Improvement In Ductility Of Friction Stir Welded Al-mg-si Alloy T4 Sheet

摘要

Tailored blank for body panels is an ecological technology, but there are few practical examples in aluminum alloys. In addition, press formability of welded Al-Mg-Si alloy sheet is relatively low because of softening in the heat affected zones (HAZ) near the weld line. In terms of welding method, high quality joints can be achieved by friction stir welding (FSW) because the welding is carried out under the melting point of the base metal. In this study, improvement of formability was examined in the friction stir welded Al-Mg-Si alloy T4 sheet. The hardness of the FSW joint was the lowest in the HAZ, while those in the parent metal and the stir zone were higher. The hardness in the stir zone was the lowest immediately after welding, but it became almost the same as parent metal after natural aging because of its higher age hardening rate. On the other hand, the hardness in the HAZ slightly decreased because of heat generation during FSW. This hardness after natural aging became the lowest because it increased a little. The heat treatment subsequently after FSW was examined to improve above problem. The hardness distribution of the joint was improved by the heat treatment. That is, the hardness in the parent metal became the lowest by the heat treatment. As the result of the heat treatment, fracture was occurred in the parent metal by tension test, and the elongation was improved. Moreover, the maximum forming height in dome height test increased by 15%.