Effects of Heat Input on Weld Microstructure and Properties in Keyhole TIG Welding of Invar 36 Alloy

The Invar alloy is widely used for aircraft wing mould manufacturing. In this work, keyhole-tungsten inert gas (K-TIG) butt welding was used to join 10 mm thick Invar 36 alloy plates. The effect of heat input on the microstructure, morphology and mechanical properties was studied by using scanning electron microscopy, high energy synchrotron X-ray diffraction, microhardness mapping, tensile and impact testing. It was shown that regardless of the selected heat input, the material was solely composed of austenite, although the grain size changed significantly. The change in heat input also led to texture changes in the fusion zone, as qualitatively determined with synchrotron radiation. With increases in heat input, the impact properties of the welded joints decreased. The coefficient of thermal expansion of the joints was measured, which demonstrated that the current process is suitable for aerospace applications.

Automated summary

In this study, keyhole-tungsten inert gas (K-TIG) butt welding was used to join 10 mm thick Invar 36 alloy plates, and the effects of heat input on the microstructure, morphology, and mechanical properties were investigated. The results showed that regardless of the heat input, the material consisted solely of austenite, although the grain size changed significantly. The change in heat input also resulted in texture changes in the fusion zone, which were qualitatively determined using synchrotron radiation. Increases in heat input led to a decrease in the impact properties of the welded joints. The coefficient of thermal expansion of the joints was measured, demonstrating the suitability of the current process for aerospace applications.