PROCESS OF PRODUCING HEAT-TREATABLE ALUMINUM ALLOY SHEET

Abstract: A process of producing aluminum sheet articles made of 6000 or 2000 series aluminum alloy suitable for manufacture into automotive parts. The process comprises direct chill casting the alloy to produce a cast ingot, scalping the cast ingot to form a scalped ingot, homogenizing the scalped ingot at a temperature between 480 and 580 DEG C for less than 48 hours to form an homogenized ingot, hot rolling the homogenized ingot to an intermediate gauge to form an article of intermediate thickness, and cold rolling the article of intermediate thickness to final gauge, wherein the cold rolling reduces the thickness of the intermediate sheet article by an amount in the range of 15 to 40 % to the final gauge. By limiting the amount of reduction brought about by cold rolling, roping effects exhibited in the fimal product in T4 temper (normally following solutionizing and pre-aging) can be reduced or eliminated. In fact, the cold rolling step can be eliminated entirely, if a suitable reduction of sheet thickness can be achieved by hot rolling alone.

Description: PROCESS OF PRODUCING HEAT-TREATABLE ALUMINUM ALLOY SHEET TECHNICAL FIELD This invention relates to a process of producing aluminum alloy sheet material having good formability and yield strength improvement when subjected to the painting and baking operations typically employed during the fabricating automotive parts. More particularly, although not exclusively, the invention relates to the production of aluminum alloy sheet material suitable for fabricating automotive parts that are visible in the finished vehicles, such as automotive skin panels and the like. BACKGROUND ART The automotive industry, in order to reduce the weight of automobiles, has increasingly substituted aluminum alloy panels for steel panels. Lighter weight panels, of course, help to reduce automobile weight, which reduces fuel consumption, but the introduction of aluminum alloy panels creates its own set of needs. To be useful in automobile applications, an aluminum alloy sheet product must possess good forming characteristics in the as-received (by the auto manufacturer) T4 temper condition, so that it may be bent or shaped as desired without cracking, tearing or wrinkling. At the same time, the alloy panels, after painting and baking, must have sufficient strength to resist dents and withstand other impacts. Several aluminum alloys of the AA (Aluminum Association) 2000 and 6000 series are usually considered for automotive panel applications. The AA6000 series alloys contain magnesium and silicon, both with and without copper but, depending upon the Cu content, may be classified as AA2000 series alloys. These alloys are formable in the T4 temper condition and become stronger after painting and baking (steps usually carried out on formed automotive parts by vehicle manufacturers) . Good increases in strength after painting and baking are highly desirable so that thinner and therefore lighter panels may be employed. To facilitate understanding, a brief explanation of the terminology used to describe alloy tempers may be in order at this stage. The temper referred to as T4 is well known (see, for example, Aluminum Standards and Data (1984), page 11, published by The Aluminum Association) and refers to alloy produced in the conventional manner, i.e. without intermediate batch annealing and pre-aging. This is the temper in which automotive sheet products are normally delivered to parts manufacturers for forming into skin panels and the like. T8 temper designates an alloy that has been solution heat-treated, cold worked and then artificially aged. Artificial aging involves holding the alloy at elevated temperature (s) over a period of time. T8X temper refers to a T4 temper material that has been deformed in tension by 2% followed by a 30 minute treatment at 111 ° C to represent the forming plus paint baking treatment typically experienced by formed automotive panels. An alloy that has only been solution heat-treated and artificially aged to peak strength is said to be in the T6 temper, whereas if the aging has taken place naturally under room temperature conditions, the alloy is said to be in the T4 temper, as indicated above. Material that has undergone an intermediate batch annealing, but no pre-aging, is said to have a T4A temper. Material that has undergone pre-aging but not intermediate batch annealing is said to have a T4P temper, and material that has undergone both intermediate annealing and pre- aging is said to have a T4PA temper. In prior US patent 5,616,189 issued on April 1, 1997 to Jin et al., assigned to the same assignee as the present application, a process of producing aluminum sheet of the 6000 series is described having T4 and T8X tempers that are desirable for