Lightweight bicycle had been fabricated from aluminium alloy tubing, with joints made by adhesive bonding. When the frame fractured near one of the joints, the owner requested that a repair be made using conventional gas tungsten arc welding. Shortly thereafter, the frame broke again. This time the fracture was adjacent to the repair weld and the the characteristics of the break were different. The first fracture was somewhat brittle in nature, the second fracture occurred in the tube material, not the weld itself.
If the material had been cold drawn aluminium tubing (i.e. strain hardened), explain what might occurred during repair. What is the possible cause of the second fracture?
The Attempt at a Solution
Cold drawn products could have internal cracks which the heat from welding causes thermal cracks to occur.