DE69820058T2 - METHOD FOR PRODUCING A SHEET FROM HEAT-TREATABLE ALUMINUM ALLOY - Google Patents

Description

technical Area

The invention relates to a method for producing an aluminum alloy sheet material with good improvement the formability and the tensile strength if the paint and baking operations that typically used in the manufacture of automotive parts be subjected to. More specifically, if not exclusively, concerns the invention the production of an aluminum alloy sheet material, which is suitable for the production of automotive parts which in the finished vehicles are visible, for example from automotive exterior panels and the same.

State of technology

The automotive industry has purpose reducing the weight of automobiles increasingly steel panels replaced by aluminum alloy panels. Lighter panels help of course in reducing automobile weight, thereby reducing fuel consumption is reduced, however, introduces the introduction of aluminum alloy panels its own set of needs. In order to it for Suitable for automotive applications, must be an aluminum alloy sheet product good shaping properties in the as received (by the car manufacturer) T4 temper so that it is as desired without Fracture formation, crack formation or wrinkling can be bent or shaped. simultaneously have to the alloy panels are sufficient after painting and baking Have strength so that they are resistant to denting and withstand other forces.

For Automotive panel applications are typically various aluminum alloys the AA (Aluminum Association) 2000 and 6000 series. The AA6000 series alloys contain magnesium and silicon, both with and without copper, however, they can be dependent are classified as AA2000 series alloys based on the Cu content. These alloys can be shaped in the T4 temper state and become after painting and baking (steps that are common on molded automotive parts carried out by the vehicle manufacturer) more firmly. Good gains the strength after painting and baking are highly desirable, so that thinner and therefore lighter panels can be used.

To simplify understanding is a brief explanation below the terminology used to describe alloy stamps is used. The temper called T4 is general known (see for example Aluminum Standards and Data (1984), Page 11, published from The Aluminum Association) and features in conventional Alloys made wise; H. without intermediate discontinuous glow and pre-aging. This is the temper used in automotive sheet metal products to the parts manufacturers for the formation of external panels and the like is delivered. T8 temper identifies an alloy that is heat-treated, cold processed and then artificial was aged. artificial Aging closes maintaining the alloy at one or more elevated temperatures Period. T8X temper denotes a T4 tempering material, that deforms under tension by 2% and then after a 30-minute treatment at 177 ° C was subjected to what the shaping and lacquer baking treatment represents, the molded automotive panels usually Experienced. An alloy that is only heat-treated and artificial has aged to maximum strength is referred to as T6 temper, whereas if aging occurs naturally under room temperature conditions has taken place, the alloy is said to be in the T4 temper will be as stated above. Material that is an intermediate discontinuous Tempering but has not undergone pre-aging is considered in the T4A temper designated located. Material that is pre-aged but not intermediate has undergone discontinuous tempering is in the T4P temper and material that is both an intermediate temper and a T4PA is known as temper.

In earlier U.S. Patent 5,616,189, issued April 1, 1997 by Jin et al. and from the same applicant as the present application is a process for the preparation of Aluminum sheets of the 6000 series described the T4 and T8X temper have the for the manufacture of automotive parts are desirable. The procedure includes, after cold rolling, performing solution treatment (Heat to 500 to 570 ° C), followed by a quenching or cooling process that is carefully controlled cooling steps includes, which creates a "pre-aging" degree becomes. This procedure results in the formation of finer stable Precipitation clusters that have a fine, well-dispersed precipitation structure while the painting / baking procedure to which automotive panels are subjected, and consequently promotes a relatively high T8X temper.

More 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 to ambient temperature with significantly lower Ge speed. The desired intermediate temperature can be achieved in one or more steps.

Unfortunately, sheet metal products suffer made in this way from directly cooled (DC) cast ingots become, often of a phenomenon this is known as roping, ridging, or "color brushing" line formation (hereinafter the term "roping" is used). This develops through the stress component perpendicular to the rolling direction in sheet metal production, which is created when the sheet metal becomes one Automotive part is molded. Roping is the irregular pattern the surface relief, that is caused by locally inhomogeneous deformation, that strong in the rolling direction of the sheet metal Article is aligned. These bands of locally inhomogeneous deformation manifest themselves as visible surface curl, which is the final surface polishing of the automotive product.

