Metal Matrix Composite Structures Tooling and Fabrication Processes 700752
An extensive secondary fabrication program was conducted in aluminum-boron composite material under both contract and independent research and development funding. Forming, joining, and machining of diffusion-bonded sheet material was investigated during the fabrication and final assembly of a fullsized missile payload adapter. Brake bending was done at room and elevated temperatures with the filaments in various orientations. Stretch forming was attempted. The minimum radius of bend of roll formed sheet was established. Joining studies included mechanical fastening at various thicknesses and orientations. Fusion welding was unsatisfactory due to the melting of the filaments. Resistance spot welding was highly successful and good weld strengths and properties were obtained. Machining of composites was done with diamond tools. Chipless methods proved satisfactory with such processes as electrodischarge and ultrasonic machining. Tape consolidation by both high-pressure bonding and low-pressure braze bonding was used to produce tubes, I-beam, and angles from aluminum-boron. Mechanical tests proved the high strength of the composite shapes.
Recent investigations include methods of increasing transverse strength such as stainless steel wire, titanium-backed tape, and heat treatment of matrix. Some of these investigations are summarized and recent developments in secondary fabrication and autoclave technology are discussed in detail. The current state-of-the-art in aluminum-boron processing is discussed along with advantages and disadvantages.