STTR Friction Stir Processing for Superplastic Forming

Friction stir welding (FSW) is a solid state joining process with unique characteristics that offer opportunities for cost savings, new fabrication methods, and new structural designs. FSW eliminates many of the problems associated with fusion welding techniques. In addition, FSW generates a “stir zone” microstructure that consists of very fine, equiaxed grains that are ideal for post-weld forming operations such as superplastic forming. Superplastic forming (SPF) with diffusion bonding (DB) has been used in titanium alloys in the past to create low-cost, integrally stiffened components with significant geometric complexity. This powerful combination of processes offers considerable design flexibility and low production costs for high-performance applications, especially in the aerospace industry. Multi-sheet SPF/DB structures with complex external geometries with integrally constructed internal stiffening elements are used in numerous aerospace applications. By replacing DB with FSW in aluminum then using SPF for panel structures, a new technology emerges that will have a vast number of applications in commercial and government aerospace and land based transportation systems. The effort defined here will develop and demonstrate processing methods for combining FSW and SPF. FSW/SPF panels will be built and tested to validate the overall process, as well as examining material properties. BENEFITS: The lightweight yet structurally strong panels using FSW/SPF will reduce weight and cost in military applications: navy ships, ground based vehicles and aircraft. The same benefit will apply for commercial transport aircraft. The potential applications are vast and will revolutionize an entire segment of manufacturing for the light, strong panels that comprise the backbone of these applications. Eventually, with the development of rapid manufacturing methods, this technology will be an important component in automotive manufacturing.