High Energy Hydroforming Friction Stir Welded 2050 Al-Li Blanks for Aerospace Domes and Cones

Friction stir welded aluminum (FSW) blanks offer larger blank sizes than available at the mill in single width plates. Large blanks made from aerospace-grade aluminum alloys are essential for making large domes and cones for launch vehicles and crew vehicles. Previous research efforts have demonstrated >5m FSW blanks can be formed into large domes or cones using spin forming, but the subsequent solution heat treatment consistently led to Abnormal Grain Growth (AGG). The AGG phenomenon occurs because the FSW blanks must be spin formed in the -O annealed temper to withstand the high strain process without cracking. Unless mitigated by a complex thermomechanical treatment the solution heat treatment process may lead to the onset of AGG where a small number of grains grow much larger than the surrounding matrix. The large grains and bimodal grain-size distribution ultimately leads to unacceptable ductility in the short transverse direction of the part. Alternatively, explosive hydroforming is a nascent process that can be applied to large and thick aerospace-grade aluminum alloy blanks in the -T3 temper and only require a post-forming artificial aging process to a -T8. Ability to produce T84 properties offers a significant tensile property advantage over the lower T62 properties available via the conventional spin forming, SHT and aging process. It also simplifies the process and eliminates distortion and residual stresses that may be generated during the post SHT water quench of the parts. Avoiding the SHT process mitigates AGG and also eliminates the need for almost nonexistent drop-furnace quench baths that can accommodate a part size larger than 5m in diameter. This presentation summarizes a Lockheed Martin-led effort that demonstrated explosive hydroforming of a of a 1.9m diameter, 39mm thick 2050 aluminum lithium FSW blank. Details will be provided on the process flow, mechanical properties, and metallography. This work was performed in partnership with NASA Langley Research Center (LaRC) under a NASA Announcement of Collaboration Opportunities program. Test material, 2050-T34 plate, was supplied by Constellium who developed the aging practice needed to attain the T84 properties.