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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 | J A N U A R Y 2 0 1 9 2 8 grain size but can adversely affect hem- ming performance, were limited to low- er levels than competitive alloys. The Cu level was set extremely low: Having formed an alliance with Japan’s Kobe Steel in 1990, Alcoa was well acquaint- ed with the Japanese automakers’ sus- picion of the corrosion resistance of any Cu-containing 6xxx alloy. The improved formability of the 6022 sheet product was largely realized. It exhibited excel- lent flat hemming performance and was capable of forming the difficult in- ner panels for closure parts. Chrysler was the first to put 6022 ABS into production for the skins of the 1997 Plymouth Prowler and for their first mass-production aluminum hood on the 1998 Chrysler Concord. Its adoption by Nissan for the hood and trunk lid of the 2002 Altima sedan validated the decision to adopt a near Cu-free composition. Many of the second generation ABS alloys (Alcoa’s 2008, RMC’s 2010 and 2038) had not survived Ford’s se- lection process in large part due to low strength after paint bake. RMC joined forces with Sumitomo in a collaboration focused on improving the paint bake re- sponse; metallurgists knew that, in real- ity, much of the preciously short time at temperature was spent dissolving pre- cipitates that had formed during natu- ral aging (T4). Metallurgists found they didn’t need a stronger alloy, but needed a tempered product that would harden faster in the short paint bake cycle. Alu- minum suppliers set out to find a “pre- age” process that could be applied at the mill without greatly affecting the T4 strength and formability. The results of the Reynolds/Sum- itomo work enabled the first practical application for pre-aging. Production trials with small coils were run at the Reynolds McCook plant by J.D. Bryant, but installation of commercial equip- ment never took place. The key to their patent was the immediate (within min- utes) reheating of the quenched strip to the desired pre-aging temperature. Bry- ant and coworkers had discovered that room temperature aging of the coils for times as short as one hour severe- ly degraded the beneficial effects of the pre-aging treatment. Thus, using a batch furnace to re- heat the coils after quenching was not possible. The solution was to use an immediate reheat to ~80°-100° C at the exit of the heat treat line. Because large coils inherently cool very slowly, pre-aging takes place as the coil grad- ually cools to room temperature. This method proved to be an effective and economical way to accomplish pre-ag- ing because it did not require extra han- dling of the coils or add an extra step (and cost) to the production path. In Japan, Kobe Aluminum had conducted previous work on the subject of pre-ag- ing with the goal of quenching directly to the pre-age temperature. However, this process proved difficult to imple- ment in production. Reynolds licensed its patent to Alcoa, which was implemented at the new Danville, Illinois, heat treat facili- ty in 1997. Today virtually all lines that produce 6xxx ABS utilize this or similar concepts. Various methods of reheating the strip may be used, and gas or infra- red heaters have been used successfully to heat the moving strip. The properties of T4 sheet are basically unchanged while the paint bake strengths are in- creased by 50-100% (Fig. 7). Pre-aging works well for all the major ABS alloys. Importantly, it makes the near Cu-free alloys such as 6016 capable of developing high strength after paint bake despite their low T4 strength. Different commercial tem- per designations for pre-aged sheet have been used by ABS suppliers: T4P, T4PX, and T43. The original internal Al- coa designation for this temper was T4E29. The pre-aged temper designa- tion T43 was registered with the Alumi- num Association. Practically all ABS for outer panels where dent resistance is TABLE 1 – 6022 AND OTHER ABS ALLOYS Alloy Year Producer Si Fe Cu Mn Mg Cr Zn V 2008 1987 Alcoa 0.50 – 0.8 0.40 0.7 – 1.1 0.30 0.25 – 0.50 0.10 0.25 0.05 2010 1990 RMC 0.50 0.50 0.7 – 1.3 0.10 – 0.40 0.40 – 1.0 0.15 0.30 … 6009 1976 Alcoa 0.6 – 1.0 0.50 0.15 – 0.6 0.20 – 0.8 0.45 – 0.8 0.10 0.25 … 6010 1976 Alcoa 0.8 – 1.2 0.50 0.15 – 0.6 0.20 – 0.8 0.60 – 1.0 0.10 0.25 … 6111 1982 Alcan 0.6 – 1.1 0.40 0.50 – 0.9 0.10 – 0.45 0.50 – 1.0 0.10 0.15 … Ac120/6016 1977/1984 Alusuisse 1.0 – 1.5 0.50 0.20 0.20 0.25 – 0.6 0.10 0.20 … 6022 1995 Alcoa 0.8 – 1.5 0.05 – 0.20 0.01 – 0.11 0.02 – 0.10 0.45 – 0.7 0.10 0.25 … 1997 Plymouth Prowler featuring aluminum skins.