Research On Mechanical Properties And The Distortion Behavior Of Weld Joint Of Tailored Welded Blanks

The further processability and usability of weldment are determined by mechanical properties of welding joint. Microstructure and properties of the joint could change after welding, and these changes would make a influence on the comprehensive properties of the welding joint. Then it could occur buckling deformation in welding thin plates, and this could inevitable even for the high-energy density welding like laser beam welding. The tailored blanks of thin plates are widely used in manufacturing industry especially in automotive, because they have lots of advantages like saving material, convenient welding, good design flexibility and so on. Nowdays, though the demand of these tailored blanks are increasing, the konwledge of deformational behavior in welding and the characteristic of mechanical behavior of the joint are not sufficient.In this study, the mechanical properties of the joint of the tailored blanks with dissimilar thickness were investigated by experiment, and together with the finite element method the rule of stress-strain and the deformation of the weldment were studied. Firstly, microstructure and mechanical properties of joint which was gotten from plate HC340LAD+Z and plate HSLA340+Z with thickness of 1.7mm and 2.6mm respectively were researched. Secondly, a heat source model was established and its reliability was also verified by the following tests, and then the influence of welding process to the destribution of temperature-sensitive was studied. Finally, the deformational behavior and the forming mechanism of tailored blanks with dissimilar thickness were studied.The results show that, 1) the welding formability of thin plates with dissimilar thickness by laser is good, the transition of weld beads are smooth and the appearance of the whole weldment seemed fine. There are large lath-shaped martensites across the weld with tiny acicular ferrite and grainy carbide among them. In the heat affect zone there are pearlite and which are finer than those in the base metal. The strength of the joint is higher than that in the base metal, and the weld metal have the ability of deformation in some degree. 2) the 3D Gauss heat source model matches the laser welding well in this process. The phenomenon of thermo-sensitivity in welding is controled by optimizing the welding technological parameters, and finally the mechanical properties of welding joint are improved. 3) the temperature difference and also the stress difference between the top and the bottom surfaces that adjacent to the thick side in the weld region are higher in the welding joint with dissimilar thickness. And finally, the deflection in the thick plate side is a little higher than that in the thin one.