November/December AMP_Digital

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 7 higher temperatures and dissolve when the temperature is raised quickly. Short aging times were insufficient to provide adequate strength after paint. RMC’s 2038 alloy (with higher Mg and Si com- pared to 2036) performed much better during short paint bake cycles. Development of X6111 incorporat- ed several other notable composition changes. Cu additions were shown to improve formability and increase the response to paint bake for a 6010 base alloy as shown in Fig. 1 and Table 3. The base composition of X6111 was fixed at ~0.7 versus the 0.3% for 6010. The Fe content was kept low to improve sheet bendability, while an optimum Mn level (0.20−0.25%) was proposed to control grain size and sheet toughness. Alloy 6111 faced the same prob- lem in the U.S. automotive market as 2038 had two years earlier. Ford had only one hood in production, and GM had cancelled most of its aluminum ap- plications. 6111 would see limited ap- plication on some GM hoods, but there was simply no market. The first real customer was AM General, who had en- countered formability difficulties with 6013 on some parts of the Humvee (Fig. 2). Alloy 6111 provided the right combination of strength and formability. COMPOSITES ENTER AUTO MARKET When GM launched the plas- tic-clad Pontiac Fiero in 1983, it sig- naled a switch in strategy—away from aluminum and toward composites as the preferred solution for weight sav- ings. In 1985, GM announced the for- mation of Saturn Corp., devoted to developing and producing convincing rivals to the Japanese imports. When its TABLE 3 — 6111 DEVELOPMENT Alloy Year Producer Si Fe Cu Mn Mg Cr 2036 1970 RMC 0.50 0.50 2.2 - 3.0 0.10 - 0.40 0.30 - 0.6 0.10 2038 1980 RMC 0.50 - 1.3 0.6 0.8 - 1.8 0.10 - 0.40 0.40 - 1.0 0.20 6061 1935 Alcoa 0.40 - 0.8 0.7 0.15 - 0.40 0.15 0.8 - 1.2 0.04 - 0.35 6063 1944 Alcoa 0.20 – 0.6 0.4 0.10 0.10 0.45 - 0.9 0.10 6009 1976 Alcoa 0.6 - 1.0 0.50 0.15 - 0.6 0.20 - 0.8 0.45 - 0.8 0.10 6010 1976 Alcoa 0.8 - 1.2 0.50 0.15 - 0.6 0.20 - 0.8 0.60 - 1.0 0.10 6111 1982 Alcan 0.6 - 1.1 0.40 0.50 - 0.9 0.10 - 0.45 0.50 - 1.0 0.10 Fig. 1 — Effect of copper content on tensile properties of 6010-type alloys. Y.S. = yield strength. P.B. = paint bake [5] . Fig. 2 — AM General high mobility multipurpose wheeled vehicle (HMMWV).