Joint properties of friction welded joint between pure magnesium and pure aluminium with post-weld heat treatment

• A characteristic of pure Mg/pure Al friction welded joint by PWHT was clarified.
• As-welded joint had the intermetallic compound layer (IMC) at the weld interface.
• IMC generated and grew at the weld interface with PWHT.
• The joints autogenously fractured at the weld interface after PWHT.
• The fracture occurred by thermal stress in radial and/or circumferential directions.

The present paper described the investigation of the joint properties of friction welded joint between pure magnesium (CP-Mg) and pure aluminium (CP-Al) with post-weld heat treatment (PWHT). The joint in as-welded condition fractured from the adjacent region of the weld interface, although that had the same strength as the tensile strength of the CP-Al base metal. This joint had the intermediate layer (interlayer) consisting of intermetallic compound (IMC) on the weld interface, and its thickness was below approximately 1 μm. Most of joints subjected to PWHT autogenously fractured at IMC interlayer and that mainly occurred between Mg2Al3 and Mg17Al12 although those layers had a little each other at the fractured surfaces. The IMC interlayer grew to CP-Mg and CP-Al sides, and its thickness increased with increasing heating temperature and/or heating time. The main reasons for the autogenous fracture from the adjacent region of the weld interface of the joint were considered the growth of IMC interlayer of the joint during PWHT process. Furthermore, that fracture of the joint was thought the generating of the thermal stresses in the radial and/or circumferential directions during the cooling stage of PWHT process.

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