Forming of AMAG 7xxx Series Aluminium Sheet Alloys

Transcription

1 1 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Author: Company: Dipl.-Ing. Torsten Grohmann, MBA AMAG rolling GmbH Abstract Currently, the aluminium demand in the automotive industry rises steeply to levels never seen before. Beyond common AlMg (5xxx) and AlMgSi (6xxx), a run for applying ultrahigh strength AlZnMg(Cu) (7xxx) alloys started recently. For 7xxx series, temperature assisted forming procedures unveil their potential in terms of high crash performance combined with significant weight savings. The presentation will elaborate on the three forming processes WARM Forming, W-Temper Forming and HOT Forming in combination with the sheet grades AMAG TopForm UHS (AA7075) and the new AMAG Introduction Cars are safer than ever before, not least because they are made of high-strength, lightweight materials that are optimally adapted to meet crash management and structural requirements. A perfect example of that is AMAG TopForm UHS (Ultra High Strength), a special aluminium alloy that is ideally suited to substitute conventional materials in these areas. Developed based on many years experience in the field of highest-strength alloys for the aircraft industry, it combines low weight, strength, extremely high energy absorption capacity, excellent formability, and recyclability. In close cooperation with leading automotive manufacturers and innovative tier-1 suppliers, an optimized lightweight construction material for aerospace applications is now being used in cars. AMAG TopForm UHS is an AA7075-type alloy (AlZn5.5MgCu), optimized for warm forming in the long-term stable T6 peak age delivery temper. This alloy has twice the strength of an AA6016 alloy, so components made of AMAG TopForm UHS can substitute press-hardened steels in the automotive industry, for example in B-pillars, bumper beams or side impact beams. Here, the addition of copper leads to the desired increase of strength and also inherently makes the EN AW 7075 AMAG TopForm UHS

2 2 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann grade SCC (Stress corrosion cracking) prove. Adhesive bonding and resistance welding is possible and overcome the obstacles of hot solidification cracks with conventional welding operations. To overcome fusion-welding issues, AMAG developed within the EU funded ALIVE project a high strength non-copper 7xxx series based on the AA7021. It is called AMAG as the development headed for an in-service yield strength of more than 400 MPa with an acceptable stress corrosion cracking performance. Within the chemical limits of the EN AW 7021 it is possible to achieve this objective, but only at a peak strength temper derived from long hours heat treatment. For the integration into the automotive process chain with a loss of strength while Warm Forming or for W-Temper and Hot Forming with only a short heat treatment in the paint shop, the alloying had to be changed to gain a sufficient level of strength. Therefore, AMAG increased the Mg and Zn content to enhance strength, and designated the new alloy with a plus and call it AMAG The following table indicates the chemical composition of the new alloy. Si Fe Cu Mn Mg Cr Zn Ti Zr min. max > > Table 01: Chemical composition of AMAG Both alloy families, the copper and non-copper containing 7xxx series increase their strength significantly by precipitation hardening. For comparison, Table 2 shows the typical mechanical properties of AMAG TopForm UHS and AMAG in peak age temper T6: Alloy YS [MPa] UTS [MPa] A50 [%] AMAG TopForm UHS AA7075 (AlZn5.5MgCu) AMAG AA7021 (AlZn5.5Mg1) AA7020 (AlZn4.5Mg1) Table 2: Typical mechanical properties of 7xxx series alloys in peak age temper T6

3 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 3 AMAG is focussing on the development of 7xxx series alloys with specific strengths on the same level with press hardening steels for the automotive industry as shown in Figure 1: Figure 1: Banana diagram with the density specific tensile strength for steel and aluminium However, AlZnMg(Cu) alloys of the 7xxx series with tensile strength up to 700 MPa used in the aerospace industry for decades have to be tailored to automotive requirements to utilize the significant weight saving potential. A successful transfer to the automotive industry requires innovative solutions to replace cost-intensive forming and additional heat treatment procedures in the aerospace and sports industry. In terms of forming three different processes were investigated for the use of 7xxx series in the automotive area: Warm Forming of AMAG TopForm UHS enables the series production of the BMW i8 side impact beam with significant weight savings and an excellent crash performance. A direct contact heating station increases the blank temperature to 200 C within seconds immediately followed by isothermal forming in warm dies. Short cycle times, low capital expenditure and no need for further heat treatment are the advantages.

