Microstructure development in Pulsed Laser Welding of Dual Phase Steel to Aluminium Alloy

Lap joining of aluminium 6061 and dual phase (DP 600) steel was carried out in pulse welding mode using a high power diode laser. The effect of laser parameters (laser power, scanning speed and pulse duration) on the microstructural evolution during conduction welding was studied. The large difference in thermal and physical properties of DP 600 and Al 6061 alloy results in the formation of brittle intermetallic phases along the interface of the weld zone. At a laser power of 4 kW, scanning speed of 5 mm/s and pulse duration of 10 ms the thickness of the intermetallic phase formed was found to be reduced i.e. in the range of 1- 7 μm. The porosity in the weld zone were mainly due to the entrapment of the zinc vapors during welding because of its low vaporization temperature compared to DP 600 and Al 6061 alloy. Microstructural characterization of the intermetallic phases was done using scanning electron microscopy, X-ray diffraction and the phase composition were characterized using energy dispersive spectroscopy. The micro-hardness testing was to evaluate the mechanical properties of the lap joint. A maximum hardness of 461 HV was observed along the weld- aluminium interface owing to the presence of hard and brittle Fe2Al5 and FeAl3 intermetallic phases.