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In a drive to reduce overall vehicle weight, automotive manufacturers continue to look to aluminum alloys as a solution to provide complex lightweight structures. Precipitation hardened 6000 series aluminum alloys offer a mature commercially viable solution which may be produced using several different forming methods including the extrusion process. In some cases, aluminum products may be produced at a temper suitable for forming and later precipitation hardened to a temper with mechanical properties that meet structural requirements. Direct extrusion press capabilities continue to expand. In an effort to improve productivity, the runout lengths for presses have increased in an effort to reduce dead cycle time inherent to billet heating and loading. Long runouts, however, result in larger differences in pressure applied during extrusion. This pressure variation, confounded with differences in quenching and stretching, causes variation in the extruded product.

6061-O temper extruded rod may be used as feed stock in forming processes for automotive pressure vessel applications. Key parameters for forming are the strength and hardness of the material. The purpose of this paper was to reduce variation in hardness to achieve a process capability index of 1.33 or greater. Among the process steps affecting hardness, annealing is the most critical. Initially, the process showed unacceptable hardness variation. Initial anneal recipes called for a 4-hour soak at 775°F (413°C). Initial process capability for hardness was a Cpk of 1.12, with tensile strength readings very close to the upper specification limit. Initial temperature uniformity surveys of the anneal oven showed a large variation in temperature distribution, with some areas of the oven staying below 650°F (343°C). Initial improvement efforts focused on soak time.