the production of automotive parts (the disclosure of this patent is incorporated herein by reference) . The process involves subjecting a sheet product, after cold rolling, to a solutionizing treatment (heating to 500 to 570°C) followed by a quenching or cooling process involving carefully controlled cooling steps to bring about a degree of "pre-aging." This procedure results in the formation of fine stable precipitate clusters that promote a fine, well dispersed precipitate structure during the paint/bake procedure to which automotive panels are subjected, and consequently a relatively high T8X temper. Specifically, the quenching or cooling process involves cooling the alloy from the solution heat treatment temperature to an intermediate temperature without interruption and, without further interruption, cooling the aluminum alloy further to ambient temperature at a significantly slower rate. The intermediate target temperature may be approached in a single step or multiple steps . Unfortunately, sheet products produced in this way from direct chill (DC) cast ingots often suffer from a phenomenon known as roping, ridging or "paint brush" line formation (the term "roping" is used henceforth) . It is developed due to the component of strain transverse to the rolling direction in the sheet product which is applied as the sheet is formed into an automotive part. Roping is the non-uniform pattern of surface relief, caused by locally inhomogeneous deformation, which is heavily orientated in the rolling direction of the sheet article. These bands of locally inhomogeneous deformation manifest themselves as visible surface undulations, which detract from the final surface finish of the automotive product. Roping has been encountered by others in this art, and it has been found that roping may be inhibited by modifying the sheet production method so that recrystallisation occurs at an intermediate stage of processing. The inhibition of roping is addressed, for example, in US Patent No. 5,480,498 issued on January 2, 1996 to Armand J. Beaudoin, et al . , assigned to Reynolds Metals Company, and also in US Patent No. 4,897,124 issued on January 30, 1990 to Matsuo et al., assigned to Sky Aluminum Co., Ltd. In these patents, roping is controlled by introducing a batch annealing step (e.g. heating at a temperature within the range of 316 to 538 °C) at an intermediate stage of the sheet product formation, e.g. after hot rolling but before cold rolling, or after an early stage of cold rolling. However, it has been found that, if an intermediate batch anneal of this kind is carried out on sheet made of 6000 or 2000 series aluminum alloy, there is a reduction not only of the T4 temper strength, but also of the T8X temper strength when the alloy is subjected to the solutionizing treatment/controlled cooling steps of the Jin et al. patent. Therefore, attempts to control or prevent roping reduce or eliminate the benefits of the favourable T4/T8X temper characteristics that are otherwise achievable for these types of alloys. There is consequently a need for an improved process of producing aluminum automotive alloy sheet products of the 6000 or 2000 series that exhibit little or no roping while maintaining desirable T4/T8X characteristics. SUMMARY OF THE INVENTION An object of the present invention is to provide an improved method of reducing or inhibiting roping tendencies in aluminum alloy sheet products of the 6000 or 2000 series, while maintaining acceptable T4 and T8X properties . Another object of the invention is to provide an improved process of reducing or inhibiting roping tendencies in 6000 series or 2000 series aluminum alloy sheet products. According to one aspect of the invention, there is provided a process for producing aluminum sheet articles made of 6000 or 2000 series aluminum alloy, in which a cast ingot is formed by direct chill casting, the ingot is scalped to form a scalped ingot, the scalped ingot is homogenized at a temperature between 480 and 580 °C for less than 48 hours to form an homogenized ingot (preferably by a simple ingot heating practice to peak temperature at the higher end of the stated temperature range) , and the homogenized ingot is rolled to form a sheet article of final gauge, characterized in that said homogenized ingot is rolled to final gauge directly by hot rolling, or by hot and optionally cold rolling to form an article of intermediate gauge that requires a reduction in thickness in the range of 15 to less than 40% to reach final gauge, followed by cold rolling said article of intermediate gauge to form said sheet article of said final gauge. In this application, the term "cold rolling" may be taken to mean rolling operations carried out at temperatures from ambient to a maximum of about 150°C. The term "hot rolling" may be taken to