Effect of interfacial characteristics on magnesium to steel joint obtained using FAST

Abstract

Friction-stir Assisted Scribe Technique (FAST) was used to join AZ31 magnesium alloy to Zn-coated steels including hot-dipped galvanized 590 and electroplated 270 steel with and without coating. The mechanical properties and performance of a FAST joint are governed by its underlying interfacial and microstructural characteristics, which in turn are determined by the FAST tool and process parameters. The FAST tool was utilized to create a different scribe engagement depth that can vary the extent of chemical intermixing and size of mechanical hooks. Microstructure and chemistry investigations on the weld interface were assessed using scanning electron microscopy and electron dispersive spectroscopy. Mechanical properties including lap shear tensile strength and micro and nano hardness at different interfacial regions were correlated to the local microstructures. A finite element-based modeling approach was developed to identify optimal interfacial characteristics that lead to a desired mechanical performance. The results of the computational model were compared to the experimental observations. A sensitivity analysis was conducted to study the variation in the mechanical response and failure modes of the joint with respect to the interfacial characteristics. Results indicate that interfacial characteristics including hook shape can have a significant impact on the joint strength and failure modes.