4 4 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann The temper W characterizes an unstable state directly after solution heat treatment with good forming properties. Consequently, the solution annealing furnace, the quench and the lubrication station have to be located in the press shop. Solution annealing for 7xxx alloys is carried out at more than 400 C, followed by a quench. After coating with a conventional drawing oil, pressing of the cold blank starts at ambient temperature. For the final use, the component needs to increase the strength by artificial ageing. From equipment point of view, Hot Forming is similar to the press hardening of boron manganese steels. The process starts with solution annealing at some 400 C in a furnace next to the press. In contrast to W-Temper Forming, the quench is obsolete, as the hot blank is directly transferred to the press, formed and quenched between the cooled dies. To save separate artificial ageing, the thermal sequence of car body dryer, e-coat, seam sealing dryer, base and clear coat curing in the paint shop is sufficient for exploiting up to 90 % of the full age hardening potential. 2 Forming 2.1 WARM Forming of AMAG TopForm UHS AMAG TopForm UHS is an AA7075 type alloy (AlZn5,5MgCu) and is optimized for warm forming in the long-term stable T6 peak age delivery temper. This alloy has higher strength compared to non-cu derivatives and is combined with controlled solution annealing, quenching and artificial ageing at aircraft certified continuous coil treating lines ensure reproducible constant properties and reduce the investments and processes needed at the car manufacturer. Figure 2 demonstrates the split of the production process in the rolling mill and the press shop for quality, cost and environmental reasons. As one can see, the rolling mill carries out most of the necessary process steps especially solution annealing and artificial ageing at high temperatures respectively long hours.

5 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 5 Figure 2: Temperature-time-diagram for the production and pressing of AMAG TopForm UHS If we examine the press shop process in more detail in Figure 3 we can see that it takes just a few seconds to heat up the blank to app. 200 C in a direct contact heating station: Figure 3: Warm Forming of AMAG TopForm UHS in two steps: Direct contact heating of the blank and transfer in a heated die within a couple of seconds

6 6 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann Because of the high reflectivity, conventional furnaces are not the first choice as it takes too long and therefore reduces the strength of the material. Nevertheless, specialized NIR (Near Infrared) furnaces successfully bring the material to 200 C at a rather fast speed. After a fast transfer of the warm blank, isothermal forming starts in the press with dies also kept at temperatures of around 200 C. It is essential to restrict the temperature exposure in terms of time and temperature to keep the ultra high strength of the material delivered to the press shop in temper T6 as illustrated in Figure 4: 550 YS R P0,2 [MPa] s 45 s 60 s 180 s 300 s 300 T6 180 C 200 C 230 C 250 C Figure 4: Yield strength decline of AW-7075-T6 temperature & time wise (without ageing) Ductility and formability of aluminium increase significantly by employing higher temperature as demonstrated in the Forming Limit Curve (FLC) in Figure 5. Especially heat-treatable aluminium alloys benefit from considerably lower deformation resistances and forces. The FLC compares the formability of AMAG TopForm UHS at different temperatures in the range of 200 C with the standard cold forming procedure of a typical AA6016 automotive alloy in temper T4. At 170 C the forming limit curve comes near to the AA6016 T4 curve especially for plain strain conditions. A further increase to 230 C improves forming significantly and even for the stretch-forming path AMAG TopForm UHS reach formability of AA6016 T4 cold forming. Because real forming processes are

7 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 7 non-linear combinations of different forming paths the adequate temperature between 170 and 230 C has to be chosen and tried out for each part individually. Figure 5: Forming limit diagram AMAG TopForm UHS at different temperatures vs. AA6016 T4 WARM Forming at 170 to 230 C leads to lower flow stresses, failure strains and press forces as shown in Figure 6 and Table 3: Figure 6: Influence of temperature and drawing velocity on AW-7075-T6

