Direct keyhole laser welding of aluminum alloy AA5754 to titanium alloy Ti6Al4V

Abstract

The tensile strength of direct AA5754/Ti6Al4V joints performed by high speed Yb:YAG laser welding is found to be determined by morphology and phase content of dissimilar interface formed between contacting Al-rich and Ti-rich melted zones. Three types of contact interfaces were observed: (1) thin (<20 μm thick) interface composed mostly by TiAl and formed under 0.2 mm beam shift to Al side and linear energy of welding ≥37.5 kJ/m; (2) cracked interface (190–300 μm thick) composed by Al3Ti and other Al–Ti intermetallics and formed under beam shift at 0.2 mm to Ti side and linear energy ≥37.5 kJ/m; (3) malaxated interface composed of layers and isles of Ti3Al and TiAl forming in other tested conditions and favored by welding speed >10 m/min. Maximal linear tensile force (220 N/mm for 2 mm thick weld) can be attained when thin contact interface is formed. In this case, the fracture starts in intermetallics-rich zone but propagates mainly in Al-rich melted zone, when in other cases it occurs in brittle intermetallic layers.