Yoshihiro Okumoto

Laser pressure welding of aluminium and galvannealed steel

Dissimilar metal joints of galvannealed 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. In 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 optical microscope, and the layer thicknesses were measured. The thicknesses were in the range of 7–20 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 aluminium sheet. In the peel test of the specimens subjected to the laser beam of 1200–1400 W power under the 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. In order to know the reason for such high strength of joints with thick compound layers and the joining mechanism, the compound layer was observed by the HR-TEM. The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al + Zn. Moreover, the intermetallic compound was identified as FeAl, Fe2Al5, Fe4Al13, and Fe2Al5Zn0.4 phase by electron diffraction. The Fe3Zn10 (Γ phase) of Fe–Zn intermetallic compound was confirmed on a Fe base material. It is assumed that the joining areas were heated in a range of 782°C more than 665°C, a melting point of Al, by laser irradiation because the δlk phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10 μm 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.

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

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 Fe2Al5Zn0.4. 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.

Laser pressure welding of Zn-coated steel and pure aluminum

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.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 thic...

HR-TEM observation of laser pressure weld of galvannealed steel and pure aluminium

Laser pressure welding was conducted by changing the laser power and the roller pressure in the previous experiment. It was revealed that dissimilar metal welding of galvannealed steel and pure aluminium was feasible in a wide range of welding conditions. When the roller pressure was more than 1.96 kN at the laser powers equal to or less than 1400 W, the joint strengths were so high that the specimens in the tensile shear and the peel tests fractured in the A1050 parent metal. In order to know the reason for such high strengths of joints with thick compound layers and the joining mechanism, the compound layer was observed by HR-transmission electron microscopy (TEM). The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al + Zn. Moreover, the intermetallic compound was identified as FeAl, Fe2Al5, Fe4Al13 and Fe2Al5Zn0.4 phase by electron diffraction. The Fe3Zn10 (Γ phase) of Fe–Zn intermetallic compound was confirmed on a Fe base material. It is guessed that the joining areas were heated at a range of 782°C more than 665°C, a melting point of Al, by laser irradiation because the δlk phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10 μm thicker. The reason for the production of high-strength joints with a relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.