EP2698216B1

EP2698216B1 - Method for manufacturing an aluminium alloy intended to be used in automotive manufacturing

Info

Publication number: EP2698216B1
Application number: EP13178860.6A
Authority: EP
Inventors: David A. Tomes, Jr.
Original assignee: Arconic Technologies LLC
Current assignee: Arconic Technologies LLC
Priority date: 2012-08-16
Filing date: 2013-08-01
Publication date: 2021-03-31
Anticipated expiration: 2033-08-01
Also published as: EP2698216A1

Description

FIELD OF THE INVENTION

The present disclosure relates to uses of continuously cast aluminum-magnesium alloy sheets components in automotive manufacturing. In particular embodiments, the sheet is annealed to an O-temper and has a yield point elongation less than 0.6%.
The present disclosure also relates to methods for manufacturing an aluminum alloy in a continuous in-line sequence wherein the aluminum alloy is adapted and intended to be used in the manufacturing of an automobile. The present disclosure also relates to the use of an aluminum alloy manufactured with such a method for components in automotive manufacturing.

BACKGROUND INFORMATION

Conventional methods of manufacturing of aluminum alloy sheet for use in commercial applications are known.
For example, U.S. Patent No. 7,182,825 discloses a method of making aluminum alloy sheets in a continuous in-line process. A continuously-cast aluminum alloy strip is optionally quenched, hot or warm rolled, annealed or heat-treated in-line, optionally quenched, and preferably coiled, with additional hot, warm, or cold rolling steps as needed to reach the desired gauge. The process can be used to make aluminum alloy sheet of T or O temper.
U.S. Patent No. 6,672,368 discloses a method of continuously-casting aluminum alloy strips. The entire contents of U.S. Patent No. 6,672,368 is incorporated herein in full. The method includes continuous casting aluminum alloys between a pair of rolls. Molten aluminum alloy is delivered to a roll bite between the rolls and passes into the roll nip - or point of minimum clearance of between the rolls - in a semi-molten state. A solid strip of cast aluminum alloy exits the nip at speed ranging from 7.62 to 121.92 meters per minute; alternatively from 15.24 meters per minute to 106.68 meters per minute.
U.S. Patent No. 5,655,593 describes a method of making aluminum alloy sheet where a thin strip is cast (in place of a thick ingot) which is rapidly rolled and continuously cooled for a period of less than 30 seconds to a temperature of less than 176.67°C. U.S. Patent No. 5,772,802 describes a method in which the aluminum alloy cast strip is quenched, rolled, annealed at temperatures between 315.56° and 648.89°C for less than 120 seconds, followed by quenching, rolling and aging.
U.S. Patent No. 5,356,495 describes a process in which the cast strip is hot-rolled, hot-coiled and held at a hot-rolled temperature for 2-120 minutes, followed by uncoiling, quenching and cold rolling at less than 148.89°C, followed by recoiling the sheet.
US 2005/0211350 A1 relates to a method of making aluminum alloy sheet in a continuous in-line process is provided. A continuously-cast aluminum alloy strip is optionally quenched, hot or warm rolled, annealed or heat-treated in-line, optionally quenched, and preferably coiled, with additional hot, warm or cold rolling steps as needed to reach the desired gauge. The process can be used to make aluminum alloy sheet of T or O temper having the desired properties, in a much shorter processing time. The T or O temper may be selected by annealing the strip to achieve an O temper or solution heat treating the strip to achieve a T temper, and, if a T temper is desired, quenching the strip subsequent to the solution heat treating. The invention further provides a hot or warm rolling step wherein the strip is substantially reduces to a final thickness about 10-65% from a casting thickness.
WO 1998/40528 A1 relates to a process of producing an aluminum alloy sheet article of high yield strength and ductility suitable, in particular, for use in manufacturing automotive panels. The process comprises casting a non heat-treatable aluminum alloy to form a cast slab, and subjecting said cast slab to a series of rolling steps to produce a sheet article of final gauge, preferably followed by annealing to cause recrystallization. The rolling steps involve hot and warm rolling the slab to form an intermediate sheet article of intermediate gauge, cooling the intermediate sheet article, and then warm and cold rolling the cooled intermediate sheet to final gauge at a temperature in the range of ambient temperature to 340°C to form said sheet article. The series of rolling steps is carried out continuously without intermediate coiling or full annealing of the intermediate sheet article. The invention also relates to the alloy sheet article produced by the process.

