Dimensional Variation in Long Runout Length Direct Extruded 6000 Series Aluminum Alloy

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. The purpose of this study is to report the results of a variation study of extruded product before and after stretching. Results are correlated to position in the extrude length and thermal history related to quench. The post extrusion stretch-to-straighten operation yields different results based on the length of time in quench. This observation led to a more in-depth analysis of % stretch. Results of dimensional variation as function of % stretch are reported with a proposed optimum % stretch to reduce dimensional variation. These results are mapped to the quench duration and delay in the long length runout. Preliminary data is also provided comparing extrusions with different geometries as well.