The Latest Trends in Aluminum Alloy Sheets for …

1 The Latest Trends in Aluminum Alloy Sheets for automotive Body Panels Takeo SAKURAI; Material & Process Research Section, Aluminum Sheets & Coils Department Moka Plant, Aluminum &. Copper Company .. developmental status of Aluminum Alloy Sheets for .. automotive panels.. In 1985, the Mazda RX-7 applied Aluminum Alloy .. sheet for its body panel (hood) for the first time in .. Japan. Since then, Aluminum panels have been used .. mostly for sport cars and luxury sedans until early 1990s. Honda Motor Co., Ltd. presented the all- .. Aluminum body NSX for the first time in the world. Subsequent collapse of bubble economy reduced the Automobiles are becoming heavier in order to satisfy applications of Aluminum panels to new models, requirements such as safety ( , collision safety and however, Aluminum panels started to be used again pedestrian protection), drivability, comfort and in around 1999 when global environmental issues larger interior space.

2 Meanwhile, automobiles have became a major concern. lists the vehicle to meet more stringent regulations against exhaust models in Japan using Aluminum panels as of 2006. emissions, including CO2 and NOX emissions, to More recently, Aluminum panels are being used for protect the environment. The European Commission, a wider variety of models, such as the Toyota Crown for example, has announced a policy to reduce CO2 ( ), Toyota Prius, Subaru Legacy, Nissan Fuga emissions down to 140 g/km or less by 2008 and to (Infiniti M35/M45, . )6) and Nissan Skyline 130g/km or less by 2012. Japanese regulations to reduce CO2 emissions will also be tightened to a level Table 1 Examples of Aluminum closer panels for automobiles comparable to that of the European Commission by Car maker Model Application parts 2012.

3 Thus, reducing fuel consumption is now CROWN Hood imperative for all the automobile manufacturers. TOYOTA CROWN MJ Hood Various measures are taken to reduce fuel PRIUS Hood, Back-door consumption including new power trains involving LS Hood hybrid systems or advanced diesel engines. Above GS Hood TOYOTA(LEXUS). all, automotive weight reduction is regarded as one SC Hood, Roof of the most effective means for decreasing fuel IS Hood consumption. One hundred kilograms of weight DAIHATSU COPEN Hood, Roof reduction improves fuel consumption by 1 km/L, FUGA Hood, Door, Trunk-lid according to the Japanese 10-15 mode measurements1). CIMA Hood, Trunk-lid automotive weight reduction has been achieved NISSAN SKYLINE Hood traditionally by reducing thickness of steel- sheet STAGEA Hood body panels by increasing the strength of the steels, Fairlady Z Hood however, this approach is limited because of the LEGACY Hood, Back-door resultant reduction in panel stiffness.

4 For this reason, SUBARU INPRESSA Hood lighter materials are being studied extensively to FORESTER Hood replace the steels. Especially, Aluminum alloys have RX-8 Hood, Rear-door MAZDA. started to be used for various automotive parts for its ROADSTER Hood, Trunk-lid low specific gravity (approximately 1/3 of steel). LEGEND Hood, Trunk-lid, fr-fender HONDA. Now the use of Aluminum Alloy is not limited to S2000 Hood conventional castings such as engine blocks, but LANCHER Evo. Hood, Roof, Trunk-lid extends to hoods, trunk lids, outer panels such as doors MITSUBISHI PAJERO Hood and protection covers including heat insulators2)-5). AUTORUNDER Roof The present paper describes the Latest Trends and Source Japan Aluminum Association KOBELCO TECHNOLOGY REVIEW NO. 28 OCT. 2008 22.. shows the development history of Aluminum Alloy Sheets for automotive panels9).

5 In Japan, Al-Mg alloys with minor addition of Zn were first used when Aluminum Alloy Sheets started to be used for automobiles in 1985. Around the same time in EU. and USA, either 2000 series (Al-Cu) alloys or 6000. Source Toyota Motor Corporation series (Al-Mg-Si) alloys with minor addition of Cu Fig. 1 Example of application of Aluminum hood (TOYOTA. were used to serve the purpose. Currently, as the CROWN) requirements for automotive panels has diversified, 6000 series (Al-Mg-Si) alloys are predominantly used Al- sheet Trunk-lid . worldwide with a few exceptions of 5000 series (Al- Hood Al- sheet Mg) alloys . This is because the requirements for the material properties now include not only strength and formability, but also corrosion resistance, hemming formability, surface characteristics and weldability.

