EP0902842B2 - Method of producing a component - Google Patents

Abstract

Building component is made of an alloy containing (in wt.%): 0.3-1.6 Si, 0.3-1.3 Mg, max. 0.5 Fe, max. 0.9 Cu, max. 0.5 Mn, 0.05-0.3 V, max. 0.3 Co, max. 0.3 Cr, max. 0.8 Ni, max. 0.3 Zr, max. 0.05 other alloying elements, and a balance of Al.

Description

The invention relates to a method for producing a component according to the preamble of claim 1.

The crash behavior is an increasingly important aspect in vehicle construction. This applies to road traffic as well as to rail traffic.

Road and rail vehicle manufacturers are increasingly considering dimensioning special components or even entire assemblies of the vehicle in such a way that they absorb as much energy as possible in the event of a collision in order to reduce the risk of injury to passengers.

In addition to the structural design of these so-called crash elements, the mechanical properties of the materials used and joining zones are of crucial importance. The aim is to maximize absorption of energy before breakage. This can be achieved by a low ratio of yield strength to strength. An important material feature is also a high elongation. Joining zones, such as the weld seam, should differ as little as possible in their mechanical properties from the base material. With extruded profiles, a good elongation also in the transverse direction is of great importance.

Also note the requirements for the finished component. By design, for example, a certain level of strength, certain minimum values of elongation, corrosion resistance or other essential characteristics can be specified.

The aluminum materials that are today being processed into crash elements include, in particular, standard alloys of the AlMgSi type. Although alloys of this type bring good conditions for energy-absorbing parts in terms of their elongation and formability compared to other alloy systems such as AlZnMg, a further optimization of the properties is desirable.

The AA6005A alloy currently used in wagon construction has a number of problems in manufacturing, which are related to the tendency to recrystallize coarsely. With a coarse grain structure, it is difficult to keep the prescribed bending radii, which enhances the tendency to form grain boundary holes during welding. This leads to a high number of nonconformities in production. If this is to be avoided, it must be produced in such a way that the profile cross section has predominantly fiber structure. This is currently only possible with an alloy composition that leads to higher press forces and significantly lower press speeds. But this means that big productivity losses have to be accepted.

Components used in automotive engineering as safety parts often do not have to achieve the high strength values prescribed for wagon construction. On the other hand, the extruded components used in automotive often have profile wall thicknesses of the order of 1mm or even less. These low wall thicknesses can not or no longer economically pressed from alloys with too high strength.

An alloy according to any one of the features of claim 1 is disclosed in DE-A-32 43 371 and in US-A-5 527 404. From aluminum paperback (1983), pp 141-143, the course of the hot curing in AlMgSi known.

The invention has for its object to provide a material with particularly good deformability with good mechanical properties of the component. The material is said to have a comparable or lower strength level with the AA6005A alloy but to provide greater manufacturing safety and higher productivity.

For the inventive solution of the problem leads a method having the features of claim 1.

The alloy used is much less sensitive to quenching in terms of strength and elongation than the alloy AA6005A, and even with wall thicknesses of 6 mm, a fine grain still occurs throughout. Thus, the alloy is basically suitable for use with large profiles.

For components with high strength requirements, as used for example in wagon construction, the content limits for silicon and magnesium in% by weight are preferably set as follows: silicon 0.45 to 0.75, especially 0.55 to 0.65 magnesium 0.45 to 0.65, especially 0.50 to 0.60

For components with lower strength requirements, such as those used in automotive engineering as extruded profiles with partially small wall thicknesses of 1 mm or less, the following content ranges in wt.% For silicon and magnesium preferably apply: silicon 0.45 to 0.60, especially 0.45 to 0.55 magnesium 0.40 to 0.60, especially 0.45 to 0.55

For in addition to silicon and magnesium in the inventive alloy further contained elements the following preferential ranges apply in% by weight: iron 0.18 to 0.25 copper 0.08 to 0.16 manganese 0.05 to 0.10 vanadium 0.06 to 0.15 chrome Max. 0.08, preferably max. 12:01 titanium Max. 12:05

The use of the novel alloy composition for the production of components with high energy absorption capacity leads to a favorable microstructure of the component structure. The smallest possible grain size for improving the deformation properties is achieved with the alloy composition according to the invention.

The special heat treatment gives the component particularly good properties with regard to energy absorption combined with good strength values.

