INVESTIGATIONS ON FORMABILITY OF A 2-PLY LAMINATE COMPOSITE SHEET METAL AT ELEVATED TEMPERATURE

Abstract

In pursuit of newer lightweight components, metallic laminate composite sheet, also termed as clad sheet, emerges as a solution to meet the demand for automotive and aerospace applications. The present work focuses on the effect of warm forming temperature on the tensile properties, microstructural characteristics, formability, and residual stress of a 2-ply clad sheet composed of SS430 and AA1050 layers with total thickness of 2mm. Four different temperatures are selected for characterization: room temperature, 180°C, 220°C, and 300°C. The tensile properties of the clad and the individual layers are determined as per ASTM E8M standard using a universal testing machine integrated with an environmental chamber facility. The normal and planar anisotropy of the clad sheet and individual layers are determined by evaluating the R value (Lankford value) in directions 00, 450 and 900 with rolling direction. The tensile properties and anisotropy are used to predict the finite element simulation of the deep drawing. An analytical model is also developed to determine the punch force during the deep drawing operation, incorporating the anisotropy of the parent layers. The microstructural investigations of the clad interface and the parent layers are done through electron back scatter diffraction technique. The thermo-mechanical effects on the different texture components of the material like pole figures, inverse pole figures, kernel average misorientation, geometrically necessary dislocations and misorientation angle (high-angle and low-angle grain boundaries) are examined. The forming limit diagrams are plotted at different temperatures through the limiting dome height experiments, with and without the use of MoS2 lubricant. The H13 tool steel is used to fabricate the die, blank holder, and punch for the limiting dome height and deep drawing experiments. The experiments are also conducted to determine the limiting draw ratio at different elevated temperatures. The strength values of the clad sheet decrease as the temperature increases, whereas the ductility reduces significantly. The decrease in ductility at vii elevated temperature is primarily due to the increase in the fraction of high-angle grain boundaries which obstructs the dislocation movement during plastic deformation. The strength and ductility of the clad sheet are primarily influenced by the properties of the SS430 component. The formability of the clad sheet decreases with increasing temperature on account of the increasing sticking friction between the sheet and tools. The MoS2 lubricant tends to reduce the friction between the tool surfaces and hence improves the formability at the elevated temperatures. When compared to the specimen at room temperature, the limiting draw ratio of the lubricated clad sheet rises by 11% at 300°C. The experimental results are in good agreement with the predictions and the developed analytical model.