Analysis about formation and microstructure of laser-weldingtailored-blanks with unequal thickness of high strength steels

Two kinds of high-strength-steel sheets, HSA340 (2.0 mm, 1.5 mm) and H340LAD+Z(0.7 mm), were introduced.They were arranged in pairs and welded together by laser welding on principle of similar strength but unequal thickness.The special cross-section of welded joints was chosen for metallographic examination and hardness measurement.The results show, in the welding process, the microstructure of the weld will have great diversity at local region closing each parent metal because of the different cooling condition of each parent metal.The width of heat affected zone (HAZ) in laser-welding-tailored-blanks is narrow, the remarkable boundary divides the HAZ with the parent meal and weld, and not only the grain size but also the microstructure in the HAZ are also fine.And the hardness of the weld and the HAZ are higher than that of parent metal.The joints of tailored blanks will be obviously improved when the incident position and incident angle of laser beam were set rationally.