American Machinist

Welding beryllium takes special care: because of the metal's sensitivity to weld cracking, pay particular attention to grade selection and processing variables.

ALTHOUGH BERYLLIUM is weldable by gas-tunsten-arc (GTA), gasmetal-arc (GMA), and electron-beam (EB) methods, precautions are required to ensure sound welds, reported Mary Ann Hill, Brian K. Damkroger, and Raymond D. Dixon, staff members, Los Alamos National Laboratory Los Alamos, NM) and Erica Robertson, Air Force Office of Scientific Research, Bolling Air Force Base (Washington, DC), at ASM Intl's (Materials Park, Ohio) Weldability of Materials Conference in Detroit last October. The precautions are required, they noted, because of the metals's sensitivity to hot cracking at defects, and sub-solidus cracking.

Hot cracking is attributed to an aluminum-rich grain-boundary film that results from the rejection of aluminum during solidification due to the high partitioning coefficient (ratio of solid to liquid metal in solution) of aluminum in beryllium, and the marked difference in the melting points of the metals: 660'C and 1289'C respectively. This problem is accentuate at the weld centerline because of th greater concentration of aluminum, grain boundary orientation, and high tensile stresses normal to the weld.

Material defects, such as oxide particles, voids, and inclusions may act as sites for weld defects. The greater the oxide content of the metal, the greater the occurrence of weld undercutting and porosity. These weld defects, which limit ductility, stem from a beryllium-oxide film that forms on the surface of the weld pool and has the appearance of a flux. The film interferes with the welding process and increases weld-pool turbulence, causing the metal to erode unevenly and the film to mix into the weld pool. …

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