Effects of laser oscillating frequency on energy distribution, molten pool morphology and grain structure of AA6061/AA5182 aluminum alloys lap welding

This paper studied lap welding on 1.5 mm AA6061 and AA5182 aluminum alloy sheets with laser beam circular oscillation. The joint form is commonly used in new energy car bodies to achieve the purpose of reducing weight and combining the strength and toughness of two aluminum alloys. The effects of oscillating frequency on the weld formation, grain structure and mechanical properties were mainly investigated combining with numerical simulation. The asymmetric weld morphology and the influence of frequency on weld formation were studied by energy distribution, temperature histories and keyhole depth. The increase of frequency can cause the actual heat input, linear energy and keyhole depth to decrease, resulting in the molten pool to change from an elongated droplet shape to a nearly elliptic shape, and the transition from keyhole mode to conduction mode, thus the grain size gradually reduced. The columnar crystals width in the left and right sides were different, attributing to the different solidification parameters at the both sides of the same isotherm. The tensile strength can reach the maximum value of 156 MPa, where the lap surface was the main source of crack. The dilution of the strengthening phase and the grain size together affected the internal microhardness distribution of the weld. A wide HAZ (heat affected zone) was presented in the oscillating weld. This work can provide a research basis for the optimization of the weld formation, grain structure and properties of this kind of joint, which has potential application in the new energy vehicles.