Comprehensive evaluation of the effect of large extrusion ratio on the microstructure and performance of Al/Al bimetallic composite tubes

Abstract

Bimetallic composite tubes prepared by hot extrusion are usually assembled in parallel with the billet, which usually results in a low extrusion ratio and reduced production efficiency. In this study, Al/Al bimetallic composite tube with excellent surface quality were successfully prepared using AA6061 aluminum alloy and AA1060 aluminum alloy as the original materials and a special conical assembly form at 450°C and a large extrusion ratio of 21 by hot extrusion process. Macroscopic observation of the distribution of the two materials in the wall of the composite tube shows that the Al/Al composite tube combines well along the extrusion direction, the wall thickness of the inner and outer walls is gradient distribution along the extrusion direction, the stable extrusion stage accounts for 60 % of the total length, about 110 cm, and combines well in the circumferential direction as well. The bonding strength of the Al/Al composite tube is above 120 MPa, which is higher than the ultimate tensile strength (UTS) of the original AA1060 aluminum alloy and achieves metallurgical bonding. In addition, the UTS of the composite tube has reached the requirement of existing Al/Al composite products and has better plasticity. The microstructure near the interface of the composite tube shows no holes and inclusions on the interface, and the grains of the two materials have been refined to a certain extent, and the transmission electron microscope (TEM) results reflect that the two materials are in a coherent relationship. And the simulation of composite tube extrusion was conducted. The influence of the microstructure evolution on the mechanical properties and the bonding mechanism of the composite tube are discussed based on the microstructure evolution at the interface of the composite tube and the simulation results.