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A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 8 1 9 After extensive design iterations, the new concept went into produc- tion on some GM hoods and achieved full optimization years later on the 1997 Ford Ranger. The hood featured a 0.85-mm outer and 0.8-mm inner us- ing 6111-T4 (Fig. 5). In practice, the de- sign created some difficulties. It only became strong after the adhesive had cured, necessitating special handling precautions until then. The most diffi- cult issue was that it was impossible to correct small dents on the skin because the hood inner prevented access. Originally, Alcoa pushed alloy 2008 as a hemmable replacement for 2036 that would also enable a downgaug- ing from the contemporary 1.0 mm to 0.9 mm on the strength of its superior hardening performance. Unfortunate- ly, the alloy development team failed to notice changes in the E-coat process. New formulations had enabled the paint shops to lower the cure tempera- ture from the previous 215°C to 175°C (425°F to 350°F). Alloy 2008 did not re- spond adequately to such a low tem- perature, so it failed as an outer skin solution. However, it did offer improved formability over 2036, and most impor- tantly, its lower yield strength in T4 sig- nificantly reduced the springback of inner panels. This provided a meaning- ful reduction in tool development time, and more than anything else, this factor propelled it into production on Ford’s 1992 Crown Victoria hood inner, whose design mirrored the Town Car. Alloy 2008 made history when it enabled the only part ever to switch from steel to aluminum—gauge for gauge in the same tools—for the Ford Panther plat- form differential cover. RMC responded with 2010-T4, but apart from several tri- als, it never made it into production. ASIAN INTEREST PEAKS Interest in aluminum auto body sheet was not confined to the U.S. or Eu- rope. The Japanese manufacturers had also taken notice, but they proceed- ed cautiously. Similar to the U.S., Jap- anese interest in aluminum auto body sheet began in response to the 1973 oil crisis. However, unlike the U.S. ap- proach, Japanese aluminum producers followed a collaborative method, ini- tiating studies with the automakers to help define critical characteristics. The response was that formability was the most important attribute and strength was secondary. Unlike their U.S. coun- terparts, the Japanese aluminum com- panies could focus efforts on clearly defined objectives, supported by po- tential customers. Starting in 1978, their goal was to develop a skin-capa- ble alloy with better formability than 5182-O, but one that would not suffer regression during the paint bake cycles. It also meant they had to find a way to prevent Lüders bands. The industry fol- lowed Alcoa’s original approach, fo- cusing on 5xxx alloys, and adding Cu to stabilize the yield strength during baking. The first alloy to see production was Sumitomo’s GZ45, used by Mazda on the RX-7 Turbo II [7] . Natural age hard- ening issues later prompted deletion of zinc and the resultant alloy was re- named GC45. The search for improved formability continued, pushing Mg levels higher. Practical considerations stopped the Mg race at 5.5%. Oth- er companies followed a similar path, like Kobe’s KS5022, KS5023, KS5030, KS5230, and KS5032 and Sky Alumi- num’s TG series, developing alloys with high Mg, added Cu, and sometimes Zn [8] . These alloys sawmultiple applica- tions in the Japanese domestic market, with only selected models exported. The limitations of these types of alloys soon became evident and the focus switched to 6xxx. The Japanese market had two unique conditions: First, E-coat oven temperatures were already down to 175°C and second, the TABLE 5 — EARLY JAPANESE ALLOYS Alloy Year Producer Si Fe Cu Mn Mg Cr Zn 5182 1967 Alcoa 0.20 0.35 0.15 0.20 - 0.50 4.0 - 5.0 0.10 0.25 GZ45 1978 Sumitomo 0.25 0.40 0.30-0.40 0.20 4.0 - 5.0 0.10 1.4 - 1.6 GC45/5022 1995 Sumitomo 0.25 0.40 0.20 - 0.50 0.20 3.5 - 4.9 0.10 0.25 GC55/5023 1995 Sumitomo 0.25 0.40 0.20 - 0.50 0.20 5.0 - 6.2 0.10 0.25 Fig. 5 — 1997 Ford Ranger “teacup” hood inner. 1991 Acura NSX, Honda’s all-aluminum supercar.