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- Englisch (8)
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- Corrosion behavior (3)
- Microstructure (3)
- AZ31 Magnesium Alloy (2)
- AZ31B (2)
- 7108 aluminium (1)
- Alloy 7108 (1)
- Aluminium alloy (1)
- Arc Weld (1)
- Circular patch test (CPT) (1)
- Corrosion Fatigue (1)
Polyvalent Ions - Their Behaviour in the Glass Melt and their Influence on Glass Crystallisation
(1998)
The relation between microstructure and corrosion behavior of GTA welded AZ31B magnesium sheet
(2007)
Welding of AZ31B magnesium alloy was carried out using gas-tungsten arc (GTA) welding. The microstructure and the corrosion behavior of welded magnesium AZ31B alloy were investigated. ac and dc polarization tests were carried out on the welded Mg sheet. The microstructure was examined using optical and electron microscopy (TEM and SEM), X-ray analysis and EDS. Scanning Kelvin probe force microscopy (SKPFM) was used in order to measure the Volta potential of different phases relative to the matrix. The results showed that the GTA process effected both the microstructure and the corrosion behavior. These results can be explained by the effects of the process on microstructure of AZ31B Mg alloy sheet such as grain size and precipitates caused by the change in precipitation and recrystallization behavior.
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.