2008 Volume 26 Issue 2 Pages 174-180
Dissimilar metals joints of Zn-coated 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 through the fθ 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 joints 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 aluminum sheet. In the peel test of the specimens subjected to the laser beam of 1200 to 1400 W power under the roller pressure of 2.94 kN, the specimen fracture took place in the base aluminum sheet. Even if the compound layer was thick, high joint strength was obtained. On the other hand, the specimen fractured in the weld interface at the laser power of 1500 W. The results of XRD on the peel test specimen surface identified that the intermetallic compound on the GA steel side was Fe2Al5Zn0.4. Moreover, the aluminum parts adhering to the GA steel side were confirmed. These results suggest that the fracture in the peel test occurred between the compound layer and A1050 and partly in the base aluminum. Micro-Vickers hardness test was performed to examine the hardness distribution in the compound layer. The hardness values near A1050 and GA-steel were about 100 and 470 Hv, respectively. It suggests that the compound layer should not necessarily consist of brittle intermetallic compounds. It is therefore concluded that the laser pressure welding could produce high strength joints of GA-steel and A1050 dissimilar materials.