Formability and Fatigue Behavior of Tailor (Laser) Welded Blanks for Automotive Applications

The drive towards weight reduction in the automotive industry has led to the use of tailor welded  blanks  (TWBs).  This  work  is  aimed  at  evaluating  the forming  and fatigue  behavior  of  the  TWBs  with  different  thickness  combinations  and compositions. Forming tests were carried out to determine the forming limit diagrams (FLDs) of the TWBs, and compared with those of the individual steel sheets. The results showed that the FLDs of the TWBs lie in-between those of the individually formed steel sheets that comprise the TWBs. A semi-empirical relation based on the mean values of the strain-hardening  exponents (n-values) and of the thickness of the base metals was developed to calculate the FLDo of the TWBs. The calculated FLDo  values  were  found  to  be  in  good  agreement  with  the  experimentally determined  values.  The  fatigue  tests  showed  that  TWBs  made  from  zinc coated/galvanized steels exhibited a lower fatigue limit, as compared with the TWB combinations  from  comparable  uncoated  steel.  This  was  attributed  to  the intergranular  cracking  in  the  galvanized  TWBs,  caused  by the  presence  of  zinc penetrating beneath the sheet surface.