TRANSIENT LIQUID PHASE JOINING OF CARBON AND STAINLESS STEELS TO ALUMINUM ALLOY USING GALLIUM METAL
B.S. Chongqing University of Technology, Chongqing, China 2011
The objectives of this thesis is to develop a metallurgical understanding of joining two dissimilar metals via transient liquid phase (TLP) bonding. TLP Joining of 1020 carbon steel and 304L stainless steel to 6061-T6 Aluminum (Al) alloy were carried out using gallium (Ga) as filler metal. Joints were fabricated using different bonding temperatures and holding times. The microstructures for each sample were examined via optical microscopy and scanning electron microscopy (SEM). Tensile tests were performed for representative samples from each bonding system. Micro-hardness profile across the bonding region for each sample was also obtained.
Sound joints were obtained. The brittle Fe2Al5 intermetallic compound was identified in the midst of reaction layers of the 1020 steel/Ga/6061-Al joints. The sample processed at 450oC for four hours showed the highest tensile strength of 81.0 MPa. On the other hand, no brittle intermetallic compound was identified at the bonding regions of the 304L Stainless Steel/Ga/6061-Al joints, The highest tensile strength of 100.0 MPa were measured for the samples fabricated at 330oC for six hours.
It was determined that the Ga film promotes the formation of the narrow transient liquid layer that aided in the isothermal local solidification, and enhanced the inter-diffusion of the iron and aluminum atoms. The weakening of mechanical properties on 6061-Al observed from both systems is due to overaging and the embrittlement caused by excessive amount of Ga that segregated into the Al.