The heat treatment, which can also be combined with paint firing, especially in the automotive industry, is the generation of the overaged state, T72, which is achieved by annealing between 190 and 230 ° C. for an annealing time of 1 to 5 hours.

The components according to the invention are in the simplest case extruded profiles. However, it is also conceivable components that are finished, starting from an extruded profile as a preform, by hydroforming. According to a further variant of the invention, the component may also be a forged part.

A preferred use of the inventively manufactured component is seen as a safety part in vehicle construction.

The advantages of the alloys used for the production of crash elements according to the invention as well as the special heat treatment of the aging are further substantiated by the following description of test results.

Pressing tests with the high-strength alloy according to the invention (alloy C, see below) have shown that the pressing speed can be significantly increased compared to AA6005A. In an operating test with a press technically difficult base plate for a railroad car, for example, the pressing speed could be increased by 70% without the alloy showing edge cracks, the limitation being given by the maximum permissible pressing force of the press. An average increase in the press speed of 50% with the alloy according to the invention compared to the alloy AA6005A may be assumed to be realistic.

The mechanical properties of the alloys used according to the invention were determined in a tensile test and on the basis of fatigue tests for the heat treatment conditions T6 (full cure) and T64 (partial cure).

Heat treatment state T6

This condition is set by a storage of 10 h at 160 ° C. The heat treatment time is still below the maximum hardness, which is achieved at 160 ° C for about 20 h.

The characteristics of the tensile test can vary depending on the exact analysis, degree of deformation, profile thickness and cooling conditions. Based on previous experience, the following minimum values have been established: Profile thickness range 2 - 4 mm 4 - 8 mm Rp0.2 rm A5 Rp0 Rm A5 [MPa] [MPa] [%] [MPa] [MPa] [%] base material 230 275 10 230 270 8th Butt joint (MIG) 120 180 .. 115 165 ..

The typical values of the yield strength are around 240 MPa, the strength in the base material along 290 MPa, and the strains A5 by 12%. In the transverse direction, yield strength and strength are about the same. A5 drops to 6% from. All tested transverse samples contained profile seams and sample molds. In no case, a break was found in the immediate vicinity of the squeeze, which is due to the particularly fine grain in the press seam area due to the high degree of deformation. The hardness is in the range of 94 to 105 HB.

The characteristic values of the welded connection apply to MIG machine welding. In the specified thickness range, the characteristic values differ only slightly when using SG-AlMg4, 5Mn, SG-AlMg5 and SG-AlSi5 filler metals. Errors such as edge misalignment due to the problems of welding large profiles affect the results more. The typical values of the processed weld joint are 130 MPa for Rp0.2, 210 MPa for Rm and 4% for A100. These are achieved in a test after about 30 days after welding. The cold curing in the heat affected zone is not completed after this time. In a test after about 90 days, a further increase of Rp0.2 is found by about 10 MPa, while the strength increases only slightly, and the strain remains constant within the measurement accuracy.

In the fatigue test, the following values were determined: N *) = 10 ⁴ > 10 ⁷ Δδ Δδ [MPa] [MPa] Basic material (longitudinal) 110 Butt joint (MIG) 90 45 with seam exaggeration 95 55 without night elevation *) N = number of load changes

The value for the base material was determined on 3 mm thick sections. Under comparable conditions, AA6005A typically achieves values <100 MPa. The values of the welded connection were determined on 4 mm thick samples.

Heat treatment condition T64

This condition is achieved by aging for 8 h at 140 ° C.

The characteristic values of the tensile test in the partially cured state T64 were defined for the definition of the crash tolerance: Profile thickness range 2 - 4 mm Rp0.2 rm A5 [MPa] [MPa] [%] base material 140 - 180 > 220 > 18 Butt joint (MIG) > 120 > 180 > 5 (A100)

The typical values of the strength in the basic material along are 255 MPa, the strains A5 by 22%. In the transverse direction, the strength drops slightly to 250 MPa. A5 drops to 12%. All tested transverse samples contain pressed seams. In no case was a break found in the immediate vicinity of the squeeze seam. The hardness is in the range of 74 to 85 HB.

The typical values of the processed weld joint are 130 MPa for Rp0.2, 210 MPa for Rm and 10% for A100. Such a high elongation is extraordinary. This has a very favorable effect in the event of a crash. Here, too, higher values for Rp0.2 are reached after about 90 days of storage at room temperature.

