Aluminium Composite Material with AlMgSi Core Layer

Abstract

The invention relates to a strip consisting of an aluminum material for producing components with improved bending behavior and exacting shaping requirements, a method for producing the strip and the use of sheets produced from the strip according to the invention. The strip has a core layer of an AlMgSi alloy and at least one outer aluminum alloy layer arranged on one or both sides, made from a non-hardenable aluminum alloy, wherein the at least one outer aluminum layer has a lower tensile strength in the (T4) state than the AlMgSi layer, wherein the strip has a uniform strain (A.sub.g) in the (T4) state of more than 23% transverse to the rolling direction and, at a thickness of 1.5 mm-1.6 mm, achieves a bending angle of less than 40° in a bending test.

Claims

1. Strip consisting of an aluminium material for production of components with high forming requirements, wherein the strip has a core layer of an AlMgSi alloy of the type AA6014, AA6016, AA6060 or AA6181 and at least one external aluminium alloy layer arranged on one or both sides and made of a non-hardenable aluminium alloy, wherein the at least one external aluminium alloy layer has a lower tensile strength than the core layer of an AlMgSi alloy in state T4, in state T4, the strip has uniform elongation A.sub.g of more than 23% transverse to the rolling direction and with a thickness of 1.5 mm to 1.6 mm, a bend angle of less than 40° is achieved in the bending test transverse to the rolling direction and the at least one external aluminium alloy layer consists of an aluminium alloy type AA8xxx, AA8079 or AA1200.

2. A method of forming a component, chassis or structural part or panel in automotive, aircraft or railway vehicle construction, comprising: producing a sheet from the strip according to claim 1; and utilizing the sheet to form the component, chassis or structural part or panel in automotive or railway vehicle construction.

3. The method of claim 2, wherein the utilizing step comprises utilizing the sheet as a component, chassis part, external or internal panel in automotive engineering.

4. The method of claim 2, wherein the component, chassis part, external or internal panel is a bodywork element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] The invention will now be explained in more detail below with reference to embodiment examples in conjunction with the drawing. The drawing shows:

[0089] FIGS. 1a)-e) diagrammatically, the sequence of the embodiment example of the method according to the invention;

[0090] FIG. 2 a longitudinal ground section of a strip according to the invention, anodised, according to Barker with polarised light;

[0091] FIG. 3 in a perspective view, the experiment arrangement for performance of the bending test;

[0092] FIG. 4 in a perspective diagrammatic depiction, the arrangement of the bending punch in relation to the rolling direction on performance of the bending test; and

[0093] FIG. 5 diagrammatically, measurement of the bend angle on a bent specimen according to a further embodiment example.

DETAILED DESCRIPTION OF THE INVENTION

[0094] FIGS. 1a) to e) show first a diagrammatic flow diagram of an embodiment example of the method according to the invention for production of a strip according to the present invention, with steps a) production and homogenising of the rolling ingot, b) application of the cladding layers to the rolling ingot, c) hot rolling or roll cladding of the rolling ingot, d) cold rolling, and e) solution annealing with quenching.

[0095] First a rolling ingot 1 is cast from an aluminium alloy with the following alloy constituents in w. %:

[0096] 0.25%≦Mg≦0.6%,

[0097] 1.0%≦Si≦1.5%,

[0098] Fe≦0.5%,

[0099] Cu≦0.2%,

[0100] Mn≦0.2%,

[0101] Cr≦0.1%,

[0102] Zn≦0.1%,

[0103] Ti≦0.1%, and

remainder Al and unavoidable contaminants to maximum total 0.15%, individually maximum 0.05%.

[0104] The rolling ingot produced in this way is homogenised at a homogenisation temperature of 550° C. for 8 hours in a furnace 2, so that the added alloy constituents are distributed particularly homogeneously in the rolling ingot, FIG. 1a). FIG. 1b) now shows that aluminium alloy layers 1a and 1b are applied on the rolling ingot 1 so that these can be welded to the rolling ingot by hot rolling. The aluminium alloy layers 1a and 1b for example consist of aluminium alloys type AA8079 or AA5005A, which in material state 0 (corresponding to state T4) after solution annealing have a lower tensile strength Rm than that of the AlMgSi alloy layer, i.e. for example less than 180 MPa. However other aluminium alloys are conceivable for the external aluminium alloy layers, for example other low-alloyed aluminium alloys such as alloy types AA1XXX, for example AA1200.

