Growth And Transformation Mechanism Of Intermetallic Compounds At The Interface Of Ti-6Al-4V/Al-12Si

During the welding process of titanium alloy and aluminum alloy, it is easy to form many kinds of brittle intermetallic compounds at the interface of Ti/Al dissimilar alloys. Those compounds weak the bonding strength of Ti/Al joints. The objective of this paper is to study the effect of temperature, holding time, cooling conditions as well as the ultrasonic on the interfacial reactions during Ti-6Al-4V alloy dipping in the Al-12Si bath, clarified the intermetallic compounds growth and transformation mechanism.The phase compositions of the interfacial layer were identified by SEM observation, combined with EDS and TEM analysis. The intermetallic compound Ti7Al5Si12 is the only phase discovered at the interface when Ti-6Al-4V alloy dipping in the Al-12Si bath at 700℃, which is granular and distributing in the aluminum alloy. Extending the holding time, reducing the cooling speed or adding a long time ultrasonic, all of them can increase the thickness of the interfacial layer. The hardness of the interfacial layer is about 12.7 GPa, elastic modulus is approximately 226.8 GPa.The interfacial layer consists of three kinds of intermetallic compounds (TiSi+TiAl3+Ti7Al5Si12)When the dipping temperature is 800℃. Those compounds are a continuous thin layer TiSi nearby the titanium alloy, block-like TiAl3 as well as the strip-like Ti7Al5Si12 locates in the TiAl3 base respectively. Si exists in the block-like TiAl3, the solubility of Si in TiAl3 reaches 14at.%-15at.%. The number of Ti7Al5Si12 between TiAl3 and Al-12Si alloy increases with the decreasing of cooling speed. The hardness of the interfacial layer is about 9.2 GPa, elastic modulus is approximately 193.7 GPa. The thickness of the interfacial layer increased significantly with adding a long time ultrasonic, which accelerated the interfacial reaction between Ti/Al dissimilar alloys.According to the evolution experiments of interfacial layers, the growth and transformation mechanism of intermetallic compounds is clarified. The distribution of Si has an important influence on the interfacial reaction. Si diffuses to the interface when holding at 700℃, atoms Ti, atoms Al and atoms Si react at the interface of Ti/Al-12Si and create intermetallic compound Ti7Al5Si12. With the rising of temperature, Ti7Al5Si12 happens to decompose and TiAl3 is one of the products, while Si exists in TiAl3 at the form of solid solution, once the temperature is high enough, atoms Ti and atoms Al at the interface will react directly and generate intermetallic compound TiAl3, the thickness of the TiAl3 layer adds gradually with the increasing of holding time. During the process of cooling down from 800℃, Si in the aluminum alloy diffuses to the interface, the TiAl3 will reacts with Si and form the compound Ti7Al5Si12.