Microstructural evolution and mechanical properties of dissimilar friction stir lap welding aluminum alloy 6061-T6 to ultra low carbon steel.

Abstract

Joining of steel- aluminum thin sheets has been extensively studied at the beginning of 2000 years for automotive applications, in a regard to reduce vehicle weight, reducing the emissions while improving the energy security of the country.In this context the purpose of this work is to realize and study the dissimilar lap joint between a 6061-T6 aluminum alloy and ultra low carbon steel. A recent welding technique, known as "friction stir welding" was used. Joints have been obtained using coated WC–Co tools in terms of durability, the effects of process parameters including welding speeds (50 to 400 mm/min) at a constant rotation rate (1200 tr /min) and Offset in steel plate (0.2 mm) on the microstructures and mechanical properties of the joints were investigated. The joints were evaluated by mechanical testing and metallurgical analysis. Tensile shear tests, optical microscopy, and scanning electron microscopy with energy dispersive spectroscopy (EDS) were the main techniques used. The results showed that with increasing the welding speed, the tensile strength of the joints, increased up to a maximum value. The 3.6 KN maximum value of the tensile strength achieved a traverse speed of 200 mm/min. Microstructure characterization suggested that higher joint strengths were associated with thinner, ≈ 1 µm thick intermetallic reaction layers at joint interfaces.