To document the mechanical properties in the weld seam area, 2 mm thick tensile specimens were machined from 6 mm thick welded profile sections parallel to the welding direction at defined distances (positions) from the weld seam center (4 tensile specimens per position). The results are summarized in the tables below.

Tensile test parallel to the weld in the heat affected zone SG-AlMg5-filler position Rp0.2 rm Ag A5 mm MPa MPa % % 1 0 108 214 17.2 20.9 2 9 117 221 21.3 27.7 3 15 118 181 15.5 22.7 4 27 136 210 16.4 21.3 5 84 159 245 17.4 19.5

Tensile test parallel to the weld in the heat affected zone SG-AlSi5-filler position Rp0.2 rm Ag A5 mm MPa MPa % % 1 0 106 205 14.7 16.2 2 9 111 195 20.7 25.7 3 15 140 207 17.0 22.1 4 27 154 238 19.6 21.9 5 84 159 240 17.3 18.6

The positions are given at a distance from the center of the weld. Position 1 is completely in the welding material, position 5 in the uninfluenced base material.

The results show that the strength within the weld (weld metal and heat-affected zone) is relatively low compared to the base material, and that a high ductility is present throughout the area.

Investigations have led to the following result: fatigue N *) = 10 ⁴ > 10 ⁷ Δδ Δδ [MPa] [MPa] Basic material (longitudinal) 95 Butt joint (MIG) 85 45 with seam exaggeration 95 50 without night elevation *) N = number of load changes

The fatigue tests were carried out on profiles from the same production as in condition T6.

The scattering of the mechanical characteristics between strand start and end of the extruded profile are lower in the alloy according to the invention than in the alloy AA6005A. This is due to the more uniform structure and the lower quenching sensitivity. As an example, the values of an operating test on the extrusion length are listed: Tensile test base material 160 ° C 10 h along n = 6 Rp0.2 rm Ag A5 Average 241 291 10.8 12.9 standard deviation 1.4 2.1 0.3 0.5 minimum 239 288 10.4 12.3 Tensile test base material 140 ° C 8 h along n = 6 Rp0.2 rm Ag A5 Average 165 255 18.6 23.3 standard deviation 0.5 0.3 0.4 0.4 minimum 164 255 17.9 22.9

crashworthiness

The behavior in the event of a crash depends essentially on the material properties, the shape and dimension of the crash element used. A first prerequisite for the suitability of a material in a specific shape and dimension is a folding without premature breakage. To test the crash behavior are sections of pipes or hollow profiles of rectangular cross-section, which are compressed. In a first series of experiments, the alloys A, B and C were compared in a second series of experiments, the alloys B, D and E with the following compositions. Si Fe Cu Mn mg Cr Zn V Ti A 12:45 12:21 12:02 12:02 12:43 - 12:03 - 12:02 B 12:54 12:21 - 12:08 12:59 - - - 12:01 C 0.62 12:26 12:16 12:07 12:56 - - 12:10 12:01 D 12:52 12:21 - 12:08 12:57 - - 12:09 12:01 e 12:51 12:21 12:11 12:06 12:49 - - 12:10 12:01

In the upsetting tests of the first series of tests, the alloy C used always reached the highest values of absorbed energy in relation to the mass of the crash element. In this alloy, even in the T64 and T6 states, convolution without breakage and higher energy absorption was achieved with a thin tube than with T4.

In the case of square ups with a cross section of 56 x 65 mm, a length of 300 mm and a thickness of 1 mm, upsetting tests of the second series always achieved the used alloys D and E the highest values of the absorbed energy relative to the mass of the crash element. In the examples given, the condition T72 was achieved with a heat treatment of 5 hours at 205 ° C., the condition T6 by annealing for 10 hours at 160 ° C.

The results of the compression tests of the two test series are summarized in the following tables. Crash test on tubular elements Leg. Status Dia. thickness Type of absorbed Folding*) Energy / mass [Mm] [Mm] [KJ / kg] A T4 92 1.5 as 14.4 B T4 92 1.5 as 17.8 C T4 92 1.5 as 22.1 C T64 92 1.5 as 25 C T6 92 1.5 as 25.7 A T4 70 5 rs 52 B T4 70 5 rs 47 C T4 70 5 rs 58 *) as = asymmetric with nodes
rs = all-round Crash test on rectangular hollow profile elements Leg. Cooling at the press Absorbed energy / mass [kJ / kg] T72 T6 B fan 14.6 17.6 D fan 19.0 18.8 e fan 20.9 20.0 B water spray 19.1 16.8 D water spray 19.8 18.2 e water spray 21.6 18.2

structure

The alloy recrystallizes in fine-grained pressing, leaving in the grains still a remnant of a deformation structure. This is the most important basis for the superior properties in many aspects compared to the AA6005A alloy. The fine-grained recrystallization requires a sufficient degree of deformation with respect to time.

