Study On The Welding Technology And Forming Performance Of Multi-gauge High Strength Steel Laser Tailor-welded Blanks

Having largely improved body light weight process in vehicle manufacture, multi-gauge high strength steel laser tailor-welded blanks compliance to the continue development today and must be regarded by lots of auto manufacturers.Since the difficulty existed in the welding of multi-gauge high strength steel laser tailor-welded blanks, welding quality will directly affect the mechanical property. It is very important to study the effect of welding parameter to multi-gauge high strength steel laser tailor-welded blanks.This study used the analyzing of microstructure in welding seam and HAZ as foundation, discussed internal rule among the welding parameters, microstructure and welding specimen mechanical property. It will provide the direction for practice applying.In the second chapter, parameterized Steen W M's heat source model of superposition with point heat source and line heat source by generating function and transferring coordinate, introduced it into studying of multi-gauge high strength steel laser tailor-welded blanks. Theoretic outline of welding seam obtained by the model consistent well to the one got from experiment. We also calculated thermal cycling curve by the mathematics model.In the third chapter, laser welding experiment of multi-gauge high strength steel laser tailor-welded blanks was finished. We only spent very few tries of parameter debugging and obtained correct practical welding parameter with the guiding of the theoretic parameter deduced from second chapter. It avoids the blinding in welding parameter design.In the forth chapter, we discussed effect regularity of different welding power, welding speed, welding heat input to the microstructure and microhardness of welding specimen with longitudinal weld seam. Result indicated (1) width of HAZ will changed by different laser welding power and laser welding speed. (2)the amount of granular bainite and cementite will be changed by different welding power. (3) welding speed affected a lot to the precipitation amount and shape of grain boundary ferrite. (4)grain increase trend in HAZ affected by laser heat input, and use lower heat input can control the increasing trend.In the fifth chapter, we used tensile test to study the specimen mechanical property with different welding parameters. We also studied effect of different welding parameters to mechanical property by the microstructure result in chapter four. The result showed: (1)increase the welding speed appropriately can enhance the plastic nature and ductility of welding specimen if the welding quality is eligible. (2) welding specimen with larger power have lower plastic nature. (3)the true stress-strain curve will advanced by the increase of heat input. It indicated that the plastic ability will be reduced by the increasing of heat input.