Joining of dissimilar metal is challenging due to formation of oxide layer on the intermetallic compound at the joining area.Aluminium and steel bars with length of 28 mm and 47 mm, respectively, are joined via diffusion bonding in featuring gallium at the joint interface to ensure grain boundary attack especially on the embrittlement of aluminium.Experimentation is designed in accordance to Response Surface Methodology (RSM).The holistic approach of optimization technique is exploited to optimise the diffusion bonding parameters to obtain the maximum bonding strength of the dissimilar Al�Fe joint.Impact mechanical properties were evaluated at constant pressure with various heating temperature, soaking time and surface roughness.A good bonding intensifies at the early heating process of the successful bonding boundary.A small toughness value of Izod test is probably due to an incomplete bonding process, at which, air entrapment is present along the joining interface.After a complete 15 cycles of trialling, the most optimal parameters are approximately, 550 � bonding temperature, 60 min holding time and P900 grit surface roughness. © 2023, Institute of Technology PETRONAS Sdn Bhd.