Characterization of tensile properties of tailor welded IF steel sheets and their formability in stretch forming

Use of laser welded blanks of multiple sheets of material prior to forming is one of the current interests of automotive industries as it reduces manufacturing cost and weight and also improves the quality of the components. As the demand for different types of tailor welded blanks is increasing, the effects of difference in material properties, surface characteristics, weld properties and its orientation on blank formability become important in various forming processes. In this study the properties of laser welded interstitial-free steel sheet samples of different thickness and samples of same thickness but with different surface characteristics (galvanized and un-galvanized) have been characterised. The tensile properties of the welded specimens have been determined in both longitudinal and transverse directions. Weld quality has been evaluated with the help of microstructure and micro-hardness tests. Formability of these two types of tailor welded blanks has been studied by performing out-of-plane stretch forming tests using a hemispherical punch. Both experimental work and finite element analysis have been done to study the effect of thickness difference and surface properties on the formability and strain distribution. It has been found that the limiting dome height and strain distribution are greatly influenced by the difference in thickness within the blank but the difference in surface condition has a very minor effect on the overall formability.