SUMMARY OF THE INVENTION

The present invention relates to a method for manufacturing an aluminum alloy in a continuous in-line sequence as defined by independent claim 1, wherein further developments of the inventive method are provided in the sub-claims, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further illustrated by the following drawings in which:

Figure 1:: is a flow chart of the steps of the method of the present disclosure, to obtain O-temper strip, according to claim 1;

Figure 2:: depicts the as-cast microstructure of Al + 3.5% Mg alloy in transverse direction;
Figure 3:: is a schematic diagram of one embodiment of the apparatus used in carrying out the method of the present disclosure;
Figure 4:: is an additional embodiment of the apparatus used in carrying out the method of the present invention. This line is equipped with four rolling mills to reach a finer finished gauge;
Figure 5:: is an illustrative embodiment of tensile curves illustrating a correlation between tensile stress tests and yield point extension;
Figure 6:: is a graphical representation of electrical conductivity measurements of strips versus anneal temperature;
Figure 7:: is a graphical representation of yield strength measurements of strips versus anneal temperature;
Figure 8:: illustrates micrographs of partially recrystallized grain structure in an AA5182 sample;
Figure 9:: illustrates micrographs of recrystallized grain structure in an AA5182 sample in accordance with the below examples;
Figure 10:: illustrates stress-strain curves;
Figure 11:: illustrates micrographs of a grain structure of a sheet in accordance with the below examples;
Figure 12:: illustrates micrographs of a grain structure of continuously annealed coils in accordance with the below examples;
Figure 13:: illustrates micrographs of a grain structure after batch anneal for in-line hot rolled sheets in accordance with the below examples; and
Figure 14:: illustrates second phase particles and grain structures of sheets made in accordance with the below examples.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present disclosure provides a use for an aluminium alloy sheet manufactured in a continuous in-line sequence. The present disclosure also provides a method for manufacturing an aluminum alloy in a continuous in-line sequence wherein the aluminum alloy is adapted and intended to be used in the manufacturing of an automobile. The present disclosure also provides a use of an aluminum alloy manufactured with such a method for components in automotive manufacturing.
The continuous in-line sequence for manufacturing the aluminium alloy sheet comprises: (i) providing a continuously-cast thin aluminum alloy strip as feedstock; (ii) optionally, quenching the feedstock to the preferred hot or warm rolling temperature; (iii) hot or warm rolling the quenched feedstock to the desired final thickness; (iv) annealing or solution heat-treating the feedstock in-line and optionally off-line, depending on alloy and temper desired; and (v) optionally, quenching the feedstock, after which it is preferably tension- leveled and coiled. This method results in an aluminum alloy sheet having the desired dimensions and properties. In an embodiment, the aluminum alloy sheet may be coiled for later use. This sequence of steps is reflected in the flow diagram of Figure 1, which shows a continuously-cast aluminum alloy strip feedstock 1 which is optionally passed through shear and trim stations 2, optionally quenched for temperature adjustment 4, hot-rolled 6, and optionally trimmed 8. The feedstock is then annealed 16 followed by suitable quenching 18 and optional coiling 20 to produce 0 temper products 2. The annealing step 16 may be done in-line or off-line. As can be seen in Figure 1, the temperature of the heating step and the subsequent quenching step will vary depending on the desired temper.
As used herein, the term "anneal" refers to a heating process that causes recrystallization of the metal to occur, producing uniform formability and assisting in earing control. Typical temperatures used in annealing aluminum alloys range from about 315.56° to 482.22°C.
Also as used herein, the term "solution heat treatment" refers to a metallurgical process in which the metal is held at a high temperature so as to cause the second phase particles of the alloying elements to dissolve into solid solution. Temperatures used in solution heat treatment are generally higher than those used in annealing, and range up to about 571.11°C. This condition is then maintained by quenching of the metal for the purpose of strengthening the final product by controlled precipitation (aging).