8 8 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann Regarding strain rate sensitivity, higher drawing velocity requires higher drawing forces and therefore reduce the benefit of WARM Forming in terms of press dimension and accompanied investment cost. Ziehkraft [kn] C C C Ziehweg [mm] Ziehkraft [kn] 140 T=200 C b=2,3 60 b=2,2 40 b=2, Ziehweg [mm] Table 3: WARM Forming of AMAG TopForm UHS at temperatures between 170 and 230 C The resulting component in Figure 7 has a high dimensional accuracy and a property profile that is already set in the rolling mill, including high ductility and strength. As opposed to press hardening lines in the steelmaking area, large furnaces with high energy requirements and long residence times are not required with this solution. The difference, by definition, between warm forming and hot forming is that the warm forming temperature is well below the recrystallization temperature. Short cycle times, low capital expenditure and no need for further heat treatment are the advantages.

9 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 9 Figure 7: Side impact protection made from AMAG TopForm UHS 2.2 W-Temper Forming The temper W characterizes an unstable state directly after solution heat treatment and quenching of precipitation hardening alloys. Figure 10 describes the process starting with solution annealing for some three minutes at app. 450 C for AlZnMg(Cu) alloys. Because of their high quench sensitivity, Cu containing 7xxx series need a water based quench with cooling gradients exceeding 80 K/s. In contrast, non-cu 7xxx do well with just forced air cooling. To avoid distortion of the blanks we recommend cooling plates in a press line with an intermediate lubrication device before the forming station. An advantage of W-Temper Forming is the use of standard forming lubes in combination with standard not cooled or heated dies at ambient temperature. It is essential to use the supersaturated state directly after solutionizing within some 10 minutes before natural ageing impairs the good forming properties. Consequently, the solution annealing furnace, the quench and the lubrication station have to be located in the press shop. In contrast to WARM Forming,

10 10 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann components made by W-Temper Forming need artificial ageing to gain strength and corrosion performance. Here, we suggest a so-called 5-Step Paint Bake Cycle (5xPB) to utilize up to 90 % of the age hardening potential of the alloy. The 5xPB consists of the standard sequence of body dryer, e-coat, seam sealing, filler and base coat curing furnace in a paint shop with temperatures between app. 120 and 185 C for some one and a half hour. Figure 8: Schematic time-temperature diagram for W-Temper Forming Figure 9 proves the good formability of 7xxx series in the W-Temper state by getting the same drawing depth in a cross die component for 2 mm sheet as with 5182 cold forming in soft temper O /1/. Figure 9: Comparison of W-temper Forming of a non Cu 7xxx alloy with a 5182 in temper O

11 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 11 A closer look to the forming limit curve (FLC) for W-Temper Forming of the non- Cu type AMAG in Figure 10 also reveals a close performance to the cold forming of the 5182 O forming benchmark. AMAG was able to form B-pillar reinforcements on a pilot press and studied the crash performance of closed hat profiles. 0,40 0,35 major true strain ϕ 1 0,30 0,25 0,20 0,15 0,10 0,05 0,00-0,20-0,15-0,10-0,05 0,00 0,05 0,10 0,15 0,20 0,25 0,30 minor true strain ϕ 2 Figure 10: Forming limit curve for the W-Temper forming of AMAG AMAG developed the to get a final strength near to the 7075-based AMAG TopForm UHS after W-Temper Forming without a significant Cu alloying to reduce the quench sensitivity and the impact of natural ageing. It is also possible to produce B-pillar reinforcements with AMAG TopForm UHS, but the press shop has to employ high quenching gradients and need to minimize the time delay before forming. Finally, in terms of the AMAG 7021+, Figure 11 shows the flow curve for W-Temper Forming.

