The Research Of Friction Stir Brazing Of Ti/Al Dissimilar Metals

Recently,Ti/Al composite components have been widely applied in engineering field.The high-quality joints are difficultly obtained by the traditional friction stir welding because the brittle Ti-Al intermetallic compounds are easily formed at the welding interface.So 2mm thick 6082 aluminum and 1mm thick TC4 titanium alloy were lapped by friction stir brazing?FSB?method through adding the brazing filler Zn and Ni in this paper.There were two aspects in systematic research,which included the welding process study of Ti/Al dissimilar metals through adding the brazing fillers and the heat-treatment study after welding and the formation mechanism of IMCs at the welding interface.Firstly,the mechanical properties and the appearance of cross section and microstructure of Ti/Al FSB joints through adding the brazing filler Zn and Ni were investigated in different welding process parameters?thickness of brazing filler,rotation speed and welding velocity?in the welding process study.The study shows that with the ration speed increases,the failure load of joints is increased.When welding speed and the thickness of brazing filler Zn increases,the failure load firstly increases and then decreases.When the rotation speed,welding velocity and thickness of brazing filler Zn are 1600rpm,60mm/min and 0.05mm respectively,the highest failure load exceeds to 5.55KN.The macro-interlock structure can improve the joints failure load.The Zn granular is discovered in the aluminum alloy.There are no Ti-Al intermetallic compounds formed at the central area,which is replaced by ZnAl solid solution.The Ti-Al intermetallic compounds are easily formed at the marginal zone.When adding the brazing filler Ni,the joint failure load firstly increases and then decreases with the rotation speed increases.When the rotation speed is 1200rpm,the joint failure load is highest,which is 5.12KN.There are two different color layers at the interfacial central zone.Using the X-ray diffraction,the lighter layer is Al₃Ni₂IMC and the darker layer is Ni filler.To some extent,brazing filler can promote the fracture mechanism of joints transition from brittle to brittle and ductile inter-mix fracture.The micro-hardness is highest because there are some small grains in this zone,which is higher than the thermo-mechanically affected zone,the heat-affected zone and basic metal.Secondly,the influence of heat-treatment parameters?temperature and holding time?on the thickness of intermetallic compounds?IMCs?)at the welding interface and failure load in the heat-treatment study after welding.The study shows that with the heat-treatment temperature and holding time increases,the thickness of IMCs increases and the joint failure load firstly increased and then decreased.But the majority of joints failure load increases compared the unheated joints,which the failure load of the joints adding Zn increases from 5.55KN to 6.98KN and adding Ni from 5.12KN to 5.98KN.At last,the type and formation sequence and kinetic growth model of IMCs at welding interface were investigated through thermodynamics and kinetics methods.The study shows that the IMCs formation order is TiAl₂,TiAl₃,TiAl,AlZn at the Ti-Zn-Al interface?adding filler Zn?and Al₃Ni₂,TiNi,TiAl and Ti₃Al below 776K and Al₃Ni₂,TiNi,Ti₃Al,TiAl above 776K at the Ti-Ni-Al interface?adding filler Ni?.The Gibbs free energy of all IMCs increases with temperature increases.The kinetic growth increases with parabolic growth law and the growth models are W=1.82×10-6m²·s-1×e-62.98?KJ/mol?/RTt¹/2/2 and W=3.26×10-6m²·s-1×e-72.09?KJ/mol?/RTt^1/2.As a well-known fact,that the IMCs thickness is related with the heat input.The more heat input the thicker the IMCs.