New bimetal AZ31-Al2O3/AA5052 macrocomposite comprising (a) Al2O3 nanoparticle-reinforced magnesium alloy AZ31 shell and (b) aluminum alloy AA5052 millimeter-scale core reinforcement was fabricated using solidification processing followed by hot coextrusion. Microstructural characterization revealed more rounded intermetallic particle of decreased size, reasonable Al2O3 nanoparticle distribution, and non-dominant (0 0 0 2) texture in the longitudinal and transverse directions in the AZ31-Al2O3 nanocomposite shell. Interdiffusion of Mg and Al across the core-shell macrointerface into each other was also significant. Compared to monolithic AZ31, the AZ31-Al2O3 shell exhibited significantly higher hardness (+33%). In tension, the presence of Al2O3 nanoparticles (in the AZ31 shell) and AA5052 core significantly increased stiffness (+39%), yield strength (0.2% TYS) (+9%), ultimate strength (UTS) (+19%), average failure strain (+7%), and work of fracture (WOF) (+27%) of AZ31. In compression, the presence of Al2O3 nanoparticles (in the AZ31 shell) and AA5052 core significantly increased yield strength (0.2% CYS) (+58%), ultimate strength (UCS) (+4%), average failure strain (+11%), and WOF (+49%) of AZ31. The effect of joint presence of (a) Al2O3 nanoparticles (in the AZ31 shell) and (b) AA5052 millimeter-scale core on tensile and compressive properties of AZ31 is investigated in this article.