mean rolling operations carried out at temperatures of above about 300°C, and preferably at about 520°C. The invention also relates to aluminum sheet products produced by the process described above. This process is based on the finding that it is the cold rolling step that introduces a tendency to exhibit roping into the finished sheet product. If the reduction in thickness brought about in the cold rolling step is excessive (40% or more) , roping effects become unacceptable . In contrast, the hot rolling steps do not introduce a roping tendency into the finished sheet articles. Therefore, if the reduction to final gauge can be accomplished by hot rolling alone, then the cold rolling steps may be eliminated, together with any tendency to produce roping effects. In the case of the process that employs cold rolling steps, the cold rolling preferably reduces the thickness of the alloy sheet by an amount in the range of 18% to less than 40% to said final gauge, more preferably 20 to 35%, and even more preferably 20 to 30%. The process of the invention that employs cold rolling also preferably employs a heat treating step (e.g. heating the sheet to a temperature in the range of 280- 560 °C for up to 18 hours) to bring about annealing at a stage in the reduction of the thickness of the sheet following the hot rolling step, e.g. before cold rolling commences, or between cold rolling steps when more than one is employed. When the heat treating step is carried out between cold rolling steps, it is usually carried out between the penultimate and the final cold rolling steps. The 15% to less than 40% reduction in thickness is then brought about by the final cold rolling step. The processes of the invention (i.e. those both involving and avoiding cold rolling) also preferably employ a solutionizing step (e.g. heating at a temperature of 480-580°C) carried out on the sheet article of final gauge. This is preferably followed by a controlled pre- aging step of the type described in the Jin et al . patent discussed above, e.g. by cooling the sheet article rapidly from the solutionizing temperature to an intermediate temperature, and then cooling from the intermediate temperature to ambient at a slower rate (e.g. < . 2°C/hour) . The alloy on which the indicated processes are carried is preferably AA6111 aluminum alloy, but the processes are effective for other alloys of the 6000 or 2000 series, particularly if they contain Cu, e.g. alloy AA6016. Thus, a preferred form of the invention involves direct chill casting the alloy to produce a cast ingot, scalping the cast ingot to form a scalped ingot, homogenizing the scalped ingot at a temperature between 480 and 580°C for less than 48 hours to form an homogenized ingot, hot and cold rolling the homogenized ingot to an intermediate gauge to form an intermediate sheet article, heat treating the intermediate sheet article at a temperature between 280 and 560°C for up to 18 hours to form a heat treated intermediate article, and cold rolling the intermediate article between 15 and less than 40% to a final gauge. The sheet article of final gauge is then solutionized between 480 and 580°C, preferably in a continuous heat treatment furnace, rapidly cooled and then pre-aged according to the process described earlier in the Jin et al . Finally, the pre-aged material is optionally subjected to various finishing operations including levelling to obtain a flat sheet article. The material produced in this manner shows an improved bend formability, no or reduced roping (paint brush) lines after being formed into panels and higher strength during the paint cure than conventionally treated alloys of the same kind (e.g. AA6111-T4 material) . BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart showing the steps of a preferred procedure according to the present invention; Figure 2 is a flow chart similar to Figure 1 showing another preferred procedure according to the invention; and Figure 3 is a schematic representation of preferred equipment used for the procedures of Figures 1 and 2. DETAILED DESCRIPTION OF THE INVENTION As noted above, the inventors of the present invention have unexpectedly discovered that 6000 series alloy sheet materials, such as AA6111 and AA6016, and some 2000 series alloy sheet materials do not exhibit roping after hot rolling alone. The hot-rolled materials tend to show signs of roping after subsequent cold rolling of ≥30% and become fully roped at about 40% reduction. Therefore, the degree of cold work influences roping, although the underlying mechanism for this is not yet fully understood. In the following description, reference is made to procedures carried out on alloy AA6111, but this will be understood as representative of other alloys of the 6000 and 2000 series. Conventional AA6111 alloy sheet is produced from a commercial size ingot which is scalped, homogenized, hot- and cold-rolled to .