Radiative heat and mass transfer in Casson Ti-6Al-4V/AA7075 hybrid nanofluid with bioconvection and Cattaneo–Christov heat flux

This study investigates the steady two-dimensional boundary-layer flow and coupled heat, mass, and microorganism transport of a Casson hybrid nanofluid containing Ti-6Al-4V and AA7075 nanoparticles dispersed in ethylene glycol over a stretching surface. The mathematical model incorporates a transverse magnetic field, nonlinear thermal radiation, Cattaneo–Christov heat and mass fluxes, chemical reaction, convective heating, and bioconvection induced by motile microorganisms. Similarity transformations are employed to convert the governing partial differential equations into a coupled system of nonlinear ordinary differential equations, which is solved numerically using a shooting technique. The thermal and transport characteristics of the Ti-6Al-4V/AA7075–ethylene glycol hybrid nanofluid are compared with those of the corresponding Ti-6Al-4V mono nanofluid. The results show that increasing the magnetic parameter suppresses the fluid velocity because of the enhanced Lorentz resistance, whereas nonlinear thermal radiation and the temperature-ratio parameter increase the thermal field. The thermal relaxation parameter moderates the temperature distribution, while larger Schmidt number and destructive chemical reaction reduce the concentration field. Increasing the bioconvective Peclet number and bioconvective Lewis number decreases the microorganism distribution. The hybrid nanoparticle suspension exhibits a distinct thermal response compared with the mono nanofluid owing to its modified effective thermophysical properties. The present formulation provides a numerical framework for analyzing coupled radiative, non-Fourier, chemically reactive, and bioconvective transport in Casson hybrid nanofluids.