Roping has also been used by others in the experienced this area and it was found that the roping by modifying the sheet metal manufacturing process in one Way that a Recrystallization occurs in an intermediate stage of processing can be inhibited. The inhibition of roping is for example in U.S. Patent 5,480,498, issued January 2, 1996 to Armand J. Beaudoin et al., Filed by Reynolds Metals Company, and U.S. Patent 4,897,124, issued January 30, 1990 to Matsuo et al., registered by Sky Aluminum Co., Ltd .. In these patents roping through introduction a discontinuous annealing step (e.g. heating up a temperature within the range of 316 to 538 ° C) in one intermediate Controlled level of sheet metal product formation, z. B. after hot rolling but before cold rolling or after an early stage of cold rolling.

However, it was found that in the Case that a intermediate discontinuous tempering of this type with a sheet from one Aluminum alloy of the 6000 or 2000 series is carried out Reduction not only of the T4 tempering strength but also that T8X annealing strength occurs when the alloy is treated / treated controlled cooling steps from the Jin et al. Patent subject. Consequently, by Try to control or prevent roping, the benefits the preferred T4 / T8X tempering characteristics that would otherwise be with these Alloy types can be achieved, reduced or eliminated.

Accordingly, there is a need for an improved one Process for the production of aluminum alloy automotive sheet products from the 6000 or 2000 series that show little or no roping and at the same time desirable Maintain T4 / T8X characteristics.

Summary the invention

The aim according to the invention is the provision an improved method of reducing or inhibiting the tendency to form roping in aluminum alloy sheet products the 6000 or 2000 series while maintaining an acceptable T4 and T8X properties.

Another aim according to the invention is to provide an improved method of reduction or inhibition of the roping tendency in 6000 series or 2000 series Series of aluminum alloy sheet products.

According to the invention, a method for manufacturing sheetlike Aluminum alloy articles of the 6000 or 2000 series provided, wherein a cast ingot formed by direct cooling casting the ingot will form a peeled ingot peeled, the peeled Ingot is at a temperature between 480 and 580 ° C for less than Homogenized for 48 hours, forming a homogenized bar and the homogenized ingot is formed to form a sheet-like Article rolled to final thickness, where the thickness of the homogenized Barrens by hot rolling and optionally cold rolling is reduced, thereby making an article is formed with an intermediate thickness, which is a reduction in Thickness ranging from 15% to less than 30% to reach the final thickness needed followed by cold rolling the article with intermediate thickness under formation of sheet metal Article with final thickness, with the proviso that if both hot rolling as well as cold rolling to produce the article with intermediate thickness are used to temper the article before cold rolling a heat treatment step to the final thickness is carried out with the article with intermediate thickness.

In the present application the term "cold rolling" understood as rolling processes be at temperatures from room temperature to a maximum of about 150 ° C are carried out. The term "hot rolling" can be understood as rolling processes which are carried out at temperatures above about 300 ° C and preferably at about 520 ° C.

This procedure is based on the Finding it is the cold rolling step that tends to produce Roping in the finished sheet metal product. If the reduction the thickness caused in the cold rolling step is excessive (30% or more), the roping effects become unacceptable.

When cold rolling to the final thickness the thickness of the alloy sheet is preferably in the range to an extent reduced to final thickness from 18 to less than 30%, more preferred 20 to 30%.

The method according to the invention, in which cold rolling is applied to the intermediate thickness, also includes a heat treatment step (e.g. heating the sheet to a temperature in the range of 280 up to 560 ° C for up to 18 hours), which is caused by an annealing in a step of reducing the thickness of the sheet after the hot rolling step, if necessary, e.g. B. before the start of cold rolling or as claimed between the cold rolling steps if more than one is used. If the heat treatment step is carried out between cold rolling steps, it is usually carried out between the penultimate and the last cold rolling step. The 15 to less than 30% reduction in thickness is then accomplished in the final cold rolling step.

The methods according to the invention also include preferably a solution step (e.g. heating to a temperature of 480 to 580 ° C) that with the sheet-shaped article is carried out in the final thickness. This is preferably followed by a controlled pre-aging step from the Type as in the Jin et al. Patent discussed above. described, z. B. by rapid cooling of sheet metal Item from the solution treatment temperature to an intermediate temperature and then cooling from the intermediate temperature to ambient temperature at a lower speed (e.g., ≤ 2 ° C / h).