As used herein, the term "feedstock" refers to the aluminum alloy in strip form. The feedstock employed in the practice of the present invention can be prepared by any number of continuous casting techniques well known to those skilled in the art. A preferred method for making the strip is described in US 5,496,423 issued to Wyatt-Mair and Harrington. Another preferred method is as described in US Patent 6,672,368 . The continuously-cast aluminum alloy strip preferably ranges from about 0.1524 to 0.635 cm in thickness, more preferably about 0.2032 to 0.3556 cm in thickness. Typically, the cast strip will have a width up to about 228.6 cm, depending on desired continued processing and the end use of the sheet.
Figure 2 illustrates an as-cast microstructure of Al + 3.5% Mg alloy in transverse direction. The single solid strip of Figure 2 includes three general regions, or layers, including two shell regions and center layer sandwiched therebetween. In an embodiment, continuous casting results in a strip wherein the central layer constitutes between 20 to 60 percent, optionally 20 to 30 percent, of the total thickness of the strip. The molten aluminum alloy, upstream of the nip, has an initial concentration of alloying elements including peritectic forming alloying elements and eutectic forming alloying elements. Alloying elements which are peritectic formers with aluminum are Ti, V, Zr and Cr. All other alloying elements are eutectic formers with aluminum, such as Si, Fe, Ni, Zn, Mg, Cu and Mn. During solidification, dendrites typically have a lower concentration of eutectic formers than the surrounding mother melt and higher concentration of peritectic formers. Thus, in the center region upstream of the nip, the small dendrites are thus partially depleted of eutectic formers while the molten metal surrounding the small dendrites is somewhat enriched in eutectic formers. Consequently, the solid central layer of the strip, which contains a large population of dendrites, is depleted of eutectic formers (typically by up to about 20 weight percent, such as about 5 to about 20 wt. %) and is enriched in peritectic formers (typically by up to about 45 percent such, as about 5 to about 45 wt. %) in comparison to the concentration of the eutectic formers and the peritectic formers in each of the metal of the shell regions. United States Patent No. 6,672,368 includes additional disclosure regarding continuously casting that is suitable for use in connection with this disclosure.
Referring now to Figure 3, there is shown schematically a preferred apparatus used in carrying out a preferred embodiment of the method of the present invention. Molten metal to be cast is held in melter holders 31, 33 and 35, is passed through troughing 36 and is further prepared by optional degassing 37 and filtering 39 steps. The tundish 41 supplies the molten metal to the continuous caster 45. The metal feedstock 46 which emerges from the caster 45 is moved through optional shear 47 and trim 49 stations for edge trimming and transverse cutting, after which it is passed to a quenching station 51 for adjustment of rolling temperature. The shear station is operated when the process in interrupted; while running, shear is open.
After optional quenching 51, the feedstock 46 is passed through a rolling mill 53, from which it emerges at the required Final thickness. The feedstock 46 is passed through a thickness gauge 54, a shapemeter 55, and optionally trimmed 57, and is then annealed or solution heat-treated in a heater 59. Following annealing/solution heat treatment in the heater 59, the feedstock 46 passes through a profile gauge 61, and is optionally quenched at quenching station 63. Additional steps include passing the feedstock 46 through a tension leveler to flatten the sheet at station 65, and subjecting it to surface inspection at station 67. The resulting aluminum alloy sheet is then coiled at the coiling station 69. The overall length of the processing line from the caster to the coiler is estimated at about 76.2 meters. The total time of processing from molten metal to coil is therefore about 30 seconds. Any of a variety of quenching devices may be used in the practice of the present invention. Typically, the quenching station is one in which a cooling fluid, either in liquid or gaseous form is sprayed onto the hot feedstock to rapidly reduce its temperature. Suitable cooling fluids include water, air, liquefied gases such as carbon dioxide, and the like. It is preferred that the quench be carried out quickly to reduce the temperature of the hot feedstock rapidly to prevent substantial precipitation of alloying elements from solid solution.
In general, the quench at station 51 reduces the temperature of the feedstock as it emerges from the continuous caster from a temperature of about 537.78°C to the desired hot or warm rolling temperature. In general, the feedstock will exit the quench at station 51 with a temperature ranging from about 204.44° to 482.22°C, depending on alloy and temper desired. Water sprays or an air quench may be used for this purpose.
