Optimization of process parameters for enhancing the tensile strength of diffusion-bonded Al-Al and Al-Fe-Al...

Diffusion bonding has been widely investigated for dissimilar metal systems such as aluminum-steel and aluminum-titanium joints. However, systematic studies on the hot-press bonding of similar aluminum sheet joints under controlled processing conditions remain relatively limited. Furthermore, although aluminum-steel bonding has been extensively studied, research on Al-Fe-Al laminated structures, in which steel serves as a load-bearing core and aluminum acts as a protective outer layer, is still scarce. In particular, limited attention has been given to the simultaneous optimization of bonding conditions for both Al-Al and Al-Fe-Al structures within the same experimental framework. In addition, the bonding strength of diffusion-bonded laminated structures is strongly influenced by multiple processing parameters, yet the combined effects of these parameters have not been systematically optimized for dual-material laminated systems. Therefore, this study aims to investigate the hot-press bonding process of Al-Al and Al-Fe-Al stacked structures and to optimize the processing parameters to achieve improved tensile performance. In this work, the effects of pressing temperature, pressing force, holding time, cooling rate, and heating power on the bonding quality were investigated using a Box-Behnken Design. The tensile strength of Al-Al and Al-Fe-Al structures was selected as the primary response for evaluating the bonding performance. Response Surface Methodology was used to develop predictive models describing the relationship between the processing parameters and the tensile strength responses. Subsequently, multi-objective optimization using the NSGA-II algorithm was applied to determine the optimal processing conditions for maximizing the tensile strength of both bonded material systems simultaneously. The results demonstrate that the developed models can effectively describe the process-property relationships and identify a set of optimal hot-pressing parameters for improving the tensile strength of the bonded structures. Scanning electron microscopy was used as a supporting method to qualitatively examine the interfacial morphology and fracture features after bonding and tensile testing. The findings provide a process-oriented optimization framework for improving the mechanical performance of aluminum-based laminated structures and offer practical guidance for selecting hot-press bonding conditions for Al-Al and Al-Fe-Al systems.