Friction anchor welding between Al alloy and Zn-coated steel using insert steel difference in the mechanism of friction anchor welding between the types of Zn coatings on Zn-coated steel

摘要

The lap joints of upper Al alloy sheets (1.0-mm-thick A5052) and lower Zn-coated steel sheets (1.2-mm-thick Gl steel or GA steel) were welded using insert steel sheets (0.6-mm-thick SPCC) by a spot welding process with a tool having a spherical ceramic tip, i.e. 'Friction Anchor Welding.' As a result, straight (not-rugged) steel projections were formed in the Al alloy sheets for both the Gl and GA, while steel projections were not formed for the Gl, rugged steel projections were formed for the GA without the insert steel sheets. In addition, the tensile shear strength for the Gl was greater than that for the GA. In other words, the tensile shear strengths reached about 3.9 kN/point for the Gl and about 3.2 kN/point for the GA, which were greater than those of the welds without the insert steel sheets. On the other hand, the cross tensile strengths for the Gl and GA were almost the same, which reached about 2.6 kN/point. Additionally, for the Gl, the Zn layer on the Gl steel sheet melted and was totally removed due to the pressure and heat caused by the rotating tool, which facilitated the welding between the SPCC and Gl steel sheets. For the GA, however, the Zn-Fe layer on the GA steel sheet changed to a solid-liquid mixture and was not completely removed, which prevented the welding between the SPCC and GA steel sheets. Therefore, the thickness of the steel-steel welded region (i.e. the SPCC-GI or the SPCC-GA welded region) for the Gl was greater than that for the GA. We estimated that the difference in this thickness is significantly related to the fracture mechanism during the tensile shear test and the cross tensile test.