Hot or warm rolling 53 is typically carried out at temperatures within the range of about 204.44° to 548.89°C, more preferably 371.11° to 537.78°C. The extent of the reduction in thickness affected by the hot rolling step of the present invention is intended to reach the required finish gauge. This typically involves a reduction of about 55%, and the as-cast gauge of the strip is adjusted so as to achieve this reduction. The temperature of the sheet at the exit of the rolling station is between about 148.89° and 454.44°C, more preferably 287.78° to 426.67°C, since the sheet is cooled by the rolls during rolling. Preferably, the thickness of the feedstock as it emerges from the rolling station 53 will be about 0.0508 to 0.381 cm, more preferably about 0.0762 to 0.2032 cm.
The heating carried out at the heater 59 is determined by the alloy and temper desired in the finished product. For T tempers, the feedstock will be solution heat-treated in-line, at temperatures above about 510°C, preferably about 526.67°-537.78°C. Heating is carried out for a period of about 0.1 to 3 seconds, more preferably about 0.4 to 0.6 seconds.
When 0 temper is desired, the feedstock will require annealing only, which can be achieved at lower temperatures, typically about 371.11° to 510°C, more preferably about 426.67°-482.22°C, depending upon the alloy. Again, heating is carried out for a period of about 0.1 to 3 seconds, more preferably about 0.4 to 0.6 seconds.
Similarly, the quenching at station 63 will depend upon the temper desired in the final product. For example, feedstock which has been solution heat-treated will be quenched. preferably air and water quenched, to about 43,33° to 121.11°C, preferably to about 71.11°-82.22°C and then Coiled. Preferably, the quench at station 63 is a water quench or an air quench or a combined quench in which water is applied first to bring the temperature of the sheet to just above the Leidenfrost temperature (about 287.78°C for many aluminum alloys) and is continued by an air quench. This method will combine the rapid cooling advantage of water quench with the low stress quench of air jets that will provide a high quality surface in the product and will minimize distortion. For heat treated products, an exit temperature of 93.33°C or below is preferred.
Products that have been annealed rather than heat-treated will be quenched, preferably air- and water-quenched, to about 43.33° to 382.22°C, preferably to about 360° to 371.11°C for some products and to lower temperatures around 93.33°C for other products that are subject to precipitation of intermetallic compounds during cooling, and then coiled.
Although the process of the invention described thus far in one embodiment having a single step hot or warm rolling to reach the required final gauge, other embodiments are contemplated, and any combination of hot and cold rolling may be used to reach thinner gauges, for example gauges of about 0.01778-0.1905 cm. The rolling mill arrangement for thin gauges could comprise a hot rolling step, followed by hot and/ or cold rolling steps as needed. In such an arrangement, the anneal and solution heat treatment station is to be placed after the final gauge is reached, followed by the quench station. Additional in-line anneal steps and quenches may be placed between rolling steps for intermediate anneal and for keeping solute in solution, as needed. The pre-quench before hot rolling needs to be included in any such arrangements for adjustment of the strip temperature for grain size control. The pre-quench step is a pre-requisite for alloys subject to hot shortness.
Figure 4 shows schematically an apparatus for one of many alternative embodiments in which additional heating and rolling steps are carried out. Metal is heated in a furnace 80 and the molten metal is held in melter holders 81, 82. The molten metal is passed through troughing 84 and is further prepared by degassing 86 and filtering 88. The tundish 90 supplies the molten metal to the continuous caster 92, exemplified as a belt caster, although not limited to this. The metal feedstock 94 which emerges from the caster 92 is moved through optional shear 96 and trim 98 stations for edge trimming and transverse cutting, after which it is passed to an optional quenching station 100 for adjustment of rolling temperature.
After quenching 100, the feedstock 94 is passed through a hot rolling mill 102, from which it emerges at an intermediate thickness. The feedstock 94 is then subjected to additional hot milling 104 and cold milling 106, 108 to reach the desired final gauge.
The feedstock 94 is then optionally trimmed 110 and then annealed in heater 112. Following annealing in the heater 112, the feedstock 94 optionally passes through a profile gauge 113, and is optionally quenched at quenching station 114. The resulting sheet is subjected to x-ray 116, 118 and surface inspection 120 and then optionally coiled.

