Investigations on deformation mechanism of double-sided incremental sheet forming with synchronous thermomechanical steel-aluminum alloy bonding

Abstract

Lightweight Al/steel laminated parts are required for industrial applications due to their relatively high service performances. In this work, truncated conical parts are fabricated from separated DC05/AA5052 sheet via newly proposed synchronous thermomechanical manufacturing concept combined with pin-less friction stir welding and incremental forming processes. To clarify the deformation and bonding mechanisms, simplified quasi-static element loading model is built for analyzing localized stress and strain distribution. Both theoretical and experimental results indicate axial forming force in this synchronous thermomechanical process lowers than that in conventional friction stir welding. Analytical temperature model for evaluated elements is also established based on heat generation and conduction relationship. 420℃ is the favorable steady maximum temperature to promote mechanical and metallurgical bonding under localized loading effects, which can avoid producing over-thick brittle Fe-Al intermetallic compounds. Sound formability, hook defect elimination, and higher bonding strength of the process are contributed by the well-controlled heat-force coupling effect. Qualitative and quantitative assessments in terms of geometric accuracy, stress triaxiality, surface roughness and gradient microstructures of fabricated parts are made to further represent forming performances. The proposed process and the models are helpful in promoting the development of synchronous thermomechanical forming systems for challenging materials.