Interface optimization design and bonding mechanism of friction rolling additive manufactured aluminum/steel dissimilar metal

Abstract

The aluminum/steel dissimilar structure is a cornerstone for lightweight components and equipment. Yet, traditional fusion welding methods' high heat input frequently gives rise to detrimental defects such as porosity, cracks, and excessively thick intermetallic compound layers (IMCLs) at the interface. To overcome these challenges, this paper innovatively combines low heat input solid-state friction rolling additive manufacturing (FRAM) and strategic interface design to achieve reliable bonding between these dissimilar metals. Our investigation found that conventional FRAM (C-FRAM), hindered by inadequate heat input, struggled to facilitate continuous atomic migration, leading to incomplete joint formation. However, the introduction of arc-assisted FRAM (Aa-FRAM) significantly increased aluminum/steel mixing, fostering interdiffusion of interface atoms under high temperature and pressure conditions. This resulted in the formation of uniform 2.3 μm IMCLs composed of Fe₇Al₁₁, Fe₄Al₁₃, and FeAl₆, and the nanoscale amorphous layer was found between IMCLs and steel. The metallurgical bonding was successfully established at the Aa-FRAM interface. Moreover, by using arc/micro-hole assisted FRAM (AHa-FRAM), which machined an array of micro-holes on the steel surface, we further optimized the aluminum-steel interface bonding quality. The plasticized aluminum alloy (Al alloy) seamlessly flowed into these micro-holes, creating a robust “self-riveting” structure that bolstered mechanical interlocking at the interface. Consequently, we achieved a high-strength joint with an exceptional ultimate tensile strength (UTS) of 167.2 MPa. In addition, the crystallographic analysis showed that the grain size was significantly refined by using the two auxiliary methods, which played a fine grain strengthening role on the interface. This paper innovatively improves the interface bonding between Al alloy and steel through the combination of solid-state FRAM and interface design, thereby opening up a new pathway for the manufacture of aluminum-steel dissimilar structural components.