Dissimilar metals joints of galvannealed steel (GA-steel) and commercially available pure aluminum(A1050 sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. In this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metals sheets. In addition, the laser beam was scanned at various frequencies and patterns though the ƒθ lens using two dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined. The compound layers in the weld interface were observed by optical microscope, and the layer thicknesses were measured. The thicknesses were in the range of 7 to 20 μm . The mechanical properties of welded joinnts were evaluated by the tensile shear test and the peel test. In the tensile shear test, the strengths of the joints produced under the most welding conditions were so high that the fracture occurred through the base alumimum sheet. In the peel test of the specimens subjected to the laser beam of 1200 to 1400 W power under the roller pressure of 2.94kN, the specimen fracture took place in the place in the base aluminum sheet. Even if the compound layer was thick. high joint strength was obtained. In order to know the reason for such high strength of joints with thick compound layer and the joining mechanism, the compound layer was observed by the HR-TEM. The TEM observation results revealed that the mein phase in the compound layer was the solid solution of Al + Zn. Moreover , the intermetallic compound was identified as FeAl, Fe
2Al
5, Fe
4Al
13 and Fe
2Al
5Zn
0.4 phase by electron diffraction. The Fe
3Zn
10(Γphase) of Fe-Zn intermetallic compound was confirmed on a Fe base meaterial. It is guessed that the joining areas were heated in a range of 782℃ more than 665℃, a melting point of the Al, by laser irradiation because the δ
1K phase aspect was not confirmed. Because the surface of A1050 and Zn plated layer were meltedd thinly, hte layer was over 10μm thicker. The reason for the production of high strength joints with the relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.
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