The alloy with which the specified Processes carried out is preferably an AA6111 aluminum alloy, the processes are also for other alloys of the 6000 or 2000 series are effective, in particular if they contain Cu, e.g. B. Alloy AA6016.

Consequently, a preferred one Embodiment according to the invention direct cooling casting of the alloy producing a cast ingot, peeling of the ingot forming a peeled Ingot, homogenize the peeled ingot at a temperature between 480 and 580 ° C for less than 48 hours, which creates a homogenized bar Hot- and cold rolling the homogenized billet to an intermediate thickness, making an intermediate Sheet metal article is formed, heat treatment of the intermediate Sheet metal articles at a temperature between 280 and 560 ° C for up to 18 hours, making a heat-treated intermediate Article is formed, and cold rolling the intermediate article by between 15 and less than 30% of the final thickness. The sheet-shaped article In the final thickness, solution treatment is then carried out between 480 and 580 ° C., preferably in a continuous heat treatment furnace, cooled quickly and then as in the Jin et al. pre-aged. Finally the pre-aged material will undergo various finishing measures subject, including Leveling, whereby a flat sheet-shaped article is obtained.

The manufactured in this way Material shows improved bendability, no or reduced roping ((Color brush) lines) after reshaping into panels and higher strength during the paint curing than in conventional Alloys of the same type treated in this way (e.g. AA6111-T4 material).

Short description of the figures

1 Fig. 4 is a flow diagram showing the steps of a preferred approach according to the invention;

2 is similar to a flow chart 1 which shows a method not belonging to the invention; and

3 Figure 3 is a schematic representation of the preferred equipment required for the procedures according to 1 and 2 is used.

detailed Description of the invention

As stated above, they have The inventor of the present invention unexpectedly discovered that alloy sheet materials 6000 series, such as AA6111 and AA6016, and some Alloy sheet materials of the 2000 series after hot rolling alone show no roping. The hot rolled Materials tend to show signs of roping after subsequent cold rolling to ≥ 30% to show and show complete Roping at around 40% reduction. As a result, the degree of cold working affects roping, although the underlying mechanism for this is not yet Completely is understood.

The following description will refer to procedures performed with AA6111 alloy, however, it is understandable that this representative for others Alloys of the 6000 and 2000 series is.

Conventional AA6111 alloy sheet is made from a commercial size ingot that has been peeled, homogenized and hot and cold rolled to ≥ 60% before being solution heat treated (solutioned) to adjust the T4 temper. Such a material tends to roping during shaping (the standard test is to deform the sheet in the transverse direction by 15% and then to slightly stone the surface ("stone")). According to the invention, a substantially roping-free sheet material can be produced, provided that the extent of the cold reduction after hot rolling is between 15 and less than 30%, more preferably 18% to less than 30%, even more preferably between 20 and 30%. Below 15 cold reduction, coarse grains can form during the solution treatment, and these produce an "orange peel" pattern after molding. Such an appearance is called unacceptable bel viewed, especially in automotive exterior panel applications.

The production of a hot rolled quality material (Roughing sheet), which takes between 15 and 30% final cold rolling, in a commercial facility is very difficult. Unlike the production of re-rolled material with a very small thickness the only way to achieve such conditions is to include one heat treatment with intermediate thickness after initial Cold rolling. It should be noted that the purpose of the intermediate heat treatment reducing the stored energy of the hot and cold rolled Material without excessive coarsening of Precipitate is. Coarse particles are difficult to completely dissolve during solution treatment and are not desirable since they are the increase in strength caused by the pre-aging process is achieved, the following the solution treatment of the Material carried out in final thickness is, as in Jin et al. Patent (U.S. Patent 5,616,189), adversely affect. About that are also unsolved Particles undesirable, since they make it difficult to have consistent mechanical properties to achieve.

