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Schlagworte
- AZ31 Magnesium Alloy (1)
- Aluminium alloy (1)
- Arc Weld (1)
- Corrosion Fatigue (1)
- Crack growth (1)
- Salt Water (1)
- Solidification cracking (1)
- Strain rate model (1)
Gas tungsten arc welds made on wrought magnesium AZ31 plate have
been characterized for corrosion in saline solution (3.5% NaCl). Microstructural
changes induced by the welding process resulted in different
environmental behaviour of each zone (BM-base metal, HAZ-heat affected
zone and FZ-fusion zone). The faster kinetics of corrosion in FZ and especially
HAZ are attributed to (a) the coarse microstructure, consisting of
large grains, and (b) very small amounts of ß-phase in the grain boundaries.
Also, hardness traverses have shown that these zones are weaker
than the base metal. Based on the significant effect of grain size on strength
in magnesium alloys, the weld metal grains have been systematically refined
using controlled oscillation during welding, and by adding a grain
refiner to the weld pool. Detailed microstructure analyses have been carried
out and the relationships between corrosion behaviour, mechanical
properties and microstructure (grain refinement and second-phases formation)
are highlighted.
The occurrence of solidification cracking during welding remains a little understood phenomenon, in spite of extensive studies and tests performed to evaluate and compare the relative weldability of many different alloys. From an approach often adopted in the welding community attributed to Prokhorov, solidification cracks are believed to form when a critical tensile strain is exceeded, specific to the alloy, assuming that the mushy-zone has limited ductility. Tensile stresses and strains normally form behind a moving weld pool as a result of solidification shrinkage and thermal contraction, as influenced by welding parameters and the degree of restraint.