Metallurgical aspects in laser welding of steels and aluminum alloys

Abstract

Rapid cooled microstructures, solid state transformation, hardness distribution, porosity formation, hot cracking and crack susceptibility are discussed as the metallurgical aspects in laser welding of carbon steels, stainless steels and aluminum alloys in present paper. In the cases of CO2 and YAG laser welding, the thermal cycles during welding of carbon steels showed a rapid heating rate of 10 5 k/s and a rapid cooling rate of 10 4 k/s.The solid state transformations during the thermal cycle are different from that in steel welds by arc. The microstructuture in heat affected zone is consists of ferrite band or matrix and hard martensite colonies with high carbon. It seems a kind of composite materials. The hardness distribution of steel welds by laser is different from that of arc welds in which the location of maximum hardness is coarse grain zone. However, it is the center of fusion zone or near the base metal in laser welds of carbon steel. Even in ultra low carbon steel welds, the hardness of weld metal is higher than 200 Hv and the microstructure is bainitic ferrite and low carbon martensite which have a low cold crack susceptibility.In addition, two mechanisms of porosity formation in laser welding of aluminum alloys including A3003, A5052, A5083, A5182 and A6061 alloys were investigated using the fundamental knowledge and the solidification crack susceptibility in laser welding of A5052, A5083, A6061 and A7N01 alloys were studied for the application of laser welding in industries.Rapid cooled microstructures, solid state transformation, hardness distribution, porosity formation, hot cracking and crack susceptibility are discussed as the metallurgical aspects in laser welding of carbon steels, stainless steels and aluminum alloys in present paper. In the cases of CO2 and YAG laser welding, the thermal cycles during welding of carbon steels showed a rapid heating rate of 10 5 k/s and a rapid cooling rate of 10 4 k/s.The solid state transformations during the thermal cycle are different from that in steel welds by arc. The microstructuture in heat affected zone is consists of ferrite band or matrix and hard martensite colonies with high carbon. It seems a kind of composite materials. The hardness distribution of steel welds by laser is different from that of arc welds in which the location of maximum hardness is coarse grain zone. However, it is the center of fusion zone or near the base metal in laser welds of carbon steel. Even in ultra low carbon steel welds, the hardness of weld ...