The intermediate heat treatment preferably includes a warming the sheet to a temperature between 280 and 560 ° C and hold in the warm bath for up to 18 hours. The minimum time required for heat treatment is depends depends on the temperature used. At the upper end of the temperature range the minimum time required can be very short (practically none Time at the peak temperature), however, for the specialist is the time required in any case can be easily seen. The material is preferably discontinuously in coil form a temperature of ≤ 350 ° C for up to Treated for 18 hours. Alternatively, higher discontinuous annealing temperatures can be used and shorter Times can be applied by holding the material for about 1 hour at a temperature of about 400 ° C is exposed. At temperatures between 350 and 400 ° C, the heat treatment times should for the reasons mentioned above however, be minimized to avoid excessive particle coarsening becomes.

After the heat treatment, the Cold rolling started or completed to the final thickness, and the material in final thickness is preferably a solution step Subjected at a temperature of 480 to 580 ° C, preferably in a continuous annealing and solution heat treatment line, and is then subjected to pre-aging.

A preferred pre-aging process involves rapid cooling of the sheet from the solution temperature to a temperature in the range of 65 to 75 ° C, followed by a slower one cooling down to ambient temperature at a speed of ≤ 2 ° C / h.

A more complex pre-aging process however, includes four continuous cooling phases or sequences: first is determined by the temperature of the solution heat treatment to a temperature between about 350 and 220 ° C with a Speed of more than 10 ° C / sec but not more than 2000 ° C / sec cooled; second, the alloy sheet is from about 350 to about 220 ° C to between about 270 and 140 ° C cooled at a rate greater than about 1 ° C but less than about 50 ° C / sec; thirdly will continue to roughly 120 to 50 ° C cooled at a rate of more than 5 ° C / min but less than 20 ° C / sec; and fourth is by chance 120 to 50 ° C at a rate of less than about 10 ° C / h to ambient temperature cooled.

The above pre-aging (or quench) process can with an additional Step of winding the sheet before the last step of cooling the Sheet at ambient temperature at a rate of less than 10 ° C / h carried out become.

Alternatively, the quench process the forced cooling the sheet by water cooling, water mist cooling or Forced air cooling, Winding the sheet at a temperature of 50 to 100 ° C and then cooling the Include coil at a speed less than about 10 ° C / h. At the most preferably leaves the sheet the forced cooling with a temperature of between 120 and 150 ° C, and the sheet is preferred wound at a temperature of between 60 and 85 ° C.

The general stages of the above procedure are in 1 of the accompanying drawings. This shows the use of cold rolling steps and an intermediate heat treatment. In contrast, shows 2 of the accompanying drawings a procedure which is not part of the invention, in which no cold rolling steps take place and the hot rolling is carried out to the final thickness. In both cases, quenching and pre-aging steps are carried out with the material in its final thickness.

3 is representative of the device used for the various steps of the preferred embodiment of the method according to the invention. A DC cast bar 10 is first homogenized at 11 and then in a roll mill 12 to form a hot-rolled material (re-rolled material) in coil form 13 hot rolled. The arrows 14 . 15 and 16 indicate alternative routes. The arrow 14 relates to a rolled material 13 hot rolled to the final thickness, a method not belonging to the present invention. This material undergoes a solution treatment step and a pre-aging procedure in a continuous annealing and solution heat treatment line 17 subjected, whereby an end product is obtained in the T4 temper, which is suitable for delivery to automotive parts manufacturers.

The arrow 15 indicates a route from the hot rolled material 13 is taken that is not yet in its final thickness. The material is first subjected to a cold rolling step at 18, whereby a material is obtained that is still not in the final thickness. This material is then subjected to heat treatment in a discontinuous annealing furnace 19 or in a continuous annealing line 20 subjected. The heat treated product is then in a roll mill 21 subjected to final cold rolling to the final thickness, experiencing said reduction in thickness from 15 to less than 30. The same solution and pre-aging steps as described above can then be carried out in the street 17 be performed.

The arrow 16 indicates the possibility that the cold rolling only after the heat treatment in the furnace 19 or the street 20 as previously described (ie in this case there is no pre-cold rolling in the mill 18 ). The subsequent steps are then the same as for the material, the arrow 15 follows.

