Abstract
The authors have investigated on surfacing technique on aluminum alloys by using gas tungsten arc welding (GTAW) process. The used filler metals were composite cored wire of seamless tube type and 1.2 mm in diameter. They were of Al-Cu composition with varied copper contents of 60, 70 and 80%. Each wire consisted of a copper tube sheath and an aluminum solid wire enclosed.
The authors investigated the effects of arc current and weld cooling rate on microstructure, hardness distribution and porosity formation. They studied through chemical analysis the oxide film that covered the surfacing weld metal. They also analyzed the gases evolved in vacuum from machine cut porosities.
The hardness in cross section of Al-70%Cu surfacing weld metal decreased from 270 HV to 170 HV with an increase of surfacing current in the case of helium shielding. Helium shielding drastically reduced the porosities that existed in the case of argon shielding. The remaining porosities became smaller than 0.2 mm in diameter. Moreover, the dual shielding by argon-helium gases was found to eliminate perfectly the porosity formation in the surfacing weld metal. Chromatography analysis revealed that the gas in porosities was dominantly hydrogen. The thickness of oxide film on the argon shielded weld metal surface was found to be remarkably greater than that of helium shielded weld metal, and thereby it might have caused more porosities in the case of argon shielding.
