 Bal 6.0 1.8 0.56 0.2 0.35 0.10 <009 TABLE 3 Tyw.,au Twgwamm Thtim xt:Wu Vc) (-C1 rr (rrvi Alloy 1 500 500 100 Alloy 2 565 490 100 2.7 Alloy -3 585 4,80 100 2.8 SUBSTITUTE SHEET WO 92/03586 PCT/AU91/00376 25 TABLE 4 LABORATORY STUDY EXAMPLE 2 Gauge ShtAnn N.A C.W. AA(1) AA(2) YS UTS EL Earing Dome Rev LD. (mm) (Clhr) (hs) (hrs) (hrs) (MPa) (MPal (psi) Al 0.320 Al 0.320 Al 0.320 Al 0.320 Al 0.320 Al 0.320 Al 0.320 Al 0.320 Al 0.342 Al 0.321 Al 0.320 Al 0.328 At 0.320 Al 0.329 Al 0.328 Al 0.305 Al 0.311 A2 0.320 A2 0.326 A2 0.320 A2 0.307 A2 0.296 A2 0.322 A2 0.325 A2 0.320 A2 0.320 A2 0.320 A2 0.320 A2 0.320 A2 0.323 A2 0.320 A2 0.326 A2 0.320 A3 0.325 A3 0.341 A3 0.330 A3 0.295 A3 0.315 A3 0.327 A3 0.315 A3 0.326 A3 0.331 A3 0.348 A3 0.328 A3 0.351 A3 0.326 500/1 48 500/1 48 500/1 48 500/1 48 5001 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 5001 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 500/1 48 121/3 121/3 121/3 121/3 121/3 121/3 121/3 121/3 121/3 121/3 121/3 121/1 121/3 121/6 121/6 121/24 121/24 121/3 121/6 121/6 121/6 121/24 121/24 121/24 121/3 121/3 121/3 121/3 121/3 121/3 121/3 121/3 121/1 121/24 121/24 121/24 121/6 121/6 121/6 121/3 121/3 121/3 121/3 121/3 121/3 121/1 155/3 155/3 155/3 155/3 155/3 155/3 155/3 155/3 155/3 155/3 155/3 155/4 115/3 155/3 155/3 155/3 155/3 155/3 155/3 155/3 15514 155/4 155/3 155/3 15513 155/3 155/3 155/4 318 304 315 181 316 332 324 372 353 383 369 375 373 374 400 473 418 423 439 263 386 424 417 467 441 456 448 335 324 339 228 343 351 349 391 390 483 392 395 395 393 501 478 435 464 471 492 473 448 451 468 454 463 475 62 81 84 84 88 106 184 98 >108 104 >108 >110 102 >108 >108 >112 >109 108 SUBSTITUTE SHEET WO 92/03586 PCT/AL191/00376 26 Figure 9 demonstrates the effect of cold rolling -alloy 2: Figures 10(a) and 10(b) demonstrate the effects of secondary artificial ageing on material of alloy 2 vork with prior cold A Ww- (cw) treatment from 0-60%. The alloy of Figure 10(a) has undergone a solution heat treatment of 500°C for 2 hours, 0 hours natural ageing, cold working and united artificial ageing at 121°C for 3 hours. In Figure 10(c), the alloy has undergone solution heat treatment at 500°C for 2 hours, 48 hours of natural ageing, cold working and an initial artificial ageing at 121°C for 3 hours.

Table 4 demonstrates the response of alloys 1,2 and 3 of Example 2 to varying effects of cold working and artificial ageing.

The column marked C represents the reduction during a cold working step. The columns AA(1) and AA(2) are expressed in the form T/t where T is the temperature OC of that step of heat treatment and t is the time in hours the material is held at that temperature.

The column marked N. A. represents the natural ageing time. SHT/ANN is the solution heat treatment/annealing temperature and time expressed in the T/t format given for the artificial ageing step [AA(1) and The remaining columns represent SUBSTITUTE SHEET WO 92/03586 PCT/AU91/00376 27 the properties of yield strength, ultimate tensile strength, elongation, earing and dome reversal pressure respectively.

A number of sheet alloys were formed into cups for body making and the earing levels measured. The cups were then formed into bodies on a can body maker.

Each of the example results is from a successful can body free of holes or surface marking. The buckle resistance of selected cans was measured on a conventional buckle resistance testing machine.

From the results the alloys demonstrate a very high tensile strength with ductilities in excess of The earing levels of can bodies made from the alloy of the invention show earing levels between 0 These levels are on average 1% lower for a given condition than that of can bodies made from 3004 alloys.

The dome reversal pressures for these cans made from alloys of the invention at the same thickness as cans made from 3004 are far in excess of 3004 values.

Dome reversal pressures for cans of 3004 alloy are typically about 90 p.s.i. maximum whereas the cans of the same thickness made from the invention alloys is between 100 and 115 p.s.i.

