Abstract
Behavior of TIG arc spot welds of Al alloy A5083 thin plate during cooling and solidification process was investigated by the following methods.
Temperature of welds was measured during heating and cooling process by using very slender thermocouples. Weld specimen was broken at any time during cooling and solidification process by using a high speed breaking apparatus.
Afterwards, morphological macro- and micro-structures of fracture surface were observed using electron microscope.
The results obtained are as follows:
1) There developed a liquefied grain boundary, which is called a brittle zone, and a partial liquefied grain boundary, which is called low ductility zone, in HAZ when some time passed after arc stop.
2) Solidification end was determined by confirming disappearance of liquid phase on fracture surface. As a result, it was found that the temperature of solidification end of weld metal was considerably lower (440-425°C) than solidus temperature (579°C) of base metal.
3) CCSP diagram was obtained from fractography analysis by determining solidification end, which was difficult to determine from analysis of cooling and solidification curve.