welding behavior

The alloy is easily weldable. In the case of butt joints from profile sections, which were worked out from large profiles and welded with SG-AlMg4.5Mn filler material, no significant grain boundary openings have been observed for wall thicknesses up to 6 mm.

corrosion

Comparative corrosion tests were carried out on alloy B T6, AA6005A T6 and on alloy C T6 and T64. An RID test was performed on the base material, the salt spray test on welded sample sections. The RID test (24 h in a solution of 3% NaCl + 0.5% HCl at room temperature) revealed a clear differentiation: Alloy AA6005A was attacked down to a depth of about 250 μm. The other alloys and states showed only occasional approaches of intercrystalline corrosion. The salt spray test according to DIN 50021 SS (5% NaCl solution at 35 +/- 2 ° C) showed no differentiation between the alloys and states after 1000 h. A special susceptibility to corrosion of one of the materials can not be derived from the experiments carried out.

Conclusions

The alloy is well suited for use in vehicle construction. The characteristic values of the tensile test required for the base material and the welded joint are reliably achieved. The alloy can be used equally well for small and large profiles. It is equally suitable for crash elements and components produced by hydroforming.

Due to the lower quench sensitivity and the fine-grained recrystallization of the alloy, the production reliability is considerably better than with the alloy AA6005A.

The press speed can generally be increased by more than 50% compared to AA6005A.

Pressed seams do not have a negative effect on the mechanical properties.

When welding with SG-AlMg filler materials, no grain boundary openings of a size are formed in the thickness range in which the alloy recrystallizes fine-grained, which have a significant influence on the mechanical properties of the welded joint, if the solidification shrinkage is not extremely hindered. This affects a good elasticity. In particular, the variant partially cured T64 is characterized by a small decrease in the characteristic values of the welded connection compared to the base material.

Overall, the alloy has proven to be an alloy with a good property combination of strength, elongation, weldability and production safety.

Claims (12)

1. Process for manufacturing a component in the form of a crash element for the manufacture of vehicles from an alloy of the AlMgSi type containing, in wt. %, silicon 0.40 to 0.80 magnesium 0.40 to 0.70 iron max. 0.30 copper max. 0.20 manganese max. 0.15 vanadium 0.05 to 0.20 chromium max. 0.10 titanium max. 0.10 zinc max. 0.10 and further elements each individually at most 0.05, in total at most 0.15 and the remainder aluminium, characterised in that the component is transferred by a heat-treatment of 1 to 5 h at 190 to 230°C to an overaged condition (T72).
2. Process according to claim 1, the alloy contains, in wt. %, silicon 0.45 to 0.75, preferably 0.55 to 0.65 and magnesium 0.45 to 0.65, preferably 0.50 to 0.60.
3. Process according to claim 1, characterised in that the alloy contains, in wt. %, silicon 0.40 to 0.60, preferably 0.45 to 0.55 and magnesium 0.40 to 0.60, preferably 0.45 to 0.55.
4. Process according to one of the claims 1 to 3, characterised in that the alloy contains 0.18 to 0.25 wt. % iron.
5. Process according to one of the claims I to 3, characterised in that the alloy contains 0.12 to 0.16 wt. % copper.
6. Process according to one of the claims 1 to 3, characterised in that the alloy contains 0.05 to 0.10 wt. % manganese.
7. Process according to one of the claims 1 to 3, characterised in that the alloy contains 0.06 to 0.15 wt. % vanadium.
8. Process according to one of the claims 1 to 3, characterised in that the alloy contains at most 0.08, preferably at most 0.01 wt. % chromium.
9. Process according to one of the claims 1 to 3, characterised in that the alloy contains at most 0.05 wt. % titanium.
10. Process according to one of the claims 1 to 9, characterised in that the component is manufactured in the form of a section made by extrusion.
11. Process according to one of the claims 1 to 9, characterised in that the component is manufactured from an extruded section subjected to pressure from within.
12. Process according to one of the claims 1 to 9, characterised in that the component is manufactured in the form of a forging.