In all cases according to the invention, cold rolling is carried out after the heat treatment to reduce the thickness of the intermediate product to the final thickness to an extent in the range from 15 to less than 30%. If this degree of decrease in thickness between the hot rolled roughing material 13 and the final thickness of the product is not sufficient, a preliminary cold rolling in the mill can be carried out before the heat treatment 18 be performed. The degree of decrease in thickness caused by cold rolling before the heat treatment step does not affect the roping effect. It is cold rolling after this heat treatment that must be carefully controlled to avoid introducing roping characteristics into the product.

The method according to the invention is designed to an optimized sheet material with a good combination of bend formability, Surface appearance after molding and paint firing reaction. That in this Wise manufactured material is compared to the conventional Product that is currently commercially available is superior considered.

The present invention and its The following comparative examples and Examples understandable are not to be considered as limiting the scope of the present invention are.

Comparative Examples 1 to 3

Three bars with AA6111 composition were of commercial size made by direct cooling casting. The bars were peeled at 560 ° C homogenized and hot rolled to 2.54 mm thickness. Two of the hot rolled Coils were heated together up to 400 ° C in a batch oven, hold for 1 hour and then cool with a blower annealed. All coils were reduced to the final thickness with 59 and 64 of 1.03 or 0.93 mm cold rolled. The cold rolled coils were at 560 ° C a solution treatment subjected to between 65 and 75 ° C wound up and cooled to room temperature at a rate of ≤ 2 ° C / h. The Materials were then subjected to finishing, cleaning, Leveling and cutting measures which included. The tailored samples were used for characterization of the materials used.

The stretch properties in the vertical direction were measured using standard ASTM samples followed at a crosshead speed of 2.54 mm / min to 0.025 load from 12.7 mm / min to failure. The flexibility of materials were evaluated using the ASTM E290-B7 standard Test procedure determined. The material's microstructure became optical examined. A roping test was carried out by 45 mm deformation wide panels by 15% in the vertical direction and then light Stones of the surface to illustrate the topography.

Table 1 summarizes the properties of conventional ones and discontinuously tempered materials like from the plant get together.

Conventional AA6111 properties, Example 1 in Table 1, in tempered condition as received and fired, are 140 MPa YS, 276 MPa UTS and 26% El, or 269 MPa YS, 344 MPa and 19% El. The material as received showed bending formabilities (r / t) of 0.4 and 0.5 in the longitudinal and transverse directions, respectively. The grain size of the material was 35 × 15 μm. The material showed significant roping after being deformed by 15 in the transverse direction.

Examples 2 and 3 in Table 1 represent properties of two AA6111 coils which were batch annealed together in a batch furnace. It can be seen that the properties of the two coils differ significantly, which clearly shows the problems associated with the discontinuous annealing process when trying to achieve consistent properties. These differences existed due to different amounts of coarse Mg ₂ Si / Si precipitated. The alloy according to Example 2 showed more coarse particles than that from Example 3. In general, the paint burning reaction of the discontinuously tempered material was less than that of its non-discontinuously tempered counterpart (cf. Example 1 with Examples 2 and 2 in Table 1). As noted above, this difference is largely related to the fact that the discontinuously annealed material does not respond to the pre-aging treatment.

The discontinuously tempered Material showed no roping, which is consistent with the teaching of U.S. Patents 4,897,124 and 5,480,498 from Sky Aluminum and Reynolds Metal Company, respectively is. However, the discontinuously tempered products could not Produce paint burn resistance to an extent that they normally do observed in the products which are not tempered discontinuously becomes. About that in addition, the properties of the discontinuously tempered Materials difficult to process in a commercial processing environment Taxes.

This illustrates the need for the Development of a better manufacturing process for automotive sheet metal applications.

Examples 1 and 2

The present example 2 is not erfindungemäß.

Two bars with AA6111 composition were of commercial size commercially produced in direct cooling casting. The bars were peeled and at 560 ° C Completely homogenized. One of the bars was 2.54 mm thick and the others hot rolled to 2.3 mm thickness. The hot rolled Coils 2.54 and 2.3 mm thick were cut to a thickness of 1.5 or 1.3 mm cold rolled. The cold rolled coils were then at 550 ° C heat-treated in a continuous annealing furnace and cooled rapidly. The heat treated Coils 1.5 and 1.3 mm thick were then opened up by 33 and 20%, respectively the final thickness of 1.0 mm cold rolled. The cold rolled coils were at 550 ° C solution treated, cooled quickly, between 65 and 75 ° C wound up and then at a speed of ≤ 2 ° C / h to room temperature cooled. The materials were then cut without leveling. The Tailored samples were used to characterize the materials used.

