Mechanical properties of laser-pressure-welded joint between dissimilar galvannealed steel and pure aluminium

Abstract

Dissimilar metal joints of Zn-coated Galvannealed steel (GA steel) and commercially available pure aluminium (A1050) sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. By this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metal 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 an optical microscope and the layer thicknesses were measured. The thicknesses ranged from 7 to 20 μm. The mechanical properties of the welded joints were evaluated by the tensile-shear test and 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 aluminium sheet. In the peel test of the specimens subjected to a laser beam of 1200–1400 W power under roller pressure of 2.94 kN, the specimen fracture took place in the base aluminium 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 a laser power of 1500 W. The results of X-ray diffraction on the peel test specimen surface identified that the intermetallic compound on the GA steel side was Fe₂Al₅Zn_0.4. Moreover, the aluminium 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 aluminium. A 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, which suggests that the compound layer should not necessarily consist of brittle intermetallic compounds. It is therefore concluded that laser pressure welding could produce high strength joints of GA steel and A1050 dissimilar materials.

Keywords:

• laser
• laser pressure welding
• dissimilar metal joint
• intermetallic compound
• galvannealed steel
• aluminium

Acknowledgements

We would like to express our profound gratitude for the financial assistance given to this study as part of the 2005 Industrial Technology Research Support Project of the New Energy and Industrial Technology Development Organization (NEDO).