Cold extrusion processing of metal matrix composites with eco-friendly lubricants

This study investigates the cold extrusion of metal matrix composites with an emphasis on sustainable manufacturing practices. The influence of extrusion die angle, lubricant type (four renewable-source oils and one mineral oil) and composite architecture on material flow behaviour is evaluated. Five composite configurations, including laminated billets and chip-reinforced composites produced from recycled steel chips, were experimentally extruded using die angles of 45° and 60°. Material deformation was quantified through experimental visioplasticity, allowing measurement of local true strain at central and lateral positions, and was systematically compared with three-dimensional finite element method (FEM) simulations. The results demonstrate that composite architecture and die geometry strongly govern strain distribution and deformation homogeneity, while lubricant selection significantly affects extrusion force and local strain gradients. Statistical analysis confirms that lubricant effects extend beyond dynamic viscosity alone. Renewable-source oils exhibited deformation behaviour comparable to the mineral lubricant, with castor oil showing favourable tribological performance under certain conditions. FEM simulations showed strong qualitative agreement with experimental material flow patterns and provided insight into stress and velocity fields during extrusion. The findings highlight an integrated experimental–numerical approach for analysing composite extrusion and support the feasibility of combining recycled reinforcements with bio-based lubricants in advanced metal forming applications.