>60% before being solution heat treated (solutionized) to impart the T4 temper. Such material exhibits roping upon forming (the standard test is to strain the sheet by 15% in the transverse orientation and then to stone the surface lightly) . According to the present invention, a substantially roping-free sheet material can be produced, provided the amount of cold reduction after hot rolling (if cold rolling is required at all) is <40%, preferably between 15% and less than 40%, and more preferably 18% to less than 40%, more preferably 20% to 35%, and most preferably between 20% and 30%. Below 15% cold reduction coarse grains may be formed during solutionizing and they produce an "orange peel" pattern after forming. Such an appearance is considered unacceptable, especially in exterior automotive panel applications . Producing a quality hot rolled material (re-roll sheet) that will undergo between 15 and 40% final cold rolling in a commercial plant is very difficult. Other than by producing very thin gauge re-roll, the only way to obtain such a condition is to include an intermediate gauge heat treatment after initial cold rolling. It should be noted that the purpose of the intermediate heat treatment is to reduce the stored energy of the hot and cold rolled material without allowing extensive coarsening of precipitate particles. Coarse particles are difficult to fully dissolve during solutionizing and are undesirable because they adversely affect the strength increase achieved by the pre-aging process, carried out following solutionizing of the final gauge material, as described in the Jin et al . patent (US Patent 5,616,189). Moreover, the undissolved particles are undesirable as they make it difficult to achieve consistent mechanical properties. The optional heat treatment involves heating the sheet to a temperature between 280 and 560°C and heat soaking for up to 18 hours . The minimum time required for the heat treatment is dependent upon the temperature employed. At the high end of the temperature range, the minimum time required may be very short (essentially zero time at the peak temperature) , but a person skilled in the art will readily appreciate the time required in any particular case. Preferably, the material is batch heat- treated in coil form at a temperature less than or equal to 350°C for up to 18 hours. Alternatively, higher batch annealing temperatures and shorter times may be used, subjecting the material to a temperature of about 400°C for approximately 1 hour. However, at temperatures between 350 and 400°C, the heat treatment times should be minimized to avoid excessive particle coarsening for reasons mentioned above. After the heat treatment, cold rolling to final gauge is commenced or completed and the final gauge material is preferably subjected to a solutionizing step at a temperature of 480-580°C, preferably in a continuous anneal and solution heat treating line, and is the subjected to pre-aging. A preferred pre-aging process involves rapidly cooling the sheet from the solutionizing temperature to a temperature in the range of 65 to 75°C, followed by slower cooling to ambient at a rate of <. 2°C/hour. However, a more complex pre-aging process involves four uninterrupted cooling phases or sequences: first, from the solution heat treatment temperature to a temperature between about 350°C and about 220°C at a rate faster than 10°C/sec, but no more than 2000°C/sec; second, the alloy sheet is cooled from about 350°C to about 220°C to between about 270°C and about 140°C at a rate greater than about 1°C but less than about 50°C/second; third, further cooling to between about 120°C and about 50°C at a rate greater than 5°C/min. but less than 20°C/sec; and fourth, from between about 120°C and about 50°C to ambient temperature at a rate less than about 10°C/hr. The above pre-aging (or quenching) process may be carried out with an additional step of coiling the sheet before the final step of cooling the sheet to ambient temperature at a rate less than 10°C/hour. Alternatively, the quenching process may involve forced cooling the sheet by means of water cooling, water mist cooling or forced air cooling, and coiling the sheet at a temperature of 50 to 100°C, then allowing the coil to cool at a rate of less than about 10°C/hour. The sheet most preferably exits the forced cooling at a temperature of between 120 to 150°C and the sheet is preferably coiled at a temperature of between 60°C and 85°C. The general stages of the procedure indicated above are shown in Figure 1 of the accompanying drawings. This shows the use of cold rolling steps and an intermediate heat treatment. In contrast, Figure 2 of the accompanying drawings shows a preferred procedure in those cases