Formability analysis of micro-alloyed sheet metals reinforced by additive manufacturing

Abstract

Additive manufacturing (AM) offers the possibility of locally reinforcing sheet metal or sheet metal products by adding patches that are metallurgically bonded to the substrate. Due to the high design freedom of AM, patches can be easily adapted to loads in geometry and thickness. However, the heat input and the high cooling rates during AM processes have a strong influence on the microstructure in the patch as well as in the substrate, which will affect forming properties. The aim of this work is to investigate the influence of patches produced by laser material deposition (LMD) on formability of micro-alloyed sheet metals. After determining a suitable process window for metallurgically bonded patches without cracks and pores, investigations were carried out on the microstructure and mechanical properties of reinforced samples. This work includes metallographic examinations using optical microscopy, hardness measurements and tensile tests. The formability of sheets with local reinforcement was investigated by stretching and Nakajima tests. The heat input creates a heat affected zone (HAZ) directly next to the patches with a reduced strength, caused by recrystallization that may lead to failure in the forming process and thus limits the forming capacity of locally reinforced sheet metals. A subsequent laser heat treatment can homogenize the properties in the HAZ.