[0105] The rolling ingot 1 with the applied aluminium alloy layers or cladding layers is hot rolled, in the embodiment example according to the invention shown in FIG. 1c), by reversing through a hot-roll mill 3, wherein the rolling ingot 1 has a temperature of 400 to 550° C. during hot rolling. In this embodiment example after exiting the hot-roll mill 3 and before the penultimate hot-roll pass, the hot strip 4 preferably has a temperature of at least 400° C., preferably 470 to 490° C. Preferably at this hot-strip temperature, the hot strip 4 is quenched using a plate cooler 5 and the working rolls of the working roll mill 3. For example the hot strip is here cooled to a temperature of 290 to 310° C. before the last hot-roll pass, so that this can be carried out safely and without difficulty and the hot strip can be cooled further. For this the plate cooler 5, indicated merely diagrammatically, sprays cooling rolling emulsion onto the hot strip and ensures an accelerated cooling of the hot strip to the said temperatures. The working rolls of the hot-roll mill are also loaded with emulsion and cool the hot strip 4 further in the last hot-roll pass. After the last roll pass, the hot strip 4 has a temperature of 230 to 200° C. at the exit from the plate cooler 5′ in the present embodiment example and is then coiled via the recoiler 6 at this temperature.

[0106] Because the hot strip 4 immediately at the exit from the last hot-roll pass has a temperature of over 135° C. to 250° C., preferably 200 to 330° C., or optionally is brought to said temperatures in the last two hot-roll passes using the plate cooler and working rolls of the hot-roll mill 3, the hot strip 4, despite the increased coiling temperature, has a crystalline microstructural state which leads to very good uniform elongation values A.sub.g in state T4 of more than 23%, preferably more than 25%. Despite the frozen microstructural state, the hot strip can be processed and coiled with relatively high speed at said temperatures. The hot strip is coiled via the recoiler 6 with a thickness of 3 to 12 mm, preferably 3 to 5 mm. Since no coarse Mg.sub.2Si precipitations can form at the relatively low coiling temperatures, the core alloy layer has a particularly advantageous crystalline state and can therefore be cold rolled very well, for example using a cold-rolling mill 9, and recoiled onto the recoiler 8, FIG. 1d).

[0107] The resulting cold-rolled strip 11 is coiled. Then it undergoes solution annealing at a temperature of typically 500 to 570° C. and quenching 10, FIG. 1e). For this it is again decoiled from the coil 12, solution-treated and quenched in a furnace 10, and recoiled into a coil 13. After natural ageing at room temperature, the aluminium strip can then be delivered in state T4 with maximum formability.

[0108] With greater aluminium strip thicknesses, for example for chassis applications or components such as for example brake anchor plates, alternatively piece annealing can be carried out and the sheets quenched afterwards.

[0109] In state T6, which is achieved by artificial ageing at 100° C. to 220° C., the strip according to the invention shows a further rise in yield point value so that particularly high strengths are achieved. The artificial ageing can take place for example at 205° C. for 30 minutes. The strips produced according to the embodiment shown here, from an aluminium alloy composite material, after cold rolling for example have a thickness of 0.5 to 4.5 mm. Strip thicknesses of 0.5 to 2 mm are normally used for bodywork applications and strip thicknesses of 2.0 mm to 4.5 mm for chassis components in motor vehicle construction. In both application fields, the improved uniform elongation values are a decisive advantage in the production of components since usually very strong forming of the sheets is carried out and nonetheless high strengths are required in usage state T6 of the end product. The improved bendability of the strips according to the invention, which as already stated above allow particularly small bend angles, is added on top of this.

[0110] To achieve the improved bending behaviour, it is advantageous if the external aluminium alloy layers have grain sizes of less than 50 μm, preferably less than 25 μm. A longitudinal ground section according to Barker through an embodiment example of a strip 1 produced according to the invention is shown in FIG. 2 in greatly magnified view. It is clear that the external aluminium alloy layer 1a, which is here formed by an aluminium alloy type AA8079, has a much smaller grain size than the core alloy layer. In this embodiment example average grain sizes of around 20 μm were measured.

[0111] FIG. 3 shows in a perspective view the test arrangement for performance of bending tests to determine the maximum bend angle. The tests are based on the specification 238-100 of the Association of the German Automotive Industry (VDA). The test arrangement consists of a bending punch 14, which in the present case has a punch radius of 0.4 mm. The specimen 15 was previously cut to size 270 mm×60 mm transverse to the rolling direction. The specimen 15 was then expanded with pre-elongation of 10% transverse to the rolling direction, with a pre-elongation speed of 25 mm/min and a free clamping length of 150 mm. Then from this the specimen 15 was cut to a size 60×60 mm and placed in the bending jig. The bending punch 14, which, as shown in FIG. 4, runs parallel to the rolling direction so that the bending line 18 also runs parallel to the rolling direction, now presses the specimen with force F.sub.b between two rollers 16, 17 with roll diameter of 30 mm which are arranged spaced apart by twice the specimen thickness (table 2) or twice specimen thickness plus 0.5 mm (table 3). The bending force F.sub.b is measured while the bending punch 14 bends the specimen 15. When the bending force F.sub.b reaches the maximum and then falls by 30 N, the maximum achievable bend angle is reached. Specimen 15 is then taken from the bending jig and the bend angle measured as shown in FIG. 5.