The graph of Figure 11 illustrates the effect ageing has on the tensile properties of alloys 2 and 3 SUBSTITUTE SHEET WOb 92/03586 PCr/A U91 /00376 28 and Figure 12 shows a comparison between tensile properties for the invention alloys and that of 3004.

Figure 12 shows how the invention alloys between lines A and B have tensile strengths about 20 40% higher than 3004 type alloys (conventional can stock) with ductilities in excess of 4% and are therefore superior in a number of properties.

A stronger can body material means that the wall thickness of a can body can be reduced whilst maintaining standard 3004 rigidity and buckle resistant.

EXAMPLE 3 As discussed earlier for an alloy to be suitable as can end stock, minimum post bake strength and ductility properties are required.

An alloy with the composition of alloy 3 in Example 2 are subjected to the following processing steps.

1. Hot rolling to 3.0 nun.

2. Cold rolling from 3.0 to 0.8 mm.

3. Anneal at 345 0 C for 1 hour.

4. The material was sectioned into 2 samples with one sample cold rolled to 0.43 and the other to 0.355 mm.

SUBSTITUTE SHEET WO 92/03586 PCT/A U91/00376 29 Both samples were subjected to a solution heat treatment at 500°C for 1 hour before being water quenched.

6. Both samples were then cold rolled to 0.315 mm representing a cold rolling reduction of 30% and respectively.

7. The samples were then sectioned to produce 8 samples and all samples were subjected to natural ageing for 24 hours.

8. The samples were subjected to artificial ageing at 121oC for 3 hours or 6 hours.

9. Half the samples were then baked at 205°C for minutes.

4esfed Tensile tests and cups were then -ed for each sample and the results tabulated in Table Table 6 illustrates the drop in strength and ductility properties as a result of a bake used by can end producers.

From the results of Example 3, it can be seen that a can end produced in accordance with the invention has post bake properties which exceed the minimum requirements of strength and ductility.

Present can end stock alloy AA5182 has a yield stress of 325 MPa, ultimate tensile stress of 370 MPa SUBSTITUTE

SHEET

WO 92/03586 PCT/AU91/00376 30 and an elongation of It can be seen that post bake properties of can end stock in accordance with the alloy and process of the invention, has properties comparable with conventional can end stock.

SUBSTITUTE SHEET TABLE HEAT REDUCTION POST YIELD UTS ELONGa UITS-l,, ALLOY TREAT (ROLLING) BK UNITS_ 'C/hrs *C/rnlns MPa MPa L A3 121/3 10 403 447 N A3 121/6 10 440 474 N A3 121/3 30 433 464 7(15) P A3 121/6 30 464 487 6 Q A3 121/3 10 205/20 334 337 R A3 121/6 10 205/20 326 367 S A3 =121/3, 30 205/20 342 376 T 121/6 30 205/20 335 371 TABLE 6 PRE AND POST BAKE COMPARISON HEAT REDUC- YIELD U.r.s. ELONGATION TREAT ALLOY TION PRE POST PRE POST %PRE JPOST BAKE DROP DROP BAKE BAKE DROP DROP BAKE BAKE 121/3 A3 10, 403 334 67 16.7 447 377 79 15.6 9.0 121/8 A3 10 440 326 14 3.2 474 367 107 22.6 8.0 J 12113 A3 30 433 342 91 21.0 464 376 88 18,9 7(15)1 121/6 A3 30 464 335 129 27.8 487 37 1 38 6.5 WO 92/03586 PCT/AU91/00376 33 Figure 13 basically illustrates the main adantages of the invention over conventional can stock alloys. Cans with comparable strength mean lower cost of alloy from thinner material allowing less material to be consumed to make the same number of cans.

As demonstrated by the Examples, can body can be produced with strength, ductility and anisotropic properties which far exceeds properties obtainable from conventional body stock alloys. As it is possible to also produce can end stock, using the alloy and produced in accordance with the invention, having the necessary properties to produce can ends, a two piece beverage container can be produced from the same alloy type with the same alloy composition.

The claims form part of the disclosure of this specification.

SUBSTITUTE SHEET

Claims (24)

1. A process for producing an aluminium can stock from aluminium alloy including 3.0 to 8.0 wt% zinc, 0.5 wt% magnesium, less than 0.7 wt% iron, 0.01 2.0 wt% silicon, 0.05 0.9 wt% copper, 0.1 1.1 wt% manganese, less than 0.3 wt% chromium and incidental impurities less than a total of 0.15 wt%, and the balance aluminium, said process comprising the steps of forming melt of the alloy metal suitable for casting, casting the melt into a form suitable for rolling, homogenizing the alloy material to produce a homogenized material, hot rolling the homogenized material to an intermediate thickness, to produce a strip or sheet and cold rolling the strip or sheet, solution heating and quenching the strip or sheet, allowing the strip or sheet to stand at room 15 temperature, performing finish rolling by a cold rolling reduction within the range of 2 to 85% and artificially ageing the cold rolled strip or sheet material to the desired S: ductility and strength properties.

