Effect of crystal structure of matrix layers on microstructure,texture and corrosion characteristics of multilayered composites

Abstract

Multilayered composites are often composed of metals with different crystal structures such as face-centred cubic (FCC), body-centred cubic (BCC), and hexagonal-centred cubic (HCP). These composites are widely used in automobile components. To study the effect of crystal structure on the evolution of microstructure, development of texture, and variations of corrosion behaviour, the Cu (FCC), St (BCC) and Ti (HCP) layers were separately bonded to Mg (HCP) layer by accumulative roll bonding (ARB) process. The fabricated Cu/Mg/Cu, St/Mg/St and Ti/Mg/Ti composites were then characterised and the findings were compared. The evolution of morphologies showed the most uniform reduction of layers’ thickness in Cu/Mg/Cu and the largest fraction of shear bands in Ti/Mg/Ti composites up to middle deformation passes. Also, the most uniform distribution of fragments was seen in Cu/Mg/Cu composite after the seventh deformation pass. Comparing the development of grain size of Mg layer in all three composites showed the lowest average of grain size in Cu/Mg/Cu composites. The average grain size of Mg layer in Cu/Mg/Cu, St/Mg/St and Ti/Mg/Ti were 4.7, 5.2 and 6.5 µm, respectively. Furthermore, the development of texture in Mg layer exhibited a circle-to-oval transition of the basal texture appearance over deformation passes. However, this transition was more significant in Cu/Mg/Cu and Ti/Mg/Ti composites. In addition, the hardness of Mg layers in Cu/Mg/Cu, St/Mg/St and Ti/Mg/Ti were 80.5, 76 and 78 HV, respectively after the seventh deformation pass. The highest hardness increment was 33.5 HV in Cu/Mg/Cu while the lowest hardness increment was 22.5 HV in Ti/Mg/Ti. Furthermore, the corrosion resistance of composites decreased with an increase in deformation passes although better corrosion resistance and lower degradation rate were observed in Cu/Mg/Cu composite.