Abstract
Titanium alloy TA15 and aluminium alloy Al2024 were welded by tungsten inert-gas arc welding using AlSi12 filler wire. Microstructure and phase constituents of weld zone near Ti/Al interface were analyzed by means of scanning electron microscopy and X-ray diffraction. Initiation and propagation of welding cracks near Ti/Al interface were investigated. Supplementary measures on controlling of cracking were clarified. Titanium and aluminium alloys were partially fusion welded in the upper part while brazed in the middle and bottom parts of the joint. In Ti/Al fusion zone, intermetallics Ti₃Al+Ti₅Si₃, TiAl+Ti₅Si₃ and TiAl₃ formed as three layers orderly from titanium side to weld metal. Near Ti/Al brazed interface, intermetallics Ti₅Si₃ and TiAl₃ formed as two layers from titanium side to weld metal. Two kinds of cracks appeared near Ti/Al interface. One kind initiated in weld zone with high residual stress; the other initiated in brittle Ti-Al intermetallics. Preference propagation paths of cracks are along the interfaces between different intermetallic layers or cross micro-defects near Ti/Al interface.

Key words
titanium, aluminium, fusion welding, brazing, welding crack

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