12 12 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann Figure 11: Flow curve for AMAG for the W-Temper forming process 2.3 HOT Forming Equipment wise, Hot Forming is similar to the press hardening of boron manganese steels and therefore the idea is to utilize these globally available sites. Figure 12 describes the process starting in the press shop with solution annealing for some three minutes at app. 450 C in a conventional furnace. In contrast to W-Temper Forming, the quench is obsolete, as the hot blank is directly transferred to the press, formed and quenched between the cooled dies. Figure 12: Schematic time- temperature diagram for the HOT Forming of 7xxx series

13 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 13 In contrast to the martensitic strengthening mechanism for press hardening MnB5 steels, the 7xxx series aluminium components produced by HOT Forming need artificial ageing for gaining strength and also in terms of corrosion performance. The thermal sequence of car body dryer, e-coat, seam sealing, filler and base coat curing in the paint shop is sufficient for exploiting up to 90 % of the full age hardening potential as shown later in Chapter 3. 7xxx series benefit from energy efficient low temperature paint shop processes as temperatures between 120 and 160 C are sufficient for the artificial ageing for this alloy type. In addition, thermal shielding of structural components in the paint shop by the outer skin of the body in white are not an issue as for 6xxx series. AMAG proved the HOT Forming concept by producing B-pillar reinforcement with a partner in the automotive industry. Figure 13 also shows the ambition to create a simulation environment for HOT Forming of 7xxx series, here for AMAG TopForm UHS. Figure 13: HOT Forming simulation of AMAG TopForm UHS for a B-pillar reinforcement, Courtesy of the EU ALIVE project As for all new processes, there are still issues to solve. For HOT Forming, this is especially true for the tribology at temperatures of 450 C for aluminium. Feasibility studies with boron nitride or molybden sulfide suspensions show the need for optimization to reach series production level. While some authors focus on the systematic investigation on wear

14 14 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann with solid lubricants /2/, others try to solve the HOT Forming tribology issue with PVD or CVD wear protection coatings on forming dies /3/. Nevertheless, widespread available and accepted press shop technology for press hardening of steel across the globe makes it extremely useful to pursue the HOT Forming process of ultra high strength aluminium of the 7xxx series like AMAG s TopForm UHS to further lightweight cars. 3 Properties For 7xxx series AlZnMg(Cu) alloys both,adequate age hardening and corrosion performance after employing cost efficient automotive processes are decisive to leave the aerospace area. Therefore, the following two chapters elaborate on mechanical and corrosion properties for WARM Forming, W-Temper Forming and HOT Forming with the standard 5xPB paint shop process utilized for artificial ageing at no extra cost. 3.1 Mechanical Warm Forming: Regarding mechanical properties, Figure 14 shows the yield and ultimate tensile strength in the delivery temper T6 indicated by 25 and two WARM Forming temperatures of 200 respectively 230 C. A variation of the paint bake temperature of 170, 185 and 200 C demonstrate the need to limit the maximum temperature in the paint shop.

15 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 15 YS RP0,2 [MPa] UTS Rm [MPa] Warm Forming temperature [ C] Paint Bake temperature [ C] Figure 14: WARM Forming and Paint Bake Simulation for AMAG TopForm UHS A stable press shop process is critical for the efficient integration of AMAG TopForm UHS into the automotive process chain. In principle, the variation of warm forming temperature leads to different mechanical properties after the press shop. In contrast to the well-known 6xxx AlMgSi series, the additional heat treatment in a paint shop can further decrease the strength of AMAG TopForm UHS due to overaging or dissolution of metastable precipitations. Whereas forming temperatures can go up to 200 or 230 C for a minute or two, the paint bake temperature should be limited to 190 C because of the long soaking time increased to one hour as a worst-case scenario for this diagram. One has to keep in mind, that AMAG TopForm UHS is delivered in peak age temper T6 and therefore blank heating and forming need to be limited to a minute as shown in the test series and paint shop temperatures should not exceed 190 C to keep as much strength as possible. With direct contact heating in a press with hot plates, the cycle time goes down to some seconds in practice. In figures 14 and 15 the strength axis starts at 300 MPa exceeding the maximum yield strength of standard aluminium automotive alloys.