[0112] As representative of a typical AlMgSi alloy, the alloy Core1 was used as a core alloy layer, the alloy constituents of which are shown in table 1. In addition two different external aluminium alloy layers Clad1, Clad2 were used, the composition of which is also shown in table 1.

TABLE-US-00001 TABLE 1 Si Fe Cu Mn Mg Cr Zn Ti Alloy w. % w. % w. % w. % w. % w . % w. % w. % Core1 1.3 0.20 — 0.06 0.3 — — 0.03 Clad1 0.125 1.11 0.0002 — — — 0.0029 — Clad2 0.14 0.25 0.03 0.02 0.9 — — —

[0113] Taking into account the method described in FIGS. 1a)-e), strips were produced and solution annealed. In the test series shown in table 2, the solution annealing took place in the laboratory using a salt bath on sheets cut from correspondingly roll-hardened strips with final thickness. The specimens were then quenched in the water basin and aged for 7 days. This corresponds approximately to state T4 as also achieved in mass production by the use of a continuous strip furnace.

TABLE-US-00002 TABLE 2 Test Annealing in Thickness R.sub.p0.2 Rm A.sub.g A.sub.80 mm Bend No. Alloy salt bath mm N/mm.sup.2 N/mm.sup.2 % % angle VLG1 T4 Core1 60 sec 1.58 108 222 24.0 29.2 49.3 520° VGL2 T4 Core1 20 sec 1.58 111 224 24.4 29.4 47.5 540° VGL3 T4 Core1 60 sec 1.58 110 225 24.7 30.4 48.5 540° Inv 1 T4 Core1 + 60 sec 1.58 94 196 24.3 29.8 36.9 Clad1 540° Inv 2 T4 Core1 + 20 sec 1.58 93 199 25.3 30.9 37.3 Clad1 540° Inv 3 T4 Core1 + 60 sec 1.58 93 199 24.6 30.3 36.0 Clad1 540° VGL4 T4 Core1 60 sec 1.50 103 213 24.4 28.6 50.2 520° VGL5 T4 Core1 20 sec 1.50 102 216 25.5 31.0 47.5 540° VGL6 T4 Core1 60 sec 1.50 102 216 24.7 29.5 44.3 540°

[0114] It is evident from table 2 that the embodiments Inv1, Inv2, Inv3 according to the invention, in comparison with the comparative examples VLG1-VLG6, achieve significantly smaller bend angles i.e. the opening angle of the bent specimens were significantly smaller than in the comparison strips. The bend angles amounted to 36° to 37.3° in the alloy strips clad according to the invention. The unclad comparative examples however only showed minimum bend angles of more than 44°. The uniformity elongation A.sub.g of the embodiments according to the invention, despite the cladding layer arranged on both sides, was still very high at over 24%.

TABLE-US-00003 TABLE 3 Bend Test Position Thickness R.sub.p0.2 Rm A.sub.g A.sub.80 angle * No. Alloy in strip mm N/mm.sup.2 N/mm.sup.2 % % ° Inv5 T4 Core1 + Strip 1.50 85 187 25.7 29.9 31.4 Clad1 start Inv6 T4 Core1 + Strip 1.50 84 186 26.0 29.9 31.5 Clad1 centre Inv7 T4 Core1 + Strip 1.50 92 198 23.3 27.5 36.4 Clad2 start Inv 8 T4 Core1 + Strip 1.50 93 196 23.2 27.4 36.3 Clad2 end VGL7 Soft AA5182 Strip 1.50 138 278 23.4 26.0 68.7 start * Bend angle measured with modified roll spacing

[0115] Table 3 shows the measurement results of embodiments according to the invention which were produced totally industrially, i.e. here too, the solution annealing step to achieve state T4 in tests Inv5 to Inv8 was carried out in a continuous strip furnace. All measurements given in table 3 were taken on strips with thickness 1.50 mm and hence on slightly thinner strips in comparison with the measurements in table 2. Strips Inv5 to Inv8 were also aged for 19 days at room temperature. For comparison, table 3 shows an aluminium alloy AA5182 typically used for automotive engineering. In the bending tests, in contrast to table 2, a modified roll spacing was selected which corresponded to twice the thickness of the specimen to be measured plus 0.5 mm. This test arrangement, conventional in the automotive industry, gives very reproducible measurement results for the minimum bend angle. For the comparison example VGL7, only a minimum bend angle of 68.7° could be achieved. The embodiment examples according to the invention, however, achieved bend angles of minimum 31.4° and hence are particularly suitable for example for the production of flanged folds, as occur frequently in automotive engineering. The improved bending behaviour is reflected in particular in the improved appearance of the bend edge, which has a very homogenous appearance because of the fine-grained recrystallised external aluminium alloy layer.