where cold rolling steps are not involved and hot rolling proceeds to final gauge. In both cases, quenching and pre-aging steps are carried out on the material of final gauge . Figure 3 is representative of the apparatus employed for the various steps of the preferred form of the process of the invention. A DC cast ingot 10 is first subjected to homogenization at 11 and then hot rolling in a rolling mill 12 to form a hot-rolled material (re-roll) in coil form 13. The arrows 14, 15 and 16 indicate alternative routs. Arrow 14 relate to a re-roll material 13 hot rolled to final gauge. This material is subjected to a solutionizing step and pre-aging procedure in a continuous annealing and solutionizing heat treatment line 17 to give a final product in T4 temper suitable for delivery to an automobile parts manufacturer. Arrow 15 indicates a route taken by hot rolled material 13 that is not in final gauge. The material is first subjected to a cold rolling step at 18 to produce a material that is still not in final gauge. This material is then subjected to a heat treatment in a batch annealing furnace 19 or in a continuous annealing line 20. The heat treated product is then subjected to final cold rolling to gauge in a rolling mill 21, undergoing the stated reduction in thickness of 15% to less than 40%. The same solutionizing and pre-aging steps may then be carried out in line 17, as previously described. Arrow 16 shows the option of carrying out cold rolling only after the heat treatment in furnace 19 or line 20, as previously described (i.e., there is no preliminary cold rolling in mill 18 in this case) . The subsequent steps are then the same as for the material following arrow 15. In all cases, it will be seen that cold rolling is either not employed at all, or it is used after the heat treatment to reduce the thickness of the intermediate product to final gauge by an amount in the range of 15% to less than 40%. If this degree of thickness reduction between the hot-rolled re-roll 13 and the final gauge product is not sufficient, preliminary cold rolling may be carried out prior to the heat treatment in rolling mill 18. The degree of thickness reduction produced by cold rolling prior to the heat treatment step does not influence the roping effect. It is cold rolling after this the heat treatment that has to be carefully controlled to avoid imparting roping characteristics to the product . The process of the invention is designed to produce an optimized sheet material with a good combination of bend formability, surface appearance after forming and paint bake response. The material produced in this manner is believed to be superior to the conventional product commercially available at the present time. The present invention and its advantages will be understood from the following Comparative Examples and Examples, which are not intended to limit the scope of the present invention. COMPARATIVE EXAMPLES 1-3 Three ingots of AA6111 composition of commercial size were direct chill cast. The ingots were scalped, homogenized at 560°C, hot rolled to 2.54 mm gauge. Two of the hot rolled coils were annealed together by heating up to 400°C in a batch furnace, held for 1 hour and then cooled with a fan. All coils were cold rolled with 59 and 64% reduction to the final gauge of 1.03 and 0.93 mm, respectively. The cold rolled coils were solutionized at 560°C, coiled between 65 and 75°C and cooled to room temperature at a rate <2°C/hour. The materials were then subjected to finishing operations which included cleaning, levelling and cut-to-length operations. The cut-to-length samples were used to characterize the materials. Tensile properties in the transverse direction were determined using standard ASTM specimens at a cross head speed of 2.54 mm/minute to 0.025 strain followed by 12.7 mm/minute to failure. The bendability of the materials was determined using the standard ASTM E290-B7 test method. The microstructure of the material was optically examined. A roping test was performed by straining 45 mm wide panels by 15% in the transverse orientation and then lightly stoning the surface to highlight the topography. Table 1 summarizes the properties of conventional and batch annealed materials as received from the plant . Table 1 Mechanical Properties of AA61 11 Alloys in Different Tempers Notes: 'Yield Strength 2 Ultimate Tensile Strength 'Total Elongation "Strain Hardening Index 5 Longitudinal Direction 6 Transverse Direction Simulated by 2% stretch plus 'Ah @ 177°C Conventional AA6111 properties, Example 1 in Table 1, in the as-received and paint bake tempers are 140 MPa YS, 276 MPa UTS and 26%E1 and 269 MPa YS, 344 MPa and 19%E1, respectively. The as-received material showed bend formabilities (r/t) of 0.4 and 0.5 in the longitudinal and transverse directions, respectively. The