EXAMPLES

Strips of AA 5182 composition (SAL1) and 0.254 cm thickness were continuously cast in a casting apparatus as described within United States Patent No. 6, 672,368. In one case, a variation was introduced to the composition of AA 5182 by increasing the Cu content outside the AA range (SAL2) for the purpose of increasing O-temper yield strength, Table 1. The strips were hot rolled in line to 0.1524, 0.127 and 0.1016 cm corresponding to hot reductions of 40, 50 and 60% respectively. These samples were batch annealed at temperatures between 315.56° and 454.44°C. Mechanical properties of the samples were measured by tensile tests and the yield point extension (YPE) was determined from the tensile curves following the procedure illustrated in Figure 5. Electrical conductivity measurements were made to monitor recrystallization and precipitation out of solution in samples annealed at different temperatures. Grain structure and average grain size were determined by optical microscopy after anodizing. Selected samples from this series were subjected to simulated continuous anneal in a salt bath at 537.78°C for 30 seconds after which they were cooled in still air or quenched in water. Tensile test evaluation and microscopy work were carried out on the samples as above. This family of samples was prepared with no cold work during processing.
One coil of AA 5182 composition was processed to test gauge by cold rolling. It had been hot rolled in-line from 0.29464 cm to 0.1778 cm thickness after which it was cold rolled to test gauge of 0.1016 cm. The annealing was done in a continuous heat treat line at 537.78°C after which it was forced air cooled. This coil had a cold work of 43% prior to annealing. Tensile testing and microscopy were carried out on samples of the coil.
A thicker strip of 0.3683 cm was cast and hot rolled in-line to 0.29972 cm gauge (17% hot work) and batch annealed at 454.44°C/2h. Samples of this coil were then cold rolled in the laboratory to 0.2286, 0.1524 and 0.0762 cm gauge corresponding to cold work level of 25, 50 and 75% respectively. This set of cold rolled samples was batch annealed at 398.89°C in a laboratory furnace and was evaluated as above by tensile testing and optical microscopy. Tensile testing was done at a strain rate of 2x10^-3 s^-1 using standard laboratory equipment and procedures. The sensitivity of the results to strain rate was not separately studied. For selected samples, mechanical properties and YPE were determined in three directions: longitudinal, transverse and 45 degree to the rolling direction.
Two families of 5182 were cast as ~ 0.1 cm thick strip and were hot/warm rolled in-line to different thicknesses, Table 1. Samples A, B and C were selected to be within the composition limits of AA 5182 (SAL1 composition). The Cu content of alloys D, G and H was increased to ∼0.20% for a higher O-temper strength (composition SAL2). These latter three samples are therefore outside the AA 5182 composition limit with respect to Cu. Both families of alloys were rolled in-line to 0.1524, 0.127 and 0.1016 cm gauge that corresponded to hot reduction of 40, 50 and 60% respectively, Table 1. All samples were batch annealed for 2 hours at several temperatures between 315.56 and 454.44°C. The progress of annealing was assessed by tensile testing, electrical conductivity measurements and microscopy.
Electrical conductivity measurements are shown in Table 2. For the as-rolled material, conductivity was between 24.3 and 24.9% IACS. It increased after batch annealing and reached 28.8-29.7% at 371.11°C after which point further changes were small, Figure 6. Yield strength of the samples showed the opposite trend. As annealing temperatures were increased, the yield strength of the as hot rolled material reduced sharply, Figure 7. The largest reduction occurred at 398.89°C and higher temperatures. The fully annealed strength levels were reached only for 426.67 and 454.44°C anneals. This conclusion was supported by microscopy work which showed partially recrystallized structures at 371.11, 398.89 and 426.66°C anneals, Figure 8. Typical micrographs of fully annealed structures for 454.44°C are shown in Figure 9. Detailed measurement of mechanical properties and evaluation of YPE values in this batch of samples was therefore done on samples annealed at 454.44°C only. Tensile properties of the fully annealed samples measured in the longitudinal, transverse and 45 degree directions are shown in Table 2. The properties generally showed relatively little dependence on the direction of testing. The SAL2 composition did indeed increase the yield strength by about 1 ksi. In the longitudinal direction of the 0.1016 cm thick sheet, for example, the YS was 139.274 MPa for sample A85 (SAL1 composition) and this increased to 144.790 MPa in D85 sample (SAL2).

The yield point elongation was evaluated from the tensile test curves only for the longitudinal direction tests, Table 3. Two tensile curves, one with a YPE of 0.52% (sample D85) and the other with no YPE (sample H85), are shown in Figure 10 as examples. The YPE values observed in the samples were respectively 0.46, 0.32 and 0.30% for the 0.1524, 0.1016 and 0.0762 cm thick sheet samples of SAL1 composition. This indicated that the lowest YPE value corresponded to the lowest degree of hot rolling. SAL2 composition produced somewhat higher YPE with value of 0.46% for 0.127 cm sample and 0.052% for 0.1016 cm sample. The 0.1016 cm sample showed no discernible YPE (H85 in Table 3 and Figure 10).

Table 2: Electrical conductivity of SAL1 (A, B and C) and SAL2 (D, G and H) alloys in annealed state. Processing path: hot roll in-line to gauge, Table 1

	anneal	gauge, cm sample	0.1016 A	0.127 B	0.1524 C	0.1016 D	0.127 G
			electrical conductivity, % IACS
AR	as rolled		24.9	24.7	24.3	24.8	24.6
600	batch 315.56/2hr		26.8	26.4	25.9	26.7	26.5
650	batch 343.33/2hr		28.4	28.1	27.7	28.4	28.4
700	batch 371.11/2hr		29.4	29.3	28.8	29.7	29.6
750	batch 398.89/2hr		29.5	29.6	29.1	29.9	29.8
800	batch 426.67/2hr		29.5	29.4	29.1	29.8	29.7
850	batch 454.44/hr		29.4	29.4	29	29.6	29.4

SP 1000/30S	flash 537.78/30s				24.5	24.8	24.6

Notes: 1. Samples A, B and C are within AA 5182 composition range (SAL1)
2. Samples D, G and H contain higher level of Cu for additional strength (SAL2)

Table 3: Tensile properties and yield point extension (YPE) in the longitudinal direction for SAL1 (A, Band C) and SAL2 (D, G, and H) samples after furnance anneal at 454.44°C. The samples were prepared by in-line hot rolling only, see Table 1.

