Feasibility studies of a novel extrusion-roll-bonding technology

Abstract

In the aerospace industry, aluminium rib-structural integral panels are one of the parts with high structural efficiency on aircraft and used for the fuselage, wings, and floors. These aluminium airframe components constitute 70% weight of civil aircraft, such as the Boeing 777. These rib-structural integral panels are currently produced by machining accounting for > 90% wastage of materials. Thus, developing a new high-efficiency cost-effective manufacturing technique for these airframe panels is of a great commercial incentive. This study aims to propose, design, manufacture and understand a novel extrusion-roll-bonding (ERB) technology, which involves the extrusion and roll bonding of layer-by-layer aluminium strips. During the rolling process, solid-state pressure bonding occurs between aluminium strips. High bonding quality is ensured by effectively breaking the original oxide film through the extrusion and rolling the extruded strips within an oxygen-free environment. Detailed equipment designs are conducted, considering operating temperature, extrusion geometry, roller dimension, and maximum extrusion and roll bonding forces. A pilot ERB test equipment satisfying all design specifications is built and used to produce ERBed, AA1060 Al-alloy parts. To understand the effect of processing parameters on ERB bonding mechanisms, systematic investigations on the variation of rolling thickness reduction, temperature, extrusion speed, roller diameter and heat treatment are conducted. How these variables affect the bonding strength and interface microstructure are revealed. The bonding qualities are evaluated through miniature tensile tests for strength and ductility, while the interface microstructure is characterised using an optical microscope (OM), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The feasible ERB processing parameters are determined to enable the extrusion layers to be fully bonded. This research has confirmed that the innovative ERB process is feasible and has a high potential to efficiently and cost-effectively produce aluminium rib-structural integral panels.