Possibility of direct friction welding between type 7075 aluminum alloy and low carbon steel

This paper describes the effect of the friction welding condition on the tensile strength of the friction welded joint between type 7075-T6 aluminum alloy (A7075) and low carbon steel (LCS). The joint did not achieve 100% joint efficiency (100% efficiency) and it fractured at the weld interface which had slight A7075 adhering to the LCS side of the fractured surface. The joint efficiency increased with decreasing friction pressure. Also, the joint did not achieve 100% efficiency although the joint efficiency increased with increasing forge pressure. When the joint was made with a forge pressure of 180 MPa or higher, some joints had poor tensile strength such as below approximately 25% efficiency, and other joints achieved over 60% efficiency. That is, the joints made with same friction welding condition had a scattering in the joint tensile strength. In addition, a scattering of the joint tensile strength increased with increasing forge pressure. In particular, the joint with poor tensile strength had cracks in the flash of the A7075 side, and they reached to the weld interface. Moreover, the ratio of the generated cracks increased with increasing forge pressure. On the other hand, the joint with relatively good tensile strength such as approximately 50% efficiency had cracks in the A7075 flash, but that did not reach the weld interface. The crack in the A7075 flash seems to be a cause of poor plastic deformation ability of the A7075 base metal. Thus, the joint strength had a scattering, although the joint should be made with high forge pressure in order to obtain high tensile strength. Hence, the direct joining of the A7075 and LCS by friction welding was difficult because the crack generation in the A7075 flash can not be avoided.