			longitudinal tensille properties				grain size
	hot roll gauge	hot reduction	UTS	YS	elongation, %		L	T	mean	st
	cm	%	MPa	MPa	total	uniform	µm	µm	µm
		BATCH ANNEAL 454.44°C/2h
A85	0.1016	60	306.8166865	139.2740914	22.4	20.6	46	18.2	31.9	0
B85	0.127	49	303.369308	129.6214316	21.0	17.8	48	26.3	37	0
C85	0.1524	40	306.1272108	131.000383	21.8	19.5	56	30.3	43.0	0
D85	0.1016	59	312.3324921	144.789897	21.0	18.8	37	18.2	27.6	0
G85	0.127	49	313.0219678	139.2740914	21.4	18.9	43	21.7	32.6	0
H85	0.1524	36	324.053579	153.0636054	20.4	18.1	56	31.3	43.5

			297.8535	152.37413	26.9	21.8	17			1

Notes: 1. See Table 1 for the compositions of the alloys

Detailed measurements on samples of AA 5182 composition (coil 100803a7) showed that the highest YPE was observed when the pulling direction was transverse to the rolling direction. The values of YPE were 0.22, 0.20 and 0.44 % in the longitudinal, 45 degree and transverse directions respectively.
In all samples, the grains were pancaked in the longitudinal direction and equiaxed in the transverse direction, Figure 9. As a result, measured grain size was substantially larger in the rolling direction, Table 4. For SAL1, for example, longitudinal grain sizes were 56, 48 and 46 µm and the transverse grain sizes 30.3, 26.3 and 18.2 µm for the samples reduced by 40, 50 and 60% respectively. Similar observations applied to the modified alloys D, G and H (SAL2) which showed somewhat finer grains, Table 4. It was clear that the grains became finer, especially in the transverse section, at higher hot rolling reduction.
The continuous anneal procedure was simulated by dipping the samples of sheet in a salt pot at 537.78°C for 30 seconds after which they were cooled either in still air or by quenching in water. Tensile properties and YPE measured in three directions on these samples are shown in Table 5. Regardless of the degree of prior hot reduction, method of cooling from anneal and direction of testing, the YPE values were all around 0.50%. The yield strength of the sheet also appeared to have somewhat increased by this anneal procedure. Most importantly, however, total elongation values increased from a level of ~21% to 26-28% range. A similar level of increase was noted also in the uniform elongation values, Table 5.

With respect to electrical conductivity, the samples flash annealed at 537.78°C for 30 seconds in a salt bath showed virtually no change compared to the as-rolled material, Table 2 and Figure 6. Applicants believe that the sample was recrystallized as was evident from the grain structure in Figure 11. This indicated the increase in conductivity in batch annealed samples was largely due to precipitation during the anneal cycle rather than the presence of cold work. Flash anneal may have prevented the solutes from dropping out of solution as a result of which the change in conductivity was small. Additional effects could come from dissolution of the Mn precipitates and especially Mg₂Si into the matrix during the flash anneal which could have balanced the increase in conductivity due to the elimination of cold work.

Table 5: Yield point elongation (YPE) after simulated continous anneal (537.78°C /30s) of material hot rolled in-line to gauge in comparison with material cold rolled by 43% and then continous annealed in coil form in Danville

				longitudinal					transverse					45 degree
alloy	hot roll gauge	flash anneal	cooling method	UTS	YS	elongation, %		YPE	UTS	YS	elongation, %		YPE	UTS	YS	elongation, %		YPE
	cm			MPa	MPa	total	uniform	%	MPa	MPa	total	uniform	%	MPa	MPa	total	uniform	%
SAL1	0.1524	537.78'C	water	303.36931	144.7899	27.5	24.5	0.52	302.679832	146.168848	26.5	22.1	0.56	296.474551	142.032	27.5	22.8	0.53
SAL1	0.1524	30s	quench	302.67983	146.16885	26.2	21.8	0.54	304.058784	148.926751	27.8	23.1	0.52	296.474551	144.1004	28.0	24.8	0.51
			mean	303.36931	145.47937	26.9	23.2	0.53	303.369308	147.5478	27.2	22.6	0.54	296.474551	143.4109	27.8	23.8	0.52

SAL2	0.1524	537.78'C	air	308.88511	152.37413	25.4	24.0	0.51	326.122006	155.132033	27.2	22.6	0.50	319.227249	151.6847	28.5	24.0	0.50
SAL2	0.1524	30s	cool	308.88511	148.92675	28.8	26.1	0.51	326.811482	159,268887	27.5	22.6	0.52	321.295676	152.3741	27.8	22.7	0.51
			mean	308.88511	150.99518	27.1	25.1	0.51	326.811482	157.20046	27.4	22.6	0.51	320.606201	152.3741	28.2	23.4	0.51