16 16 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann Crash series with hat profiles and side impact beams proved the superior performance in terms of penetration depth, late crack initiation and a maximum of absorbed energy compared to its Al-peers. Lateral crash situations suit perfectly to the ultra-high strength of AMAG TopForm UHS whereas crash box applications will not work as the average bending angle prohibits folding of the material. W-Temper and HOT-Forming: Figure 15 and 16 exhibit strength respectively ductility after the standard automotive 5-step paint shop process (5xPB) as mean values derived from B-pillar prototypes. 5xPB summarizes car body dryer, e-coat, sealing, filler and basecoat curing with temperatures between 120 and 185 C suitable for artificial ageing of 7xxx series alloys without the need for separate age hardening furnaces. The comparison with a 125 C treatment for 24 hours shows that the standard 5xPB paint shop process exploits up to 90% of the full age hardening potential of both AMAG TopForm UHS (7075) and A yield strength of more than 400 MPa derives from HOT Forming and W-Temper Forming in combination with paint shop curing processes. Ductility is sufficient for applications like side impact protections but limited to 10 %. YS Rp0,2 [MPa] UTS Rm [MPa] C 5xPB 5xPB Hotforming W-Temper Figure 15: HOT resp. W-Temper formed B-pillars: AMAG TopForm UHS (7075) vs

17 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys Elongation A50 [%] Elongation Ag [%] C 5xPB 5xPB Hotforming W-Temper Figure 16: HOT resp. W-Temper formed B-pillars: AMAG TopForm UHS (7075) vs Corrosion Generally speaking, the corrosion performance of AlZnMg(Cu) 7xxx series alloys is weaker compared to standard aluminium automotive sheet alloys. Regarding filiform corrosion, the scribe creepback is several times higher and therefore the use is limited to structural parts. Here, the structural integrity has to be kept also in a corrosive environment. Therefore, 7xxx series automotive alloy need to be inherently stress corrosion cracking (SCC) prove to prevent the growth of cracks in corrosive environments in combination with internal or external stresses when corrosion protection coatings fail. Several laboratory investigations proved that 7075 based AMAG TopForm UHS sheet in the delivery temper T6 but also after WARM Forming or solutionizing and proper quenched

18 18 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann in the press shop with a paint bake simulation fulfils the highest aerospace standards regarding SCC with lifetimes exceeding more than 720 hours in ASTM G 47 testing. Regarding SCC, copper is beneficial as it enters the ignoble η phase (MgZn 2) and makes it less anodic. Therefore, the is more susceptible to SCC than the AMAG TopForm UHS with some 1.5 % Cu, but fulfils the requirements of the ASTM G47 also in temper T6. AMAG tested SCC according to ASTM G47 and the stricter DIN in an acidic environment and investigated on etching of surfaces and punch cut edges. According to ASTM G47 also punch cut specimens passed. Milled Specimen Punch Cut Specimen Original Original Temper Lot Etched Etched Etched Surface Surface DIN ASTM DIN DIN DIN G47 310, 118 >720 T /01 > > >720 T6 + PB 57844/01 > 720 > 720 >720 >720 Table 4: Stress corrosion cracking of the new AMAG with milled vs. punch cut edges Due to the test results of the DIN AMAG recommends tempering for coarsening of the ignoble MgZn 2 precipitates and copper entering them to reduce the electrochemical potential difference to the aluminium matrix in the grain boundaries. Therefore, the distance of the anodic grain boundary precipitates grows and the potential at the crack tip moves upwards, both reducing the stress corrosion crack growth velocity. The paint bake process (PB) in the automotive process chain is sufficient for the new AMAG to fulfil the requirements for both SCC tests for material delivered in temper T6 with and without etching and punch cut edges. Table 5 shows Transmission Electron Microscopy (TEM) micrographs of AMAG in Temper T4 and T6 with and without a paint bake (PB) cycle. T4 describes the material after solutionizing and seven days of natural ageing. A continuous sequence of small grain boundary precipitates lead to an anodic dissolution in a corrosive environment forced by stresses. With artificial ageing the size of the grain boundary precipitates grows. Moreover,

19 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 19 the distance between them goes up to 200 nm, what is important for the reduction in stress corrosion cracking susceptibility as the anodic reaction velocity slows down. T4 T4+5xPB T6 T6+5xPB Table 5: Transmission Electron Microscopy (TEM) of AMAG in different temper states. 4 Summary / Outlook This paper examined two AMAG 7xxx series AlZnMg(Cu) automotive alloys in combination with WARM, W-Temper and HOT Forming summarized in Table 6. Overall, the feasibility of forming 7xxx series with yield strength of more than 400 MPa for automotive applications was proven with density specific tensile strength on press hardened steel levels.

