Simultaneous Friction Welding and Characterization of Joints Between 7075-T6 Al Alloy and Low-Carbon Steel Using Pure Al as an Insert Metal

Direct friction welding between type 7075-T6 aluminum alloy (AA7075) and low-carbon steel (LCS) is extremely difficult, since AA7075 flash has cracks that reach the weld interface during the welding process. In this study, to obtain a joint with no cracks in the flash, AA7075 and LCS were simultaneously friction welded by using pure Al (CP-Al) as an insert metal. The resulting joint had no cracks in the AA7075 flash. When joints were made at a friction pressure of 36 MPa, the joint strength increased with the applied friction time; a friction time of 6.5 s or longer provided approximately 40% of the tensile strength of the LCS base metal. Moreover, the joint strength for a friction time of 6.5 s increased with increasing forge pressure; a forge pressure of 450 MPa provided approximately 71% of the tensile strength of the base metal. That is, the joint strength was higher than the yield strength of the LCS base metal. This joint did not have any not-joined regions or any intermetallic compound layer at both weld interfaces. These results indicate that a good joint between AA7075 and LCS can be easily made by simultaneous friction welding with CP-Al as an insert metal.