2. The process in accordance with claim 1 wherein 20 the aluminium alloy has a zirconium level of less than 0.01 wt%.

3. The process in accordance with claim 1 or claim 2 whereby the alloy material has a metal matrix which has an alpha phase dispersed therethrough. 25 4. The process in accordance with claim 1 or claim S: 2 wherein the finish rolling step is a cold rolling reduction of between 10 The process in accordance with claim 1 or claim 2 wherein the finish rolling step is a cold rolling reduction of 30

6. The process in accordance with claim 1 or claims 2 wherein zinc is present in the range of 4 6.5 wt%, magnesium 1.0 2.5 wt% manganese, 0.3 0.8 wt% silicon 0.15 0.3 wt%, iron up to 0.45 wt%, copper 0.10 0.50 wt% and chromium up to 0.05 wt%.

7. The process in accordance with claim 1 wherein the step of artificially ageing the strip or sheet is carried out at a temperature between 120°C to 260°C.

8. The process in accordance with any one of claims 1 7 wherein after the hot rolling step the strip or sheet is hot coiled at a sufficiently high temperature to allow the nC:Jli:B8376 9 Septombor 1994 35 coiled strip or sheet to anneal while In the coiled state.

9. The process in accordance with any one of the preceding claims wherein the cold rolling step after the hot rolling step includes a full anneal or recovery intermediate anneal during the cold rolling step. An aluminium can stock produced from an alloy having 3.0 8.0 wt% zinc 0.5 3.0 wt% magnesium less than 0.7 wt% iron, 0.01 2.0 wt% silicon, 0.05 0.9 wt% copper, 0.1 1.1 wt% manganese, less than 0.3 wt% chromium, incidental impurities less than a total of 0.15 wt% and the balance aluminium wherein the alloy material is formed into a melt, cast into a form suitable for rolling and homogenised to produce a homogenised material, the homogenised material is then hot rolled to an intermediate thickness to produce a strip or sheet and cold rolled before being solution heat treated and quenched, the strip or sheet is allowed to stand at room temperature and a finish rolling is then performed on the strip or sheet by a cold rolling reduction within the range of 2 to 85% and then the strip or sheet is artificially aged to the desired ductility and strength. a. ft o ora ae oo o e* ooo oeoo eo eo o e o *e o *o

11. 10 wherein

12. 10 wherein 25 2.5 wt%.

13. wherein 0.8 wt%.

14. 10 wherein wt%. wherein

16. 10 wherein

17. wherein

18. wherein wt%.

19. An aluminium can stock in accordance with claim the zinc composition is in the range of 4 6.5 wt%. An aluminium can stock in accordance with claim the magnesium composition is in the range of 1.0 An aluminium can stock in accordance with the manganese composition is in the range of claim 0.3 An aluminium can stock in accordance with claim the silicon content is in the range of 0.15 0.3 An aluminium can stock in accordance with claim iron content is less than 0.45 wt%. An aluminium can stock in accordance with claim copper is in the range of 0.10 0.50 wt%. An aluminium can stock in accordance with claim chromium is in the range of less than 0.05 wt%. An aluminium can stock in accordance with claim zirconium is present in an amount less than 0.01 The aluminium can stock in accordance with claim BC:JH:#8376 ii August 1994 36 wherein zinc is present in the range 4 6.5 wt%, magnesium 2.5 wt%, manganese 0.3 0.8 wt%, silicon 0.15 0.30 wt%, iron less than 0.45 wt%, copper 0.10 0.50 wt%, chromium less than 0.05 wt% and zirconium less than 0.01 wt%.

20. The aluminium can stock in accordance with claim wherein after the hot rolling step and prior to the cold rolling step, the strip or sheet is hot coiled at a sufficiently high temperature to allow the strip or sheet to anneal while in the coiled state.

21. The aluminium can stock in accordance with any one of claims 10 20 wherein the finish rolling reduction is in the range of 10 to

22. The aluminium can stock in accordance with claim wherein the finish rolling reduction is in the range of 15 to

23. The aluminium can stock in accordance with any one of claims 13 or 22 wherein the strip or sheet is *ee* artificially aged at a temperature between 120°C and 260*C.

24. A two piece beverage container, comprising a 20 body portion and an end portion wherein the can stock for said body portion and said end portion is produced by the process in accordance with any one of claims 1 to 9.

25. A two piece beverage container in accordance with claim 24 wherein said container has a dome rever-al of 25 above 100 psi.

26. A can body produced by deep drawing the can stock of any one of the claims 10 23 having an average earing level of less than 2%.

27. A process of producing an aluminiui can stock substantially as hereinbefore described with reference to the accompanying drawings.

28. An aluminium can stock substantially as hereinbefore described with reference to the accompanying drawings. DATED: 9 September 1994 CARTER SMITH BEADLE Patent Attorneys for the Applicant: COMALCO ALUMINIUM LIMITED BC:J1I:#0376 9 Soptombor 1994