grain size of the material was 35 x 15 μm. The material showed considerable roping after straining 15% in the transverse orientation. Example 2 and 3 in Table 1 represent properties of two AA6111 coils that were batch annealed together in a batch furnace. It can be seen that the properties of the two coils differed significantly from each other, which clearly shows problems associated with the batch annealing process when attempting to achieve consistent properties. These differences were due to the differences in the amount of precipitated coarse Mg 2 Si/Si . The alloy of Example 2 showed more coarse particles than those in Example 3. Generally, the paint bake responses of the batch annealed material was lower than its non-batch annealed counterpart (compare Example 1 with Examples 2 and 3 in Table 1) . As mentioned above, this difference is mostly related to the fact that the batch annealed material does not respond to the pre-aging treatment. The batch annealed material did not show roping and this is consistent with the teaching of the US Patent Nos . 4,897,124 and 5,480,498 assigned to Sky Aluminum and Reynolds Metal Company, respectively. However, the batch annealed products could not provide paint bake strength to a level normally seen in the non-batch annealed product. In addition, the properties of the batch annealed material are difficult to control in a commercial processing environment. This illustrates a need to develop a better fabrication process for automotive sheet applications. EXAMPLES 1 AND 2 Two ingots of AA6111 composition of commercial size were commercially direct chill cast. The ingots were scalped and fully homogenized at 560°C. One of the ingots was hot rolled to 2.54 mm gauge and the other was hot rolled to 2.3 mm gauge. The hot rolled coils at 2.54 and 2.3 mm gauges were cold rolled to 1.5 and 1.3 mm gauges, respectively. The cold rolled coils were then heat treated at 550°C in a continuous annealing furnace and rapidly cooled. The heat treated coils at 1.5 and 1.3 mm gauge, respectively, were cold rolled by 33 and 20% to the final 1.0 mm gauge. The cold rolled coils were solutionized at 550°C, rapidly cooled and coiled at between 65 and 75°C and then cooled to room temperature at a rate <2°C/h. The material was then subjected to the cut-to-length operation without any levelling. The cut-to-length samples were used to characterize the materials . It can be seen that the YS of the materials of Examples 1 and 2 in Table 2 are quite close in both as-received and the paint bake tempers. Table 2 Mechanical Properties of AA6111 Alloy Produced According to the Present Invention The YS of the as-received materials in Table 2 are lower than that of Comparative Example 1 (Table 1) . This difference is primarily because the fact that the materials were not subjected to levelling operations. The bend formability of the materials in Examples 1 and 2 are different from one another but represent an improvement from that of the regular material - compare Comparative Example 1 in Table 1 with Examples 1 and 2 in Table 2. The paint bake response of the Examples 1 and 2 materials is better than those obtained from the batch annealed materials in Table 1. The 33% cold rolled material showed reduced roping while 20% rolled material did not show any roping. Generally, the surface appearance of the two materials after subjecting to the roping test were better than the conventional material. The grain size of the 20% cold rolled material is higher than that of its 33% cold rolled counterpart . The grain size ranges obtained from both these Examples are within the normal product range . EXAMPLE 3 One commercial sized ingot of AA6111 composition was direct chill cast, scalped, homogenized at 560 °C, hot and cold rolled to an intermediate 1.25 mm gauge. The material was then heat treated at 300°C for 4 hours in a batch furnace and cold rolled to the final 1.00 mm gauge. The cold rolled coils were solutionized at 550°C and rapidly cooled on a continuous annealing line, coiled at between 65 and 75 °C and then cooled to room temperature at a rate <2°C/h. The material was sampled to evaluate different properties. The tensile properties of the AA6111 material are listed in Table 3. Table 3 Mechanical Properties of AA61 11 Alloy Produced According to the Present Invention The properties are similar to those obtained from Examples 1 and 2 in Table 2. The bend formability and paint bake response are better than conventional material (Comparative Example 1 in Table 1) . The roping characteristics of the material are also better than the conventional material. It is clear from the above Examples that the proposed process provides a sheet product that is better in terms of bend formability, roping and paint bake response than product available in the marketplace today.

