It is demonstrated how the current trend towards high speed, narrow groove welding, and the corresponding shift towards high base metal dilution, may result in decreased weldability for 6xxx and 7xxx aluminium alloys. In particular, variations in base metal dilution for extrusion alloys 6082 and 7108 have been examined for welds made with 5183, 5356, 5654, and 4043 filler alloys, particularly at high dilution ratios. The less common filler alloys 5039 and Safra 66 are also considered Dilution curves superimposed upon existing hot cracking curves show that cracking susceptibility increases rapidly with base metal dilution for these alloys. Establishing an upper limit for dilution to avoid hot cracking, for a specific engineering application, also requires a knowledge of restraining conditions. For conditions of high restraint, i.e. rigid fixturing, enforcing an upper limit for base metal dilution will become critical. The effect of dilution on weld strength is also considered. (C) 1997 The Institute of Material.
