Al 합금과 스테인리스강의 고상 확산접합성 연구

Abstract

A Study on the Solid Diffusion Bonding of Al Alloy/STS Steel

Microstructural analysis and tensile testing of directly diffusion -bonded joints of A6061(T6) to STS316L were conducted in order to evaluate the joinability of aluminum alloy to stainless steel. Diffusion bonding of A6061(T6)/ STS316L was carried out at 748∼883K for 30min∼150min applying 1∼8 MPa in vacuum degree of 10-5 Torr.

SEM observation revealed that the reaction layer was formed at the A6061(T6)/STS316L interface. It was refered that the intermetallic compounds such as FeAl3, Fe2Al5 were identified in the reaction layer in the different literature. However, various intermetallic compounds which is not same as FeAl3, Fe2Al5 were founded in this experiment. It was explained that the reaction layer was formed by reciprocal action of reaction and diffusion. The tensile strength of A6061(T6)/ STS316L joints was risen up to about 140 MPa. The fracture modes shifted from the ductile fracture to the brittle fracture in reaction layer with increasing of the temperature.

XRD analysis revealed that the fracture surface contains a large amount of Al elements in the temperature of 748∼803K. It was identified that the fracture occurred at the A6061 side at this temperature. However, it was identified that the fracture occurred at the intermetallic compounds in the temperature above 813K.

Main conclusions are obtained as follows

1. The most suitable bonding conditions which the tensile strength of the joints was risen up to 140 MPa were clarified to be the bonding temperature of 748∼803K, the time of 90∼150min, the pressure of 1∼3 MPa and vacuum degree of 10-5 Torr.

2. In the temperature of 748∼803K, tensile strength of the joints was increased by reciprocal action of reaction and diffusion with increasing of the temperature. However, in the temperature above 813K, tensile strength of the joints was decreased by excessive formation of brittle intermetallic compounds and by transmitting cracking due to thermal stress.

3. In the temperature of 748∼803K, fracture occurred at the A6061 side in ductile fracture modes. However, in the temperature above 813K, fracture occurred at the interface in brittle fracture modes.

4. In the temperature of 748∼803K, it seems that Fe, Cr, Ni and other elements of STS 316L side diffuses into A6061 side, therefore the tensile strength is risen by forming thin and strongly combined reaction layer. However, in the temperature above 813K, it seems that the above elements diffuses excessively into A6061 side, therefore the tensile strength falls down by forming thick and brittle reaction layer and by inducing stress concentration at the intermetallic compounds inside of reaction layer in the interface.