It can be seen that the YS values of the materials of Examples 1 and 2 in Table 2 both in temper as preserved as well as in the lacquer bake are quite close together.

The YS values of the materials as obtained in Table 2 are lower than in Comparative Example 1 (Table 1). The reason for this difference is mainly that the materials have not been subjected to any leveling treatment. The bendability of the materials from Examples 1 and 2 are below different, but represent an improvement over the conventional material - cf. Comparative Example 1 in Table 1 with Examples 1 and 2 from Table 2. The paint firing reaction of the materials from Examples 1 and 2 is better than that which is obtained with the discontinuously annealed materials from Table 1.

The 33% cold rolled material showed reduced roping, whereas the 20% rolled material at all showed no roping. General was the superficial appearance of the both materials after the roping test better than the conventional one Material. The grain size of the 20% cold rolled material is larger than that of its 33 cold-rolled counterpart. The grain size ranges, that were obtained from these two examples are within of the normal product range.

Example 3

A bar with AA6111 composition became commercial size produced in direct cooling, peeled, at Homogenized at 560 ° C, and hot and cold rolled to an intermediate thickness of 1.25 mm. The material was then for 4 hours at 300 ° C heat treated in a batch oven and to a final thickness of 1.00 mm cold rolled. The cold rolled coils were in one continuous annealing line at 550 ° C solution treated and cooled down quickly, between 65 and 75 ° C wound up and then at a speed of ≤ 2 ° C / h to room temperature cooled. A material sample was used to determine various properties taken.

The stretch properties of the AA6111 Materials are given in Table 3.

Table 3 Mechanical properties of AA6111 alloy produced according to the invention

The characteristics are similar to those which were obtained with Examples 1 and 2 in Table 2. bend formability and the paint firing reaction is better than the conventional one Material (Comparative Example 1 in Table 1). The roping characteristics of the material are also better than the conventional one Material.

From the examples above it is clear that this proposed method provides a sheet metal product with regard to Bendability, roping and paint burning reaction is better than that currently available on the market Product.

Claims (9)

Process for the production of sheet metal articles Aluminum alloy of the 6000 series, in which a cast ingot formed by direct cooling casting the ingot is peeled to form a peeled ingot which peeled Ingot is at a temperature between 480 and 580 ° C for less homogenized than 48 hours, creating a homogenized ingot is formed, and the ingot is formed to form a sheet metal article rolled to final thickness, where the thickness of the homogenized ingot by hot and optionally cold rolling is reduced, thereby making an article is formed in intermediate thickness, which is a reduction in the thickness in Range from 15 to less than 30% needed to reach final thickness followed by cold rolling the article in intermediate thickness, which makes the sheet metal article is formed in final thickness, with the proviso that when both hot and Cold rolling applied to manufacture the article in intermediate thickness a heat treatment step with the article in intermediate thickness for tempering the article cold rolling to the final thickness. A method according to claim 1, characterized in that the hot rolling an article in Zwi Schendicke is formed, which requires a further reduction in thickness from 18 to less than 30% to reach the final thickness. Method according to claim 1, characterized in that by hot rolling an intermediate thickness article is formed, which is a further reduction the thickness of 20 to less than 30% to reach the final thickness needed. Method according to claim 1, characterized in that at least a cold rolling step after the hot rolling step to complete the formation of the article in intermediate thickness is applied. Method according to claim 1, characterized in that the heat treatment the warming of the item to a temperature in the range of 280 to 560 ° C for up to Includes 18 hours , Procedure according to at least any of the preceding claims, characterized in that a solution treatment step with the article in its final thickness. Method according to claim 6, characterized in that the Solution treatment step is carried out at a temperature in the range of 480 to 580 ° C. Method according to claim 6 or 7, characterized in that the article following the Solution treatment step at a rate of more than 2 ° C / h to an intermediate temperature and then from that intermediate temperature at a rate of 2 ° C / h or less is cooled to ambient temperature. Procedure according to at least any of the preceding claims, characterized in that the aluminum alloy AA6111 is.