With the increasing demand for lightweight ship superstructures and specialized vessel types, mixed structures combining steel and aluminum alloys are becoming more common. However, the significant differences in thermophysical properties between these two materials make reliable joining a persistent technical challenge in shipbuilding.
When addressing the steel-aluminum joining issue, Jiangsu Haizhongzhou Shipping Industry Co., Ltd. first establishes a fundamental principle: direct fusion welding is not adopted. Direct welding of steel and aluminum generates brittle intermetallic compounds at the interface, forming a weak layer that is highly prone to cracking during service. The industry consensus is to use bimetallic transition joints.
Transition joints are manufactured through an explosion cladding process. Under the impact of immense energy, a metallurgical bonding layer is formed at the steel-aluminum interface. This thin-layer structure achieves atomic-level bonding between the two materials, with an extremely narrow transition zone. The prefabricated steel-aluminum transition joint has steel on one end and aluminum alloy on the other, each connected to the corresponding hull structure using conventional welding processes for like materials.
The key to applying transition joints lies in controlling heat input. Because the bimetallic interface inside the joint may be damaged by high temperatures, interpass temperature must be strictly controlled during welding. Typically, low-heat-input pulsed MIG welding or TIG welding is employed, with temperature monitoring during the welding process to ensure that the interface temperature always remains below the safe threshold.
Post-joining corrosion protection also requires special attention. A galvanic potential difference exists between steel and aluminum, making the contact area highly susceptible to electrochemical corrosion in humid environments. The standard practice is to apply multi-layer coating protection over the entire joint area, with particular care to completely cover the steel-aluminum junction line. Meanwhile, insulating gaskets and sleeves are used for fasteners to prevent direct contact between steel bolts and aluminum plates. In hull design, measures are also taken to isolate steel-aluminum contact surfaces and prevent seawater ingress.
Currently, Haizhongzhou Shipbuilding has developed mature application processes and acceptance standards for transition joints in the connection areas between aluminum alloy superstructures and steel main hulls. The reliable application of this technology makes it possible to lower the vessel's center of gravity and improve stability, while also accumulating valuable experience for further exploration of multi-material hull structures.