Claims: WHAT WE CLAIM IS: 1. A process for producing aluminum sheet articles made of 6000 or 2000 series aluminum alloy, in which a cast ingot is formed by direct chill casting, the ingot is scalped to form a scalped ingot, the scalped ingot is homogenized at a temperature between 480 and 580°C for less than 48 hours to form an homogenized ingot, and the homogenized ingot is rolled to form a sheet article of final gauge, characterized in that said homogenized ingot is rolled to final gauge directly by hot rolling, or by hot and optionally cold rolling to form an article of intermediate gauge that requires a reduction in thickness in the range of 15 to less than 40% to reach final gauge, followed by cold rolling said article of intermediate gauge to form said sheet article of said final gauge. 2. A process according to claim 1, characterized in that said hot rolling produces an article of intermediate gauge requiring a further reduction in thickness of 18 to less than 40% to reach said final gauge. 3. A process according to claim 1, characterized in that said hot rolling produces an article of intermediate gauge requiring a further reduction in thickness of 20 to 35% to reach said final gauge. 4. A process according to claim 1, characterized in that said hot rolling produces an article of intermediate gauge requiring a further reduction in thickness of 20 to 30% to reach said final gauge. 5. A process according to claim 1, wherein both hot rolling and cold rolling are employed, characterized in that a heat treating step is carried out on said article of intermediate thickness to anneal said article prior to said thickness reduction in the range of 15 to less than 40%. 6. A process according to claim 5, wherein at least one cold rolling step is employed after said hot rolling to complete formation of said article of intermediate thickness . 7. A process according to claim 5 or claim 6, characterized in that said heat treatment comprises heating said article to a temperature in the range of 280- 560°C for up to 18 hours. 8. A process according to any preceding claim, characterized in that a solutionizing step is carried out on said article of final gauge. 9. A process according to claim 8, characterized in that said solutionizing step is carried out at a temperature in the range of 480-580°C. 10. A process according to claim 8 or claim 9, characterized in that, following said solutionizing step, said article is cooled rapidly to an intermediate temperature and then cooled from said intermediate temperature to ambient temperature at a slower rate. 11. A process according to claim 10, wherein said slower rate is 2°C/hour or less. 12. A process according to any preceding claim, characterized in that said aluminum alloy is AA6111. 13. An alloy sheet article of 6000 or 2000 aluminum alloy having potential T8X temper and substantially no roping tendencies, characterized in that said alloy is produced by a process according to any one of claims 1 to 12. 14. An alloy according to claim 13, characterized in that said alloy is AA6111.

Inventors: BURGER GENE BRUCE, EVANS DANIEL RONALD, GUPTA ALOK KUMAR, JEFFREY PAUL WILLIAM, LLOYD DAVID JAMES, MAROIS PIERRE HENRY, BURGER, GENE, BRUCE, EVANS, DANIEL, RONALD, GUPTA, ALOK, KUMAR, JEFFREY, PAUL, WILLIAM, LLOYD, DAVID, JAMES, MAROIS, PIERRE, HENRY
Applicants: ALCAN INT LTD, BURGER GENE BRUCE, EVANS DANIEL RONALD, GUPTA ALOK KUMAR, JEFFREY PAUL WILLIAM, LLOYD DAVID JAMES, MAROIS PIERRE HENRY, ALCAN INTERNATIONAL LIMITED, BURGER, GENE, BRUCE, EVANS, DANIEL, RONALD, GUPTA, ALOK, KUMAR, JEFFREY, PAUL, WILLIAM, LLOYD, DAVID, JAMES, MAROIS, PIERRE, HENRY
Application year: 1998
Main classification: C22F1
IPC codes: C22F1