Dissimilar metals joints of Zn-coated steel sheets and pure aluminum were produced using the laser pressure welding method by changing the laser power and the roller pressure. In this method, dissimilar metals sheets were set between the twin rolls. These sheets were opened to make up the wedge-shaped-gap. A 2 kW YAG laser beam was irradiated into a wedge-shaped-gap by a f:θ lens and scanned at various frequencies and patterns using two dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined.
The laser pressure welding experiments conducted by changing the laser power and the roller pressure indicated that welding is possible under all conditions. The intermetallic compounds were observed by optical microscope, and the layer thicknesses were measured. When the laser power was 1300 W, the intermetallic compounds layer thickness was about 15 µm. Very small voids were observed in the welded interface at the laser power of 1500 W, and the intermetallic compounds layer thickness was about 7 µm. The tensile shear strength and the peel strength of welded joints were evaluated. In the tensile test, the strengths of the joints yielded in most welded conditions were so high that the fracture occurred in the aluminum parent metal. In the peel test, at the laser power of 1200-1400 W and the roller pressure of 2.94 kN, the specimen fracture occurred in the aluminum parent metal. On the other hand, the specimen fracture occurred in the welded interface when the laser power was 1500 W. In the TEM observation results, the Zn phase was formed in the aluminum parent metal. Moreover, the intermetallic compound was identified as Fe4Al13 phase by electron diffraction. The joint strength was high even if the intermetallic compound layer was thick. The reason for such high strength is attributed to an intermetallic compound dispersed finely in the (Al+Zn) phase.