The new insight into the effect of Er on microstructure and mechanical properties of laser welded 6082-T6 aluminum alloy

During high-power laser welding (>5 kW) of 6xxx aluminum alloys, the evaporation of low-melting-point elements and the formation of heterogeneous microstructure are detrimental to the mechanical properties of welded joints. The micro-alloying of filler material is an important approach to address it. Here, the effect of different content addition Er to filler material on the microstructure and tensile properties of welded joints was investigated. After the addition of Er, Al 10 ErFe 2 , Al 8 Fe 4 Er, and Al 3 Er phases were formed. The addition of 0.4 wt% Er reduced the average area of Mg 2 Si from 0.109 μm 2 to 0.047 μm 2 , and that of the Fe-containing phase from 0.202 μm 2 to 0.077 μm 2 . The refinement of Mg 2 Si is attributed to local compositional undercooling effects. The reduction in size of Fe-containing phases results from the formation of Al 8 Fe 4 Er and Al 10 ErFe 2 . The addition of Er contributed to grain refinement in the fusion zone. However, increasing the Er content did not enhance the refinement effect. As the Er content rose from 0.2 wt% to 0.8 wt%, the average grain size decreased from 48 μm to 44 μm. Al 3 Er is not the factor governing grain refinement, but the solute restriction growth effect of Er. The optimal tensile properties were achieved by 0.4 Er joint. Compared with 5356 joint, the 0.4 Er joint exhibited a 16.5 % increase in tensile strength, reaching 261 MPa, and a 1.19-fold improvement in elongation, attaining 6.8 %. The second phase strengthening is the main factor of welded joint reinforcement, followed by grain refinement and solid solution strengthening.