Ductility characteristics of commercial aluminium alloys between liquidus and solidus temperatures during welding and evaluation of weld solidification cracking susceptibility

摘要

This paper describes an investigation of the ductility characteristics of solidifying weld metal by external restraint solidification cracking tests, i.e. the Trans-Varestraint test and slow-bending Trans-Vares-traint test. The minimum augmented strain necessary for crack initiation (ε_(min)), brittleness temperature range (BTR), and critical strain rate for temperature drop (CST) are selected from the ductility characteristics as criteria for evaluation of the weld solidification cracking susceptibility. The solidification cracking susceptibility of 16 types of 1000-7000 series commercial aluminium alloys is also qualitatively evaluated by self-restraint solidification cracking tests, i.e. the ring casting test, GTAW crater test, Houldcroft test, and fan-shaped test. The grain size of the weld metal, the dihedral angle of eutectic products at the grain boundaries and the amount of eutectic products are also measured as metallurgical factors. The correlation between the results obtained in the self-restraint cracking tests and the criteria adopted for the ductility characteristics and metallurgical factors are discussed. CST is the most suitable criterion for evaluation of the weld solidification cracking susceptibility of Al alloys, because the crack susceptibility monotonically decreases with an increasing CST. ε_(min) and BTR are also important criteria for indication of the threshold at which the crack susceptibility begins to increase sharply. When ε_(min) > 0.22% and BTR < 43℃, Al alloys show very low solidification cracking susceptibility. Among the metallurgical factors, the dihedral angle and grain size are well correlated with the solidification cracking susceptibility, whereas the amount of eutectic products is not.