20 20 Forming of AMAG 7xxx Series Aluminium Sheet Alloys Torsten Grohmann AMAG 7075 AMAG TopForm UHS Forming WARM Forming ++ + W-Temper Forming + ++ HOT Forming Corrosion Stress corrosion cracking ++ + Joining Fusion Welding - + Self-pierce riveting Resistance spot welding Crash Performance WARM Formed ++ + (lateral) HOT resp. W-Temper + + Table 6: Evaluation of AMAG TopForm UHS (AA7075) vs. AMAG WARM Forming starts with peak age temper T6 material with solution annealing and artificial ageing carried out in the rolling mill resulting in uniform mechanical properties and a high ductility combined with an excellent crash performance. In the press shop, a direct contact heating station increases the blank temperature to some 200 C within seconds followed by isothermal forming in warm dies. Low capital expenditure balance limited WARM Forming capabilities compared to W-Temper or HOT Forming. Regarding Warm Forming, AMAG TopForm UHS on basis of the EN AW 7075 performs slightly better compared to the new because of a lower decrease of the strength while heating up due to the presence of the S-Phase. For W-Temper Forming, the press shop has to install a furnace for solution annealing at 450 C with soaking time on a minute scale and a quench right before forming at ambient temperature. The AMAG with a lower quench sensitivity and a slower natural ageing than the TopForm UHS is recommended for W-Temper Forming. HOT Forming makes the quench obsolete with a cooled die forming and quenching the solutionized hot blank. The formability of 7xxx series for both forming processes is comparable to the cold forming of the well know 5182 grade in soft temper O with tribology aspects to be solved for the press hardening MnB5 type equipment for HOT Forming of aluminium. A standard 5-step paint shop process (5xPB) exploits up to 90 % of the full strength potential without employing a separate age hardening furnace.

21 Torsten Grohmann Forming of AMAG 7xxx Series Aluminium Sheet Alloys 21 In terms of corrosion, 7xxx series alloys have a weaker general corrosion performance not acceptable for outer skin but keep the structural integrity. This is especially true for the Cu containing 7075-based AMAG TopForm UHS with an excellent stress corrosion cracking (SCC) performance. A quench rate of more than 80 K/s for HOT Forming is necessary to avoid intergranular corrosion. Corrosion protection coatings and especially the avoidance of punch cuts are recommended for the first use of AMAG in the automotive area. If it comes to fusion welding, solidification cracking limits the use and leads to spot welding, screwing of adhesion for Cu containing 7xxx series. If joining is an obstacle, AMAG with a limited copper content may be a solution. Finally, 7xxx series aluminium sheets offer a high light weighting potential with several concepts for forming available. First series application in the automotive segment e.g. the side impact protection beam of the BMW i8 prove the concept but work is still necessary for a wider use. Shock heat treatment of natural aged AlZnMg(Cu) is worth investigating in the time to come. Literature /1/ Oberhauser P. Sotirov N. Grohmann T /2/ Tomala A Hernandez, S. Rodrigez-Ripoll Badisch, E. /3/ Merklein, M. Lechner, M. Kuppert, A. Performance of high strength AlZnMg(Cu) aluminium alloys after W-temper and warm forming TTP 2013 Conference, 2013 Sept , 2013, Graz Tribological performance of some solid lubricants for hot forming through laboratory simulative tests Tribology International 74 (2014) Trends in der Aluminium Umformung Innovative Umformtechnik, 2012 Nov. 9