Beryllium Precipitation

Beryllium copper gets its strength from heat treatment, not from welding. When welding, you have to be careful that the alloy doesn't overheat and the fine beryllium precipitates dissolve or coarsen. That makes the material softer at the weld and prone to cracking. If you re-age the parts after welding, you get the original properties back. Also, make sure not to inhale any dust or fumes when grinding and welding, that stuff is toxic.