Characterization of the interface of co‐extruded asymmetric aluminum‐titanium composite profiles

Abstract

The combination of different light alloys enables lightweight solutions with tailor‐made properties at the macroscopic global as well as at the microscopic scale. In this context co‐extrusion by a lateral angular co‐extrusion (LACE) process offers a great potential for advanced profiled structures. While titanium alloys show particular high mechanical strength and good corrosion resistance, aluminium alloys provide a considerable high specific bending stiffness along with low materials costs. The mechanical properties of metallic compounds strongly depend on the bonding mechanisms, which are initiated during processing. In order to enable a rigid adhesive bond between Al and Ti in this study the extrusions were processed by means of a newly developed lateral angular co‐extrusion that is a modified equal channel angular pressing process (ECAP). Latter is known for promoting diffusion bonding by reducing the activation energy. Hence, the study is focused on the general manufacturing of Al–Ti‐compounds by lateral angular co‐extrusion. The second aim of the study was to investigate the development of the bonding zone during processing. Experiments were made with the material combination Al99.5 and titanium grade 2. The bonding zones of the co‐extruded samples were analyzed by scanning electron microscopy and energy dispersive X‐ray analysis. The bond strength was determined by quasi‐static tensile tests. Compared to the as‐extruded condition an intermetallic layer was formed during heat treatment. The layer was characterized by scanning electron microscopy and electron probe micro analysis.

Lateral Angular Co-Extrusion: Geometrical and Mechanical Properties of Compound Profiles

“…The bond formation in the compound forging was thus somewhat better, which can be substantiated by the joint forming, and thus by the more extensive formation of new surfaces in the process [14]. In the LACE process, on the other hand, only the aluminum is formed and the relative movement of the materials to each other [11] forms the joint between the partners. The strength of the joining zones is nevertheless promising to withstand the subsequent die forging process.…”

“…Compared with previous works [12], in which a steel rod was fed into the process, a significantly improved coaxial positioning of the reinforcing element was achieved using the new guiding mandrel part and the resulting, more uniform material flow inside the novel tool. It should be noted that in the original LACE process with a titanium sheet used as external reinforcement there is no offset, since the compound profile was manufactured asymmetrically for process-related reasons [11]. However, in the case of co-extrusion processes that use wire reinforcements, deviations from the expected position of the reinforcing elements could also be detected [17].…”

“…With the LACE process (Lateral Angular Co-Extrusion) developed by Grittner et al, reinforcing elements such as titanium sheets and flat profiles that are already relatively rigid can be fed laterally, and thus continuously into the extrusion process [11]. A laboratory-scale LACE process has already been developed within the CRC 1153, which provided a round rod made of 20MnCr5 steel with an aluminum cladding made of EN AW-6082.…”

Mechanical Properties of Co-Extruded Aluminium-Steel Compounds

“…This process was labelled lateral angular co-extrusion (LACE) by the authors. In [4], the feasibility of the co-extrusion of asymmetric aluminium-titanium compound profiles was shown. In this case, the aluminium was extruded perpendicular to the titanium profile and redirected inside the tool in order produce an asymmetric compound profile.…”