SAL2	0.1016	537.78°C	air	301.99036	153.75308	27	24.2	0.52	302.679832	150.305703	29.9	27.2	0.51	297.164027	149.6162	31.3	28.4	0.52
SAL2	0.1016	30s	cool	301.99036	150.3057	26.3	24.0	0.52	299.232454	150.995178	26.5	25.1	0.52	297.853502	146.8583	31.7	23.9	0.52
			mean	301.99036	152.37413	26.7	24.1	0.52	301.300881	150.995178	28.2	26.2	0.52	297.853502	148.2373	31.5	26.2	0.52

SAL2	0.127	537.78°C	water	306.12721	151.68465	24.8	21.7	0.50	305.437735	149.616227	28.4	23.3	0.52	299.92193	148.9268	28.0	24.4	0.50
SAL2	0.127	30s	quench	307.50616	153.06361	26.4	22.3	0.49	304.748259	150.995178	25.9	24.0	0.50	300.611405	148.2373	29.6	26.6	0.50
			mean	306.81669	152.37413	25.6	22.0	0.50	305.437735	150.305703	27.2	23.7	0.51	300.611405	148.9268	28.8	25.5	0.50

HOT ROLLED IN-LINE FROM 0.2946 to 0.1778 cm, COLD ROLLED by 43% TO ANNEAL GAUGE (cast: 110509)
5182	0.1016	anneal in Danville		296.47455	149.61623	25.6	24.3	1.19	292.337697	152.37413	31.0	27.6	1.29	286.132416	145.4794	30.2	27.8	1.27
5182	0.1016	anneal in Danville		298.54298	154.44256	27.2	21.0	1.25	290.958745	149.616227	28.5	23.9	1.26	286.132416	146.8583	29.6	26.8	1.25
			mean	297.8535	152.37413	26.4	22.7	1.22	291.648221	150.995178	29.8	25.8	1.28	286.132416	146.1688	29.9	27.3	1.26

DPW Ingot an nnealed				297.8535	152.37413	26.4			291.648221	150.995178				286.132416	146.1688	29.9

The grain size in the samples was found to be generally equiaxed with a mean diameter of 24 µm in the longitudinal direction and 21 µm in the thickness direction, Table 4. Representative micrographs are shown in Figure 11.
Both continuous anneal and batch anneal procedures were evaluated for cold rolled sheet. The continuous anneal test was done on a coil of 0.1016 cm thick sheet in a heat treat line at a temperature of 537.78°C (cast 110509). This material had been cold rolled by 43% from 0.1778 cm coil hot-rolled in-line. The difference in the overall mechanical properties of this material was relatively small in comparison with the hot-rolled material subjected to simulated continuous anneal, Table 5. The YPE values measured were, however, much higher. The mean values were respectively 1.22, 1.28 and 1.26% in the longitudinal, transverse and 45 degree directions. This evaluation showed thus that YPE increases substantially if the material is subjected to cold work even at a relatively modest 43%. The grain structure was generally equiaxed, Figure 12 and Table 6. The mean grain size was 14.1 µm when measured in the thickness direction. It was somewhat larger in the rolling direction and transverse direction, 19.4 and 20.2 µm, respectively. The mean grain size for this sheet was taken as 17.9 µm, the average of the three measurements.
In a second set of tests, batch anneal was done on material cold rolled from 0.29972 cm thick feedstock that had been made by in-line hot rolling (∼19%) in the plant from an as-cast strip of 0.3683 cm thickness. The hot rolled sheet had a mean grain size of 38 µm and produced a YPE value of 0.38% when tested in the longitudinal direction after a simulated batch anneal at 454.44°C/2 h, Table 7 and Figure 13. YPE in the transverse and 45 degree directions were too small for accurate measurement. The hot rolled and annealed sheet was then cold rolled by 25, 50 and 75% after which a final anneal was done at 298.89°C/2h. The grain sizes were 28, 17 and 12 µm (Figure 13) and YPE in the longitudinal direction were respectively 0.34, 0.97 and 1.34%, Table 7. The yield stress of the cold worked samples increased from 113.07 MPa to 117.90 MPa for 25% cold rolling, and to 131.69 MPa and 142.72 MPa for 50 and 75% rolled materials, respectively.

The sheet evaluated was hot rolled in line from ingot to 0.3429 cm gauge (3.43 mm) and then cold rolled by 56% to 1.5 mm thickness (0.1524 cm) and was batch annealed at 398.89°C/2 h. The grains were equiaxed with a mean size of 17 µm, Figure 14. This sheet was characterized for YPE in three directions, Table 8.