6 Presents the compositions and properties of typical Aluminum alloys used for automotive Door Al- sheet panels8). The 6000 series alloys constitute the Fig. 2 Example of application of Aluminum body panel mainstream of alloys used for automotive panels (NISSAN FUGA)6 because they are heat-treatable and their strengths can easily be controlled by heat treatments. In (Infiniti G35). Many Aluminum panels are used for addition, the 6000 series alloys may also be adapted hoods or bonnets. Recent models employ Aluminum to exhibit bake hardening which occurs during the panels for trunk lids, rear doors and roofs7), 8). baking step after painting in the automotive In Europe, automotive use of Aluminum raised manufacturing process. The bake hardening features sharply between 2000 and 2002.

7 Aluminum Alloy of the alloys improve dent resistance and enables panels are now used for more than million reduction of the sheet thickness and weight. The bake vehicles every year. The Renault Clio (sold as hardenability depends on the baking conditions Lutecia in Japan) is a high volume model employing which differ slightly by countries. The baking an Aluminum Alloy panel for its hood, and about process is treated at higher temperatures, around 180. forty thousand vehicles of the model are produced to 200 C, in EU and USA, while the treatments at every month. Other examples of high volume models lower temperatures for short period ( ,170 C x 20. include the Mercedes-Benz E-class and BMW 5 min) are preferred in Japan. The alloys for outer series, both of which are produced in volumes panels are required to harden under the baking greater than twenty thousand a month.

8 Furthermore, conditions described above, however, conventional the uses of Aluminum Alloy panels in those vehicles 6000 series alloys were unable to harden sufficiently are expanding. The BMW 5 series, for example, has under such conditions. Extensive studies10)-12) revealed an all- Aluminum frame and panels for the structure that pre-aging steps as shown in provides bake in front of its A-pillar. Audi presented, as early as 1992, an all- Aluminum body car, the Audi A8, having Table 2 Development history of Aluminum Sheets for a space frame structure and is regarded as a automotive panels forerunner in the use of Aluminum panels for 1985 1990 1990 1998 1999 2005. automobiles. In 2006, after presenting the Audi A2. Al-Mg Series Alloy Al-Mg Series Alloy Al-Mg-Si Series Alloy and new Audi A8, the company started using a High strength & AA5022, AA5023 High bakehardability hybrid material structure for the new Audi TT JAPAN.

9 High formability High formability Al-Mg-Si Series Alloy Hemming model, in which steel Sheets are partially used with High bakehardability SS mark free an Aluminum space frame and joined together. The High formability Al-Mg Series Alloy expanding automotive use of Aluminum in Europe Al-Cu Series Alloy Al-Mg-Si Series Alloy Al-Mg-Si Series Alloy seems relevant to the more stringent regulation on AA2036, AA2008 AA6022, AA6016 AA6022, AA6016. US & EU. CO2 emissions which becomes compulsory in 2012. Al-Mg-Si Series Alloy Al-Mg-Si Series Alloy AA6009, AA6010 AA6111. 23 KOBELCO TECHNOLOGY REVIEW NO. 28 OCT. 2008. Table 3 Chemical compositions and mechanical properties of Aluminum alloys for automotive body sheet Chemical compositions (wt ) Mechanical properties Alloy TS YS El. Si Fe Cu Mn Mg Cr Zn Ti n-Value r-Value (MPa) (MPa) ( ).

10 AA5022 275 135 30 5000 AA5023 285 135 33 . series AA5182 265 125 28 AA5052 190 90 26 AA6022 275 155 31 6000. AA6016 235 130 28 series AA6111 290 160 28 Developed 6000 series Alloy Conventional 6000 series Alloy Solution heat 350. treatment Aged at 170 . 300. Proof stress (MPa). 250. Developed process 200. 100 2h 150. 70 Pre-aged at 50 . 100 Pre-aged at 70 . WQ Pre-aged at 100 . 50. Conventional process T4 10 100 1,000 10,000. AS Aging time (min). Fig. 3 Effects of pre-aging on bake hardenability in 6000 series alloys 50nm days Fig. 4 TEM microstructures of aged 6000. 1 23 7 30. series alloys (aged at 180 for Pre-aging (aged at 50 for 2h) 60min). Reversion 80 represents the microstructure of a newly developed Alloy which can be hardened during low temperature 70. Hardness (HV). baking.