<p>In this study, we prepared a copper/steel bimetal by gravity casting, systematically investigated the influence of Al content on the microstructure and mechanical properties of the bimetal, and revealed the mechanism of Al on the interfacial bonding properties using first-principles calculations. The results show that the introduction of Al increases the content of the <i>δ</i>-phase in the bimetallic copper layer, and <i>δ</i>-phase structure undergoes an isolated island-discrete distribution-continuous mesh evolution. Simultaneously, the formation of fine and dispersed Al₂O₃ precipitated phases promotes significant grain refinement. The addition of Al led to the thickening of the interfacial transition layer and improvement of the bonding strength. However, the presence of Fe3P brittle intermetallic compounds in the transition layer at high Al content was observed. This reduces the binding strength of the interface. The interfacial properties of the Cu(110)/<i>γ</i>-Fe(110) model before and after Al doping were calculated using first principles. The bonding energy at the interface increased, and the replacement energy and interfacial energy decreased. The results of the charge differential density and density of states showed that the addition of Al is beneficial for the enhancement of the interfacial Fe–Cu bonding and strengthening of the Fe–Cu metal.</p>