Table 6: Grain size measurements from cast 110509. Manufacturing path: In-line hot roll from 0.295 cm as cast gauge to 0.178 cm cold roll to 0.1016 cm, continuous anneal in Danville line at 537.78°C.

	grains intercepted in 1000 µm			grain size, µm
	widht x	thickness z	lenght y	widht x	thickness z	lenght y
	55	73	57	18.2	13.7	17.5
	50	78	55	20.0	12.8	18.2
		71	50		14.1	20.0
	49	64	49	20.4	15.6	20.4
	54	71	48	18.5	14.1	20.8

mean	52.0	71.4	51.8	19.3	14.1	19.4

	sample 2 from cast 110510
	53	73	45	18.9	13.7	22.2
	57	81	50	17.5	12.3	20.0
	49	72	45		13.9	22.2
	56	77	53	17.9	13.0	18.9
	53	75	52	18.9	13.5	19.2

mean	67.0	75.4	49.0	18.3	13.3	20.5

Table 8: Influence of testing direction on yield point extension (XPE) in 5182-0 made from ingot (DPW coil number 333-421). Hot roll gauge:0.3429 cm, cold roll to final gauge (53%), furnance anneal at 398.89°C.

		test direction		elongation
	test gauge cm	test direction	TYS MPa	UTS MPa	total %	uniform %	grain size µm	YPE
879934-L1	0.163068	L	133.482496	289.23506	22.72	22.39	17	0.78
879934-L2	0.163322	L	132.310387	289.09716	18.67	18.25	17	07.3

879934-45-1	0.163576	45 degree	127.415109	275.16975	27.19	26.90	17	09.5
879934-45-2	0.163576	45 degree	126.932476	272.20501	26.60	26.29	17	09.8

879934-LT1	0.164084	T	132.172492	276.61765	25.60	25.30	17	10.2
879934-LT2	0.16383	T	133.758286	277.9966	24.18	23.86	17	10.4

The longitudinal direction provided the lowest YPE values of 0.78 and 0.73 % in two samples. Highest YPE values were observed in the transverse direction that had a mean value of 1.03%. An intermediate value of 0.97 was measured in the 45 degree direction. These values are considered typical for AA 5182 made from ingot following regular plant practices for hot and cold rolling.
Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appending claims.

Claims

Method for manufacturing an aluminum alloy in a continuous in-line sequence, comprising:
i) providing a continuously-cast thin aluminum alloy strip;

ii) in-line hot rolling the continuously-cast strip; and

iii) annealing of the hot rolled continuously cast strip to O-temper having a yield point elongation less than 0.6%,
wherein the aluminum alloy is used in the manufacturing of an automobile, characterized in that the continuously cast strip is cast in a horizontal twin roll casting apparatus, the horizontal twin roll casting apparatus having a nip formed between two casting rolls, and wherein during casting a point of complete solidification of the Al-Mg alloy is formed at the nip, such that the component is free of stretch strain marks, wherein the aluminum alloy is an Al-Mg alloy and more precisely an AA5182 alloy having an increased Cu content of 0.2%, wherein the continuously-cast strip has a thickness ranging from 0.1524 to 0.635 cm before hot rolling, wherein during in-line hot rolling the thickness of the continuously-cast strip is reduced by 40, 50% or 60%, and wherein the annealing of the hot rolled continuously-cast strip is performed between 315.56 and 454.44°C for 2 hours.
The method of claim 1,
wherein annealing the hot rolled continuously cast strip is performed in-line.
The method of claim 1,
wherein annealing the hot rolled continuously cast strip is performed off-line.
The method of claim 1 or 2,
wherein after annealing the strip has a mean average grain size of less than 50 micrometers, preferably less than 30 micrometers, and more preferably less than 25 micrometers.
The method of one of the claims 1 to 4,
wherein after annealing the strip has a mean average grain size between 25 and 50 micrometers.
The method of one of the claims 1 to 4,
wherein after annealing the strip has a mean average grain size between 5 and 25 micrometers.
The method of one of the claims 1 to 6,
wherein the continuously cast strip has a thickness of 0.254 cm before hot rolling.
The method of one of the claims 1 to 7,
wherein a yield point elongation after the annealing step is less than 0.6% and preferably between 0.3% and 0.52%.
The method of one of the claims 1 to 8,
wherein the annealing step is performed at 454.44°C for 2 hours.
The method of one of the claims 1 to 9,
wherein the continuously cast strip is hot rolled to a thickness between 0.1016 cm and 0.1524 cm.
Use of an aluminum alloy manufactured with a method according to one of the claims 1 to 10 for components in automotive manufacturing.